Preparation and characterization of a-chitin whisker-reinforced chitosan nanocomposite films with or without heat treatment Jittrawadee Sriupayo a , Pitt Supaphol a , John Blackwell b , Ratana Rujiravanit a, * a The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand b Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA Received 11 April 2005; accepted 13 July 2005 Available online 19 September 2005 Abstract a-Chitin whisker-reinforced chitosan nanocomposite films were prepared by solution-casting technique. The a-chitin whiskers were prepared by acid hydrolysis of a-chitin from shrimp shells. The length of the as-prepared whiskers ranged between 150 and 800 nm, while the width ranged between 5 and 70 nm, with the average values being about 417 and 33 nm, respectively. The addition of a-chitin whiskers did not affect much the thermal stability and the apparent degree of crystallinity of the chitosan matrix. The tensile strength of a-chitin whisker- reinforced chitosan films increased from that of the pure chitosan film with initial increase in the whisker content to reach a maximum at the whisker content of 2.96 wt% and decreased gradually with further increase in the whisker content, while the percentage of elongation at break decreased from that of the pure chitosan with initial increase in the whisker content and leveled off when the whisker content was greater than or equal to 2.96 wt%. Both the addition of a-chitin whiskers and heat treatment helped improve water resistance, leading to decreased percentage of weight loss and percentage degree of swelling, of the nanocomposite films. q 2005 Elsevier Ltd. All rights reserved. Keywords: Nanocomposite; a-chitin whisker; Chitosan; Mechanical properties; Swelling behavior 1. Introduction Nanocomposites are a relatively new class of composites with at least one phase having a dimension in the vicinity of 1–1000 nm. As most of the present-day nanofillers used to prepare nanocomposites with synthetic polymeric materials are inorganic (Schmidt & Malwitz, 2003), their processa- bility, biocompatibility, and biodegradability are much more limited than those of naturally organic ones. In nature, a large number of animals and plants synthesize extracellu- lar high-performance skeletal biocomposites that consist of a matrix reinforced by fibrous biopolymers (Neville, 1993; Preston, 1967). Cellulose is a classical example where the reinforcing elements exist as whisker-like microfibrils that are biosynthesized and deposited in a continuous manner (Itoh, O’Neil, & Brown, 1983; Itoh & Brown, 1984). Favier, Chanzy, and Cavaille ` (1995) was the first to prepare cellulose whiskers from tunic of tunicate Microcosmus fulcatus by acid hydrolysis (i.e. tunicin whiskers) and use them as reinforcing nanofillers in a terpolymer of styrene and butyl acrylate (i.e. poly(S-co-BuA) latex). Since then, tunicin whiskers have been used as reinforcing nanofillers in poly(b-hydroxyoctanoate) (PHO) (Dubief, Samain, & Dufresne, 1999), poly(hydroxyalkanoate) (PHA) (Defresne, Kellerhals, & Witholt, 1999), plasticized maize starch (Neus Angles, & Dufresne, 2000a,b), and poly(oxyethylene) (Samir, Alloin, Sanchez, & Dufresne, 2004). Cellulose whiskers from wheat straw can also be prepared and have been used as reinforcing nanofillers in poly(S-co-BuA) latex (Dufresne, Cavaille ` & Helbert, 1997; Helbert, Cavaille `& Dufresne, 1996). Whiskers from other polysaccharides, such as starch (Dufresne, Cavaille `, & Helbert, 1996; Dufresne & Cavaille `, 1998) and chitin (Marchessault, Morehead, & Walter, 1959; Revol & Marchessault, 1993), can also be prepared. Unlike tunicin whiskers which can only be prepared by hydrolysis in strong sulfuric acid (H 2 SO 4 ) solutions (Favier et al., 1995; Dubief et al., 1999; Defresne et al., 1999; Neus Angles, & Dufresne, 2000a,b; Samir et al., 2004; Helbert et al., 1996; Dufresne et al., 1997; Marchessault et al., 1959; Carbohydrate Polymers 62 (2005) 130–136 www.elsevier.com/locate/carbpol 0144-8617/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2005.07.013 * Corresponding author. Tel.: C66 2 218 4132; fax: C66 2 215 4459. E-mail address: ratana.r@chula.ac.th (R. Rujiravanit).