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CFC/ITTO/72 PD103/01 Rev.4 (I)
Demonstration of Rubberwood Processing Technology and Promotion of Sustainable Development in China and Other Asian Countries
RUBBERWOOD IN CHINA - RESOURCE, MARKET AND PROCESSING TECHNOLOGIES
CFC/ITTO/72 PD103/01 Rev.4 (I) Project Groups
July, 2009 Beijing
Project technical and scientific staff:
Prof. YE Kelin, director of CRIWI, the Project Coordinator;
Prof. LU Jianxiong, deputy director of CRIWI, Project Technical Leader
Prof. JIANG Mingliang, Project Deputy Technical Leader
Dr. ZHAO Youke, Project Secretary, Research Scientist of the Project
Ms. XIONG Manzhen, Project Secretary
Prof. JIANG Xiaomei, Research Scientist of the Project
Prof. ZHOU Yongdong, Research Scientist of the Project
Associate Prof. ZHANG Yisheng, Research Scientist of the Project
Associate Prof. GAO Ruiqing, Research Scientist of the Project
Associate Prof. LI Xiaoling, Research Scientist of the Project
Implementing institutions:
Research Institute of Wood Industry (CRIWI),
Chinese Academy of Forestry (CAF)
Wan Shou Shan, Beijing, 100091
P. R. CHINA
Tel: (+86-10) 6288-9410
Fax: (+86-10) 6288-1937
E-mail: [email protected]
Place and the date the report was issued:
Beijing, July 18, 2009
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Project number: CFC/ITTO/72 PD103/01 REV.4 (I)
Host Government: P. R. CHINA
Execute Agency: Research Institute of Wood Industry (CRIWI),
Chinese Academy of Forestry (CAF)
Project Coordinator: Prof. YE Kelin
Starting date of the project: October, 2005
Duration of the Project (months): 42 months
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Table of Contents The Rubberwood Utilization in China ..............................................................................................1
SUMMARY ..............................................................................................................................1 1. THE RUBBER TREE PLANTING AND RUBBERWOOD RESOURCES........................2 2. THE INFLUENCE AND STATUS OF WOOD SUPPLY ....................................................3 3. THE STATUS OF RUBBERWOOD UTILIZATION...........................................................5 4. The effects after technical improvements..............................................................................6 5. STRATEGIES FOR THE PROMOTION OF RUBBERWOOD INDUSTRY DEVELOPMENT .....................................................................................................................7 REFERENCE............................................................................................................................8
Wood Properties of Plantation Rubberwood in China ......................................................................9 SUMMARY ..............................................................................................................................9 1. MATERIALS AND METHODS.........................................................................................10 2. RESULTS AND DISCUSSIONS........................................................................................11 3. GENERAL CONCLUSION ...............................................................................................17 REFERENCE..........................................................................................................................17
Rubberwood Preservation by Friendly Preservatives .....................................................................19 SUMMARY ............................................................................................................................19 1. RUBBERWOOD DEGRADATION...................................................................................20 2. TREATING METHOD FOR RUBBBERWOOD...............................................................20 1. EXPERIMENTAL METHODS ..........................................................................................22 2. RESULTS............................................................................................................................23 3. CONCLUSIONS.................................................................................................................23 REFERENCES........................................................................................................................26 1. MATERIALS AND METHOD...........................................................................................27 2. RESULTS............................................................................................................................29 3. CONCLUSIONS.................................................................................................................29
Drying Techniques of Rubberwood ................................................................................................30 SUMMARY ............................................................................................................................30 1. AIR-DRYING OF RUBBERWOOD..................................................................................31 2. KILN DRYING OF RUBBERWOOD ...............................................................................39 REFERENCES........................................................................................................................52
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The Rubberwood Utilization in China
Zhang Yisheng Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] Gao Ruiqing Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] Zhao Youke Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] Feng Shanghuan Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China Wang Huaiqiong Wood Industry Development of Hainan State Farms Ltd. Haikou 570105, China E-mail:[email protected] J. Ratnasingam Faculty of forestry, University Putra Malaysia 43400 UPM, SERDANG, SELANGOR MALAYSIA E-mail: [email protected] Lu Jianxiong Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] Ye Kelin Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected]
SUMMARY
Based on the investigation on the distribution of rubberwood plantation in South China, the factors affecting the rubberwood supply were analysed and it is estimated that the domestic annual supply of rubberwood is between 800,000 m3 and 1,900,000 m3. Considering the rubberwood processing status and the improvement of rubberwood processing technology, the main developable strategies fro the promotion of rubberwood industry are suggested as: 1)Rational allocation of resources to ensure sustainable supply of rubber wood; 2）The rules or standard of rubberwood products should be made at national level.
Keyword: Rubberwood, Technical improvements, Developable strategies
Natural rubber is one of the most important commodities in the world, and the world’s natural rubber industry has been transformed significantly over the years, while its market has become more open, with a greater degree of globalization. The world natural rubber production capacity is increasing remarkably, and the plantation area and yield of rubber are fluctuated with the change of natural rubber price. Consequently the production of rubberwood, as the other kind of rubber tree production, was fluctuated accordingly. How to increase the contribution of the rubberwood industry to the national economy through more efficient utilization, and how to upgrade the competitiveness of rubberwood products compared with other tropical wood by means of technical guidelines and demonstration, are the key points for a sustainable development of rubberwood industry. To realize such a sustainable development, this paper will focus on the rubberwood sawn timber industry in China, especially in relation to its market and development
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issues.
1. THE RUBBER TREE PLANTING AND RUBBERWOOD RESOURCES
Generally rubber tree is just suitable to be planted between 10 degrees of southern latitude and 15 degrees of northern latitude in the tropical region, including Asia, Africa and Latin America. The total rubber planting area is more than 9,000,000 ha in the world, and more than 90% of which is in Asia, mainly including Thailand, Indonesia and Malaysia. The other Asian countries with rubber plantation include India, Vietnam, China, Sri Lanka, Philippines, Burma and Cambodia.
1.1 The geographical distribution of rubber plants in China
China has a successful precedent to plant rubber trees in the area of northern latitude 18-24 degrees, which is out of the tradition plantation area. Through developing rubber planting in high degree of latitude region, China becomes one of the main nature rubber producers in the world. The rubber plantations are mainly located in Hainan, Yunnan, Guangdong, Guangxi and Fujian etc., and the total rubber plantation area is about 776,000 ha. (Table 1), in which Hainan province is about 402,000 ha and Yunnan Province is about 334,000 ha. The total natural rubber yield in 2006 is 537,000 ton (dry), which makes China to be one of five biggest rubber production countries. The crude rubber yield of the Hainan and Yunnan covers about 46.01% and 49.11% of the national total yield respectively. Yunnan province produces 150 kg/per Mu (one Mu is 666.7m2, or 1/15 ha,) dry crude rubber, which is in the leading level of the world. The Xishuangbanna region is the main rubber production area in Yunnan province. The resource of rubberwood from renewed rubber plantation is also mainly from Hainan and Yunnan provinces. The quality of rubberwood from eastern and southern parts of Hainan is not good as that in Yunnan Province because of more occurrence of typhoon in Hainan. For example, the height and diameter of rubber tree in Hainan province are less than that in Yunnan province. Both the yield of crude rubber and rubberwood log in Yunnan are about as twice as that in Hainan province.
1.2 The area of rubber plants
Currently the annual consumption of crude rubber in China is more than 2,000,000 ton, in which about 550,000 ton is produced in China, and more than 70% of the total demand depends on import. It is estimated that in the incoming 5-10 years the yearly demand of crude rubber will be increased by 5-8%. However, the increasing potential in crude rubber production in China will be very limited. According to the report by Mrs Zhu Xiuyan, the Chinese natural rubber association president, only 1,000,000 ha, which is less than 5% of the national territory area, is suitable for rubber tree planting. Moreover, as a result of the weather condition and limited soil resource, the potential of rubber yield increasing resulting from enlarging plant area is very limited in China.
1.3 Rubberwood logging
The rubber harvest season is from March 25th to December 25th every year in Hainan province, and from April to November 25th in Yunnan province. The state-owned rubber trees to be cut for renewal is usually 25-30 years after the rubber’s first harvesting, and that for the private rubber trees is only 15-20 years because of the bad cutting technique and poor management. Since the growth period of rubber tree lasts many years, the supply ability of the crude rubber yield and rubberwood yield is hard to be enlarged in a short time. Generally the average proportion of renewed rubber trees is 1.5-2% each year, the maximum of that is 10%. The volume of felled rubber trees for renew with diameter more than 5 cm in Hainan province is 4-5 m3 per mu and that in Yunnan province is 10-12 m3 per mu. So the total rubberwood log yield per mu is from 75 to
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180 m3 based on different planting sites. Suppose 20 years of renewal period, the total annual rubber wood yield in China is 800,000 m3-1,900,000 m3. Generally the annual rubber wood yield in China is about 1,000,000 m3, while the annual rubber wood yield is about 800,000 m3 in recent years due to the high price of the crude rubber and the extension of rubber tree renewal period.
Table 1 the rubber plant area and crude rubber yield in 2006 in China
Item Unit Total Fujian Guangdong Guangxi Hainan Yunnan
The rubber plant area 103×ha 776.2 0.1 35.4 4.4 402.2 334.1
In which, newly planted 103×ha 57.6 1.7 21.4 34.5
In which, available for
latex harvest 103×ha 477 0.1 29.2 3 291.4 153.3
Output（Dry crude rubber） Ton 537,983.0 32 25,395.0 813 247,505.0 264,238.0
Source from: China agriculture yearbook
2. THE INFLUENCE AND STATUS OF WOOD SUPPLY
The factors influencing rubber wood supply are: 1) the renewal quantity of the old rubber trees, 2) the renewal quantity of existing rubber trees for new rubber species and new introduced forest management technique, 3) the cutting amount of rubber trees due to typhoon, insects attack and freeze harm, 4) the influence of heavy rain in harvest season on the cutting and transportation of rubberwood trees The other related factors that influence the rubber wood supply include the change of crude rubber price and the change of wood market condition.
2.1 The influence and situation of natural rubber price
The factors that influence the crude rubber price are as follows:
2.1.1 The supply of crude rubber in international market and the exportation condition of main rubber producing countries
2.1.2 The international market trading condition
2.1.3The agreement by International Nature Rubber Organization (INRO) members.
2.1.4 The production and consumption of natural rubber in China.
2.1.5 The importation policies of natural rubber in China.
2.1.6 The production and the application status of the synthesized rubber, including the market status of crude oil which has closed relationship with synthesized rubber
2.1.7 The development status of the main rubber application industry, such as the tire and automobile industry
2.1.8 The season change, the climate change and other substitutes of agriculture crops
2.1.9 Political factors: The fluctuation of the policy and political situation
Currently the main influence factor is market demand. In the past 20 years, the automobile industry in China and Thailand has been developing rapidly, which resulted in a big natural rubber demand and therefore an ever increase of the international rubber price. Driven by the high profits, the Chinese rubber plantation area enlarges quickly. The increasing trend is showed in Fig1 (The rubber planting and harvest area in 2000-2006 in China). Among these 7 years, the average annual increasing rate of new rubber tree planting area is 33.5%, and the average annual increasing rate of
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plant area for latex harvesting is 1.89%. In the meantime, some aged rubber trees which should be renewed are still serving for rubber harvesting because of their quicker and higher profit, as a result, the rubberwood logging is postponed. These cause the decreasing of rubber wood yield in the long term.
2.2 The influence and status of the timber market 2.2.1 Wood demand
China is a big country for sawntimber production and consumption, while the forest (timber) resource per capita is quite small. Since 1998, wood from the natural forest reduces gradually because of the Natural Forest Protection Policy. However China has a large population, the demand of wood for infrastructure and related trade is very huge. Therefore, the gap between wood demand and supply is becoming bigger and bigger. The annual wood demand is estimated to be 300,000,000~330,000,000 m3. The domestic timber gap between wood demand and supply will reach to more than 160,000,000 m3 if the log harvest is strictly according to the state quota plan. Based on the annual analysis of forest consumption data, the biggest annual supply ability of domestic timber is 230,000,000 m3 (suppose an over harvest of 120,000,000 m3 above the plan), so the gap is at least 70,000,000--100,000,000 m3 each year. It is estimated that in 2015, the total wood demand will be 460,000,000 m3 and the gap will be 170,000,000 m3. Now in China, the main method to shorten this gap is to import wood. The annual wood demand in China increases by 1.5% every year. In this situation, it will be helpful to make full use of rubber wood to minimize the gap between wood demand and supply in China.
Fig1 The rubber plant and harvest area in 2000-2006 in China
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2000 2001 2002 2003 2004 2005 2006
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Total rubberplant area
Area increasedthis year
Areaavailabelforlatex
2.2.2 The trend of wood importation
Nowadays, more and more attention has been paid on the development of local industry and environment protection by the government, therefore, more and more strictly trade protective policies have been made, which has a great influence on the supply channel of China’s wood. The fact is Malaysian and Indonesian governments have made a policy to ban the export of all rubberwood and rattan primary products to promote domestic furniture industry development. The rubberwood in China is mainly from Thailand and Cambodia. Meanwhile the economic
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development ministry of Russia has also approved a draft on increasing the log exportation tax from 25% to 80% in 2009, which was 6.5% in 2006. This will cause a great influence on the Chinese furniture industries since 70% of raw material in China comes from Russia now. As a result, some furniture companies begin to use more and more particle boards and bamboo rather than wood. Meanwhile, North American wood market is greatly influence by the American financial crisis. In this situation, more and more woods are imported from Canada. China would feel more political and environmental stress when the wood supply is heavily depend on the import. In this case, to use more plantation wood resource and wood based materials will be a good complementary way. All above indicated that the rubberwood market has a great potential in the future.
