Effects Of Starch Modification On The Structure And Properties Of Starch-Polyvinyl Alcohol-Laponite RD Nanocomposite Films

Considering environmental issues and energy crisis caused by the use of plastics,people pay more attention on the development of natural polymers.Starch has been recognized as one of the most potential biodegradable polymers to replace fossil-based plastics.However,native starch has poorer thermoplastic property,poorer mechanical property and lower water barrier property,which limit its applications.Blending is an effective method to improve the properties of a single polymer.Starch,polyvinyl alcohol(PVA),laponite RD(LRD)are an common multiphase system.The properties of a multiphase system are not only determined by the structures of each component but also determined by the compatibility between each component and the dispersibility of nano particals in matrix.To improve the dispersibility of LRD and the compatibility among different components,a-amylase,pullulanase and hydrogen peroxide were used to modify the starch,then casting method was used to prepare starch-PVA-LRD nano-composites,DSC,TG/DTA,FTIR,XRD and SEM were used to investigate the effect of emzyme content on the structure,mechanical properties,WVP.The main results include:(1)After modified by a-amylase,the degree of hydrolysis of starch increased,the amylose content,the molecular weight and the viscosity of the starch decreased.Compared to the nano-composite without treatment,the modified nano-composites showed smoother surface suggesting that the compatibility between different components improves.The modified starch-PVA-LRD displayed a decreased tensile strength and an increased breaking elongation,an increased water vapor permeability and thermal stability.(2)After modified by pullulanase,the degree of hydrolysis of starch increased,the amylose content of starch increased,the molecular weight and the viscosity of the starch decreased.Compared to the nano-composite without treatment,the dividing line of the nano-composites is more obvious and the uniformity is poor.The modified starch-PVA-LRD displayed an increased tensile strength and a decreased breaking elongation,an increased water vapor permeability and thermal stability.(3)The pullulanase hydrolyzed starch was oxidized with wet hydrogen peroxide.With the oxidation degree of starch increasing,the tensile strength of starch-PVA-LRD nano-composite increased,the elongation at break decreased and the WVP increased.The toughness of films enhanced.