impregnation modification of sugar palm fibres with phenol formaldehyde and unsaturated polyester

Fibers and Polymers 2013, Vol.14, No.2, 250-257

250

Impregnation Modification of Sugar Palm Fibres with Phenol Formaldehyde and

Unsaturated Polyester

M. R. Ishak1,4*, Z. Leman

2, S. M. Sapuan

2,3,4, M. Z. A. Rahman

5, and U. M. K. Anwar

4,6

1Department of Aerospace Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia2Department of Mechanical and Manufacturing Engineering, University Putra Malaysia, 43400 UPM Serdang,

Selangor, Malaysia3Institute of Advanced Technology (ITMA), University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia4Institute of Tropical Forestry and Forest Products (INTROP), University Putra Malaysia, 43400 UPM Serdang,

Selangor, Malaysia5Centre of Foundation Studies for Agricultural Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

6Wood Finishing Laboratory, Forest Research Institue of Malaysia (FRIM), Kepong, Kuala Lumpur, Malaysia

(Received September 5, 2011; Revised May 25, 2012; Accepted June 15, 2012)

Abstract: This study investigated the effects of impregnation modification via vacuum resin impregnation on physical andmechanical properties of sugar palm (Arenga pinnata) fibres. The fibre was evacuated at a constant impregnation pressure of1000 mmHg impregnation times (0, 5, 10, 15, 20 and 25 min) with two different impregnation agents: phenol formaldehyde(PF) and unsaturated polyester (UP). A notable improvement in the physical properties of sugar palm fibres was observedafter they were impregnated with PF and UP for 5 min, shown by the reduction of their moisture content (91 % and 89 %,respectively) and water absorption (43 % and 41 %, respectively) compared to the control sample. However, no significantimprovement (p≤0.05) in the physical properties of fibre was observed when the impregnation time was extended (from 10 to25 min) using both impregnation agents. As for the mechanical properties of the fibre, significant improvement was observedafter they were impregnated for 5 min. The fibres impregnated with UP resulted in better fibre toughness and improvedmechanical properties as shown in their higher tensile strength and elongation at break compared to the fibres impregnatedwith PF. Both the physical and mechanical properties showed no significant improvement (p≤0.05) after time forimpregnation was extended (from 10 to 25 min) using both impregnation agents. Therefore, it can be concluded that thephysical and mechanical properties of sugar palm fibre could be enhanced by impregnating the fibre with thermosettingpolymer (PF and UP) for 5 min. It was shown that impregnation with unsaturated polyester (UP) showed better improvementthan phenol formaldehyde (PF). In addition, this study also concluded that the unsatisfactory enhancement of the propertiesof sugar palm fibre even after the impregnation time was extended from 10 to 25 min was due to the use of low impregnationpressure of 1000 mmHg.

Keywords: Polymer matrix composite, Thermosets polymer, Mechanical properties

Introduction

A number of studies on the development of bio-composite

materials made from plant-based fibres have been carried

out. Some examples of plant based natural fibres include

kenaf, jute, oil palm, pineapple leaf, banana pseudo stem,

sugarcane bagasse, flax, basalt and sugar palm fibres [1-7].

All of those plant-based natural fibres have similar qualities:

they can be attained easily as they are available in large

quantities and they are relatively low in cost and density.

Apart from that, these plant-based fibres have high specific

properties that make them friendlier to human health and

environment and they are biodegradable when disposed [8-13].

For these reasons, they have become the preferred materials

to be used in place of glass fibre and would also serve as

alternative sources of timber which is now facing the

problem of deforestation [14-16]. Although extensive efforts

and studies have been carried out in order to use natural fibre

as composite reinforcement, bio-composites made from

natural fibre have very limited applications in outdoor

environment. Like wood, the properties for natural fibres are

known to be highly hygroscopic. Natural fibre is also

hydrophilic in nature due to the presence of hydroxyl (OH)

groups throughout its structure especially at cellulose and

hemicelluloses portions [17]. When natural fibre is exposed

to high humidity environment, these hydroxyl groups attract

and hold water molecules through a chemical bond called

hydrogen bonding. The prolonged water exposure causes the

fibre to degrade biologically because when the organisms

recognise the carbohydrate polymers (mainly the hemicelluloses)

in the cell wall, they produce a very specific enzyme system

capable of hydrolysing these polymers into digestible units.

