Modification of microstructural morphology and physical performance of chitosan films

Abstract

The development of performance driven materials from bio-renewable resources requires certain chemical modifications, which maintain the microstructure and inherent characteristics without major alteration and the durability of the final products. In the present study, chitosan (N-deacetylation derivative of chitin) films were generated from an aqueous acetic acid solution of chitosan and treated with methanol and ethylene glycol diglycidyl ether (EGDE). The cross-sectional surface microstructures of the untreated and treated films were analyzed using the technique of atomic force microscopy (AFM). The dry mechanical, water absorption, resistance to enzymatic digestion and thermal transition characteristics of the films due to treatment with methanol and EGDE were also studied. Under AFM all produced films exhibited a granular morphology with different nanoparticle or granule size and hill-valley-structure in the cross-sectional surface. The cross-sections of both untreated and methanol treated chitosan films showed a quite dense and uniform coverage with nanoparticles. However, the EGDE treated chitosan film's cross-section contained very scattered distribution of the granules with different vertical distances. The untreated chitosan film showed an average tensile strength of 59 MPa, modulus of 1477 MPa and ultimate elongation of 43%. The methanol treatment had marginal influence on tensile properties of the chitosan film, but the treatment with a mixture of 0.25 M EGDE in methanol increased the tensile modulus and decreased the ultimate elongation without affecting the maximum stress. However, the chitosan film treated with EGDE showed an improved resistance to swelling in water at pH range of 5.2–9.1. The EGDE treated film had a significantly improved resistance to digestion by several enzymes (e.g., pepsin, papain, lipase and protease). The differential scanning calorimetric (DSC) analysis revealed that these chemical treatments increased the glass transition temperature ( T g) and heat of enthalpy (Δ H) of the chitosan film.