104 world journal of textile engineering and technology

104 World Journal of Textile Engineering and Technology, 2020, 6, 104-111

E-ISSN: 2415-5489/20 © 2020 Scientific Array

Effects of Fluorine Rubber Compounds on Physical Properties of Various Reinforcing Agents According to the Type and Blending Content of Additives

Hyun-Ho Park and Chang-Seop Lee*

Department of Chemistry, Keimyung University, Daegu, 42601, Republic of Korea Abstract: Various reinforcing agents, acid acceptors, and vulcanization activators were blended with fluorine raw material rubber of different types and contents to investigate the hardness, tensile strength at fracture, elongation, and modulus according to the type and blending ratio of the additive. Tensile stress was also measured when the specimen was at 100% elongation. In addition, compression set that showed elastic variation at room or high temperatures were determined to assess the impact of blending agent. The hardness of general compounds should be 70 ± 5 pts. The tensile strength at fracture should be 130 ± 10 kgf/cm2 and the elongation should be 200 ± 50%. The content of compound that satisfied these conditions was 20 phr for reinforcing agents (N990), 3 phr for acid acceptors (MgO), 6 phr for vulcanization activators (Ca(OH)2), based on 100 phr for raw material rubber. Furthermore, additives that affected heat-resistance were acid acceptors. Among them, magnesium oxide worked as an effective heat-resistance enhancing additive for maintaining elasticity following heat resistance.

Keywords: FKM, Reinforcing agent, Acid acceptor, Vulcanization activator, Physical properties, Heat-resistance properties.

INTRODUCTION

Rubber is used widely in various functional parts of many industrial sectors including automobile, train, industrial machines, semiconductors, information communication, and so on, which can functionalize heat resistance, durability, and vibration and noise insulation due to its elastic restoration and vibration reduction features. Recently, advanced products poised to become first class products are showing gradual increase of rubber parts in almost all mechanical products including automobiles to achieve high quality and high reliability in addition to basic functions. There is also growing demands for material performance technologies for rubber parts [1]. With increasing interest in stability and durability, development of technologies that can enhance durability and reliability of rubber parts used as elemental parts of each function are being required [2].

There are more than 10 types of rubber including thermoplastic rubber used in industries today. Recently, physical properties, rheological properties, and heat-resistant and chemical-resistant properties of rubber have been significantly improved compared to rubber materials used in the past through various R&D such as improved material properties, fluidity, and processing methods. These rubbers are now being used in forms with improved functions compared to the past [3].

*Address correspondence to this author at the Department of Chemistry, Keimyung University, Daegu, 42601, Republic of Korea; Tel: +82-53-580-5192; Fax: +82-53-580-5056; E-mail: [email protected]

Rubber elastomer is the most common chemical material that makes up automobile parts. It has advantages such as low production cost, unique flexibility, machinability, elasticity, and so on. In addition, it has functions that metals and inorganic materials do not have. Rubber elastic parties are used for parts requiring elasticity in automobiles and functional materials that require heat-resistance, weatherproofing, chemical corrosion-resistance, and fire-retarding. In the case of rubber products exposed to high temperature environments such as radiant heat of engines, high levels of heat-resistance are needed. Furthermore, rubber products must have cold-resistance to maintain their shapes during winter seasons, They also must be physically stable with resistance against various types of fluid pressure. They must have durability and chemical-resistance that can withstand chemical corrosion. They also need be weather-proof to satisfy distinct specifications of materials applied to each part. Fluorine rubber (FKM) is a highly functional rubber elastomer that satisfy these requirements. It can be called special rubber. Fluorine rubber is a compound polymer material with an amorphous structure devised to have post-vulcanized rubber features. It can be used in a wide range of temperatures and in extremely inferior environmental conditions such as having direct contact with industrial oils and fuels [4, 5].