2.2.3 The fluctuation of wood price
The fluctuation of wood price directly influences the tropical wood production and management. Currently the exchange rate of US dollars keeps going down, the timber price in north America goes down. The price of timber from Africa also decreases because of the decreasing total demand from Europe and China. The price of Southeast Asian timber increases by 10% due to the rise in oil and corps price. The timber imported from Russia decreases by 30% because of Russian new high tax policy, therefore, the wood sales in Northeast China goes down. In the meantime, due to the decrease of furniture export, wood demand for furniture decreases. As a result, the final price of wood has somewhat decreased. Compared with other imported wood which has the similar usage, the rubberwood is lower in price, and is becoming more and more popular. The price increased by about 100 yuan/m3 compared with that in last year. Now the price of rubberwood timber is 1430-2400yuan/m3, the price of Thailand-imported rubberwood timber is 2800-3300yuan/m3.
3. THE STATUS OF RUBBERWOOD UTILIZATION
The research on rubberwood economic value began in 1950's. The rubberwood is named as "the ivory wood", its uniform colour , beautiful wood grain, medium density (about 0.6 gs/cm3) , homogeneous texture, good mechanical processing properties and good size stability makes it to be a high-quality raw material that can be used for furniture, veneer for decoration, as well as wood based panel.
The utilization of rubberwood as a sawntimber subjects to the preservative treatment. The little size logs or branches are used for particleboard, plywood and medium density fiberboard. Different specification and grade of the preservative sawntimber can be accordingly used for furniture, finger-joint glue lumber, blockboard, wood modeling, decorated veneer and handicraft product etc. The preservative treatment is a key technique for the utilization of the rubberwood as a sawntimer. In China the annual rubberwood output value reaches to 2,000,000,000 yuan, annually 1,000,000 m3 rubber timbers is transformed from discard to treasure, which not only leads to "alternative" protective effect to nature forest in tropical region but also makes profit of rubber plantation.
3.1 The processing and the usage of rubberwood sawntimber
Because of the shortage of the timber resources, branches and small size logs (dia.5-20 cm) which are occasionally used as plywood or timber materials are fully utilized in China as veneer for plywood or furniture materials. The rubberwoods are usually cut into a board in live saw with only a specific thickness, but are seldom to be cut with a specific width or length, which depends only
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on the size of the log. The board used for furniture is specified by such thickness value as 3.5/4.5/5.5/6.5/7.5cm while the length is generally between 1-2.2m, the width is not specified. The price of the board could be as higher of 1.8 times which depends on its size. Short boards are usually finger jointed or to be made into blockboard and furniture small parts. Some related department is drafting standards for rubberwood sawntimber.
Large sawing equipment is not suitable for rubber wood due to its small diameter and bend shape. Since the low labour cost in China, the rubberwood processing is a kind of high labour intensive processing. The environment-friendly preservative treatment is widely used in big and medium-sized factories currently, and the furnace-type hot air drying is used instead of normal kiln drying. The residuals and most sawdust are mainly used as furnace fuel, and sometimes the sawdust is used for mushrooms cultivation. The non-dimension sawntimber (the width and length is not in specified size) can well utilize rubber wood of different size, and therefore, is the main product type of sawntimber. The recovery rate is about 60%. The imported rubberwood in China market are mainly dimension timber, which is 37% higher in price than domestic rubberwood timber.
3.2 Sale of rubberwood sawntimber
The non-dimension rubberwood sawntimber is packed and classified by the thickness rather than its length and size. The trade of rubberwood timber is by the weight of wood, like the trade of redwood in China. The quality of rubberwood log in Yunnan province is thought to has a better quality than that from Hainan, and therefore, the price is 50-100 yuan/m3 higher than from Hainan province’s. The domestic rubberwood sawntimber mainly comes from the Hainan and Yunnan, and the transport cost is high. It costs about 130 yuans/m3 for the transport from Hainan, to the Zhujiang River and 300 Yuans/m3 from Yunnan, and the transportation from Yunnan to triangle region in Yangtze River costs 400 yuans/m3. Sawntimber transport cost takes up a very big proportion in the price of Yunnan rubberwood. Half of Yunnan rubberwood sawntimber is being second processed before the transportation to the consumption region, Hainan sawntimber is mainly exported. Customers can get sawntimber by two ways: one is to wholesell or retail in trade market, the other is directly from factory.
3.3 Rubberwood sawntimber for value-added products
The proportion of board with width above 15 cm and thickness above 7.5 cm is small due to the small diameter of rubber wood. The length of the board is usually below 2.2 m. Much smaller branches or log is used for furniture pillars. Due to the great difference in rubberwood diameter, the processing waste and branch is usually processed into small size board, then bleached by heat water, and finally finger-jointed into large timber whose price is 1800-4500 yuan/m3, which added 1.5-4 times value after the processing. Other value-added methods include producing small-scaled woody ware, such as handicraft, toy, and cutlery. One more value-added method is to slice finger-joint timer into veneers (thickness 0.3-0.5 mm, and the price is 4-5 yuan/m2), which added value by 2 times.
4. The effects after technical improvements
For the Hainan General State Farm as an example, through the promotion by the “Demonstration of rubberwood processing technology and promotion of sustainable development in China and other Asian countries” [CFC/ITTO/72-PD 103/01 Rev.4（I）], the local rubberwood utilization techniques were improved.
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4.1 The establishment of enterprise codes and criterions
Now in Hainan, the qualities of rubberwood sawntimber are with big differences because of different techniques used in different enterprises, so that market reputation and price are influenced. For example, some sawmills just use cold solution dipping method and the preservatives concentration and absorption are not enough; and some sawmills dry rubberwood with high final moisture content just to save drying cost. Through this project, a series of enterprise codes and criterions including sawing, preservation, air seasoning, kiln drying and packaging were established, which are great helpful to promote the rubberwood processing technique and quality levels in Hainan.
4.2 Environmental concept strengthened
In the past, the main preservative used in almost all sawmills is NaPCP, which is great harmful to environment. Through this project, many environmental friendly preservatives were introduced, such as boron based preservatives and FB, F1, F2, WF-03 anti-mould formulas.
4.3 Improvement of preservation technique
Through this project, and new measurement meter was introduced to industrials to online detecting and adjusting the solute concentration, which could more precisely control the preservative absorption, not only to keep the treatment quality, but also to save cost.
5. STRATEGIES FOR THE PROMOTION OF RUBBERWOOD INDUSTRY DEVELOPMENT
4.1 Rational allocation of resources to ensure sustainable supply of rubber wood. The rubber plant is mainly for producing rubber, it should be integrated managed considering the integrated profits of forest output, rubber tree species, trees planting and cutting programming. Besides the yield of latex, the yield and quality of rubberwood should also be considered
4.2 The management and processing techniques should be strengthened, and the different processing scales should be supported. The processing scale depends on collection and supply ways of rubberwood log. Currently the rubberwood processing technology is not good in China, technique support is essential for a better processing. For some places, more efficient and larger-scale manufacture is encouraged to be established. In this way, the rubberwood could be used in more efficient and environment-friendly way.
4.3 Promoting the production of dimension timber. To produce the dimension timber or non-dimension timber is depending on the processing technique and rubberwood supply quality in different factories. To produce more dimension timber is encouraged since it usually means a good quality and more added values.
4.4 The improvement in rubberwood preservative treatment techniques and sawntimber quality. The rubberwood is easily decayed and moulded. Exposed in the open air, the green log with bark will be decayed in 1-2 month(s), the timber will be moulded in 7-10days. Therefore, if the rubberwood can not be processed in time, it must be treated by preservatives. Presently the timber colour will be browning after the treatment, which degrades the quality of the timber. In addition, the application of preservative treated wood is restricted due to the safety reason. All these need technique improvement in preserve treatment and drying.
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4.5 Encouraging intensive processing instead of preliminary processing for more added values. Application of rubberwood in the new fields should be explored. For example, after adequate treatment, the rubberwood might be used as a high quality packing material for international trade.
4.6 Regulation, rules or standard of rubberwood products should be made. Nowadays, the rubberwood trades are carried out only under the agreement of both sides. There is no related standard on the specification, colour, preservatives etc. Such standard should be made soon to promote the development of rubberwood industry and to facilitate the management of the rubberwood market.
REFERENCE
Song Chen.The exploitation present condition of rubber wood in world. The forestry science and technology communication, 1988.3 P38 ～ 39s
Futures trading post crude rubber futures contract in Shanghai trades an operation a manual Xu Meiqi.The rubber wood exploitation foreground in the Chinese wood quality furniture. The
market report, in 1999 April 13th version No.6 Over 70% depend to import, can Chinese rubber's breaking through siege the Hainan have conduct
and actions? 2007-12-2010:31:21 source from: Hainan newspaper
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Wood Properties of Plantation Rubberwood in China
Zhao Youke Research Institute of Wood Industry, Chinese Academy of Forestry, P. O. Box 18, Beijing, China, 100091 E-mail:[email protected] Jiang Xiaomei Research Institute of Wood Industry, Chinese Academy of Forestry, P. O. Box 18, Beijing, China, 100091 E-mail: [email protected] Lu Jianxiong Research Institute of Wood Industry, Chinese Academy of Forestry, P. O. Box 18， Beijing, China, 100091 E-mail:[email protected]
SUMMARY
In order to fully utilize the rubberwood (Hevea brasiliensis) as a solid wood product, the machining (including planing, sanding, boring and shaping) & coating properties (adhesion and wearability of coating), have been tested on the specimens from 27 rubberwood trees grown in Hainan, China according to ASTM DF1666, D3359-93 & GB/T17657-1999 method. The results showed that the machining and painting properties of rubberwood are all excellent and within the Grade I range, which is better than that of furniture common used species such as oak, walnut and birch. Therefore, from the aspect of machining & coating properties, the rubberwood is good for solid wood products such as furniture and flooring. In addition, the physical and mechanical properties of rubberwood in China and other countries, as well as other furniture-making common used species were adopted from other literature references for the comparison of physical and mechanical properties among them.
Keyword: Wood properties, rubberwood, plantation
From the word rubberwood (Hevea brasiliensis), it can be seen that the important productions of rubberwood are rubber and wood. General speaking, the rubberwood tree has a 25-to-30-year-long period of latex production, and after that it is no longer economic to produce latex but its trunk can be utilized as wood for economic purpose. Nowadays in China, the rubberwood trees are planted in Hainan, Yunnan Guangdong, Guangxi, Guizhou and Taiwan. In which, the south part of Hainan and Xishuang Banna in Yunnan are 2 of the most suitable places for growing rubberwood and therefore have the biggest planting areas. Statistic shows the annual production of rubberwood in China is around 1 million m3, which is an important part in wood supply.
As we all know, rubberwood is very susceptible to fungi and insects due to high content of carbohydrates in parenchyma cells, the preservation of the rubberwood has attracted a lot of attentions, and so far, rubberwood could be well preserved. This provides a basic need for the utilization of rubberwood for solid wood products. In this situation, the utilization of rubberwood for more value-added products such as furniture and flooring drives people to systematically study the properties of rubberwood, including the mechanical properties, coating properties and machining properties. This paper evaluates such machining & coating properties. In addition, the
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physical and mechanical properties of rubberwood from China were compared with other furniture-making common used wood species, as well as the rubberwood from other countries.
1. MATERIALS AND METHODS
1.1 Materials and methods
Totally 27 rubberwood central lumbers with 2 meters in length, 45 mm in thickness and 35 years in age from 27 rubberwood trees grown in Hainan have been selected for machining & coating properties assessment after drying in Hainan Nongken timber Co. The properties of 4 common wood-working operations used in the manufacture of wood products such as planing, sanding, boring and shaping are assessed respectively using ASTM D1666 method [2002] which divides the quality into 5 grades according to the degree of defects and the impact of defects on the following machining process:
Grade I: Excellent (no defects)
Grade II: Good (light defects which can be eliminated by light sanding)
Grade III: Fair (some obvious defects which can be eliminated by sanding)
Grade IV: Poor (deep and big defects which is hard to eliminate)
Grade V: Very poor (prohibited to use)
For each grade, the related point is given, namely 5 points for Grade I, 4 points for Grade II, 3 points for Grade III, 2 points for Grade IV, 1 point for Grade V. The planing, sanding, boring and shaping assessment is based on the points which equals to the sum of the proportion of each grade multiplied by related points of each grade. According to the calculated points, the related grade is estimated (excellent (4-5 points), good (3-4 points), fair (2-3 points), poor (1-2 points), and very poor (<1point)).
The specimen size and the amount of testing specimens are listed in Table 1.
