xylan on cellulose nanowhiskers matrix

Due to the ever-increasing global demand for materials, international dependence on conventional petroleum resources and environmental concerns, there is considerable interest in the development of alternative and sustainable products, manufactured by green technologies. In an effort to address these challenges, cellulose, the most globally abundant naturally occurring polymer has attracted significant attention for the development of novel biobased materials that are renewable, sustainable and biocompatible. Among the proposed applications is the utilization of cellulose nanowhiskers (CNW) as reinforcement or nanofillers for the manufacture of degradable engineered biocomposites with unique properties, including high mechanical strength, low thermal expansion and density, unique morphology, self-assembly and optical properties. CNW from biomass are a class of rod-like crystals with dimensions of 100 nm to microns in length and 5–50 nm in diameter. These are mostly obtained by controlled acid hydrolysis of cellulose fibers that selectively hydrolyzes the amorphous regions, leaving behind the less reactive crystalline regions. Several recent studies on CNW and their derivatives indicate the potential biofilm applications of CNW. For example, Goetz et al. prepared nanocomposite films from CNW, poly(methyl vinyl ether-co-maleic acid) and poly(ethylene glycol) with improved crosslinking density, water sorption properties. Peng et al. prepared films based on hemicelluloses and cellulose nanofibers with enhanced mechanical properties. Xylan from wood with a β-(1–4)-D-xylopyranosyl backbone to which arabinopyranosyl, glucuronic acid and acetyl substituents are attached, constituting 25–35% of dry biomass, represents another abundant biopolymer. Xylan can be used to form films, which in combination with biodegradability make it another interesting alternative to the petroleum-based materials for biorefinery products. Xylan based films and coatings show low oxygen and grease permeability with relatively improved properties in tensile strength. The natural association of xylan with cellulose through interactions between substituted, linear regions of the chains has been studied extensively in the pulp paper industry to improve processing and mechanical properties of the pulp. Based on such interactions, the current work will not only examine the potential for depositing xylan on a CNW matrix to prepare novel films under mild conditions, but also to understand how expected improvements depend on the dispersion and distribution of xylan in CNW matrix as well as the interaction between the matrix and the reinforcing phase. Bionanocomposite films were successfully prepared through a simple and green route by an adjustment of pH to deposit birch wood xylan onto poplar CNW matrix followed by a dialysis, sorbitol addition and solution casting with compositions as described in Table 1. In an effort to study the effect of deposition process on film physicochemical properties, control group films were prepared following exactly the same procedures, except for pH adjustment and dialysis. Films were conditioned at 50% relative humidity and 23 °C for 24 h and characterized for tensile strength and strain, as summarized in Fig. 1. The tensile strength of pH adjusted films increased from 24.5 MPa to a maximum of 46.3 MPa with 6.3% xylan deposition amount, while there was a decrease in strain, ranging from 8.6 to 7.2%. When the xylan deposition was greater than 6.3%, there was a decrease in tensile strength with a leveling-off in the strain, which could be due to lower film density (Table 2). Films that were pH adjusted and School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th St., Atlanta, GA 30332, USA. E-mail: [email protected]; Fax: +1-404-894-9701; Tel: +1-404-894-4578 Louisiana Forest Products Development Center, LSU Agricultural Center, Louisiana State University, Baton Rouge, LA 70894, USA USDA-Forest Service, Southern Research Station, 2500 Shreveport Highway, Pineville, LA 71360, USA