Influence of chitin nanocrystal content on intermolecular interactions, crystallinity, and properties of...

Binary starch-chitosan composites, despite biological advantages, suffer from limited crystallinity, and suboptimal water vapor and oxygen barrier performance. This study investigates the role of chitin nanocrystals (ChNCs) in modulating the molecular interactions, crystalline structure, and functional properties of starch-chitosan composite films. Films were prepared by solution casting with ChNC loadings of 0, 2.5, 5, and 10 wt% and characterized using spectroscopic, diffractometric, thermal, mechanical, and barrier techniques. FTIR analysis revealed ChNCs strengthen interpolymer hydrogen bonding between starch hydroxyl and chitosan amino groups. XRD indicated that ChNCs partially restore crystallinity in the otherwise amorphous blends, with α-chitin diffraction peaks emerging at loadings as low as 2.5 wt% and becoming more defined at higher concentrations, particularly in chitosan-containing matrices where ChNCs appear to act as heterogeneous nucleation sites. At 2.5 wt%, tensile strength increased from 20.98 to 36.32 MPa, WVTR decreased from 6.55 to 5.77 g·m^-2·d^-1, and OTR decreased from 5.82 to 4.62 cc·m^-2·d^-1. TGA showed a 14-17 °C decrease in the principal DTG peak temperature with ChNC incorporation alongside a monotonic increase in char yield, indicating preserved overall thermal stability. These findings indicate that ChNCs function not as inert fillers but as active mediators of polysaccharide chain organization, offering a molecular-level strategy for tuning the structure-property relationships of starch-chitosan biopolymer systems. The optimal 2.5 wt% formulation is positioned for short-shelf-life food-packaging applications such as fresh-produce wraps, bakery overwraps, and lined paperboard for dry foods.