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Journal of Forestry Research ISSN 1007-662X J. For. Res.DOI 10.1007/s11676-015-0033-0

Organo-silane compounds in mediumdensity fiberboard: physical andmechanical properties

Hamid Reza Taghiyari, Ali Karimi &Paridah Md. Tahir

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ORIGINAL RESEARCH

Organo-silane compounds in medium density fiberboard:physical and mechanical properties

Hamid Reza Taghiyari • Ali Karimi •

Paridah Md. Tahir

Received: 24 November 2013 / Accepted: 29 December 2013

� Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

Abstract We studied the effects of nanoparticles of

organo-silane (NOS) compounds in the size range of

20–80 nm on physical and mechanical properties in med-

ium density fiberboard, and used NOS at four consumption

levels of 0, 50, 100, and 150 g kg-1 dry wood fibers.

Density of all treatments was kept constant at 0.67 g cm-3.

The water-repellent property of organo-silane significantly

reduced water absorption (WA) and thickness swelling but

mechanical properties declined due to the reduced pro-

portion of wood-fiber as organo-silane was added to the

matrix: the compression ratio of MDF panels and the

integrity among wood-fibers both declined, resulting in

reduced mechanical properties. We recommend use of 50 g

of NOS/kg wood-fiber to improve WA and thickness

swelling while retaining acceptable mechanical properties.

Keywords Composite-board � Medium-density

fiberboard (MDF) � Nanotechnology � Physical and

mechanical properties � Water-repellant � Organo-silane

Introduction

Composite-boards offer the advantages of a homogeneous

structure and the use of raw materials without restrictions as

to shape or size, and many technologies have been devel-

oped to limit formaldehyde emissions (Valenzuela et al.

2012). Wood-composite panels and profiles are, therefore,

expanding worldwide. In fact, wood-based composite pro-

ducts are commonly substituted for solid wood in today’s

building structures (Eshaghi et al. 2013). The main factors

that influence the properties and quality of the panels are the

density of the panel, geometry and moisture content of the

particles, the pressing cycle, and the quantity and type of

adhesive. The production of wood composites has increased

dramatically over the past three decades. Their use, how-

ever, is often limited due to high sensitivity to moisture and

decay (Baileys et al. 2003; Gardner et al. 2003; Laks 2002),

as well as fire (Taghiyari 2012; Haghighi et al. 2013).

The emergence of new technologies to produce an

increasing array of new wood composite products has forced

the industry to follow-up with varied protection processes

and/or treatments to protect these new wood-based products

(Kirkpatrick and Barnes 2006). Different materials can be

easily used to modify and improve some of the undesirable

properties in composite boards or the production procedure.

In this connection, the heat-conductive nature of nanometal

particles (Ghorbani et al. 2012; Khojier et al. 2012; Poda

et al. 2013) was used to better polymerize the resin in the core

of the mat, as well as decrease gas and liquid permeability.

The improving effects of silver nanoparticles on physical and

Project funding: The project was conducted as a joint research project

and financed by SRTTU (Iran) and UPM (Malaysia)

The online version is available at http://www.springerlink.com

Corresponding editor: Yu Lei

H. R. Taghiyari (&)

Wood Science & Technology Department, Faculty of Civil

Engineering, Shahid Rajaee Teacher Training University,

Tehran, Iran

e-mail: htaghiyari@srttu.edu; htaghiyari@yahoo.com

A. Karimi

Department of Wood and Paper Science & Technology, Faculty

of Natural Resources, The University of Tehran, Karaj, Iran

A. Karimi � P. Md. Tahir

Laboratory of Biocomposite Technology, Institute of Tropical

Forestry & Forest Products (INTROP), University Putra

Malaysia (UPM), Serdang, Malaysia

123

J. For. Res.

DOI 10.1007/s11676-015-0033-0

Author's personal copy

mechanical properties of particleboard on an industrial scale,

as well as its hot-press time reduction, were also reported.

Wollastonite nanofibers were also reported to improve

thermal conductivity coefficient of medium-density fiber-

board (MDF), physical and mechanical properties, and fire-

retarding properties of MDF.

