Effect Of Nano ZnO And Nano SiO₂ On Performance Of Starch Film In Glycerol-Water Compound Plastic System

Based on the serious environmental pollution caused by the mass use of traditional petroleum-based plastic,the starch-based biodegradable film is considered to be the most potential natural,biodegradable available material,because it can be used by microorganisms in a short period of time and finally decomposed into carbon dioxide and water.However,the application of starch-based biodegradable film is limited by its poor mechanical properties and water resistance,high cost and low production efficiency.Hydroxypropyl starch is applied to prepared starch film by extrusion blow molding to improve production efficiency.The morphological and structural changes of starch granules during extrusion blow molding was also investigated.Glycerol-water composite plasticizing system was applied to reduce production cost and nano-reinforcement was added to enhance the mechanical properties of starch film and water resistance.The research provided technical support and theoretical basis for large-scale application of starch film.The main results are as follows:(1)Morphology and molecular structure of starch granules were changed clearly during extrusion blow molding.The extrusion blow molding process included three parts:blend,prill and blowing.The morphology of starch samples in the three processes was defined as powder state,masterbatch state and film state,respectively.The structures of starch powder,masterbatch and film were determined by Fourier transform infrared spectroscopy,X-ray diffraction,thermogravimetric analyzer and gel chromatograph.The results showed that the crystal form of the starch changed after twin-screw granulation and single-screw blowing process.The A type crystalline structure of powder sample transformed into V type of masterbatc state and B+V type of film state.After extrusion the short-range order reduced and the proportion of amorphous regions of the masterbatch state and film state has greatly increased,and the thermal stability decreased.In addition,the relative molecular weight of starch samples from powder state,masterbatch state to film state decreased step by step after shearing action.(2)Different properties of starch films were producecd by different proportions of glycerol(G)and water(W)composite plasticizing systems.The results showed that15%G-15%W had the best plasticizing effect.FTIR-ATR result showed that with the increase of water content from 0%to 20%,the characteristic peaks of starch film at3280 cm^-1shifted to low wavenumbers.It indicated the formation of strong hydrogen bonds among the film forming components.The short-range order of starch film decreased with the increase of water content from 0%to 15%,when the water content was 20%,the short-range order of starch film increased.For crystalline structures,all starch films present B+V,and 15%G-15%W plasticized starch film of crystallization degree had the more minivalue.The maximum weight loss was observed in 15%G-15%W plasticized starch film.The contact angle of starch film increased with the increase of water content and the surface hydrophobicity of starch film was the greatest when the water content was 15%.The contact angle of starch film decreased when the water content above 15%,while the water vapor transmittance showed the opposite trend.SEM results showed that 15%G-15%W plasticized starch film possessed relatively smooth and uniform apparent morphology.Moreover,15%G-15%W plasticized films displayed the maximum tensile strength.For the degradation properties of starch film,the results show that starch-based film can degraded over 85%within 5 weeks,with the highest degradation rate of 93.44%.It suggested that starch film had great advantages as an alternative to traditional plastics.(3)Nano SiO₂ and nano ZnO significantly(p<0.05)improved the mechanical properties and water resistance of starch film.The XRD pattern of composite films containing nano ZnO showed that starch did not interact with nano ZnO completely and retained its characteristic peaks.While the characteristic peaks of SiO₂ disappeared entirely in the composite film containing nano SiO₂.The incorporation of nanomaterials reduced the crystallinity of the composite film.The degradation temperature of the nanocomposite film also increased after the addition of nanomaterials.The results of SEM and AFM showed that the surface of the composite film with two kinds of nanoparticles was the smoothest,the surface roughness was the lowest and tensile strength and elongation at break was the largest.The starch film had a low water vapor transmittance and large contact angle because of the interaction of the two nanoparticles.