Preparation and characterization of hydroxypropyl methylcellulose/hydroxypropyl starch composite films reinforced by chitosan nanoparticles of different sizes

Edible films have provided a breakthrough in reducing environmental pollution caused by non-degradable plastics. The present work aims to prepare novel biodegradable films with improved mechanical and barrier properties. Three different sizes of chitosan nanoparticles (CSNPs) were prepared based on ionic gelation by changing the mass ratio of chitosan (CS): tripolyphosphate (TPP). Two concentrations of CSNPs (5 wt% and 10 wt%) were incorporated into a blend of hydroxypropyl methylcellulose (HPMC) and hydroxypropyl starch (HPS) to create CSNP-reinforced composite films. The physicochemical, mechanical, and barrier properties of the CSNP-reinforced films were evaluated to determine the effects of particle size on the HPMC/HPS composite films. Both concentrations of CSNPs improved the hydrophobic properties, thermal stability, mechanical properties, and permeability of the films. The contact angle of CSNP-reinforced films was increased from 51.9° to 77.3°. The temperature at which thermal decomposition occurred was increased by about 10 °C. The maximum increase in elongation at break was 19.57%, without reducing the tensile strength of the films. The water vapor permeability of the reinforced films was reduced by up to 32.99%. In addition, the particle size of CSNPs had a significant effect on the properties of the composite films. Compared with larger CSNPs, adding small CSNPs (CS: TPP mass ratio = 3:1) into the HPMC/HPS matrices can form a denser network structure of films, which can better enhance the barrier properties and mechanical properties.