The adhesion of coating is tested according to ASTMD3359-02[2002], in which, a cross-cut is made through the coating film by a multi-edges cutter to the substrate, pressure-sensitive tape is applied over the cut and then removed, and adhesion is assessed qualitatively on the 5 grades as described in Table 2 The wearability of coating is tested according to Chinese National Standard GB/T17657-1999. In this test, a Taber wearability testing machine is used and the wearability was accessed based on the weight loss per 100 rotates. The weight loss 0.08 g is accessed as Grade I, ≦
>0.08 g and 0.1 g as Grade II, >0.1 and 0.15 g as Grade I, and >0.15 g as Grade IV (not ≦ ≦
qualified). Like the assessment on machining properties, the similar point is given for different grade, and same method is adopted for the calculation of the quality points.
Table 1 specimen size and amount for testing machining properties
Machining items Thickness×width×length(mm) Specimen amount(pieces) Planing 19×102×910 27 Sanding 11×110×400 27 Boring 19×76×510 27 Shaping 19×76×510 27
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Table 2 Classification of adhesion results
Grade ASTM Classification
Description
5B The edges of the cuts are completely smooth; none of the squares of the lattice is detached.
I 4B Small flakes of the coating are detached at intersections; less
than 5 % of the area is affected. II 3B Small flakes of the coating are detached along edges and at
intersections III 2B The coating has flaked along the edges and on parts of the
squares.The area affected is 15 to 35 % of the lattice. IV 1B The coating has flaked along the edges of cuts in large
ribbons and whole squares have detached. The area affected is 35 to 65 % of the lattice.
V 0B Flaking and detachment worse than Grade 1.
In this test, 3 coating processes were adopted. The first process is to brush the water-soluble coatings 3 times, the second one is to brush polyester coatings 3 times, and the third one is to brush the water-soluble coatings twice and then to brush polyester coatings once for the outer coating.
The physical and mechanical properties of rubberwood in China and other countries, as well as other furniture-making common used species were adopted from other literature references for the comparison among them.
1.2 Equipment and parameter
Planing: KUW-500F1 automatic feeded 2 faces planner. According to ASTM, just one face is planned each time, only the top spindle is used. In the test, keep the knife parameters stable, the front cutting angle is 20°, the knife wedge angle is 39°, planing thickness includes 1.6mm and 0.8mm, the knife marks per inch is 48. According to the equation: Feed speed =(Number Knives×RPM)/( KMPI×12×25.4), the feed rate is 7.94m/min.
Sanding: WS-65 wide belt sander, the automatic feed rate is 5.8 m/min, the sanding thickness is 0.3mm, Sand twice with 120 grid sand papers.
Boring: B13S bench borer, the spindle rotation rate is 3600r/min, boring bit diameter 20mm, drill perpendicular to the surface of species, feed rate keeps slow and even, during the process, a same species board is close contact under the specimen to reduce the possibility to occur the defects.
Shaping: MX7320 straight shaper, the rotation rate is 8000r/min. specimens were bandsawn to pattern before conducting on the shaper. .Each specimen is shaped in up milling way.
2. RESULTS AND DISCUSSIONS
2.1 Machining properties 2.1.1 Planing
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Table 3 Planing results of different planing thickness
Planing thickness
Grade I proportion（%）
Grade II proportion（%）
Grade III proportion (%）
Quality points
1.6mm p 40.74 3.70 4.52 0.8mm 81.48 18.52 0.00 4.82
Planing is one of the most common and also the most important operation for wood products. The defects caused by planing will have a negative influence on the latter operations in the wood-working manufacture.
With the stable feed rate, the points for 0.8mm (4.82) is higher than that of 1.6mm (4.52) (Table 3), and both of them are in range of Grade I (excellent).The surface of planing existed only a few of fuzzy grain (Fig. 1).
Fig. 1 Planing surface: Left - Grade I specimen; Right -Grade II specimen with fuzzy grain
2.1.2 Sanding
Sanding is essential for a good coating. A good surface roughness resulted from good sanding is readily to be well painted, while sanding defects will influence the finishing of wood products. The surface roughness has relations with not only wood but also the types of sand paper.
Results showed, the proportion for Grade I (excellent) and Grade II (good) specimens is 59.26% and 40.74% respectively , the quality point 4.59, which is within the Grade I range (Table 4). The main defect is fuzzy grain. The difference between Grade I and Grade II is not distinct (Fig. 2).
Table 4 Different Grades and quality grade of sanding, boring, and shaping
Items Grade I proportion（%） Grade II proportion （%） Quality points
Sanding 59.26 40.74 4.59
Fig. 2 Sanding surface: Left - Grade I specimen; Right -Grade II specimen with slight fuzzy grain
2.1.3 Boring performance
Boring is a common operation for the wood structure joint. The bored hole should be round without any noticeable distortion and the inner surface should be smooth for good glue bonding.
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As shown in Fig. 3, Grade I and Grade II of boring is similar to that of sanding, the quality Grade value is also 4.59, showing an excellent boring property (Table 5).
Fig. 3 The torn grain and light fuzzy grain could be hardly see showing an excellent boring properties
Table 5 different Grades and quality Grade of sanding, boring, and shaping
Items Grade I proportion（%） Grade II proportion （%） Quality points
Boring 59.26 40.74 4.59
2.1.4 Shaping
Shaping is the most common method in furniture manufacture. By means of which, the value of the products could be increased in a large extent.
In this test, the specimens is the same as that in sanding test, in order to shape on the 2 ends of one specimen, the length is 510mm, which is longer than that in ASTM. As seen from table 6, the proportion for Grade I and Grade II is 66.67% and 33.33% respectively, the quality points is 4.67, suggesting an excellent property in shaping.
From Fig. 4, it can be seen that most specimens are defects free, a few with fuzzy grain and burned surface.
Fig. 4 Most of specimens are defect free, a few with fuzzy grain and burned surface
Table 6 different Grades and quality Grade of sanding, boring, and shaping
Items Grade I proportion（%） Grade II proportion （%） Quality points
Shaping 66.67 33.33 4.67
From Fig 5, it could be concluded that the rubberwood machining properties, including planing, sanding, boring and shaping are all in the range of Grade I (excellence), suggesting that the rubberwood could be easily processed with the machine, which is good for solid wood products.
13
0 1 2 3 4
Planing
Sanding
Boring
Shaping
5
Fig.5 Rubberwood machining properties (excellent (4-5 points), good (3-4 points), fair (2-3 points), poor (1-2 points), and very poor (<1point)
2.2 Coating properties 2.2.1 Adhesion of coating
Test results of the adhesion of coating test from 3 different processes are shown in table 7.As for the adhesion of coating performance, the third technique is the best, and its quality points is 4.78.
The second most is the first technique, whose quality level value is 4.33, these two are both of excellence level, and the third is inferior to the former two, with the quality level value 3.44, which means good.
Table 7 The adhesion properties of 3 coating processes
Coating Processes Grade I(%) Grade II(%) Grade III(%) Quality points The first 44.44 44.44 11.11 4.33
The second 0.00 44.44 55.56 3.44 The third 77.78 22.22 0.00 4.78
2.2.2 Wearability of Coating
Table 8 The wearability of coating of 3 different coating processes
Coating ProcessGrade I（%）
Grade II（%）
Grade III（%）
Grade 4（%）
Quality Points
The first 100.00 5.00 The second 22.22 77.78 0.67 The third 33.33 66.67 4.33
From the test results of wearability of coating (table 8), it is concluded that the wearability of coating of the first and third process is excellence ,with the quality points 5.00 and 4.33 respectively, the quality points of wearability of the second process is only 0.67, among which 77.78% of the products are unqualified (table 7).
Viewing from the combination of adhesion and wearability of coating, both the first and third process is t excellent in coating properties.
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2.3 Machining properties and coating quality: compared with others
The machining and coating properties are very important for solid wood products such as furniture and flooring. In order to better understand the machining and coating properties of rubberwood, they are compared with that of the main common used wood species for furniture, such as oak, walnut and birch [Hou Xinyi et al. 2006; Jiang Jinhui 2005 ].
Table 9 Comparison of machining & coating properties between rubber wood and others
Items Rubber wood Oak Walnut Birch
Proportion of Grade I & II 100 100 93.3 100 Planing
Properties excellent excellent excellent excellent
Proportion of Grade I &II 100 100 100 96.88 Sanding
Properties excellent excellent excellent excellent
Proportion of Grade I &II 100 100 100 100 Boring
Properties excellent excellent excellent excellent
Proportion of Grade I &II 100 82.8 90 96.7 Shaping
Properties excellent good excellent excellent
Proportion of Grade I &II 100 100 -- 100 Adhesion
Properties excellent excellent excellent
Proportion of Grade I &II 100 100 -- 100 Wearabi-
lity Properties excellent good good
From table 9, it concluded that the machining and coating properties of rubberwood are excellent, better than that of oak, walnut and birch.
2.4 Physical and Mechanical properties The mechanical properties of rubberwood from China were not conducted by this research. In order to compare the mechanical properties of rubberwood from China with other furniture-making common used wood species, as well as with rubberwood from other countries, the results of other studies were adopted from the literatures. Please note that the testing standards from different countries are not same, therefore, the results listed here are for your reference only. 2.4.1 Comparision with other furniture-making common used species in China
From table 10, it can be concluded that the
15
Table 10 Comparison of physical & mechanical properties between rubberwood and other
furniture-making common used species in China
Density
/g/cm3
Shrinkage
/%
Hardness
/N Species
Basic Air dried R T
CSPG
/MPa
BS
/MPa
MOE
/GPa
SSPG
/MPa
R E R T
Rubber wood
(Hevea
brasiliensis)
0.609 0.8 1.62 38 82 9.316 3973 3267
Oak (Quercus
mongolica)
0.603 0.748 0.18 0.32 116 12.936 7144 5909 5880
Walnut (Juglans
mandshurica)
0.42 0.528 0.19 0.30 43.32 85 11.466 3234 2734 2636
Birch (Betula
albo-sinensis)
0.49 0.179 0.320 31.36 64.68 9.016 2848 2058 2156
CSPG = compressive strength parallel to grain, BS = bending strength, MOE = modulus of elasticity, SSPG = shear strength parallel to grain, E = end, R = radial, T = tangential. 2.4.2 Comparision among different countries
The results listed in Table 11 were adopted from the literatures. Since the testing methods in different countries were different, the results are just for reference. From Table 11, it can be seen that the physical and mechanical properties of rubberwood from different countries have no big difference.
Table 11 Comparison of physical & mechanical properties of rubber wood from different
countries
Density
/g/cm3
Shrinkage
/%
Hardness
/N Countries
Basic Air dried R T
CSPG
/MPa
BS
/MPa
MOE
/GPa
SSPG
/MPa
R E R T
China 0.609 0.8 1.62 38 82 9.316 3973 3267
Malaysia 0.55 0.64 32.2 66 9.240 11.0 4320
Philippine 35.4 72.7 8.950 12.1
India 0.56 0.64 2.6-3.0 5.7-6.5 32.2 66 9.240 11.0 4350
Brazil 0.46-0.52 0.56-0.64 40.0 67.0 9.100 10.0
Peru 0.53 18.8 46.3 9.022 7.10 3001 CSPG = compressive strength parallel to grain, BS = bending strength, MOE = modulus of elasticity, SSPG = shear strength parallel to grain, E = end, R = radial, T = tangential.
2.4.3 Comparision with other furniture-making common used species in Malaysia
The physical and mechanical properties of rubberwood in China were in between with other furniture-making common used species in Malaysia, suggesting that the rubberwood in China,
16
from the consideration of physical and mechanical properties, are good for furniture making.
Table 12 Comparison of physical & mechanical properties between Chinese rubber wood and
Malaysia woods for furniture making
Density
/g/cm3
Shrinkage
/%
Hardness
/N Species
Basic Air dried R T
CSPG
/MPa
BS
/MPa
MOE
/GPa
SSPG
/MPa
R E R T
Chinese rubber
wood (Hevea
brasiliensis)
0.609 0.8 1.62 38 82 9.316 3973 3267
Teak (Tectona
grandis)
0.651 0.96 1.18 36.85 93.98 11.721 9.47 4920 5135
Dark red
meranti(Shorea
platyclados)
0.610 32.2 77 9.240 11.0 4350
Light red
meranti
(Shorea
leprosula)
0.575 75 13.600 6.8 2940
Sepetir
(Sindora
coriacea)
0.690 46.3 92 13.600 5.93 5210
Nyatoh
(Palaquium
gutta)
0.675 44.5 79 12.200 11.0 5430
Ramin
(Gonystylus
bancanus)
0.675 48.8 88 15.900 8.5 4580
CSPG = compressive strength parallel to grain, BS = bending strength, MOE = modulus of elasticity, SSPG = shear strength parallel to grain, E = end, R = radial, T = tangential.
3. GENERAL CONCLUSION
The machining and coating properties are all excellent and within the Grade I range, which is better than that of furniture common used species such as oak, walnut and birch. Therefore, from the aspect of machining & coating properties, the rubberwood is good for solid wood products such as furniture and flooring. From the aspect of physical and mechanical properties, the rubberwood in China is also good for solid wood products.