In this study, the various changes in vulcanization features, basic properties, compression features after heating and acid-resistant features contacting hydrochloric acid of FKM compounds according to

Effects of Fluorine Rubber Compounds on Physical Properties World Journal of Textile Engineering and Technology, 2020, Vol. 6 105

contents of various reinforcing agents, acid acceptor, and vulcanization activator used for fluorine rubber compounds were determined. Based on measurements of various properties and features of each FKM compound, appropriate physical characteristic values were assessed with the goal to have hardness of 70 pts, tensile strength of 100 kgf/cm2 at fracture, and elongation of 200%. Furthermore, additive factor affecting elasticity at room temperature and high temperature was computed to investigate changes of compression set after heat proofing according to additive content. The optimal type and content ratio per additive for raw material rubber were also investigated.

EXPERIMENTAL

1. Materials and Reagents

FKM G555 with fluorine content of 69% was purchased from DAKIN INDUSTRIES, LTD and used for preparing rubber specimens in this experiment.

Regarding carbon black as the reinforcing agent, N330, N550, and N774 from OCI and N800 and N990 products from Cancarb were used. Other additives used were acid acceptors such as highly active and lowly active magnesium oxide (MgO, Merck, USA), zinc oxide (ZnO, Hanil Chemical, Korea), lead oxide (PbO, Pb3O4, PENOX Korea, Korea), and calcium oxide (CaO, Hwasung Chemical, Korea). As vulcanization activator, calcium hydroxide (Ca(OH)2, Rhein Chemical, Germany) was used.

2. Blending Table

In this experiment, reinforcing agent, acid acceptor, and vulcanization activator were adjusted by type and blending ratio as shown in Tables 1, 2, 3, and 4.

3. Blending Method and Specimen Preparation

The raw material fluorine rubber was placed in a Banbury Mixer (KOBE, Japan) that was activated for 50

Table 1: The Recipe according to the Type of Reinforcing Agent

Material Name RF-1 RF-2 RF-3 RF-4 RF-5 Remarks (Unit: phr)

G555 100 100 100 100 100 FKM

MgO 3 3 3 3 3 Acid acceptor

Ca(OH)2 6 6 6 6 6 Vulcanization activator

N990 20 - - - -

N800 - 20 - - -

N774 - - 20 - -

N550 - - - 20 -

N330 - - - - 20

Reinforcing agent

Total 129 129 129 129 129

Table 2: The Recipe according to the Type of Acid Acceptor

Material Name AA-1 AA-2 AA-3 AA-4 AA-5 Remarks (Unit: phr)

G555 100 100 100 100 100 FKM

N990 20 20 20 20 20 Reinforcing agent


MgO (highly active) 3 - - - -

MgO (lowly active) - 3 - - -

PbO - - 5 - -

ZnO - - - 5 -

Pb3O4 - - - 5 -

CaO - - - - 5

Acid acceptor

Total 129 129 131 136 131

106 World Journal of Textile Engineering and Technology, 2020, Vol. 6 Park and Lee

seconds at a constant temperature of 120~130 ˚C. Afterwards, other additives such as acid acceptor and vulcanization activator were injected into the Banbury Mixer and activated for 150 seconds. After mixing, roll processes were carried out using a rubber roll mill (DAEJUNG, Korea) with a diameter of 8“, length of 20%, and rotation ratio of 1:1.25. The rotation speed was set at 18 rpm and temperature was set at 60 ˚C to mix in the roll. The compound was made in the form of a sheet. After aging for 24 hours, the time for each operation was set uniformly for 20 minutes. The specimen produced using this method was placed in a Moving Disk Rheometer (MDR P200, Alpha Technology, U.S.A.) with a vulcanization temperature set at 170 ˚C. The minimum torque (Tmax, Tmin), optimal vulcanization time that was cure time (Tc90), and the initial rubber hardening time that is scorch time (ts2) were measured. For the first vulcanization work, test specimen was produced at 140x120x2mm according to appropriate vulcanization time. The second vulcanization was carried out for three hours at 150 ˚C.