As the crystalline cellulose is primarily responsible for the

strength of the cell wall [18], biodegradation of the high

molecular weight cellulose weakens the fibre cell wall.

Subsequently, since natural fibres are made up of macrofibrils

which are held together to be one single fibre, the open

hollow macrofibrils (called cell lumen) (Figure 1) allow

water molecules to fill in cell lumen before they are being

diffused into the fibre cell wall known as bound water.*Corresponding author: [email protected]

DOI 10.1007/s12221-013-0250-0

Impregnation Modification of Sugar Palm Fibres Fibers and Polymers 2013, Vol.14, No.2 251

The diffusion of water molecules in cell wall causes the

fibre to swell, but dry condition causes the fibre to shrink.

Frequent dimensional instability (fibre swelling in humid

environment and shrinking in dry condition) would damage

the composite interfacial bonding, apart from biological

attack which would damage the fibre structure. Besides that,

the presence of moisture in the fibre would also decrease the

composite mechanical properties [18]. Besides having moisture

uptake of fibre, moisture may easily penetrate into the bond

line between the fibre and the matrix and causes swelling

and deformation of the adhesive matrix, as well as breaks the

chemical bonds and consequently, weakens the polymer

backbone [19]. This leads to poor interfacial properties,

causing a decrease in the mechanical properties of the

composites. The composites then can no longer sustain their

properties and thus, have high tendency to break. This is a

usual problem occurring in natural fibre composite products

and it explains why most natural fibre composites have very

limited, if not impossible, usage for outdoor applications.

This paper discusses the development of new fibre

treatment called impregnation modification of natural fibre

in which sugar palm fibre is physically modified via vacuum

resin impregnation process. This process involves impregnating

the fibre lumen and enclosing the fibre with resin to prevent

water penetration into the fibre and is done before the fibre

can be used for composite reinforcement targeted for

outdoor usage. Because the method used is simple and low

cost, it is expected to broaden the exploitation of natural

fibre composite which often has inadequate properties to

withstand high humid environment especially for outdoor

applications. The paper further discusses the results of the

study which aimed to look at the effects of impregnation

times on the physical and mechanical properties of sugar

palm fibres and to compare the differences of using different

polymer matrices of the two impregnation agents - phenol

formaldehyde (PF) and unsaturated polyester (UP).

Materials and Methods

Preparation of Materials

Sugar palm (Arenga pinnata) fibres for the study were

obtained from Kampung Kuala Jempol, Negeri Sembilan,

Malaysia and selected from matured sugar palm trees, aged

more than 6 years and with a height of 20 m. The fibres were

obtained from within the live palm fronds to ensure optimum

properties of sugar palm fibre [12]. These fibres were then

washed and air dried for 24 hours before being oven dried in

a Mermert-type oven at 80 oC for 24 hours. The crucial

materials used for the impregnation resin include PF with a

molecular weight of 600 and commercial grade UP type

isophtalic with a molecular weight of 2000 which were

supplied by Pultrution Innovative Sdn. Bhd., Seremban,

Negeri Sembilan, Malaysia.

Impregnation of the Fibres

The process of impregnation covered several significant

stages. The sugar palm fibres were first submerged in a 1000 ml

beaker which was filled with impregnation resin agents (PF

and UP) and placed inside a glass vessel. The glass vessel

was then evacuated at various impregnation times; specifically,

0, 5, 10, 15, 20 and 25 min at constant pressure of

1000 mmHg (133.32 kPa) before the vacuum vessel was

slowly released within 30 s. Next, the impregnated fibres

were taken out and excessive resin was then drained off for

5 min before the fibres were heated for polymerisation at

140 oC for 30 min. Finally, the cured fibres were weighed

using an analytical balance with the capability of reading up

to 0.0001 g.

Determination of Physical Properties

The weight percentage gain, density, specific gravity, moisture

content and water absorption of fibres were determined

using the following equations:

(1)

where, ma: mass of oven dry fibre/composite before impreg-

nation (g)

mb: mass of oven dry fibre/composite after impregnation

(g)

Density, (2)

where, mo: mass of oven dry fibre/composite (g)

Vg: green volume of fibre/composite (cm3)

Specific gravity, SG = (3)

where, ρf : density of fibres (g/cm3)

ρw: density of water (g/cm3)

Moisture content, (4)

where, mca: Mass of air dry fibre/composite (g)

mco: Mass of oven dry fibre/composite (g)

WPG (%)mb ma–( )

ma

---------------------- 100×=

ρg

cm3

---------⎝ ⎠⎛ ⎞ mo

vg

------=

ρf

ρw

-----

MC %( )mca mco–

mco

--------------------- 100×=

Figure 1. Cross-section of sugar palm fibre.