REFERENCE
ASTM D 1666 – 87 (Reapproved 1999). Standard Methods for Conducting Machining Tests of Wood and Wood-Base Materials. 2000
17
ASTM D3359-02. Standard Test Methods for Measuring Adhesion by Tape Test. 2002 Hou Xinyi, Jiang Xiaomei, Gao Jianmin, Yin Yafang. Study on machining properties of
Eucalyptys urophylla x E. grandis. II. Shaping, Boring, Mortising and Turning. Chinese Forestry Science and Technology. 2006, 5(2): 17-21
Jiang Jinhui. Evaluation of Butula alnoides and Castanopsis hystrix plantation wood for furniture and decorative utilization Master degree dissertation. Chinese Academy of Foresry. 2005
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Rubberwood Preservation by Friendly Preservatives
Jiang Mingliang Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, China, 100091 E-mail:[email protected] Wang Zhijuan Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, China, 100091
SUMMARY
Eight chemicals and some mixtures against Botryodiplodia theobromae Pat., Fusarium verticillioides(Sacc.)Nirenberg, Trichoderma harzianum Rifai, Trichoderma viride Pers., and Penicillium purpurogenum Stoll were conducted in laboratory by inhibition zone in the paper. The results were shown that: CBZ and benomyl as well as copper oxine alone are much high efficacy for inhibiting most of the 5 fungi than other chemicals under the test concentrations; PPZ was found to have almost no fungicidal effect at the specified concentration. The fungicidal effect of some mixtures of CTL, DDAC, Cu-8, Benomyl and were better than alone. CTL increase the inhibiting effect of 0.5% DDAC to the 5 fungi except for Trichoderma viride Pers., and it did not increase the inhibiting effect of copper oxine; 0.01-0.08% copper oxine and 0.01-0.5% DDAC increase the inhibiting effect of benomyl to most of the 5 fungi. Field test result showed that fungicide F2 alone can be used for stain control, and it is also effective to most of the mold fungal species and could be the alternate of NaPCP.
Keyword: Preservative, rubberwood, plantation
The most important rubber producing countries are Indonesia, Malaysia, Thailand, China, India, Sri Lanka, Vietnam and the Philippines. Rubberwood can be used for making a wide range of products: rubberwood-based panels (particle board, plywood, MDF, etc.), furniture and joinery products; floor tiles and parquet, moldings,etc. Rubber tree is mainly distributed in Hainan Island, Xishuangbana, Yunnan province and the western part of Guangdong province in south China. China is short of timber. Making full use of the timber can solve the problem to a certain extent.
The fresh felled rubberwood is very susceptible to fungi and insects in sub-tropical area due to high content of carbohydrates in parenchymatous cells. The common preservative, a mixture of boric acid, borax and sodium pentachlorophenol (BBP), was widely used by the treating plants in Hainan and Yunnan Provinces. But today sodium pentachlorophenol is not encouraged for lumber treatment since it is highly toxic to human and animals and it is strictly restricted or prohibited in some countries. The procedure of treating rubberwood with preservative containing only boric and boric acid quickly followed by kiln drying is encouraged to be adopted by the industries in China. At present, rubber trees are usually felled, sawn into lumber, and the lumber impregnated and dried within about 7 to 10 days in most rubberwwood processing plants in China. Few operators sprayed the logs with preservative; this could be the cause of the rather frequent occurrence of
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blue-stains which seriously affects the quality and value of the sawn lumber. As Hainan Island and coastal southern regions of China are prone to hurricane which could further delay delivery of logs to processing facilities, temporary protection of logs using cost-effective preservatives should be developed and promoted.
1. RUBBERWOOD DEGRADATION
Freshly cut rubberwood is very susceptible to mold and stain fungi, due to the relative high content of carbohydrate (such as starch) in the tissues and the high moisture content. When rubberwood is dried, mold and stain fungi stop occurrence.
1.1 Insects
Fresh or seasoned rubberwood is easily attacked by termite and insect borers mainly from bostrychidae (powder post beetles), platypodidae (ambrosia beetles), scolytidae (ambrosia beetles) and lyctidae (powde rpost beetles). Ambrosia beetles attack fresh logs and fresh sawn timber, but powder post beetles prefer seasoned timber and finished woodwork producing a fine powder from bore holes and tunnels. Platypodidae and scolytidae are the main insect pests of freshly felled rubberwood logs, fourteen species of platypodids and 51 species of scolytids were identified infecting green rubber wood according to FRIM report.
1.2 Stain and mold fungi
Fresh felled logs and timber are susceptible to stain fungi belonging to fungi Imperfecti. Botryodiplodia theobromae Pat. is the common fungi responsible for the bluish color of rubberwood. The hypha is found both in fiber and vessel lumina.
A variety of molds can live on the surface of rubberwood, these fungi thrive on carbohydrades in the parenchymacells of rubberwood, and they do not breakdown lingo-cellulosic components of the wood, so they do not affect the strength of the wood.
2. TREATING METHOD FOR RUBBBERWOOD
Untreated fresh rubberwood log and timber is susceptible to stain fungi, which discoloration of the wood, and insects which reduce the quality and durability of timber. So rubberwood should be treated, especially for furnisher making. The log should be cut into timber in 3 days, otherwise, fungicides and insects should be applied for temporary protection.
The timber should be treated by pressure or diffusion process promptly after it is cut for preventing stain fungi and insects. Rubberwood protection is classified by temporary protection and long-term protection.
2.1 Fungicides and insecticides for the temporary protection
Commercial fungicides and insecticides for agricultural uses may also be used for bamboo temporary protection. Some insecticides are included: deltamethrin, cypermethrin, permethrin, cyfluthrin, bifenthrin, chlorpyrifos, imidacloprid, fipronil, Chlorfenapyr, etc. Some fungicides are listed as: chlorothalonil, copper oxine, MBT, TCMTB, Carbendazim, benomyl, IPBC, isothiazolinone, fenpropimorph, quatery ammonium chloride, propiconazole, etc.
The fungicide formulations should be in emulsions, solutions, wetable power. Contents of active ingredients and user’s guide for the suitable concentration and strength should be included on the label of the containers.
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Commercial fungicides and insecticides can be choosed according to their availability and effectiveness by the processing plants. Sodium pentachlorophenol is not recommended for its high toxic. And its use has been strictly restricted or prohibited in some countries such as Japan and some European counties.
Pentachlorophenol is generally not acceptable internationally due to its high toxicity. It also contributes to the severe corrosion of the drying kiln components and turning wood into brown.
2.2 Long-term protection, preservatives and treating schedule
When the rubberwood is dried, no stain and mold fungi as well as decay fungi occur but power beetles can attack it, so diffusion process or pressure treatment allow the preservative to be fully penetrated into sapwood and give long term protection. Boron is the common preservative for vacuum pressure treatment for its high diffusion ability. The treated products can only be used indoor circumstance for it is leachable in rain.
The schedule of vacuum pressure of treatment is described in table 1.
The treating schedule will depends on the length of the timber and the moisture content of the timber before treatment. During the vacuum pressure treatment, the MC of timber may be 50-100%.
Table1 Schedule for the rubberwood Vacuum / Pressure treatment
Phase Vacuum / Pressure (Mpa) Duration (min)
Initial vacuum 0.083-0.099 30-45 Pressure 1.2-1.4 60-120
Final vacuum 0.053-0.086 10-20
The treating schedule will depends on the length of the timber and the moisture content of the timber before treatment. During the vacuum pressure treatment, the MC of timber may be 50-100%.
Appendix I Laboratory Test of Antistain and Antimold Formulations Five types of stain fungi were isolated from blue-stained Pinus massoniana Lamb., Pinus sylvestris var. mongolica Litu., and Hevea brasiliensis (rubberwood) and identified as Botryodiplodia theobromae Pat., Fusarium verticillioides(Sacc.) Nirenberg, Trichoderma harzianum Rifai, Trichoderma viride Pers., and Penicillium purpurogenum Stoll in the previous work, all these fungi are classified to Deuterornycotina.
A lot of literatures on chemical control of stain fungi have been reported (Lakes and Woods 1992, Wakeling 1997, etc). Since the active ingredients in some fungicidal formulations are commercially available, inhibition zone test of some formulations for controlling stain fungi isolated from some Chinese sapwood was conducted in this paper. The aim is to seek some potential alternatives to sodium pentachlorophenol, which is still used in China for controlling wood sap-stain some by sawn mills.
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1. EXPERIMENTAL METHODS
1.1 Fungal species and their characteristic Five fungal species were identified as： Bt: Botryodiplodia theobromae Pat., Fv: Fusarium verticillioides(Sacc.)Nirenberg, Th: Trichoderma harzianum Rifai, Tv: Trichoderma viride Pers., Pp: Penicillium purpurogenum Stoll.
All the 5 fungi are capable of growing under the temperature range from 10 to 35℃, and Botryodiplodia theobromae Pat. is even able to grow at 40℃, the optimum growth temperature is from 24 to 28 . The 5 fungi are basically able to grow on me℃ dium with pH value ranging from 2 to 11. More specifically, PH value from 3 to 8 was suitable for their growth, and the optimum PH value varied from 5 to 7, it seemed that staining fungi tended to grow favorably in acid environment. There were no apparently differences in the growth and staining patterns for the fungi growing under three illuminate conditions.
1.2 Fungicidal formulations for stain control Fungicidal formulations were selected for the screening test (Table 2).
Table 2 Fungicidal formulations for the stain control test
Formulations Common name Formulation types
CTL Chlorothalonil Emulsion
CBZ Carbendazim 50% wetable power
Benomyl Benomyl 50% wetable power
BAC Dodecyl dimethyl benzyl ammonium
chloride Water solution
Cu-8 Copper oxine Acetic acid solution
DDAC Didecyl dimethyl ammonium chloride Water solution
PPZ Propiconazole Emulsion
TEB Tebuconazole Emulsion 1.3 Method for stain control
Fig 1 Method for stain control, inhibition zones by fungicides
22
According to test method of Drug Compendium appendix XI A (2000) of China, 6mm filter papers were sterilized in Petri dishes. The papers were fully soaked in fungicidal formulations, and the excess formulation was removed. Then the papers were put into the Petri dish in which PDA as media and the button was fully covered and well-distributed by fungus Petri dishes were cultivated at 26-28 . After fungus growth for 3℃ -5 days and the hypha were apparently visible, the diameters of the inhibition zones were measured. 3 replicas (Petri dishes) for each formulation at each concentration test and the diameter data were calculated on the 3 replicas.
2. RESULTS
CBZ and benomyl as well as copper oxine alone are much high efficacy for inhibiting most of the above 5 fungi than CTL and quaternary ammonium chloride alone, in which CBZ and benomyl have similar inhibiting result to the 5 fungi (Table 3). DDAC and BAC have also similar effect to the 5 fungi, PPZ has almost no effect to 4 fungi at the above concentrations (Table 3), and TEB is relatively efficacy than PPZ at the same concentration to the test fungi.
The fungicidal effect of some mixtures from CTL, DDAC, Cu-8 and benomyl were better than the single chemical. CTL did not apparently increase the inhibiting effect of copper oxine by testing the mixture of CTL plus copper oxine (Table 4), and 0.5% CTL apparently increase the inhibiting effect of 0.5% DDAC to the 5 fungi except for Trichoderma viride by testing the mixture of CTL and DDAC (Table 4). 0.1-0.5% DDAC apparently increase the inhibiting effect of all CBZ formulations to Botryodiplodia thelbromae Pat. (Table 4).
0.01-0.08% copper oxine apparently increase the inhibiting effect of benomyl to the 5 fungi except for Trichoderma viride by test of the mixture (Table 5), and 0.01-0.5% DDAC apparently increase the inhibiting effect of benomyl formulations to the 5 fungi (Table 5).
The result from the inhibition zone is almost coincided by the following test of wood chips treated with fungicides and inoculated by fungus.
3. CONCLUSIONS
It is concluded from the test of inhibition zone that:
1) CBZ and benomyl as well as copper oxine alone are much high efficacy for inhibiting most of the 5 fungi than other formulations;
2) The fungicidal effect of some mixtures of CTL, DDAC, Cu-8, Benomyl and were better than alone. CTL increase the inhibiting effect of 0.5% DDAC to the 5 fungi except for Trichoderma viride, and it did not increase the inhibiting effect of copper oxine;
3) 0.01-0.08% copper oxine and 0.01-0.5% DDAC increase the inhibiting effect of benomyl to most of the 5 fungi.
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Table 3 The diameter of inhibition zone by formulations (mm)
Formulations Concen- trations of a. i.
