Kenaf Fiber-Reinforced Copolyester Biocomposites T.H. Mokhothu, 1 B.R. Guduri, 2 A.S. Luyt 1 1 Department of Chemistry, University of the Free State, Phuthaditjhaba, South Africa 2 Polymers and Composites, CSIR, Port Elizabeth, South Africa In this study the morphology and properties of a biode- gradable aliphatic–aromatic copolyester mixed with kenaf fiber were investigated. Untreated kenaf fiber, as well as kenaf fiber treated with NaOH, and with NaOH followed by silane coupling agent treatment at various concentrations, were used as fillers in the composites. The biocomposites were prepared by melt-mixing and a 10 wt% fiber loading was used for all the compo- sites. The properties of the biocomposites were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile properties, environ- mental scanning electron microscopy (ESEM), and biodegradability. The extent of silane initiated grafting was followed by gel content determination. The presence of fiber and fiber treatment influenced the determined properties in a variety of ways, but the best balance of properties were found for the copo- lyester mixed with alkali-treated fiber. This composite showed improved thermal, thermomechanical, and mechanical properties. The introduction of alkali treat- ment caused increased surface roughness in the fiber, which resulted in mechanical interlocking between the filler and the matrix, while silane treatment slightly reduced the properties. POLYM. COMPOS., 32:2001–2009, 2011. ª 2011 Society of Plastics Engineers INTRODUCTION Development of affordable composite materials from renewable resources, such as natural fibers and biodegrad- able polymers, offers both economic and environmental advantages [1–3]. The use of renewable materials contributes to global sustainability and the diminution of global warming gases. As the number of applications of composite materials continues to increase, an alternative source of polymers for composites becomes important. Biopolymers and natural fibers are potential alternatives for petroleum-based materials. Although natural fibers have advantages of low cost and low density, they are not totally free of problems. A serious problem of natural fibers is their strong polar character which creates incom- patibility with most polymer matrices. Surface treatments, although having a negative impact on economics, are potentially able to overcome the problem of incompatibility. Chemical treatments can increase the interfacial adhesion between the fiber and the matrix, decrease the water absorption of fibers, and can be considered in modifying the properties of natural fibers. Some compounds are known to promote adhesion by chemically coupling the adhesive to the material, such as sodium hydroxide, silane, acetic acid, acrylic acid, maleated coupling agents, isocyanates, potassium permanganate, and peroxide. Chemical modifications of natural fibers, aimed at improving the adhesion with a polymer matrix, were investigated by a number of researchers. Most chemical treatments have achieved various levels of success in improving fiber strength, fiber fitness, and fiber–matrix adhesion in natural fiber-reinforced composites [4]. Biodegradable polyesters are one family of polymers that have been considered as replacements for conven- tional plastic resins. Aliphatic polyesters such as the natu- rally occurring polyhydroxyalkanoate family of materials and the synthetic polycaprolactone have been investigated as possible alternatives to traditional plastics, but their material properties seriously affect the versatility of these materials [5]. A more promising alternative is an ali- phatic–aromatic copolyester of 1,4-butanediol, adipic acid and terephthalic acid, which has been commercialized under the trade names Ecoflex TM . The copolyester is pro- duced from the random polymerization of the diether oligomers ofadipic acid/butanediol and terephthalic acid/ butanediol. The kenaf fiber has recently gained a lot of attention as a biomass-based additive. Kenaf has a signifi- cantly good ability to fixate CO 2 , and its photosynthesis speed is at least three times higher than that of usual plants [6]. It can absorb 1.4 times its own weight in CO 2 and its carbon content is about 43% [7]. Kenaf has been used mainly for textiles, paper, and animal food, but com- posites of kenaf fiber and PLA [5] or composites of kenaf Correspondence to: A.S. Luyt; e-mail: LuytAS@qwa.ufs.ac.za Contract grant sponsors: The National Research Foundation, The Council for Scientific and Industrial Research, University of the Free State in South Africa. DOI 10.1002/pc.21233 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2011 Society of Plastics Engineers POLYMERCOMPOSITES—-2011