Preparation And Film Forming Property Of Double-modified Thermoplastic Corn Starch

Researching environment-friendly materials have become an urgent problem becauseof the harm brought by conventional plastics being more and more concerned. In order tostudy and develop bio-degradable starch plastics, in this study, corn starch used as rawmaterials was double-modified through mechanical force and the modifier, and thedouble-modified thermoplastic starch was obtained. Biodegradable starch plastic wasprepared by the double-modified thermoplastic starch mixed with a certain quality ofpolyvinyl alcohol. The corn starch granules became smaller by mechanical force, enhancingthe contact interaction of the modifier and the starch granules, lowering the reactiontemperature and other conditions. While adding glycerol, citric acid as modifier, the rigidstructure caused by the hydrogen bonding in the corn starch was destroyed. Thethermoplastic of the corn starch and its compatibility with polyvinyl alcohol (PVA) wereboth strengthened by the double modification. The major research contents and results wereas follows:(1) Under the condition of reaction time60min, the reaction temperature120℃and theproportion of moisture content of20%starch: citric acid: glycerol equals to1:0.4:0.3, rawcorn starch modified through the citric acid and glycerol, was synthetized for the highestdegree substitution0.165of single-modified thermoplastic corn starch. However, under thesame conditions, the raw corn starch through grinded ultrafinely and then modified by citricacid and glycerol, was synthesized for the highest degree substitution0.259ofdouble-modified thermoplastic corn starch. Citric acid had the most influence on the degreeof substitution, and then the effect of glycerol, reaction temperature, reaction time. Thestructure and the morphology of double-modified thermoplastic starch were researched byviscometer, spectrophotometer, fourier transform infrared (FTIR), differential scanningcalorimetry(DSC) and X-ray diffraction (XRD). The results showed that there were morecitric acid anhydride groups, the crystallinity and viscosity were lower, while the thermalstability and light transmission were higher in the double-modified corn starch relative tothe single-modified corn starch.(2) The raw starch/PVA composite film, single-modified thermoplastic corn starch/PVA composite film and the double-modified thermoplastic corn starch/PVA compositefilm were prepared by casting method. The quality of polyvinyl alcohol content in everycomposite film was25%of starch. The structure and nature of composite films were researched by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanningelectron microscopy, mechanical properties, water absorption and degradation. The resultsindicated that the mechanical properties and thermal stability of the double-modified starchcomposite film were impoved, while water absorption and crystallinity were lower, and thefilm performance was better, relative to the raw starch and single-modified starchcomposite films. Within a certain range of the degree of substitution, the higher the degreeof substitution was, the better the membrane performance of the composite films. Thedegradation rate of composite film prepared by the double-modified starch of the degree ofsubstitution0.259, was slower, and other indicators were better. After buried in the outdoorsoil microbial degradation for30days, the degradation rate of this kind of the compositefilm was about43％.