Bt Fv Th Tv Pp
0.05% 0 12.8 11.7 8.2 9.5 0.20% 7.4 14.1 12.2 10.3 11.1 CTL 0.50% 9.1 14.7 12.7 12.1 13.5 0.001% 36.6 0 16.5 20.0 29.6 0.005% 39.2 12.0 21.4 25.5 32.8 0.010% 40.1 14.9 22.1 26.0 36.5 0.02% 40.6 17.7 23.0 22.5 38.4 0.10% 41.2 21.0 25.3 26.8 40.3
CBZ
0.20% 43.6 24.4 28.4 29.8 42.6 0.80% 8..5 14.1 11.0 16.3 22.3 1.60% 11.9 17.5 12.7 18.1 24.2 BAC 2.00% 13.2 19.9 13.9 19.6 25.9 0.001% 32.4 0 18.7 11.4 27.8 0.005% 35.5 6.5 19.1 19.2 29.8 0.010% 37.0 9.6 19.4 20.0 30.0 0.02% 38.1 10.8 20.3 13.1 30.6 0.10% 40.7 16.6 22.3 25.5 35.6
benomyl
0.20% 50.6 21.2 29.4 28.7 38.3 0.005% 0 0 0 13.6 10.8 0.010% 9.1 0 0 17.6 13.9 0.040% 13.5 11.0 0 21.1 18.9 0.08% 21.3 16.4 14.3 19.7 22.9 0.20% 24.2 21.4 14.8 22.6 28.1
Cu-8
0.50% 41.1 30.3 17.4 31.5 36.2 0.80% 12.0 15.1 12.1 10.6 20.8 1.60% 13.1 16.4 13.4 11.1 23.1 DDAC
2% 13.4 18.0 13.9 11.9 29.0 0.005% 0 0 0 0 0 0.010% 0 0 0 20.0 0 PPZ 0.020% 0 0 0 21.9 0 0.005% 0 7.1 0 0 12.7 0.010% 0 13.2 0 13.2 16.6 TEB 0.050% 0 20.9 12.4 18.5 17.0
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Table 4 The diameter of inhibition zone by formulations (mm)
Formulations Concentrations
of a. i. Bt Fv Th Tv Pp 0.2%+0.2% 20.1 24.1 11.9 12.5 30.2 0.5%+0.2% 25.6 18.5 13.5 12.8 31.0 CTL+Cu-8 0.5%+0.5% 33.0 29.9 16.3 20.4 41.8
0.05%+0.5% 14.7 18.1 18.0 9.5 23.0 0.2%+0.5% 18.0 19.6 23.9 11.5 40.6 CTL+DDAC 0.5%+0.5% 49.1 27.5 27.9 12.7 52.7
0.01%+0.01% 21.4 14.1 28.2 32.5 41.5 0.01%+0.05% 22.3 18.9 28.9 33.9 45.6 0.01%+0.1% 23.8 24.3 30.6 35.7 46.9 0.1%+0.2% 42.3 43.0 48.6 35.2 Na
0.1%+0.5% 47.2 43.5 56.8 34.2 N
CBZ+Cu-8
0.2%+0.5% 59.7 46.6 60.3 44.3 N 0.005%+0.05% 40.5 17.6 23.8 22.6 40.8 0.01%+0.05% 43.6 17.9 26.6 25.8 42.7 0.01%+0.1% 46.4 18.3 27.8 25.5 43.5 0.02%+0.2% 48.0 19.3 28.8 26.4 44.1 0.1%+0.5% 50.0 20.6 30.2 28.7 44.6
CBZ+DDAC
0.2%+0.5% 53.2 22.7 32.0 30.4 45.2 0.2%+0.02% 8.11 19.8 15.4 17.1 27.3 0.2%+0.05% 8.42 20.0 15.7 17.4 28.6 BAC+CTL 0.4%+0.1% 17.9 23.5 19.8 19.8 29.5
0.2%+0.01% 10.4 12.5 10.2 15.2 23.7 0.4%+0.01% 11.9 14.5 13.1 17.8 25.5 BAC+Cu-8 0.4%+0.05% 16.0 16.1 14.1 18.4 27.3
aN: No fungal growth
25
Table 5 The diameter of inhibition zone by formulations (mm)
FormulationsConcentrations
of a. i. Bt Fv Th Tv Pp 0.005%+0.01% 42.7 8.9 25 17.5 32.3 0.01%+0.01% 43.1 12.2 25.6 20.8 35.3 0.02%+0.01% 46.1 13.2 25.7 21.4 35.7 0.02%+0.02% 48.9 18.3 27.0 22.9 40.0 0.1%+0.02% 50.4 29.0 31.9 22.8 53.7
Benomyl+Cu-8
0.2%+0.08% 52.9 38.7 38.1 23.8 56.3 0.005%+0.01% 44.8 16.2 22.6 21.5 36 0.01%+0.1% 45.8 20.1 26.6 29.4 39.8 0.02%+0.2% 50.4 20.0 28.1 31.0 43.5 0.02%+0.5% N 32.7 42.0 32.5 N 0.1%+0.5% N 43.1 43.7 36.7 N
Benomyl+DDAC
0.2%+0.5% N 43.3 41.4 39.1 N 0.02%+0.2% 18.0 16.3 18.0 12.0 24.8 0.02%+0.5% 22.7 20.3 20.6 14.3 31.9 Cu-8+DDAC 0.08%+0.5% 24.3 31.8 20.4 17.8 27.0
0.01%+0.005% 9.1 14.0 0 0 18.9 0.02%+0.005% 10.0 17.3 0 0 11.5 PPZ+Cu-8 0.02%+0.01% 12.5 16.7 9.5 0 14.1 0.01%+0.01% 10.2 0 12.4 0 10.9 0.02%+0.05% 17.5 15.2 16.0 0 11.6 PPZ+DDAC 0.02%+0.1% 17.0 14.3 15.5 0 12.9
0.01%+0.005% 21.8 14.5 23.9 22.8 30.4 0.02%+0.01% 19.5 19.1 25.8 25.6 32.7 PPZ+Benomyl0.02%+0.02% 23.6 21.1 26.7 26.8 33.5
0.005%+0.005% 9.1 11.1 0 0 17.7 0.01%+0.005% 10.9 14.9 0 0 21.0 TEB+Cu-8 0.05%+0.01% 15.5 22.2 0 0 28.9 0.005%+0.01% 0 0 0 0 20.5 0.01%+0.05% 17.2 19.5 17.4 15.2 23.6 TEB+DDAC 0.05%+0.1% 20.7 24.1 18.6 18.0 29.2
0.01%+0.005% 16.3 16.6 22.8 22.9 27.4 0.02%+0.01% 23.1 18.6 24.7 25.3 28.6 TEB+Benomyl0.05%+0.02% 27.1 21.8 24.2 25.9 32.2
REFERENCES
Laks, P E, Woods, T L (1992): Chlorothalonil: A new ground contact wood preservative.
IRG/WP/ 92-3712. Wakeling, R, Woods, T L (1997): Antisapstain field trials of nexgen in New Zealand.
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IRG/WP/97-30145. Wakeling, R, et al (1997): Laboratory and field trials of novel antisapstain formulations.
IRG/WP/97-30146. Cooper, J F, Riboul, D, De Vleeschauwer, M, Woods, T (1997): Migration of chlorothalonil and
carbendazim in fruits stored in wood treated with the anti-sapstain formulation Tuff Brite C. IRG/WP 97-50097.
Appendix II Technical Report of Vacuum Pressure Treatment by NaPCP Free Preservative During 2006-2007 --ITTO PD103/01 Rev.4(I) “Demonstration of Rubberwood Processing Technology and Promotion of Sustainable Development in China and Other Asian Countries”
Based on the output of ITTO PD 3/96 Rev. 2(I), pilot test of vacuum pressure treatment of NaPCP free preservative was conducted during 2006-2007.
1. MATERIALS AND METHOD
1.1 Materials
Fresh rubberwood timber. 1.2 Preservatives
The active ingredients of formulations are described in Table 1.
Table 1 The active ingredients of each vacuum pressure treatment formulations
Formulations Boric acid (%) Borax (%) F2 (%)
1 0.50 1.00 0.035-0.045
2 1.00 0.20 0.035-0.050
1.3 Test sites
Site 1：Lezhong Wood Factory, Hainan Nongken Wood Co，duration：Aug 3, 2006– May 31, 2007.
Site 2： Cangjiang Wood Plant, Xishuangbanna, Yunnan Province. duration：July 24, 2006– Oct 31, 2006. 1.4 Treating procedure
Vacuum pressure treatment was used in the following procedure.
Site 1： Initiate vacuum -0.08 M Pa for 15 min, 1.2 M Pa pressure for 35 min, final vacuum -0.085 MPa for 10 min. The average absorption was 200-250 kg/ m3. The treated timber was stacked.
Site 2： Initiate vacuum -0.08 M Pa for 15 min, 1.1 M Pa pressure for 60 min, final vacuum -0.08 MPa for 15 min. The average absorption was 200-250 kg/ m3. The treated timber was stacked.
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Fig 1 Rubberwood timberbefore treatment (Lezhong Wood Factory, Hainan Nongken Wood Co，Aug, 2006)
Fig 2 ic acid/borax/F2) (Lezhong Wood Factory, Hainan Nongken Wood Co，Aug, 2006)
Fig 3 /borax/F2) (Cangjiang Wood Plant, Xishuangbanna, Yunnan Province，Aug, 2006)
r drying after treatment (Cangjiang Wood Plant, Xishuangbanna, Yunnan Province，Aug, 2006)
Preservative (bor
Preservative(boric acid
Fig 4 Ai
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2. RESULTS
This test indicated that F2 could prevent the treated timber for 15-20 days from stain and mold. At Lezhong Wood Factory, Hainan Nongken Wood Co, there was only small mold occurrence during air drying in May 2007. At Cangjiang Wood Plant, there was only small mold occurrence during air drying from Sept to Oct, 2006. The reason is that: some treated timber was direct exposed to exterior for the leaching of fungicide after the raining, for there is limited shed for air drying.
3. CONCLUSIONS
Fungicide carbendazim (F2) only can be used for stain control, and it is also effective to most of the mold fungal species. It could be the alternate of NaPCP.
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Drying Techniques of Rubberwood Gao Ruiqing Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] Li Xiaoling Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China E-mail:[email protected] FTeng Tonglian Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China
SUMMARY
In order to gain good drying quality of rubberwood, the combination drying method of air-drying and kiln drying is recommended to dry the preservative treated rubberwood timber. Different air-drying methods were introduced and final moisture content range from 25% to 35% was reasonable to pre-dry rubberwood before kiln drying. The conventional drying could be used as a good method to dry rubberwood, and 3 drying schedules were introduced in this paper. Rubberwood with or without pith should be dried separately. Pith free rubberwood could be dried according to the higher temperature schedule C with good drying quality. Uniform spacing stickers and heavy load on the top of stack was recommended to reduce distortions. In order to keep its original color, the rubberwood should be dried acceding schedule A. And schedule B can be adopted according to the drying quality requirements of final rubberwood products.
Keyword: Rubberwood, plantation, drying
The keys to prevent rubberwood from stain fungus or decay rely on not only chemical treatment but also immediate drying so that the moisture content (MC) can reach a low level to destroy the live conditions of fungus.
Combining the pre-drying with conventional kiln drying is a practical way to prompt drying quality and reduce drying cost. The pre-drying methods include lower temperature pre-drying and air-drying. Lower temperature pre-drying must be conducted in a large pre-drying room until the moisture content reduces to 25%-30%. The advantages of low temperature pre-drying are that of free from climate infection, drying time under control and good drying quality.
Air-drying is also a pre-drying method which is popular to apply in practical production for its various advantages. Air-drying rubberwood can contribute to not only shorten drying time, reduce drying cost but also cut down energy consumption.
Kiln drying is a drying method which is practiced in a building or a metal vessel with controlled conditions of drying temperature, humidity and air velocity. The desired drying quality and finial moisture content can gained if the proper drying technology is taken. Kiln drying includes conventional drying and high-temperature drying according to drying temperature.
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1. AIR-DRYING OF RUBBERWOOD
To dry timbers in the air is called natural drying, shortly called air-drying. With this drying method, timbers are stacked in an open yard or a shed yard, and are dried by absorbing the heat in atmosphere. Air-drying has been used widely in practical production for its various advantages, such as easily to conduct, lower drying cost and etc. As usual, air-drying works as a pre-drying for kiln drying. And practice results show that air pre-drying can not only reduce drying cost and get even MC distribution, but also provide the good preparation for kiln drying if the reasonable air-drying conditions are taken. Two kinds of air-drying yards are showed in Figure 1 and Figure 2.
Figure 1 Air-drying with shed
Air-drying is mainly governed by air conditions instead of man control conditions. And air conditions are associated with climate, season, daytime or nighttime etc. But air temperature, humidity and airflow work as the main factors. The climate is various in China for its vast territory. Such as, in south sea-area it is warm and humidity, so air-drying can be conducted all year ; In summer, air temperature is high, so it’s a quickly air-drying season except the very high humidity days; In winter, air-drying slows down for the lower temperature; Spring and autumn are the most proper seasons for air-drying because of the suitable air conditions, which means, there’s enough air heat power to drive water out from timbers, and at the same time, the proper humidity keep the timbers from mould, stain and drying cracking. In the all, air conditions should be taken into consider whenever air-drying is conducted.
Figure 2 Air-drying yard in the open air
In addition, the microclimate which formed in timber yard is another factor to affect air-drying.
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This microclimate is associated with water evaporation intension, drying temperature and air circulation speed，and can affect air-drying quality and air-drying speed. 1.1 Air-drying techniques
Some air-drying techniques must be taken into account to obtain the desired drying quality during the drying. The techniques include how to arrange the timber yard, how to stack and how to control the drying time etc.
