Study on hydroxypropyl corn starch/alkyl ketene dimer composite film with enhanced water resistance and mechanical properties.

This study aimed to address the limited applicability of starch-based films in food packaging due to their inherent hydrophilicity, by developing a highly hydrophobic and mechanically reinforced film through compositing with alkyl ketene dimer (AKD). The FTIR analysis confirmed the successful introduction of AKD into the starch backbone via esterification by forming a ß-keto ester linkage. Notably, the incorporation of AKD resulted in significant improvements in the modified film (S80A20), by exhibiting a higher water contact angle (WCA) of 128.28° and a reduced water vapor permeability (WVP) to 0.81×10-10 (g m/m2 s Pa). These enhancements were attributed to the inherent low surface energy of AKD and the increased surface roughness caused by AKD recrystallization. Moreover, the mechanical properties of the films were also enhanced due to the chemical crosslinking and intermolecular hydrogen bonding, as supported by the results of relaxation temperatures and molecular dynamics simulations. Considering the environmentally friendly and biodegradable nature of all components, the prepared hydrophobic films will hopefully be applied in food packaging.

A study of starch-urea-water mixtures with a combination of molecular dynamics simulation and traditional characterization methods.

The relationships among the mixtures of starch, urea and water were intensively studied with a combination of molecular dynamics (MD) simulation and traditional characterization methods, including differential scanning calorimeter, scanning electron microscope, X-ray diffraction and Fourier-transform infrared spectroscopy, etc. In the presence of urea, the structure and morphology, as well as the thermal property of starch were significantly changed, which positively depends on the urea content in the aqueous solutions. In MD simulation, hydrogen bonds interaction as well as the distributions of starch fragments, urea and water in both molecular and atomic level were systematically studied. Hydroxyl oxygen atoms in glucose residue, nitrogen atoms in urea molecule and oxygen atom in water molecule are the main sites of the hydrogen bonding between the solute and solvent respectively. Conjunction of starch and urea becomes stronger than that of starch and water. In the course, the bulk water tetrahedral network is disturbed by urea, which has a significant influence on starch molecule movement.

Development and characterization of a hydroxypropyl starch/zein bilayer edible film.

An edible hydroxypropyl starch (HPS) based bilayer film with a waterproof layer of zein was successfully prepared through a two-step solvent casting method. The morphology, mechanical properties, as well as water barrier properties of the bilayer film were systematically studied. Results showed that bilayer film presented smooth surface morphology with an improved visibility, and there was an adhesion interface between two layers. Water resistance and UV barrier property, as well as mechanical property, were significantly improved. In addition, the interactions between starch and zein through hydrogen bonding were analyzed by Fourier-transform infrared spectroscopy (FTIR) and molecular dynamics (MD) simulation. In MD simulation, the relative trajectories were dynamically presented. Conjunction of starch and zein through hydrogen bonding among the hydroxyl and amino (carboxyl) groups was identified, and stronger affinity with starch mainly rooted from asparagine (ASN) and tyrosine (TYR) residues.