252 Fibers and Polymers 2013, Vol.14, No.2 M. R. Ishak et al.

Water absorption, (5)

where, mc1: Mass of oven dry fibre/composite before soaking in

water (g)

mc2: Mass of water swollen fibre/composite after

soaking in water (g)

Scanning electron microscope (SEM) and optical microscope

model Lieca MS 5 (with a constant magnification of 400)

were used to observe the surface and cross-sectional views

of sugar palm fibres after the impregnation process.

Determination of Tensile Properties

The control group of impregnation agent together with PF

and UP-impregnated fibres with various impregnation times

were tested according to the single fibre tensile test. A total

of 150 specimens were prepared and tested at room

temperature of 23 oC with a relative humidity of 50 % using

universal testing machine type Instron that has a load

capacity of 5 kN.

Method of Result Analysis

For the analyses of results, the mean of samples were used

to indicate if there were any changes in the physical and

tensile properties of the impregnated fibres and Standard

error was used to show if there were significant differences

between the variables. The results were statistically analysed

via social sciences (SPSS) software. One-way analysis of

variance (ANOVA), Duncan’s multiple range tests, was used

to determine whether increasing impregnation time produces

any significant effect on the physical and tensile properties

of fibre at p≤0.05. The result showed that the mean followed

with the different letters (a, b, c) for each series (0-25 min) in

impregnation agents was significantly different. In this

paper, an alpha level of 0.05 was used for all statistical tests.

In addition, linear regression analysis was used to show a

trend line in series of data. It tells whether a particular set of

data of sugar palm fibre increases or decreases in physical

and mechanical properties after the impregnation pressure is

increased. The trend lines were also used to describe the

strength of the relationship between two variables (impregnation

pressure and impregnation agent) as well as to discover if

these variables have any relationship at all or if they merely

contain redundant information.

Results and Discussions

Physical Properties of Impregnated Fibre

The effect of impregnation times (5, 10, 15, 20 and 25 min)

on WPG of sugar palm fibre is shown in Figure 2. The

results show the weight of resin that was absorbed in the

fibre after it was impregnated. It was observed that there was

no significant effect on WPG of fibres when impregnation

time was extended from 5 to 25 min for both PF and UP-

impregnated fibres. The results also showed that the fibre

impregnated with PF had slightly higher WPG than the fibre

impregnated with UP. This was indicated by their regression

trends which range from 8.24 to 9.79 % and 6.35 to 8.44 %,

respectively. In short, comparing WPG values between the

impregnation agents (PF and UP) showed that there was no

significance effect in the increase of WPG of fibre when

both impregnation agents were used.

The effect of elevating time of impregnation on SG of

sugar palm fibre is shown in Figure 3. The results obtained

in WPG showed a similar trend. No significant difference

(p≤0.05) was found within all impregnated fibres (PF and

UP) when impregnation time was extended from 5 to 25 min. It

was also observed that there was no significance effect after

using PF and UP as the impregnation agents in the increase

of SG of sugar palm fibres as shown by the linear trend in

their regression trends. In can be concluded that using PF

and UP as the impregnation agents or increasing the

impregnation time from 5 to 25 min did not give any

significant effect on the weight of the impregnated fibres.

The MC of the control group and impregnated fibres with

various times of impregnations is presented in Figure 4. A

notable improvement of physical properties of the fibres was

obvious after being impregnated with PF and UP where it

was shown that fibre MC decreased from 8.17 % in the

ranges of between 0.7-0.73 % and 0.79-0.97 %, while the

WA %( )mc2 mc1–

mc1

--------------------- 100×=

Figure 2. WPG of impregnated sugar palm fibres with PF and UP

at various impregnation times.

Figure 3. SG of impregnated sugar palm fibres with PF and UP at

various impregnation times.


reduction of MC was up to 91 % and 89 %. No significance

difference in the reduction of MC was observed between the

impregnation agents (PF and UP), as shown in Figure 4.