1.1.1 Timber yard
Timber yard is the place where the timbers are stacked. In a same timber yard, the water evaporation intension of timbers is changeable in different position. The evaporation intension is stronger at the edge of yard than that in the center of the yard; On the other hand, in a same timber stack, water evaporation speed of timbers is the fastest and slowest respectively at the top and the bottom of the stack, and at the middle of stack, the evaporation intension is one-fifth of that outside of stack. But in the foggy cold night, the water evaporation speed is faster inside than outside because of its high temperature inside of stack; In addition, the water evaporation intension in a sunny-windy day is stronger than that in an un-windy day. So there are some special requirements when the timber yard is selected and arranged.
1) The floor of timber yard must be flat and dried with slope of 0.2%～0.5% for well draining. And draining establishment must be equipped around the yard as well, besides there is no high building around the yard for well ventilation.
2) Timbers should be arranged in different stack groups in one timber yard according to species and sizes. Usually, there are 4～10 small stacks in one group. All stack groups are separated by vertical and horizontal alleyway, and vertical alleyway should be faced north to south to avoid the straight sunlight. At the same time, the vertical alleyway must be paralleled the direction of main-wind and the length of stack. The details are showed in Figure 3.
Figure 3 The collocation of hard wood in a yard (m)
3) Timber yard must smooth without weed. Draining channel must be underground. The timbers must be separated apart once they are aggrieved by fungus or mould.
4) Timber yard must be far away from residential area, boiler and high building to avoid potential fire trouble. The distance from boiler chimney must be more than 100 m, and from residential area more than 50 m. In addition, proper fire control equipments must be set around timber yard.
1.1.2 Timber stack
Timber stack must be arranged in the timber yard according to some techniques. Timbers which
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are thin or easy to be stained should be piled in the middle of yard. And timbers which have been infected by fungus must be stacked at the corner of the yard. Thus the followings must be considered when the stack is arranged.
1) The foundation of stack: The foundation of the stack is usually made of reinforced concrete, brick or wood. It is a base which can not only keep some space under the stack for well ventilation but also keep the stack stabilizing. Usually, the distance between ground and foundation is 0.4m～
0.75m, but in south of China it should be 0.5m～0.75m because of the high rain water level. The size of foundation is showed in Figure 4. Figure 5 shows a wooden stack foundation which covered with something like pitch to avoid decay. In the more, there are some crossbeams on the foundation, the distance between two crossbeams is 1.3m～1.6m for thinner one and 1.6m～2.1m for thicker one.
Figure 4 The form of stack foundation（m）
Figure 5 wooden stack foundation for air-drying
2) The size of stack: The sizes of stack are changeable with the different piling methods. The width of the stack with stickers between two layers should be less than 4m～4.5m so as to get the even drying. The size of the square stack with timbers self-crossing is governed by the length of timbers. In another way, the width of stack is affected by species and other factors. The width of stack for hard wood should be 0.9m～1.8m so that the timbers at lower layers in the stack can be dried at the same time; For very wide stack, an central air channel which is showed in Figure 6 must be kept in the center of the pile. If a stacking machine is used to pile, the width of stack is governed by the capacity of the machine, usually the width is 1.3m. If the kiln drying is needed after the air pre-drying, the width of stack should be matched with the drying kiln. The height of
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stack is governed by the intensity of the foundation and stacking methods, height of 2.7m～4.8m with handwork stacking and height of 6m～9m with machine stacking.
3) The space in the stack: The space in the stack is different according to the weather, yard and species. Timbers should be kept sparseness if the climate is humidity and air is bad ventilation; Timbers of hard to be dried should be stacked closely. The cracks between timbers are mainly determined by moisture content of timbers, size, specie and drying season. Usually, the cracks should be 20%～50% of width of timber, but less than 100% so that both the good ventilation and maximum yard capacity utilization can be available. The details about cracks are showed in table 1. The cracks along the width of stack should form vertical flue, and the width of the flue should be 20% of that of stack.。
Table 1 The cracks in a stack
The width of timber /cm The size of crack/The width of timber <25 1/2～3/4
25～45 1/3～1/2 >45 1/5～1/3
The timber easy to be face check 1/12～1/6
4) Sticker: Reasonable using of stickers can not only keep the pile stabilizing and make sure the nice drying quality but also build a fitting horizontal air pass for well ventilate. As usual, thick stickers are used for timbers with thin and high MC, and stickers used at the lower position of stack should be a littler thicker than that at the top of the stack. The more space between stickers, the better ventilation it will be, but the more warp deformations are easy to occur at the same time. In addition, timbers should not reach out of stickers for nice drying quality, and tickers should keep the same level up and down. The details about the size and space of sticker are showed in table 2.
Table 2 The size and space of sticker
Thickness of timber /mm
the space between sticker /mm
the thickness of sticker /mm
18～20 300～400 20 20～25 400～500 25 40～50 500～600 30 50～65 700～800 35 65～80 900 40
>80 1000 45
5) Making air pass in the stack: Air pass in stack includes cracks (the space between timbers), stickers spacing, vertical flue and horizontal flue. The size of air pass is closely associated with drying speed and drying quality. Small air pass make timbers easy to be infected by fungus, but large one can reduce the drying capacity.
Vertical flue is the air pass which is set along the height direction of stack. There are two kinds: one kind is that the air pass has a same width up and down, and the other is that narrow is above and wide is below. The vertical flue is different with the difference of stack width, height and cracks. As usual, the width of the first kind of vertical flue should be 3 times width of the crack, and the width of the other kind should be about 20cm and 50cm above and below respectively.
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The height of vertical flue should be as the same height of the stack or just as 2/3 of the stack. Two or three vertical flues should be setup in a stack so that the rapid drying can be obtained at lower position of the stack
Horizontal flue is the air pass which is set along the width of stack in order to enhance the ventilation in transverse direction. As usual, one horizontal flue with height of 10cm～15cm is setup every 1 meter from first layer. Horizontal flue can be made by sticker or timbers themselves.
6) The roof of stack: The roof must be setup over the stack. The slope of about 12% is needed when the roof is made to keep the rain out. In addition, roof must reach out to the stack about 0.75m in front and 0.5m in other sides. It is displayed in Figure 5.
7) Piling methods: There are many kinds of piling methods in a yard. They are flat piling (Figure 6), slope piling (Figure 5), triangle piling, furcation piling and well piling (figure 7) etc. But flat piling and slope piling are very popular because of their good drying quality.
Figure 6 Stack with central air channel (Notes：1-foundation；2-crossbeam；3-sticker；4-timber；5- central air channel)
Figure 7 Piling for short timber
For the unusual size of timbers, the piling method should be special so as to make sure the good drying quality. Timbers used in furniture and construction are piled like Figure 7, and short timbers of roughcast are piled like Figure 8.
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Figure 8 Well piling
In the practical production, if timbers are flat piled, long radial timbers should be put in the sides of stack, short tangential ones are put in the center of stack.
8) Managing the stack: Putting a mark board on the stack with specie, size, quantity and date on it so that the details of air-drying conditions can be obtained in time.
1.1.3 Air-drying time
Air-drying speed is fast in the first month whenever it is. But the drying speed distinctly slows down when moisture content reach the fiber saturation point (FSP). In this condition, drying speed is mainly governed by the climate, and the final moisture content is associated with local equilibrium moisture content. About the average monthly equilibrium MC for Haikou and Kunming are showed in table 3.
Table 3 The average monthly equilibrium moisture content (%)
Jan. Feb. Mar. Apr. May Jun.. Jul. Aug. Sep. Oct. Nov. Dec. average
Haikou 19.2 19.1 17.9 17.6 17.1 16.1 15.7 17.5 18.0 16.9 16.1 17.2 17.3
Kunming 12.7 11.0 10.7 9.8 12.4 15.2 16.2 16.3 15.7 16.6 15.3 14.9 13.5
1.1.4 Air-drying defects and protecting methods
Table 4 The protecting methods on air-drying defects
Air-drying defects The corresponding protecting methods
checks 1) Enlarge the width of stack;
2) Reduce the space between the stacks to 0.5m～0.6m;
3) Lessen the cracks between the timbers in the stack;
4) Put the stickers close to the ends of timbers as possible;
5) Make the roof resist wind, rain and sun;
6) Cover pitch at the end of timbers if possible:
warp 1) Stickers should be put on the crossbeam to keep them vertical up and
down;
2) Reduce the space between stickers;
3) The width of timbers and stickers should keep the same respectively in one
stack;
4) Roof must be setup at the top of the stack;
5) The weight on the top of stack should keep even;
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discoloration 1) Reduce the width of stack;
2) Enlarge the space between timbers;
3) Enlarge the space between stacks;
4) Make sure the good ventilation under the stack;
5) Keep assistant air passes large;
6) Timbers must be chemical treated to avoid the fungus before stacking;
Drying defects such as check, warp and decay are easily to happen during the air-drying. Checks mainly include end check, small end-to-surface check. They are caused by tensile stress which produced because of the fast water loss at the end of timber. Warp deformation often shows as bow, crook, cup and twist etc. They are mainly caused by the different shrinkage among the cross texture, radial and tangential texture. On the other hand, warp deformation are also associated with strong sun light, misused stickers and etc. Rubberwood is particularly susceptible to degradation by mould and fungus. Thus quick drying the fresh rubber timber is very important. The details about air-drying defects and corresponding protecting methods on how to keep timbers from degradation are showed in table 4.
1.2 Forced air-drying
Some fans are equipped near the stack in order to enhance the air circulation speed, this method is called the forced air-drying. It is the development of air-drying. It differs from the kiln drying with stacking in the open air yard or shed yard without controlling the air conditions. And it differs from normal air-drying with forced air circulation to quick the drying speed. The drying time of forced air-drying is shorter than that of normal air-drying, but the drying cost is higher than that of normal one. Some forced air-drying methods are available in Figure 9 to Figure 14 according to the location of fans.
1）Figure 9, Fans deliver air at the bottom of stack;
2）Figure 10, Fans deliver air between stacks;
3）Figure 11, Fans draw air between stacks;
4）Figure 12, Fans deliver air from side of stack;
5）Figure 13, Fans deliver and draw air with fans moving;
6）Figure 14, Fans deliver and draw air with air circulation
Figure 9 Fans deliver air Figure 10 Fans deliver air
at the bottom of stack between stacks
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Figure 11 Fans draw air Figure 12 Fans deliver air
between stacks from sides of stack
Figure 13 Fans deliver and draw Figure 14 Fans deliver and draw
air with fans moving air with air circulation
Usually, forced air-drying time is 1/2～2/3 of that of normal air-drying if air circulation speed is 4m/s. Forced air-drying is effective when the air humidity is lower than 90% and air temperature higher than 5 . But the cost of forced air℃ -drying is 1/3 higher than that of normal air-drying. Forced air-drying is often used in practical production for easy discoloration and soft wood. 1.3 Suggestions for Rubberwood Air-drying
The fresh timbers must be chemically treated before air-drying so as not to be decayed. Air-drying time is different with the difference of remedies and treatment methods. So some special attentions should be taken during rubberwood air-drying.
1) Choosing the yard: The air conditions (including temperature, air circulation and humidity) of yard mainly govern the air-drying speed and quality. Thus the well ventilating yard must be chosen for the pre-treated timbers with chemical remedies.
2) Air-drying time: Air-drying time is different with the difference of remedies and treatment methods. For examples, if the timbers are treated with Parachem in a simple pool, they can resist stain fungus for 10～30 days; But if timbers are treated with the same remedy but in a vacuum pressure chamber, the timbers can resist stain fungus for about two months. The air-drying time of rubberwood should not last too long especially in humidity season. The test results are showed that the proper air-drying time for rubberwood should be less than two months, and the proper final MC should be 30％～20％.
3) The stacking: Stacking methods are very important for rubberwood which is particularly susceptible to degradation by mould and fungus. Thus stickers should be ordered according to the special requirements, such as stickers must keep vertical up and down in the stack and stickers must be put close to the ends of timbers in as possible in the stack; Timbers with almost a same size are piled in one stack; Marked board with treatment time, stacking time, initial MC and final MC etc. should be stick on the stack.
4) Choosing sticker: Thick stickers are used to air-drying the thin timbers so as to enlarge the air pass in horizontal direction. When timbers with high thick are dried, the timbers can be used as stickers themselves.
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5) The arrangement of stack: There are many stacks in one yard, so stacks should be arranged in proper order so that the following serial productions can be taken out smoothly, such as the first air-dried timbers enter for the kiln drying first. In addition, stacks should be arranged along the direction of main wind; The distance from ground to the bottom of stick should keep as 50cm～
70cm. 6) Adjusting stack: When the air-dried timbers will be re-dried in the kiln, it’s better to unload
the stack so as to adjust the MC in the stack and remove timber stress. On the other hand, unloading the stack can make sure same size timbers with close MC enter for the same kiln to dry so as to get a good drying quality with less cost.
