Preparation and characterization of wheat straw fibers for reinforcing application in injection molded thermoplastic composites S. Panthapulakkal, A. Zereshkian, M. Sain * Center for Biocomposites and Biomaterial Processing, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Canada M5S 3B3 Received 17 June 2004; received in revised form 15 February 2005; accepted 15 February 2005 Available online 14 April 2005 Abstract The potential of wheat straw fibers prepared by mechanical and chemical processes as reinforcing additives for thermoplastics was investigated. Fibers prepared by mechanical and chemical processes were characterized with respect to their chemical compo- sition, morphology, and physical, mechanical and thermal properties. Composites of polypropylene filled with 30% wheat straw fibers were prepared and their mechanical properties were also evaluated. The fibers prepared by chemical process exhibited better mechanical, physical and thermal properties. Wheat straw fiber reinforced polypropylene composites exhibited significantly enhanced properties compared to virgin polypropylene. However, the strength properties of the composites were less for chemically prepared fiber filled composites. This was due to the poor dispersion of the fibers under the processing conditions used. These results indicate that wheat straw fibers can be used as potential reinforcing materials for making thermoplastic composites. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Wheat straw; Biocomposites; Natural fiber; Mechanical defibrillation; Fiber processing; Chemical pulping 1. Introduction In the last 20 years, cellulose based plant fibers ex- tracted from biomass are experiencing increased de- mand as reinforcing materials for polymer matrices. Biofiber-reinforced composites have diversified their applications into products such as building materials and structural parts for motor vehicles by replacing the petroleum derived conventional reinforcing materi- als (Pervaiz and Sain, 2004; Panthapulakkal et al., 2004; Wolcott and Smith, 2004). The extensive use of lignocellulosic fibers and their composites is because of their properties such as low density, high specific prop- erties, non-abrasive nature, high level of filler loadings, availability, renewability, safe working environment, as well as other properties. In addition to wood based fibers, several types of plant fibers have been used for making both thermoplastic and thermoset composites. These include hemp, flax, jute, sisal, bagasse, ramie and kapok (Chen et al., 1998; Gassan and Bledzki, 1997; Mwaikambo and Ansell, 2002; Joseph et al., 1996; Sain and Kokta, 1993, 1994; Sain and Li, 2003; Prasad and Sain, 2003; Vande Velde and Keikens, 2001; Woodhams et al., 1984). Agricultural products such as wheat straw, rice straw, corn cobs and corn stalks are also sources of cellulose based fibers although they have a lower cellulose content compared to wood and other plant fibers (White and Ansell, 1993). However, abundant availability of these inexpensive residues makes the refining of agro-residues acceptable for the production of high value fiber com- posites. Throughout the world, tons of unused wheat straw residues are generated every year, and only a small percentage has been used for applications such as feed- stock and energy production. Use of these agricultural crop residues could open new markets for wheat straw and improve the rural agriculture based economy. 0960-8524/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.02.043 * Corresponding author. Tel.: +1 416 946 3191; fax: +1 416 978 3834. E-mail address: m.sain@utoronto.ca (M. Sain). Bioresource Technology 97 (2006) 265–272