Effects of various cross-linking agents on the physicochemical properties of starch/PHA composite films produced by extrusion blowing

The effects of various cross-linking agents on the physicochemical properties of hydroxypropyl distarch phosphate (HPDSP)/polyhydroxyalkanoate (PHA) composite films prepared by extrusion blowing were investigated. Four types of cross-linking agents with multicarboxyl or multihydroxyl structures were used in the preparation of starch/PHA films. Scanning electron microscopy (SEM) showed that the citric acid, adipic acid, and borax cross-linked films had a more continuous and homogeneous texture than the films with boric acid. X-ray diffraction (XRD) indicated that the addition of cross-linking agents increased the relative crystallinity of the films, but hindered the formation of intercalated structures in the polymer matrix. The films containing adipic acid exhibited the highest light transmittance and the lowest water vapor and oxygen permeabilities. The films with boric acid showed the highest tensile strength, while the citric acid cross-linked films exhibited the highest elongation at break. Thermogravimetric analysis (TGA) suggested that the cross-linked films had better thermal stability than the control films. Fourier transform infrared (FTIR) analysis confirmed that the cross-linking agents participated in the intermolecular interactions of grafting or cross-linking between starch and PHA.