In this connection, the water-repellent property of org-

ano-silane (NOS).compounds was reported to decrease

liquid and gas permeability of MDF (Taghiyari 2013). The

effects of NOS on other physical and mechanical properties

were, however, yet to be studied. Our study was therefore

conducted to evaluate if NOS could contribute significantly

to reducing water absorption (WA) and thickness swelling,

while simultaneously improving mechanical properties.

Materials and methods

Specimen preparation

Wood fibers were procured from Sanaye Choobe Khazar

Company in Iran (MDF Caspian Khazar). The fibers

comprised a mixture of five species of beech, alder, maple,

hornbeam, and poplar from the neighboring forests. Boards

were 16 mm thick, and the density was kept constant at

0.67 g cm-3. The total nominal pressure of the plates was

16 MPa. The temperature of the plates was fixed at 130 �C.

Hot-pressing continued for 8 min. Urea–formaldehyde

resin (UF) was procured from Sari Resin Manufacturing

Company in Sari, Iran. We used 10 % of UF at 0.2–0.4 Pas

in viscosity, 47 s of gel time, and 1.277 g cm-3 in density

without catalyst. Ten boards were made for each treatment.

From each board, two specimens were cut for modulus of

rupture (MOR), modulus of elasticity (MOE), internal bond

(IB), WA, and thickness swelling (TS) tests.

Nano-organo-silane application

The nano-organo-silane liquid (NOS-liquid) was the resultant

product of organo silane reacted with organic reactant, pro-

duced in cooperation with Zydex Industries. Its color was pale

yellow, with the flash point at more than 85 �C and auto-igni-

tion temperature at more than 200 �C, specific gravity of

1.05 g mL-1 (at 25 �C), viscosity of 0.5–1.0 Pas (at 25 �C).

The nano-organo-silane liquid was comprised of hydroxyal-

kyl–alkoxy–alkylsilyl compounds (38–42 %); and the solvent

was ethylene glycol (58–62 %). The size range of nanoparticles

was 20–80 nm. NOS-liquid was mixed with resin in propor-

tions of 0, 50, 100, and 150 g kg-1 dry weight basis of fibers.

NOS content was based on the solid parts in the NA-suspension.

For each treatment, the weight of NOS-solids was deducted

from the fiber, and in this way, the density of panels in different

treatments with different fiber-content was kept constant. The

final mixture of NOS ? resin was smoothly sprayed on the

fibers. Resin pH and viscosity were kept constant for all treat-

ments. Four boards were manufactured for each treatment.

Boards were kept in a conditioning chamber [(25 ± 2) �C,

(40 ± 3) % of relative humidity] for 1 month before the liquid

and gas permeability specimens were measured.

Physical and mechanical tests

Physical and mechanical tests, as well as the number and

location of the specimens, were carried out in accordance

with the ISIRI 9044 PB Type P2 (compatible with ASTM

D-1037; 2007 edition) specifications. The static bending

test was performed using center-point loading over a

390 mm span. The loading speed was 2 mm min-1. All

tests were conducted using an INSTRON 4486 testing

machine. Equations 1–3 were used to calculate final values

of MOR, MOE and IB (MPa):

MOR ¼ 1:5 FL

bd2ð1Þ

MOE ¼ FL3

4bd3Dð2Þ

IB ¼ Fmax

Að3Þ

Brittleness was calculated by using the ratio (%) of the

work absorbed in the elastic region to the total work

absorbed to maximum load, as shown in Eq. 4 (Phuong

et al., 2007; Taghiyari et al. 2013):

Brittleness ¼ Area 1

Area 1þ Area 2� 100 ð%Þ ð4Þ

The proportional limit was decided by drawing a linear

correlation curve using data from 0 % load to the limit

value (R2 = 0.999).

Statistical analysis

Statistical analysis was conducted using SAS software,

version 9.2 (2010). One-way analysis of variance (ANOVA)

was performed to discern significant differences at 95 %.

Hierarchical cluster analysis, including dendrogram and

using Ward methods with squared Euclidean distance

intervals, was carried out by SPSS/18 (2010). Fitted line

plots were made by Minitab software, version 16.2.2 (2010).