4. Analysis of Physical Properties

For tensile properties, tensile strength, elongation, and 100% modulus values were measured according to ATSM D-412 under conditions of 25 ˚C and 500

mm/min with a tensile tester (Instron 10, USA). The hardness was measured using a spring-type hardness testing machine (Kobunshi Keiki Co, Ltd, Japan). The compression set for investigating the impact on heat at room temperature and high temperature was assessed room temperature of 23 ˚C for 24 hours and at 200 ˚C for 24 hours. Test specimens used for the compression set experiments were produced in a cylindrical form with a thickness of 12 mm and a diameter of 29 mm. The compression ratio was set at 25% [6].

RESULTS AND DISCUSSION

1. Vulcanization and Physical Properties of Reinforcing Agents

In this experiment, different types of carbon black as the reinforcing agent was added to FKM raw material rubber. Vulcanization features of blended rubbers were then measured using a Moving Disk Rheometer (MDR P200, Alpha Technology, USA), and the results are shown in Table 5.

As shown in Table 5, for N330 with smaller particle size, ts2 representing the initial vulcanizing time became longer. TC90 representing the appropriate vulcanization time was also increased proportionally. This is because N990 carbon black is an alkaline that can affect vulcanization reactions, thus shortening both

Table 3: The Recipe by the Content of Magnesium Oxide

Material Name MgO-1 MgO-2 MgO-3 MgO-4 MgO-5 MgO-6 MgO-7 MgO-8 MgO-9 Remarks (Unit: phr)

G555 100 100 100 100 100 100 100 100 100 FKM

N990 20 20 20 20 20 20 20 20 20 Reinforcing agent

Ca(OH)2 6 6 6 6 6 6 6 6 6 Vulcanization activator

MgO - 2 3 4 6 8 10 15 20 Acid acceptor

Total 126 128 129 130 132 134 136 141 146

Table 4: The Recipe by the Content of Calcium Hydroxide

Material Name ACT-1 ACT-2 ACT-3 ACT-4 ACT-5 Remarks (Unit: phr)

G555 100 100 100 100 100 FKM

N990 20 20 20 20 20 Reinforcing agent

MgO 3 3 3 3 3 Acid acceptor


Total 126 127 129 131 133


TC90 and ts2. However, vulcanization time became longer when neutral carbon black was added. In particular, it is estimated that vulcanization time becomes longer when the particle size is smaller [7].

Figure 1 shows physical features of FKM compounds. Figures 1a-1d show basic properties such as modulus, tensile strength, elongation, and hardness of each carbon black. Figure 1e shows compression set at room temperature and high temperature of 200 ˚C. As shown in Figures 1a-1d, for N330 carbon black RF-5 reinforcing agent with a small particle size and a large surface area, modulus, tensile strength, and hardness increased while elongation decreased. It is known that the dispersion state of carbon black filled inside rubber exists in an aggregate state because carbon black in agglomerate state breaks up during blending and becomes dispersed. This carbon black becomes agglomerated due to difference of agglomeration, creating a difference in properties. Therefore, carbon black with a small particle size and a large surface area displays superior reinforcement [8].

In addition, this occurs because of the large contact area between the raw material rubber and carbon black. Reinforcement increases when the particle’s surface area of the reinforcing agent increases while the elongation which is the rupture elongation percentage decreases according to the volume fraction of the reinforcing agent [9]. Meanwhile, when the rate of change of compression set in Figure 1e was examined, N330 carbon black RF-5 with a small particle size and a large surface area displayed decreased elasticity rate due to the increase of compression set caused by a reinforcement effect. Considering change values of the compression set at room temperature and high temperature and the vulcanization speed, the reinforcing agent suitable for FKM raw material rubber was estimated to be N990.

