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. Ishak 1,4 * , Z. Leman 2 , S. M. Sapuan 2,3,4 , M. Z. A. Rahman 5 , and U. M. K. Anwar 4,6 1 Department of Aerospace Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 2 Department of Mechanical and Manufacturing Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 3 Institute of Advanced Technology (ITMA), University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 4 Institute of Tropical Forestry and Forest Products (INTROP), University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 5 Centre of Foundation Studies for Agricultural Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 6 Wood 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 and mechanical properties of sugar palm (Arenga pinnata) fibres. The fibre was evacuated at a constant impregnation pressure of 1000 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 observed after 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 significant improvement (p ≤0.05) in the physical properties of fibre was observed when the impregnation time was extended (from 10 to 25 min) using both impregnation agents. As for the mechanical properties of the fibre, significant improvement was observed after they were impregnated for 5 min. The fibres impregnated with UP resulted in better fibre toughness and improved mechanical properties as shown in their higher tensile strength and elongation at break compared to the fibres impregnated with PF. Both the physical and mechanical properties showed no significant improvement (p ≤ 0.05) after time for impregnation was extended (from 10 to 25 min) using both impregnation agents. Therefore, it can be concluded that the physical and mechanical properties of sugar palm fibre could be enhanced by impregnating the fibre with thermosetting polymer (PF and UP) for 5 min. It was shown that impregnation with unsaturated polyester (UP) showed better improvement than phenol formaldehyde (PF). In addition, this study also concluded that the unsatisfactory enhancement of the properties of sugar palm fibre even after the impregnation time was extended from 10 to 25 min was due to the use of low impregnation pressure 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: ridzwan@eng.upm.edu.my DOI 10.1007/s12221-013-0250-0