Results and discussion

Nano-organo-silane significantly reduced WA and thick-

ness swelling in MDF (Figs. 1, 2). The lowest WA and

thickness swelling was observed in NOS-150 treatment.

H. R. Taghiyari et al.

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WA and thickness swelling, after 2 h immersion in water,

declined by 31.9 and 43.6 %, respectively, in NOS-150

treatment in comparison to the control specimen. WA and

thickness swelling gradually declined as the NOS-content

increased from 50 g kg-1 wood fiber to 150 g kg-1,

showing a direct relationship between NOS content and the

declines in WA and TS. The lowest WA and TS were

observed in the NOS-150 treatment despite the micro-voids

and cavities that were formed (Taghiyari 2013) due to the

significantly lower amount of wood fibers in this treatment.

Liquid permeability was similarly reported to significantly

decline in MDF by addition of NOS to the MDF-matrix

(Taghiyari 2013).

Nano-organo-silane had a degrading effect on all

mechanical properties of NOS-treated boards (Figs. 3, 4, 5,

6, 7). MOR decreased by 76 % in NOS-150 treatment in

comparison to the control specimen (Fig. 3). The reason

for the decline in mechanical properties was the decrease in

the wood fiber content of NOS-treated specimens. As a

rule, the density of the produced boards should be at about

0.65–0.68 g cm-3 in Iran to be compatible with the stan-

dards as well as the desirability in the commercial market;

so, the amount of NOS-suspension used for each treatment

(50, 100 and 150 g cm-3) was subtracted from the dried

wood-fibers in order to keep the density of the boards

constant at 0.67 g cm-3. Therefore, the volume of wood

fibers decreased as the NOS-content increased from 0 to

150 g cm-3. This resulted in less compression between

wood fibers in the MDF-matrix. SEM micrographs showed

scattered micro-cavities in the body of the NOS-treated

boards (Taghiyari 2013).

Of all the physical and mechanical properties, the

Duncan grouping of the hardness values was in close

compatibility with the groupings based on the specific gas

permeability values (Taghiyari 2013); that is, NOS-50 and

NOS-100 treatments were similarly grouped when both gas

permeability and hardness were measured. This indicated

that the compression between the wood-fibers on the

surface layers of the boards significantly influenced hard-

ness and gas permeability the same way.

Strong correlations were recorded between TS and WA

after 2 and 24 h immersion in water (Fig. 8a). The short

and long term physical patterns were similar, that is, the

water repellant nature of NOS significantly affected both

short and long term physical properties of TS and WA.

0

20

40

60

80

100

120

140

Control NOS-50g NOS-100g NOS-150g

Wat

er a

bsor

ptio

n (%

)

WA-2hWA-24h

A ABB

C

AAA

AB

Fig. 1 Water absorption (%) at 2 and 24 h in control, NOS-50, NOS-

100, and NOS-150 treatments (NOS nanoparticles of organo-silane).

Letters on each column represent the Duncan’s multiple range test

groupings

0

5

10

15

20

25

30

Control NOS-50g NOS-100g NOS-150g

Thic

knes

s sw

ellin

g (%

)

WA-2hWA-24h

AA

A

BBB

B

A

Fig. 2 Thickness swelling (%) at 2 and 24 h in control, NOS-50,

NOS-100, and NOS-150 treatments (NOS nanoparticles of organo-

silane). Letters on each column represent the Duncan’s multiple range

test groupings

0

5

10

15

20

Control NOS-50g NOS-100g NOS-150g

MO

R (M

pa)

A

B

CCD

Fig. 3 Modulus of rupture (MPa) in control, NOS-50, NOS-100, and

NOS-150 treatments (NOS nanoparticles of organo-silane). Letters on

each column represent the Duncan’s multiple range test groupings

0

500

1000

1500

2000

2500

Control NOS-50g NOS-100g NOS-150g

MO

E (M

pa) A

AB

BC

Fig. 4 Modulus of elasticity (MPa) in control, NOS-50, NOS-100,

and NOS-150 treatments (NOS nanoparticles of organo-silane).