2. Vulcanization and Physical Properties for Acid Acceptors

FKM compounds have high vulcanization temperatures and usage temperatures. Thus, acid acceptors must be used to neutralize hydrogen fluoride

Table 5: Cure Characteristics according to the Type of Reinforcing Agent

Item RF-1 RF-2 RF-3 RF-4 RF-5 Remarks

Tc90 8.1 8.8 10.0 11.5 13.9 min MDR 170 ˚C *20min ts2 5.9 6.3 6.9 6.9 7.0 min

Figure 1: (a) Basic properties of modulus according to the type of reinforcing agent. (b) Basic properties of tensile strength according to the type of reinforcing agent. (c) Basic properties of elongation according to the type of reinforcing agent. (d) Basic properties of hardness according to the type of reinforcing agent. (e) Changes of compression measured after heated aging test.


that occur during the process to enhance heat-resistance and vulcanization effects of FKM compounds. Acid acceptors such as MgO, PbO, Pb3O4, ZnO, and CaO were used. These acid acceptors appear to affect properties of FKM compounds depending on their ionizing tendencies. Vulcanization features of acid acceptors used in this study are shown in Table 6. Their physical features were evaluated and the results are shown in Figures 2a-2e. Vulcanization features of acid acceptor magnesium oxide that displayed the highest tensile strength and elongation as shown in Figures 2b-2c are summarized in Table 7 and their physical properties are shown in Figures 3a-3e.

When looking at vulcanization features shown in Table 6, AA-5 acid acceptor CaO showed a very late vulcanization time for starting the vulcanization effect. Therefore, such acid acceptor might be used for press items with large product dimensions. In addition, AA-4 ZnO showed especially high initial vulcanization speed. Therefore, in contrast to CaO, it can be used in parts for products that are thin. When examining physical properties as shown in Figures 2a-2e, only ZnO with a rapid ionization tendency had a fast cross-linking speed. Its elongation was low and its elastic recovery at a high temperature was poor. Therefore, it is inappropriate for products that require specific functionalities. Acid acceptors that contain Pb are rarely used due to their environmental impacts. In conclusion, other acid acceptors can be used depending on the size of the product completed with FKM compounds. However, the most suitable acid acceptor might be magnesium oxide. High activity or low activity can be selected according to needed properties.

Table 7 shows vulcanization properties of MgO most suitable for vulcanization. Figures 3a-3e show the various physical properties per MgO content. As shown in Table 7, when MgO additives increase, ts2 tends to accelerate. Considering this, it is estimated that MgO additives can affect the cross-linking open time because MgO can activate together with the vulcanization activator [10].

As shown in Figures 3a-3e, when looking at general properties such as compression set, physical properties of FKM compounds per MgO content are stable when the MgO content is 10 phr or up to MgO-7. However, when MOG content is higher, basic physical properties and compression set are increased rapidly. This appears to be due to the fact that MgO acts as a filling within a reticular structure, thus interfering with polymer chain motion. Hence, it is estimated that AA-3~5 additive content of 3~6 phr is the most suitable MgO content.

3. Vulcanization and Physical Properties According to Vulcanization Activator Content

Vulcanizing features according to the quantity of Ca(OH)2 additive acting as a vulcanization activator are as shown in Table 8. Figure 4 shows tensile strengths according to vulcanization activator content. As vulcanization activator serves to start and activate together with an acid acceptor, vulcanization time has a tendency to be shortened when the content of vulcanization activators is increased. As shown in Figure 4, when the ACT-3 additive quantity was 6 phr, FKM compounds demonstrated the highest tensile strength. When the vulcanization activator content went beyond 6 phr, tensile strength decreased as vulcanization activator content grew. This might be due

Table 6: Cure Characteristics according to the Type of Acid Acceptor

Item AA-1 AA-2 AA-3 AA-4 AA-5 Remarks

Tc90 8.1 7.2 7.9 5.0 15.5 min MDR 170 ˚C *20min ts2 5.9 5.5 5.1 4.0 10.1 min

Table 7: Cure Characteristics according to the Content of Magnesium Oxide

Item MgO-1 MgO-2 MgO-3 MgO-4 MgO-5 MgO-6 MgO-7 MgO-8 MgO-9 Remarks

Tc90 11.4 7.5 8.1 8.1 9.5 9.1 9.1 10.2 11.0 min MDR 170 ˚C *20 min ts2 7.1 5.6 5.9 6.0 6.3 5.5 4.6 2.9 1.4 min


to the fact that when vulcanization activator content increased, it became difficult to disperse. Therefore, it became deficient in its role as a vulcanization activator, thus lowering tensile strength. Hence, Ca(OH)2 content

can be selected according to the vulcanization time. Considering physical properties of FKM compounds, it is estimated that ACT-3 of 6 phr is the most suitable.