2. KILN DRYING OF RUBBERWOOD
Kiln drying is the main wood drying method because it is more mature and widely used for long time. The drying temperature of conventional kiln is always within 100 . Because of medium ℃
drying temperature and humidity adjustable, it can be used to dry almost any wood, sometimes bamboo or even medicine herbs. 2.1 Conventional drying kiln
In all conventional drying kilns, about 98% are periodic production pattern, and only 2% are continuous production pattern. And among the periodic production pattern conventional drying kilns, more than 75% are forced circulation compartment kilns, and less than 25% are natural circulation compartment kilns. And the forced circulation compartment kilns can be classified into line-shaft kiln style, cross-shaft kiln style, motor inside kiln style, side-fan kiln style and end-fan kiln style by the fan’s pattern and location inside kiln; and can be classified into steam kiln style, hot water kiln style and furnace gas kiln style by the heating sources, and can be classified into trolley loading kiln style, fork loading kiln style by the stack loading methods, and also can be classified into all-metal kiln style, brick and concrete kiln style, etc. by the kiln body patterns. Among all these patterns, the forced circulation compartment conventional kilns with top-fans and motors inside, heating by steam or hot water are the most widely used.
Figure 15 Trolley loading conventional kiln (Simpson, 1991)
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The typical trolley loading and fork loading conventional kilns are showed in Figure 15 and Figure 16.
Figure 16 Fork loading conventional kiln (Simpson, 1991)
A conventional drying kiln usually consists of following parts:
(1) Kiln body and door：kiln body patterns include all-metal body, brick body, and brick body with aluminum panel inner wall ect. All-metal body kiln using stainless or aluminum alloy as structure framework, prefabricated aluminum panel with polyurethane insulator as kiln wall, and long life duration silicon rubber as seal on the vertical lifting door, is a typical all metal body drying kiln, usually with good insulation and air proof performance.
(2) Air circulation system：The air inside kiln is circulated by fans, which are directly connected with motors, and located in the upper, side or end position inside the kiln. The air circulation speed is usually 1-3m/s. To make the circulation uniform, a series of oriented boards are put on reasonable position in the air way. To assure the durability, the air conductors should made of aluminum of stainless panels, and fans are usually made of molten aluminum or aluminum alloy.
(3) Heating and spraying system：The heat sources are steam or hot water. To reduce the cost, sometime the hot smoke from wood waste burning can be directly to use as heat source. The radiator is usually with steel pipe inside and aluminum coat and fins outside. This kind of radiator has advantages of high heat transfer efficiency, rot resistant, and long durability.
(4) Temperature and humidity system: The temperature and humidity could be controlled manually, semi-automatically, or whole automatically. Nowadays some kilns made in China use imported whole automatically controlled system, but semi-automatically controlled systems are commonly used because of precise controlling and easy to operate and use. The temperature and humidity detection usually use dry and wet bulb temperature method, and the moisture content detection could use weighing or electric resistance methods, of which the former one is more precise, and the latter one is more intuitionistic.
(5) Stacking and stack transportation system：This system consists of folks, or stacking machine, stack trolley, and unstacking machine.
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(6) Lab equipments：All the equipment in drying lab should meet the requirement of drying procedures, including electric oven with fan inside, electric balance, moisture content meter, air speed meter, saws, ruler, digital vernier calipers, and record paper, etc. 2.2 Conventional drying techniques
The conventional drying could be divided into following 3 stages:
Pre-heating stage: Pre-heating means to heat the wood to a reasonable temperature before wood drying starts. During pre-heating stage, the moisture inside wood keep not being dried because of really high relative humidity environments. The preheating temperature should be 8-10 higher ℃
than the first stage drying temperature. When the wood moisture content is above 30%, the 100% of relative humidity can be used in preheating stage, and when the wood moisture content is below 30%, the value of relative humidity can be a little higher than the EMC corresponded relative humidity. And the pre-heating time is based on the wood species, thickness, and outside climate, and the basic rule is to keep the temperature inside wood is 5-8 higher than the first stage drying ℃
temperature.
Drying stage: The drying stage just begins right after pre-heating ends. Firstly the free water inside wood evaporates at a fixed rate, and then absorptive water starts to evaporate with slowing down rate. At this stage, conditioning treatment is necessary if too much drying stress occurs; it is also called intermediate treatment. When the moisture content drops to the final required value, equalization treatment can be used to release drying residual stress and moisture content difference, and it is also called final treatment.
Cooling stage: After the final treatment, all the drying stage ends. Then close all heating and spraying valves, stop all motors and keep the vent open. The wood can be unload out of kiln when the wood cooling down.
Both inside China and abroad, the dominated drying method is conventional drying. The techniques and requirements during rubberwood drying are described as follows.
2.2.1 Reasonable stack
To ensure good air circulation inside kiln, and also to reduce distortion and end checking, the rubberwood boards need to pile into stacks as following requirements:
1) Pre-sorting the initial moisture contents of every rubberwood boards, if they are too much different, piling them into different stacks and drying separately.
2) The two ends of each rubberwood board needs to be sealed to prevent them from end checking.
3) The thickness of stickers should be uniform, renewing them at once if problem happened after use.
4) To pile the rubberwood boards with same or similar thickness in the same layer of stack. 5) The stickers near two ends of stack should be closed as near as to the ends of boards, the
sticker space should be kept within 0.5 meter, and at least 3 rows of stickers should be put along the length direction of stack.
6) Keep the same row stickers in different layers of stack should be kept in one vertical line. 7) Heavy load should be put on the top of stack to reduce distortion during drying (seeing Fig.
17). 8) The rubberwood to be dried in one kiln should be with similar size and initial moisture
content. In practice, if two different size boards are put into same kiln to be dried, the
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executed drying schedule should use that of the thicker ones 9) If the total amount of rubberwood is less than the capacity of drying kiln, it is recommended
to reduce the width of wood piles inside kiln, meanwhile keep no spare space in length and height directions.
10) The rubberwood board with pith is easy to be occurred checks and distortion during drying, so it is recommended to separate these boards from the normal ones during stacking, and then piling them in one stack. When these stacks are enough for the capacity of one kiln, drying them with special drying schedule.
Figure 17 The stack for fork-loading kiln
2.2.2 The sample board and moisture content measurement
The rubberwood moisture content could be measured by portable electric resistant or electromagnetic wave meters. The all automatically controlled kiln usually is usually equipped with online moisture content detection system, and can automatically execute and adjust the parameters according to the detected moisture content value and the drying schedules which have been stored into the system before drying.
In the semi-automatic controlled kilns, the moisture content is needed to detect manually. To make the detected moisture content more precise, the sample board should be made before drying, and it should be located to the position easily to fetch (Fig. 18).
Figure 18 Drying sample position in stack
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Sample boards include moisture content sample board and stress sample board. Before drying, the initial moisture content of sample boards should be measured and calculated. During drying, with the weight change of sample boards, its corresponding moisture content value could be calculated, and when it reaches the final moisture content requirement, the drying process could be ended. Usually two stress sample boards are prepared and one is put to the positions in a stack which drying rates is the fastest, and the other one is put to the mean drying rate position in a stack. If needed, the residual drying stress could be measured using moisture content sample boards after drying ended. The moisture content and stress sample boards could be prepared as showing in Figure 19.
Figure 19 Drying sample and MC sections
The sample board should be selected from the rubberwood sawntimber with no bark, no rot, no knot and no pith, and t should be at least 0.3 meter far away from the two ends of sawntimber. Usually 4 moisture content sample boards are selected before drying, of which two tangential boards with high initial moisture content, one tangential board with low initial moisture content, and one radial board with high initial moisture content. The two tangential boards with high initial moisture content can be put to the low drying rate position or other easy to fetch position in stack, using as moisture content detection for controlling. The tangential board with low initial moisture content and the radial board with high initial moisture content can be put to the positions with fast and low drying rates respectively, using to decide the final equalization treatment. The length of sample board is 1.0 meter, and the thickness of sample board is the same with rubberwood sawntimber, and the width of sampler board is the average width of rubberwood sawntimber. After the sample board is cut from rubberwood sawntimber, it should be weighing and sealed with waterproof materials to the two ends immediately. If stacks are still not put into drying kiln, the sample boards could be packaged by plastic film and waiting for use.
During the moisture content sample board making, two moisture contend slices with thickness of 10 to 12 mm are cut from the two ends of it. The average moisture content value of these two slices can be regarded as the initial moisture content of the sample board.
The oven dry weight could be calculated using formula (1).
Gg=(100×Gc）/(100+Wc) ………………………(1)
In which: Gg—oven dry weight, g; Gc—initial weight, g; Wc—initial moisture content, %.
During drying, the moisture content of sample board could be calculated using formula (2).
Wd=（Gd-Gg）/Gg …………………………… (2)
In which: Wd—the current moisture content, %; Gd—the current weight, g; Gg—oven dry weight, g.
If use electric resistance moisture content meter to detect the moisture content, it is recommended to adjust and revise the meter with rubberwood. To get the mean moisture content of a board, the
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pins should be inserted into the 1/5 of board thickness. 2.3 Tests on the drying characteristics and schedules of rubberwood
2.3.1 Test material Species: rubberwood（Hevea brasilie） Tree age：25-33 years producing area：(1)Xilian Farm, Hainan Province
（2）Nanmao Farm, Hainan Province Log diameter：220-450mm Log length：2,000-2,200mm
2.3.2 Drying characteristics test
In order to determine the drying schedule of rubberwood, drying characteristics were tested in the electricity heated oven. Test sample (with the size of 200×100×20 mm) were put in the oven on end with the constant temperature at 100 . Before the test, the initial status, including the weight, ℃
and the visible surface defects were measured. The initial checks were checked according to a fixed time. When the moisture content is below 1 percent, the test was over. At this time, calculate the number of all invisible drying defects, and then cut the samples to calculate the final moisture content, in the meantime, the observe the inner checks and calculate the cross-section deformation value.
Table 5 The Status of initial checks
Surface check End-surface check End check No.
Long-narrow Short-narrow Wide Long-narrow Short-narrow Wide Long small
Defects
grade
No.1 0 4 0 0 9 0 0 many 2
No.2 0 2 0 0 7 0 0 many 2
No.3 0 0 0 0 2 0 0 many 1
No.4 0 1 0 0 3 0 0 many 2
No.5 0 3 0 0 7 0 0 many 2
No.6 0 2 0 0 5 0 0 many 2
No.7 0 4 0 0 4 0 0 many 2
No.8 0 9 0 0 7 0 0 many 2
No.9 0 3 0 0 11 0 0 many 2
No.10 0 0 0 0 3 0 0 many 1
No.11 0 3 0 0 8 0 0 many 2
No.12 0 2 0 0 5 0 0 many 2
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Table 6 The Status status of internal checks and cross-section deformation after drying No. Internal checks Defects grade Deformation (A-B）mm Defects grade
No.1 No check 1 0.10 1
No.2 no check 1 0.03 1
No.3 no check 1 0.12 1
No.4 no check 1 0.18 1
No.5 no check 1 0.32 1
No.6 no check 1 0.06 1
No.7 no check 1 0.00 1
No.8 no check 1 0.17 1
No.9 no check 1 0.09 1
No.10 no check 1 0.03 1
No.11 no check 1 0.33 1
No.12 no check 1 0.25 1
Table 7 Moisture content changing during the 100 drying test (%)℃
Drying time 0 1 hour 3 hours 5 hours 7 hours 13 hours 19 hours
No.1 73.6 50.3 34.7 25.0 17.5 4.2 1.1
No.2 71.5 47.6 34.1 24.8 17.9 6.2 1.2
No.3 70.3 48.1 34.5 25.6 18.9 6.5 1.2
No.4 68.2 48.2 35.4 26.2 19.8 7.2 1.3
No.5 69.1 48.9 34.8 25.0 20.2 6.3 1.2
No.6 70.4 48.6 34.2 24.5 19.5 5.1 1.2
No.7 71.6 48.1 34.8 24.2 18.7 4.5 1.2
No.8 72.9 50.9 36.1 26.3 19.2 4.1 1.1
No.9 68.9 48.2 34.0 25.1 18.5 5.4 1.2
No.10 75.8 53.1 38.6 29.1 19.2 4.9 1.1
No.11 67.8 49.0 39.3 28.0 20.5 4.8 1.
No.12 72.0 49.2 37.5 27.9 18.7 6.7 1.2
100 drying test showed that the check of rubberwood was not serious. The main types of checks ℃
were end check, surface check and end-surface check. Although the initial moisture content of rubberwood was high, the moisture content of the surface part decreased rapidly under the FSP and begin to shrink, while that of the inner part was still higher. Therefore, the drying stress occurred and the surface check appeared. After the drying test lasted for one hour, the slight end check appeared on all the test samples, and with the test continuing, the checks became more and more seriously, even some of these end checks were stretched to the outer surface to form that called end-surface checks. When the sample’s mean moisture content reached about 30%, all the initial checks stopped. 100 drying characteristics test showed there were some surface checks, ℃
end checks and end-surface checks in the initial drying stage but not seriously (see table 5), and the defect grade of initial checks of 100 drying test was grade 2.℃
After drying test ended, the samples were sawn to make the final moisture content test sample and to check the status of internal check and to measure cross-section deformation value (A-B) (see
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table 6). The results showed there was no internal check in the rubberwood, and the defect grade of internal checks of 100 drying test was grade 1. And the cross℃ -section deformation value was very small, its defect grade of 100 drying test was grade 1 too (see table 6).℃
2.3.3 Rubberwood drying schedule test
Rubberwood drying schedules for test were made out according to the results of 100 drying ℃
characteristics testing, and all the drying schedules tests were carried out in one of the rubberwood processing mill located in Hainan Province. The test sample size of rubberwood was 800-1,200 mm long, 80mm wide and 30mm thick. After preservatives treatment, the test samples were deposited in the air-drying shelter for a short term. And then the kiln drying tests were executed in this mill. After a series of testing, 3 drying schedules were finally selected (see table 8 to 10).