The reduction of MC shows that resins were able to shield

the fibres from absorbing moisture from the surrounding

[20], indicating a success of fibre enhancement efforts in

reducing moisture absorption of natural fibre. Several previous

studies had been carried out in an effort to discover an

effective way to reduce the sorption properties of natural

fibre in the presence of moisture.

The absorption of moisture in natural fibres is basically

due to the natural response of cell wall polymers of natural

fibre which contain hydroxyl groups to the environment.

When the fibres were placed in the environment containing

moisture, the fibres absorb the moisture until the fibres and

the surrounding atmosphere achieve equilibrium. However,

fibres lose moisture when they are placed in an atmosphere

of lower relative humidity (RH) until equilibrium is attained.

After being impregnated, the fibres were enclosed with

hydrophobic polymer resin which protects the fibre from the

absorption of moisture, thereby decreasing the hygroscopicity

of the fibre. It can be observed in SEM view that after they

were impregnated for 5 min, the surface and both ends of the

impregnated fibres were enclosed with impregnation agent

PF (Figures 5 and 6) and UP (Figures 7 and 8). The SEM

micrographs in Figures 5-8 apparently show different views

compared to the unmodified fibres shown in Figures 9 and

10. These figures show that the water molecules have filled

the cell wall freely through the open lumen as well as

through micropores along the fibre surface. The MC of the

control group was found to be significantly higher compared

to the MC of the impregnated fibres, as presented in Figure 4.

Evidently, impregnation of fibres makes them highly resistant

to moisture.

It was shown that the extended time of 10 to 25 min of

impregnation did not show significant improvement in the

MC. The rate of moisture absorption of fibre impregnated

with PF was shown to be slightly lower than that of UP, as

seen in their regression trends. This is attributed to the higher

content of resin being absorbed (higher WPG). This

Figure 4. MC of impregnated sugar palm fibres with PF and UP at

various impregnation times. Figure 5. Surface of PF-impregnated fibre.

Figure 6. End surface of PF-impregnated fibre.

Figure 7. Surface of UP-impregnated fibre.

Figure 8. End surface of UP-impregnated fibre.


indicates that the extra amount of resin that enclosed the

fibre impregnated with PF increased the fibres’ resistance to

moisture compared to those fibres impregnated with UP.

The effect of impregnation time on water absorption (WA)

is shown in Figure 11. Lower values of WA show further

evidence of enhancement in physical properties of the

impregnated fibre. The enhancement in physical properties

was seen when the water absorption was significantly

reduced between 62.50 and 66.18 % (reduction of 43 %) for

PF, and between 63.35 and 68.37 % (reduction of 41 %) for

UP. The control group showed a much higher value of WA

(111.40 %). The high WA of lignocellulosic fibres (unmodified

fibre) was expected due to its chemical content that containing

OH groups especially present at cellulose and hemicelluloses

portions. This is the main mechanism that attract and hold

water molecules through a chemical bond called hydrogen

bonding.

When the fibres were being impregnated, the applied

pressure forced the resin to penetrate into all the empty

spaces before they were polymerised. The resin was forced

to fill into cell wall and lumen through both ends of fibre

where the macrofibrils were open (Figure 10). Besides

filling through these open macrofibrils, resin also penetrated

into fibre cell wall through micropores (microvoids or small

holes) found along the surface of fibre. It was formed due to

the incomplete filling of the hemicelluloses and lignin

between the microfibrils. The existence of cell wall micropores

is confirmed by several experimental studies [21]. It was

reported that a maximum size for cell wall micropores is in

the region of 2-4 nm [22]. However, since the diameter of

micropores is very small, it is impossible for the impregnation

agents used in this study to penetrate into the cell wall

through these micropores, especially for UP resin which has

a higher molecular weight of 2000. This might explain the

existence of slightly higher WA of UP-impregnated fibres

compared to that of PF-impregnated fibres, as shown in their

regression trends. The impregnation agent of PF is easier to

penetrate into the cell wall through these micropores once

the cell wall is fully swollen, a condition which allows the

interior cell wall to be accessible to the impregnation agents.

On the other hand, when fibre is oven-dried to zero moisture

content, the micropores collapse and the cell wall would not

be accessible to the impregnation agents. In order to have an

efficient penetration, the cell wall has to be in a swollen

condition to allow for sufficient time of immersion in the

impregnation agent which will enable the impregnation

molecules to diffuse into the intracellular spaces of the cell

wall. When micropores are open, the interior of the cell wall

can be accessed by entities that are smaller than the diameter

of the micropores. For this reason, many previous researchers

immersed the substrate materials in PF resin for a longer

time such as for 24 hours while some researchers did it for as

long as several days [22].