Letters on each column represent the Duncan’s multiple range test

groupings

Organo-silane compounds in medium density fiberboard

123

Author's personal copy

Furthermore, though not as high as between TS and WA, a

high R-square was recorded between MOR and IB

(Fig. 8b), and NOS had nearly similar effects on different

mechanical properties as well. A highly significant corre-

lation was found between hardness values measured at

different depths of the penetration of the hardness ball

(Fig. 9). This showed that variations in the hardness values

at different depths had a high compatibility in different

treatments. The loading strength values of hardness proved

this compatibility (Fig. 10). In the meantime, hardness also

showed high correlation with all physical and mechanical

properties. The highest correlation was found between

hardness (H5) and MOE (Fig. 11).

Cluster analysis was carried out based on all the

physical and mechanical properties of four treatments

(WA-2 & -24 h, TS-2 and -24 h, MOR, MOE, IB,

brittleness, and hardness). The results indicated close

similarity between the control and NOS-50 treatments, as

well as between NOS-100 and NOS-150 treatments

(Fig. 12). Therefore, if the final application of the boards

stipulates improved water-repellent properties, but the

mechanical properties would not be of critical importance,

NOS-100 treatment is recommended, depending on the

final application. On the other hand, if the mechanical

properties are also important, but improved water-repel-

lent properties are needed, then NOS-50 would be rec-

ommended. The mechanical properties of samples

manufactured using NOS-150 treatment were substantially

degraded and therefore this treatment is not recommended

for commercial purposes.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Control NOS-50g NOS-100g NOS-150g

Inte

rnal

bon

d (M

Pa)

A

B

CCD

Fig. 5 Internal bond (MPa) in control, NOS-50, NOS-100, and NOS-

150 treatments (NOS = nanoparticles of organo-silane). Letters on

each column represent the Duncan’s multiple range test groupings

05

10152025303540

Control NOS-50g NOS-100g NOS-150g

Har

dnes

s (M

Pa)

AAB

AB

C

Fig. 6 Hardness (MPa) in control, NOS-50, NOS-100, and NOS-150

treatments (NOS nanoparticles of organo-silane). Letters on each

column represent the Duncan’s multiple range test groupings

02468

1012141618

Control NOS-50g NOS-100g NOS-150g

Brit

tlene

ss (%

)

A

B

CC

Fig. 7 Brittleness (%) in control, NOS-50, NOS-100, and NOS-150

treatments (NOS nanoparticles of organo-silane). Letters on each

column represent the Duncan’s multiple range test groupings

Fig. 8 Fitted-line plots between thickness swelling after 2 and 24 h

of immersion in water (a), and between MOR and IB values (b)

H. R. Taghiyari et al.

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With reference to the decline in mechanical properties

due to the replacement of wood fiber by nano-organo-

silane, the authors are studying the effects of NOS treat-

ment without reducing wood fiber content. This addition of

nano-organo-silane is predicted to enhance mechanical

properties of treated fiberboard.

Conclusion

Water-repellant property of organo-silane significantly

decreases WA and thickness swelling in MDF regardless of

the micro-cavities formed and the consequently reduced

integration between wood-fibers in the MDF-matrix. There-

fore, if WA and thickness swelling are the decisive factors in

MDF production and final application, NOS should be added

to the composite matrix. Doing so enables reduction in fiber

content of panels, saving raw materials and decreasing pro-

duction costs.

MDF with higher NOS-content would have lower

mechanical properties due to the lower wood-fiber content

and formation of micro-cavities, and the consequent less

compression ratio of the panels and lower integration

between the wood fibers in the MDF-matrix.

Final application of the NOS-treated panels depends on

the desired mechanical and physical properties; if WA and

TS are vital, NOS-100 is recommended; and if the

mechanical properties are also of importance, then NOS-50

treatment would be more appropriate.

Acknowledgments The present research project was conducted as a

joint research project and financed by SRTTU (Iran) and UPM

(Malaysia) for which the authors are grateful. The authors are

thankful to Mr. Majid Ghazizadeh, the internal sales manager of Pars

Chemical Industries Company, for the procurement of the resin for

the present study. We appreciate Mr. Pezhman Nouri, specialized on

wood-composite materials, for his technical advice and support.

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