MECHANICAL AND MOISTURE BARRIER PROPERTIES OF HYDROXYPROPYL RICE STARCH AND HYDROXYPROPYL RICE STARCH-POLY(ACRYLIC ACID) GRAFT COPOLYMER FILM

Abstract

Physical properties of two cast films, namely, hydroxypropyl rice starch (HP) and hydroxypropyl rice starch-g-poly(acrylic acid) (HP-g-PAA) films were investigated. Films were evaluated for water vapour permeability, tensile strength and elongation as a function of solvent composition, different types and concentrations of plasticizers (for HP film) and acrylic acid (for HP-g-PAA film). Increasing concentrations of both glycerol and sorbitol in HP film resulted in significantly improved film extensibility but reduced film tensile strength and water vapour permeability. Water vapour permeability ranged from 0.82 to 1.58 g.mm.m-2. day-1.mmHg-1 for HP-film. Sorbitol was more effective than glycerol as a plasticizer in that sorbitol-plasticized HP-film exhibited marginally lower water vapour permeability and marginally greater tensile strength. Grafting of poly (acrylic acid) onto hydroxypropyl rice starch was evidenced by FTIR analysis whereby the existence of a peak at the wavelength 1715 cm-1 indicated the presence of a carbonyl group in the HP-g-PAA composite. Water vapour permeability ranged from 0.89 to 1.23 g.mm.m-2. day-1. mmHg-1 for HP-g-PAA film and showed an increasing trend as the concentration of acrylic acid (0-10% w/w) was increased. Extensibility of the HP-g-PAA film increased linearly with increasing concentration of acrylic acid but tensile strength of the film showed a maximum value at 2.5% w/w acylic acid.