In the present study, it is believed that the surfaces of

fibres were enclosed with cured resin (as proven in Figures

5-8), and their cell walls and cell lumens were fully or

partially filled with resin before being locked by polymerisation.

In some cases, if impregnation agents are unable to penetrate

deep in the cell wall, the resin would also enclose the exterior

surface of cell walls. In some worse cases, the impregnation

agent becomes the blocking mechanism that blocks the open

macrofibrils and cell wall micropores from water molecules

when the fibres are exposed to water or moisture which

results in the fibres to be highly resistant to water. These

phenomena can be better understood by comparing the SEM

views (with higher magnification) of end surfaces of the

macrofibrils (after being impregnated for 5 min) of unmodified

Figure 9. Surface of control specimen.

Figure 10. End surface of control specimen.

Figure 11. WA of PF and UP-impregnated sugar palm fibres at

various impregnation times.


fibres fully open (Figure 12), the PF-impregnated fibres

fully enclosed by impregnation agent (Figure 13) and the

UP-impregnated fibre fully enclosed by impregnation agent

(Figure 14).

As in the case of MC, WA of PF-impregnated fibres was

slightly lower than WA of UP-impregnated fibres as shown

in their regression trends. This is due to the fact that higher

amount of resin being absorbed (higher WPG) causes the

fibres to be more resistant to water than UP. It can also be

observed in Figure 11 that similar trend was obtained for

both impregnated fibres where their WA was significantly

reduced after being impregnated for 5 min. However, no

significant changes were evident when impregnation time

was extended from 10 to 25 min.

It is important to stress in this study that increasing the

time of impregnation even for 5 min with a pressure of 1000

mmHg did not show satisfactory improvement in the

physical properties of sugar palm fibre. This might be attributed

to the low impregnation pressure used (1000 mmHg) which

was found to be less significant in enhancing the fibre

properties despite the extended time given. This is due to the

fact that in impregnation modification, pressure treatment is

one of the factors that will aid penetration of impregnation

agent [22] into cell wall and lumen of the fibre.

Tensile Properties of Impregnated Fibre

The impregnated fibres were tested according to the single

fibre tensile test and their tensile stress-strain behaviour is

shown in Figure 15. The result shows that the fibre properties

significantly changed after being impregnated with polymer

resin. There seems to be three major stress strain curves

where each curve represents different behaviours of fibres:

control group, PF-impregnated and UP-impregnated fibres.

The highest stress is found in the fibre impregnated with UP,

followed by the fibre impregnated with PF, while control

group shows the lowest stress. As for their strain behaviour,

significant decrease in strain value following impregnation

was found at fibre impregnated with PF compared to fibre

impregnated with UP, as shown in Figure 15.

The results of tensile strengths of sugar palm fibres after

being impregnated are shown in Figure 16. Besides showing

a successful improvement in physical properties, it was also

noted that the impregnation modification on sugar palm

fibres had increased their tensile strength. After the fibre was

impregnated for 5 min, it was found that the tensile strength

of PF- and UP-impregnated fibres have significantly increased

from 241.93 MPa to 254.85 MPa and 283.75 MPa, respectively.

The increase in tensile strength of impregnated fibres was a

result of the resin that was enclosed and locked in the fibre

cell wall and lumen. Not only did it reduce the penetration of

water molecules into fibre cells, at the same time it also

reinforced the fibre structure. On the other hand, no further

increase in tensile strength was observed after impregnation

Figure 12. End surface of control specimen.

Figure 13. End surface of PF-impregnated fibre.

Figure 14. End surface of UP-impregnated fibre.

Figure 15. Stress-strain behaviour of PF and UP-impregnated

sugar palm fibres at various impregnation times.


time was extended from 10 to 25 min. It was also obvious

that the fibres impregnated with UP had higher tensile

strength than those fibres impregnated with PF, as indicated

in their regression trends. Statistical analysis of the results

also showed that there was a significant difference in the

increase of tensile strength between the two impregnation

agents (PF and UP).

As can be seen in Figure 17, impregnation of fibres

resulted in the increase of tensile modulus, indicating that

the resin locked in the fibre lumen and the cell wall enclosed

in the fibre surface had caused the fibres to become stiffer.