Table 8 Drying schedule A （Thickness:25-30mm）
Moisture
content (%)
Dry bulb
temperature
( )℃
Temperature difference
between dry bulb and wet
bulb ( )℃
Relative
humidity（%）Lasting time
Pre-treatment 55 1 95 5-6 hours
50 以上 48 3 85
50-40 50 4 80
40-30 52 6 70
30-25 55 8 65
25-20 60 12 52
20-15 65 15 45
15 以下 75 20 37
End-treatment 65 6 78 3-4 hours
Table 9 Drying schedule B （Thickness:25-30mm）
Moisture
content (%)
Dry bulb
temperature
( )℃
Temperature difference
between dry bulb and wet
bulb ( )℃
Relative
humidity（%）Lasting time
Pre-treatment 65 1 95 5-6 hours
50 以上 60 3 85
50-40 62 5 78
40-30 64 8 67
30-25 66 10 60
25-20 70 12 55
20-15 75 15 48
15 以下 80 20 39
End-treatment 85 6 60 3-4 hours
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Table 10 Drying schedule C （Thickness:25-30mm）
Moisture
content (%)
Dry bulb
temperature
( )℃
Temperature difference
between dry bulb and wet
bulb ( )℃
Relative
humidity（%）Lasting time
Pre-treatment 70 1 95 5-6 hours
50 以上 66 6 75
50-40 70 9 65
40-30 75 11 60
30-25 80 12 58
25-20 80 15 50
20-15 85 20 40
15 以下 90 25 33
End-treatment 85 6 60 3-4 hours
2.3.4 Drying schedule testing results analysis
The main indices taken into account in these drying schedule tests were the drying quality and drying speed. The objective of the tests was made out the optimum drying schedule of rubberwood with the shortest drying time at the precondition of good drying quality.
2.3.4.1 Drying quality
2.3.4.1.1 Visible drying defects
All visible drying defects, including end check, end-surface check, surface check, warp and deformation were counted after the test (see table 11). The results showed that, during the drying, the checks were not serious. The main types of checks were slight end checks, in which, some of them were developed into end-surface checks. And some small checks sometimes occurred in the surface of rubberwood boards along with the vessels, which were so imperceptible that they can be removed after planing and will not affect its use.
When drying rubberwood timber containing the pith with drying schedule B, few checks were found and only some deformation occurred; while drying with schedule C, severe checks even spits and deformation were found in about one fourth of the timber which containing pith. Considering these facts, timbers with pith and without pith should be dried respectively. Those containing pith should be dried according to schedule B and proper middle term treatment were needed, while Those pith free rubberwood timber could be dried fast according to schedule C and the drying time would be shorten.
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Table 11 Inspected Drying Indices unit: %
Drying
Schedule Index Max. Min. ó V% Average Visible drying defects
Wi 78.6 42.4 27.1 37.6 60.5
Wf 10.9 9.4 0.51 18.4 10.3
Wg 2.1 1.05 0.11 8.6 1.9
Schedule
A
Y 2.0 0.69 0.33 11.2 1.20
Surface checks and deformation were found on 5
samples containing pith; No split, warp and inner
check were found
Wi 80.1 43.3 20.6 35.2 58.6
Wf 10.1 7.6 0.98 10.6 9.2
Wg 2.0 1.30 0.53 35.1 1.5
Schedule
B
Y 1.90 0.35 0.22 19.8 1.09
End-surface checks were found on few samples, no
surface check and inner check were found. The dried
rubberwood kept the original color.
Wi 84.2 45.8 19.3 29.8 64.9
Wf 10.9 9.2 0.50 5.2 9.6
Wg 1.2 0.90 0.31 31.4 1.0
Schedule
C
Y 1.90 0.35 0.22 19.8 1.09
End-surface checks were found on a few samples,
surface checks were found on the samples containing
pith. Other samples were dried with good quality, and
the color of the samples became darker.
Note: Wi—initial moisture content; Wf—final moisture content; Wg—moisture content gradient along the thickness direction; Y—drying stress; ó—variance, V%— indicates the variance
2.3.4.1.2 Final Moisture contents (Wf)
The desired final moisture content of this test was 10%. Due to the limited test samples, 100 to 300 test samples were dried together with the timber of the factory and were put into the different kilns with capacity from 35 to 75 cubic meter. After drying, moisture contents were calculated by means of making the pieces of moisture content samples. The results showed the final moisture contents of rubberwood were around 10%, and the difference of moisture content between different samples was very small. The drying quality meets the need of grade one or grade two of national drying standard sawn timber.
2.3.4.1.3 Moisture content gradient along the thickness direction (Wg)
When drying, the water in surface layer was firstly removed from the rubberwood, so the moisture contents in different layers were different, thus the moisture content gradient existed. This gradient still existed when then drying process ended. Therefore, final treatment must have been done before the rubberwood was removed out of the kiln. The results of moisture content gradient along the thickness direction showed that the moisture content difference between different layers was small, and the drying quality was in order of grade one of national drying standard of sawn timber.
2.3.4.1.4 Drying stress index (Y)
Drying stress existed all the time during the drying because of different evaporating speed along the thickness direction, and when the stress was big enough, surface checks or internal checks appeared. Therefore, middle term treatment must have been carried out when the moisture content was at about 30% in order to reduce the drying stress. When the drying was finished, the residual drying stress still existed and would cause deformation during final using. Moisture balance treatment has been done in these tests in order to reduce the difference of moisture content between different layers or different samples, and the residual drying stress reduced a lot. The results showed that, the drying stress index was in order of grade one of national drying standard
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of sawn timber.
2.3.4.2 Deformation
Rubberwood is a fast growing species with big structure variation. When drying, they are easily
formed severe deformation, including bowing, cupping, warping and twisting. It was found that
the rubberwood deformation on the upside of the stack was bigger than the lower side because the
timber in the lower side endured large compression, thus the deformation was restricted. So in the
later testing, all the spacing stickers were kept in straight lines and some heavy load were put on
the top of stack, meanwhile the proper middle term treatment also was executed. Results showed
that all kinds of deformation greatly reduced.
2.3.4.3 Drying speed
Drying speed is also an important index. Improving the drying speed, shortening the drying time and reducing the drying costing should put into practice at the precondition of good drying quality. This will greatly improve the annual drying production amount, and thus improve the economic benefits.
Table 12 Drying time and speed of different drying period Thickness:25-30mm
Drying time of different period (h)
Drying speed of different period（%/h)
Drying Schedule
Initial MC(%)
Final MC(%)
Total drying time(h) ＞30% 30-20% ＜20% ＞30% 30-20% ＜20%
Average(%/h)
Schedule A 60.5 10.1 260 122 60 78 0.25 0.17 0.13 0.19 Schedule B 58.6 9.2 190 83 49 58 0.34 0.20 0.18 0.26 Schedule C 64.9 9.6 110 41 29 40 0.85 0.34 0.26 0.50
3 reasonable drying schedules were made out and could be used to dry wood with good quality, while the difference of drying speed was very huge (see table 12). The results showed that, the drying time was about 11 days when drying these preservatives treated rubberwood according to schedule A, about 8 days according to schedule B and about 4.5 days according to schedule C. The tests showed the rubberwood could be fast dried at some high temperature.
2.3.4.4 Rubberwood color after drying
Rubberwood is diffuse porous wood with straight grain, its heartwood and sapwood is hard to distinguish. The fresh rubberwood is light yellow in color, beautiful in grain, and well in processing. The preservative was mainly consisted with borax and boric acid and with none NaPCP, so after vacuum treating, the rubberwood almost maintained the original color. In order to keep the original natural color of rubberwood, the color of dried rubberwood was analyzed. The results showed the color of dried rubberwood had a close relationship with the drying temperature and humidity. The higher the drying temperature was, the bigger the humidity was and the longer the drying time was, the darker the color was. The rubberwood color became darker and brown when they were dried according to schedule C, while the color almost kept the original natural color when they were dried according to schedule A.
2.3.4.5 Drying costing
Drying is an important procedure in rubberwood processing, and is the most energy consumed one.
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In order to get more benefit, not only the loss caused by degrade should be reduced but also the drying cost should be strictly restricted.
The factors affects the rubberwood drying cost includes drying time, electricity consumption, vapor consumption, labor cost and equipment depreciation. In order to be convenient for comparing, the costing was calculated based upon a 50 m3 kiln. The drying costs indices includes 9kw power consumption, 5 to 8 tone vapor consumption per m3 rubberwood, and 3 labors a day. The other indices includes electricity expense (0.80 yuan/kwh), vapor expense (50 Yuan/tone) and labor expense (30Yuan/person day). Drying costing of three schedules is list as following:
Table 13 Drying costing
Electricity consumption Heat consumption Labor Total
Drying
schedule
Electricity
consumption
(kwh)
Cost
(Yuan)
Heat
consumption
(Tone)
Cost
(Yuan)
Labor
(person day)
Cost
(Yuan)
Total cost
(Yuan)
Cost per unit
(Yuan/m3)
Schedule
A 2367.0 1900.8 55.0 2750.0 33 990.0 5640.8 112.8
Schedule
B 1728.0 1382.4 48.0 2400.0 24 720.0 4502.4 90.0
Schedule
C 992.0 777.6 36.0 1800.0 14 420.0 2997.6 60.0
From table 13, it is showed that the difference of drying costs according to different drying schedules were very huge. The drying costing was 112.8 yuan/m3 when the rubberwood was dried according to schedule A, while it would be greatly reduced to 60 yuan/m3 when the rubberwood was dried according to schedule C.
2.3.5 Conclusion
(1) The drying characteristic grade of rubberwood with new preservatives treated was grade 2 of
initial check, grade 2 of internal check and grade 1 of deformation.
(2) According to the result of drying characteristic test and a series of the drying schedules tests, 3
optimum drying schedules were made.
(3) Rubberwood with or without pith should be dried separately. Pith free rubberwood could be
dried according to the high temperature drying schedule C with good drying quality which the
drying checks, deformation and moisture contents of dried rubberwood were all fit the
national drying standard of grade 1.
(4) Uniform spacing stickers and heavy load on top of stack was recommended to reduce
deformation. When drying rubberwood with pith, the drying temperature should be lower and
middle term treatment time should be increase.
(5) The color of dried rubberwood has a close relationship with the drying temperature and
humidity. In order to keep the original color of rubberwood, the rubberwood should be dried
according to drying schedule A with a lower drying temperature.
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(6) Drying time had a close relationship with the drying schedule. When drying rubberwood
according to the 3 different schedules, their drying time were 11, 8 and 45 days respectively.
(7) Drying time greatly affected the drying costing. Improving the drying speed or shortening
drying time will reduce the drying costing.
(8) Above all, in order to improve the drying efficient and reduce the drying costing, the
rubberwood should be dried according to schedule C; In the other hand, in order to keep the
original color of rubberwood, they should be dried according to schedule A; Schedule B can
also be adopted according to the requirement of final products of the rubberwood by the
manufactory.
2.4 Unloading stacks and quality inspection
When all moisture content sample boards meet the final moisture content requirement, the drying process could be ended. By closing heating and spraying valves, stopping the fan motors, and opening the vents to cool down the rubberwood, and when the temperature difference between inside kiln and outside kiln is lower than 30 , the rubberwood stacks could be unload from kiln.℃
The final drying quality could be detected and measure according to the national standard Sawntimber Drying Quality GB/T 6491-1999.
Figure 20 The positions of moisture content samples
The drying quality parameters need to be measured include average value of final moisture content, final moisture contents deviation among different position in kiln, moisture gradient along thickness direction, residual drying stress and all visible drying defects (distortion and checks).
The final moisture content detection sample positions could be designed as Figure 20 showing, at least 9 samples are must and 10 to 27 samples are necessary when the kiln size is very big.
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2.5 The dried rubberwood board storage
The wood after being dried could be stored by the following 4 ways: the first one is storage in open air; the second one is storage under shed; the third one is storage in dried board room; and the fourth one is storage in the special dried board room with EMC being adjusted. For dried rubberwood storage, one of these four ways could be selected according to the different environment and different final usage.
For storage in open air method, it is suitable for storage dried rubberwood in dry seasons for short time; mean while on top of wood piles should be covered to prevent them from rain, which could cause water absorption and preservative losing problems.
For storage under shed method, it is also suitable for storage dried rubberwood in dry seasons for short time. Though the rain has no direct influence on dried rubberwood, long time storage in humid climate may cause the moisture content of dried wood changing and increasing.
For storage in dried room method, it is suitable for storage dried rubberwood in dry seasons for long time with moisture content stable, because this room keep the dried wood isolated from outside environment.
For storage in the special dried board room with EMC being adjusted method, it is suitable for storage dried rubberwood in very humid seasons for long time. Because heating or dehumidification systems is equipped, the EMC inside the storage room could be adjusted and controlled, no moisture content changing occurs in this situation. This method is recommended to be used when the environment is very humid and the rubberwood is stored for glue joinery solid wood products.
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