Preparation And Properties Of Cross-linked Carboxymethyl Starch/Polyvinyl Alcohol Composite Films

The development of low-cost,high-performance,degradable packaging materials has become a hot topic in order to solve the environmental pollution problems caused by the consumption of petroleum resources and discarded plastics.Cross-linked carboxymethyl starch（CCMS）has good biodegradability,however,the flexibility and water resistance of the film are poor.Polyvinyl alcohol（PVA）has excellent film-forming and mechanical properties and hydrophilicity.In order to promote the application of CCMS and PVA in packaging materials and improve the comprehensive performance of CCMS/PVA composite films,in this experiment,CCMS and PVA were used as base material,using the solution casting method,adding with cross-linking agent（citric acid）,plasticizer（urea,CaCl₂）and reinforcing agent（nano-SiO₂）to prepare CCMS/PVA composite films.The effects of various base film ratio additives content,and reaction temperature on the mechanical properties,water resistance,water vapor permeability,light transmittance,thermal properties and micro-morphological structure of the CCMS/PVA composite film were investigated.（1）The effects of the base film mass ratio of CCMS and PVA,citric acid content and reaction temperature on the performance of the composite film were investigated.The results show that the higher the proportion of CCMS,the lower the tensile strength,elongation at break,transparency and production cost of the composite film.When CCMS:PVA=1:1,the mechanical properties,biodegradability and production cost of the composite membrane could be balanced.The addition of citric acid can greatly improve the flexibility,water resistance,gas barrier properties,transparency,thermal stability,thermal stability and smoothness of the composite films.The optimal reaction temperature for citric acid was 65°C.When the citric acid content was 30%,compared with pure CCMS/PVA composite film,the tensile strength,water absorption,solubility and water vapor permeability of the composite film was reduced by 47%,76%,27%,and 31%,respectively.The elongation at break,light transmittance and the thermal decomposition temperature was increased by 759%,461%and 14%,respectively.（2）The effect of organic plasticizer urea and inorganic plasticizer CaCl₂ on the performance of CCMS/PVA composite films had been explored.The results showed that the addition of urea can improve the elongation at break,water resistance and water vapor permeability of the composite films and reduce the transparency of the composite films,but had no significant effect on the thermal stability of the composite films.Under the premise of adding 30%citric acid,the effect of improving the elongation at break and hydrophobicity of the composite film was more significant when the urea content was 4%.Compared with the pure CCMS/PVA composite film,the tensile strength was reduced by 22%,the elongation at break was increased by676%,the water absorption and the solubility were respectively decreased by 73%and21%,the water vapor permeability,the light transmittance and the thermal decomposition temperature were respectively increased by 2%,78%and 13%.The results showed that the addition of CaCl₂ can reduce the flexibility,water vapor permeability and light transmittance of the composite film,and improve the water resistance and thermal stability of the composite film.When the reaction temperature was 95℃and the content of CaCl₂ was 4%,compared with the pure CCMS/PVA composite film,the tensile strength was increased by 6%,the elongation at break was reduced by 83%,and the water vapor transmission rate was reduced by 15%.When the reaction temperature was 65℃and the content of CaCl₂ was 4%,the water absorption and solubility of the composite films were reduced by 62%and 24%,respectively.（3）Nano-SiO₂ was used as a reinforcing agent,when the citric acid content was30%,the urea content was 4%,and the influence of its content on the properties of CCMS/PVA composite film was investigated.The results showed that nano-SiO₂ can improve the mechanical properties,water resistance,water vapor barrier,light transmittance and thermal stability of the composite film.When the SiO₂ content was5%,the composite films reached the best mechanical properties,and the tensile strength and elongation at break were 8MPa and 120.9%,respectively.Compared with pure CCMS/PVA composite films,it had increased by 11%and 315%,respectively.The water absorption and solubility of the composite films were reduced by 74%and26%,respectively.When the SiO₂ content was 6%,the water vapor transmission rate was reduced by 6%,the light transmission rate was increased by 341%,and the thermal decomposition temperature was increased by 15%.