Tensile modulus significantly increased (from 3.07 GPa to

3.13 and 3.11 for PF and UP, respectively) when the fibre

was impregnated for 5 min. However, the additional 5 min

of impregnation did not show significant increase in the

tensile modulus of the fibre. Contrary to the trend found in

tensile strength, tensile modulus of fibres impregnated with

PF was slightly higher than one impregnated with UP, as

shown in their regression trends. However, the difference of

using the different impregnation agents (PF and UP) was not

significant. The higher tensile modulus of impregnated

fibres was as predicted prior to the curing process, where the

impregnated fibres became stiffer compared to the control

group that was cured especially for fibre impregnated with

PF.

For elongation at break, the tensile strength and tensile

modulus showed opposite results in which they decreased

with the increase in impregnation time, as shown in Figure

18. It was evident that impregnation significantly changed

the behaviour of fibre in which the ductility of sugar palm

fibre has decreased and the properties of sugar palm fibre

were dominated by the properties of brittle impregnation

agent. With regards to fibres, it can be observed that PF-

impregnated fibres experienced significant drop in elongation

at break compared to UP-impregnated fibres, as shown in

their regression trends. This is due to the brittle nature of

thermosetting resin especially PF which is known to be very

brittle. For fibres impregnated with PF and UP for 10 to 25 min,

no significant difference (p≤0.05) in elongation at break was

observed.

Another important property that is related to the durability

of the fibre and its composite is its toughness. It can be

measured from the area under the stress strain curve. Once

the fibres were impregnated, the behaviour of fibre will be

influenced by the behaviour of impregnation agents (PF and

UP). When this happens, the fibres become stiffer and

normally lead to the decrease in their strain values, as can be

seen in Figure 18. This is due to the fact that lower strain

Figure 16. Tensile strength of PF and UP-impregnated sugar palm

fibres at various impregnation times.

Figure 17. Tensile modulus of PF and UP-impregnated sugar

palm fibres at various impregnation times.

Figure 18. Elongation of break of PF and UP-impregnated sugar

palm fibres at various impregnation times.

Figure 19. Toughness of PF and UP-impregnated sugar palm fibres

at various impregnation times.


values of modified fibre would imply reduction in their

toughness and indicate lower energy that can be absorbed by

the material before failure. Based on the area under stress-

strain curve, it was noted that after undergoing impregnation

process, the toughness of the fibre impregnated with UP was

found to be significantly (P≤0.05) consistent with the

toughness of the control group, while the fibre impregnated

with PF experienced a significant decrease, as shown in

Figure 19. In view of this, impregnation of sugar palm fibres

with UP is said to be better since the fibres are tougher

compared to the fibres impregnated with PF. In addition,

UP-impregnated fibres have significantly higher tensile

strength than both the control group and the PF-impregnated

fibres.

Conclusion

This paper has discussed the results of a study of vacuum

resin impregnation of sugar palm fibre at the pressure of

1000 mmHg with different thermosetting polymer resins (PF

and UP) at various impregnation times (0, 5, 10, 15, 20 and

25 min). The results showed significant improvement in the

physical properties of sugar palm fibres due to the reduction

of MC and WA after being impregnated with PF and UP for

5 min. However, there was no significant improvement

(p≤0.05) when impregnation time was extended from 10 to

25 min. As for the mechanical properties, it was observed

that the impregnation process had increased tensile strength

and tensile modulus and decreased the elongation at break of

sugar palm fibre compared to the control group. It was also

observed that the UP-impregnated fibres showed better

mechanical properties than PF-impregnated fibres due to

their significantly higher tensile strength and elongation at

break which in turn, resulted in better fibre toughness than

PF-impregnated fibres. As in physical properties, mechanical

properties also indicated significant improvement as a result

of the 5-min impregnation. Additional impregnation time of

10 to 25 min was found to not further enhance the properties

of sugar palm fibre. This was attributed to the comparatively

low pressure of 1000 mmHg used for the study.

Acknowledgements

The authors would like to acknowledge the Ministry of

Agriculture and Agro-Based Industry (MOA) of Malaysia

for funding the research grant (Science Fund, project

number: 05-01-04-SF1114). Part of this paper was presented

in the Eighth International Conference on Composite

Science and Technology (ICCST/8 2011) held in Kuala

Lumpur.

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