Figure 2: (a) Basic properties of modulus according to the type of acid acceptor. (b) Basic properties of tensile strength according to the type of acid acceptor. (c) Basic properties of elongation according to the type of acid acceptor. (d) Basic properties of hardness according to the type of acid acceptor. (e) Changes of compression measured after heated aging test.

Figure 3: (a) Basic properties of modulus according to the content of magnesium oxide. (b) Basic properties of tensile strength according to the content of magnesium oxide. (c) Basic properties of elongation according to the content of magnesium oxide. (d) Basic properties of hardness according to the content of magnesium oxide. (e) Changes of compression measured after heated aging test.


Figure 4: Basic properties of tensile strength according to the content of calcium hydroxide.

CONCLUSION

In this study, reinforcing agents, acid acceptors, and vulcanization activators were blended by type and content as additives used for producing FKM compounds. The optimal blending content that satisfied hardness of 70 ± 5 pts, tensile strength at fracture of 130 ± 10 kgf/cm2, and elongation of 200 ± 50% as goals was obtained by measuring vulcanization features and physical properties. The following results are obtained.

1) N990 reinforcing agent that is alkaline with a large particle size and a small cross-sectional area can affect the vulcanization speed of FKM compounds. It has good elasticity with properties maintained at room temperature and high temperature. Therefore, it is the most suitable reinforcing additive for an FKM compound. When the goal of hardness was set at 70pts, it was found that its content at 20 phr was the most suitable.

2) For acid acceptors known as initiating vulcanization, neutralizing hydrogen fluoride and raising heat-resistance, considering measurement results of compression set at high temperatures and environmental aspects, magnesium oxide is the most suitable reinforcing additive for an FKM compound. Considering the

target values of physical property required, 3 phr is the most appropriate content.

3) Considering the highest tensile strength properties and the dispersity when blending FKM compounds, the appropriate content of Ca(OH)2 that functions for vulcanizing activation is estimated to be 6 phr.

4) For a hardness of 70 ± 5 pts, tensile strength at fracture of 130±10 kgf/cm2, and elongation of 200 ± 50% targeted for FKM compounds, the most suitable blending contents were: FKM raw material rubber of 100phr, reinforcing agent (N990) at 20 phr, acid acceptor (MgO) at 3 phr, and vulcanization activator (Ca(OH)2) at 6 phr.

ACKNOWLEDGEMENT

This study was supported by “Leaders in Industry-University Cooperation +” Project funded by the Ministry of Education and National Research Foundation of Korea.

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Table 8: Cure Characteristics according to the Content of Calcium Hydroxide

Item ACT-1 ACT-2 ACT-3 ACT-4 ACT-5 Remarks

Tc90 13.4 10.1 8.1 7.4 6.4 min MDR 170 ˚C *20 min ts2 11.0 8.2 5.9 5.4 4.5 min


[8] Bhowmick AK, Hall MM, Benarey HA. Rubber Products Manufacturing Technology, New York; Marcel Dekker Inc. 1994

[9] Barlow FW. Rubber Compounding, New York; Marcel Dekker, Lnc. 1993.

[10] Ameduri B, Boutevin B, Kostov G. Fluoroelastomers: synthesis, properties and applications. Progress in Polymer Science 2001; 26(1): 105-187. https://doi.org/10.1016/S0079-6700(00)00044-7

Received on 26-11-2020 Accepted on 14-12-2020 Published on 17-12-2020

DOI: https://doi.org/10.31437/2415-5489.2020.06.8

© 2020 Park and Lee; Licensee Scientific Array. This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

104 world journal of textile engineering and technology

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