Technical Report Degradation of compressive properties of pultruded kenaf fiber reinforced composites after immersion in various solutions Norlin Nosbi, Hazizan Md Akil * , Z.A. Mohd Ishak, A. Abu Bakar School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia article info Article history: Received 15 January 2010 Accepted 20 April 2010 Available online 5 May 2010 abstract In this paper, water absorption behavior of pultruded kenaf fiber reinforced unsaturated polyester com- posites was investigated. Residual compressive properties of the composites after immersion were also reported. Composites were prepared using pultrusion method with minimum kenaf fiber content of 70% w/w. Water absorption tests were performed at room temperature under three different solutions, i.e. distilled water, sea water and acidic solution. The diffusion coefficient of water absorption and max- imum moisture content were calculated by measuring the water uptake of specimen at regular time interval. Diffusion coefficient and the highest moisture content values were recorded for composite immersed in distilled water followed by acidic solution and sea water. The water absorption of kenaf fiber reinforced unsaturated polyester composites was found to follow a Fickian’s behavior where it reach equilibrium. The compressive properties were found to decrease with the increase in the percentage of water uptake. The decay in compression properties is attributed to the plasticization of the fiber–matrix interface and swelling of the kenaf fiber. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Natural fibers form an alternative for most widely applied syn- thetic fiber in composites technology and manufacturing. The interest in natural fiber was known because it is cheap and lighter in weight which provides better stiffness per weight than glass. Furthermore, natural fiber source is renewable where it considered being green and environmentally friendly. By their fairly good mechanical properties the usage of natural fiber are retained in all sort composite preparations. Unlike natural fiber, synthetic fi- bers like glass have been used as reinforcement in composite man- ufacturing via various fabrication methods. Similarly, if natural fiber reinforced composites (NFRC) were to offer an alternative fi- ber to the composite industry, it has to accommodate all the pro- cessing avenues of it counterpart, glass fiber. There exist many natural fibers which have been explores such as sisal, jute, flax, hemp, etc. One of the popular natural fibers is ke- naf fiber. These kenaf is an annual plant due to its rapid growth and it is an inexpensive and a renewable source plant. Kenaf fiber is ob- tained from the bast of stems of plants genus Hibiscus, family of Malvaceae, species of H. cannibinus and requires less water to grow because it has growing cycle of 150–180 days with average yield of 1700 kg/ha [1]. Similarly, various composite manufacturing techniques avail- able such as, RTM, compression moulding etc. However, some of these techniques require fiber in the continuous form which is not readily available form of natural fiber. In the case of engineer- ing composites, filament winding and pultrusion methods are most popular. Pultrusion is a unique processing technique for composite manufacturing. Pultruded composite is always associated with high strength, stiffness which particularly due to high fiber con- tent, i.e. 70%. So, pultrusion is among a few composite processing techniques that could process composite with up to 70% fiber con- tent in unidirectional fiber configuration. It is a continuous mold- ing process to manufacture a composite by using continuous fiber and liquid resin. The impregnation is accomplished by guid- ing the reinforcement over and under rods located below the resin surface [2]. The fiber is dipped into impregnated resin bath and emerges via shape guidance before being heated in the die. Finally the composite is left to cool off before being pulled and cut into the required length. As we know, our surrounding area is full of moisture and air. All types of polymer composites will absorb moisture to a certain ex- tent when immersed in water or exposed to humid environment [3]. In fiber reinforced polymer (FRP), not only polymer matrix that absorb moisture but also the fiber especially the natural fiber. This particularly due to the hydrophilic nature of the natural fiber that is more sensitive towards water absorption than synthetic fiber which causing instability in the properties of the composites [4]. There are three different mechanisms that conduct the moisture 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.04.037 * Corresponding author. Tel.: +60 4 5996161; fax: +60 4 5941011. E-mail address: hazizan@eng.usm.my (H.M. Akil). Materials and Design 31 (2010) 4960–4964 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes