Abstract
Chitosan is widely used in films for packaging applications. Chitosan reinforcement by stiff particles or fibers is usually obtained at the expense of lowered ductility and toughness. Here, chitosan film reinforcement by a new type of native chitin nanofibers is reported. Films are prepared by casting from colloidal suspensions of chitin in dissolved chitosan. The nanocomposite films are chitin nanofiber networks in chitosan matrix. Characterization is carried out by dynamic light scattering, quartz crystal microbalance, field emission scanning electron microscopy, tensile tests and dynamic mechanical analysis. The polymer matrix nanocomposites were produced in volume fractions of 8, 22, and 56% chitin nanofibers. Favorable chitin-chitosan synergy for colloidal dispersion is demonstrated. Also, lowered moisture sorption is observed for the composites, probably due to the favorable chitin-chitosan interface. The highest toughness (area under stress-strain curve) was observed at 8 vol% chitin content. The toughening mechanisms and the need for well-dispersed chitin nanofibers is discussed. Finally, desired structural characteristics of ductile chitin biocomposites are discussed.
Highlights
Chitosan is a widely used biopolymer and interesting for use in packaging and biomedical applications
“The present” nanofibers illustrated in Figure 1 are aggregates of several microfibrils and much reduced protein content compared with the native structure
The chitosan polymer was obtained from Sigma Aldrich, and is a chitin derivative prepared by dissolution and deacetylation of chitin from shrimp exoskeletons
Summary
Chitosan is a widely used biopolymer and interesting for use in packaging and biomedical applications. It is commercially available as a derivative of chitin microfibrils from crustaceans. The preparation of chitosan involves derivatization through elimination of the chitin acetyl group, and the final sugar monomer is N-glucosamine. Chitin is predominantly organized in extended chain conformation and assembled in the form of microfibrils (Figure 1). This structural organization is vital for the mechanical function of cuticles and exoskeletons of insects and crustaceans (Neville, 1967; Raabe et al, 2005). Chitosan is in nature less common, but is present as a cell wall component of filamentous fungi, where chitosan biosynthesis is through deacetylation of chitin (Bartnicki-Garcia, 1968; Muzzarelli et al, 2012)
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