| The invention and use of plastics have brought great convenience to people.However,due to its non-degradation,it has led to serious environmental pollution problems attracted people’s attention to biodegradable materials.According to statistics,5%-8% of the oil produced in the world is used for the production of plastics,and this proportion is still rising.Petroleum is a non-renewable resource with limited total amount.Finding a traditional plastic substitute is an important direction for the research of polymer materials.As a renewable and biodegradable polymer material,starch-based materials have the advantages of low cost and rich source.However,the processing technology of starch-based materials is not mature enough,and the mechanical properties and waterproof properties of starch-based materials are poor,so starch-based materials are one of the directions worth studying at present.In this paper,in order to better control the processing technology of starch gelatinization and plasticization,the effects of amylopectin and amylose content,glycerol content,different crosslinking agent types and content and polyvinyl alcohol(PVA)content on starch gelatinization and starch-based film processing rheological properties were studied.Then using starch as raw material,glycerol as plasticizer,PVA as reinforcement,glutaraldehyde and citric acid as composite crosslinking agent,the mechanical properties and waterproof properties of starch-based films were improved.The starch-based biodegradable film materials were prepared by solution blending and tape casting technology.The main research results are as follows :High-purity corn amylopectin and high-purity corn amylose were selected to study the effects of amylopectin content and amylose content on starch gelatinization process and starch paste rheological behavior.The results showed that the higher the amylopectin content was,the lower the gelatinization temperature of starch was,and the starch was more prone to gelatinization.On the contrary,the higher the amylose content was,the higher the gelatinization temperature was.With the increase of amylose content,the gelatinization temperature of starch increased from70 °C to 75 °C.In the pasting process,the higher the amylopectin content is,the greater the storage modulus G’,loss modulus G’’ and viscosity ηare,and the less the amylopectin content is,the more obvious the difference is.At 80 °C,when the amylopectin content is less than 30 %,the difference between G’,G’’ and η is obvious.After gelatinization of corn starch,the starch paste with amylopectin content less than 50 % met the requirements.With the increase of amylose content,G’ and G’’increased gradually.The viscosity of starch paste increases with the decrease of temperature,and the effect of temperature on the viscosity of starch paste is more obvious.Amylose had a great influence on starch gelatinization,and amylose had a great influence on starch paste structure.Cassava starch,glycerol and PVA were selected to study the effects of glycerol content and PVA content on starch gelatinization process and starch paste rheological behavior.The results showed that the addition of glycerol increased the gelatinization temperature of starch.PVA has little effect on gelatinization temperature.During gelatinization,the G′ and G′′of starch paste increased due to the addition of glycerol.The higher of the PVA content,the smaller of the G’,G ".When the ratio of starch and PVA was 2/3,the G’,G" decreased significantly.After starch gelatinization,the higher of the glycerol content of starch paste,the smaller the the G’,G ".The the G’,G" of starch paste with 30% and 40% glycerol content were similar,indicating that the dosage of glycerol was about 30%.A certain amount of PVA increased the G’,G’’ of starch paste.Glycerol and PVA promoted the formation of starch gel structure.Cassava starch,glycerol and PVA,glutaraldehyde and citric acid were selected to study the effect of temperature on the crosslinking process,and the effect of crosslinking agent content and type on the rheological behavior of PVA/starch solution.The results showed that the crosslinking effect of citric acid was the best at 70°C-90°C,and the crosslinking effect of glutaraldehyde was the best at 80°C-90°C.The optimal crosslinking temperature for the combination of glutaraldehyde and citric acid should be about 80°C.With the increase of the crosslinking of content,the increased of the G’,G’’ and η of starch/PVA materials.Comparing the G′,G′′ of the crosslinked samples with different crosslinking agents,it was found that the optimal content of citric acid was 5%-7%,and the cross-linked starch with about 5% glutaraldehyde was the best.The cross-linking effect was the best when the cross-linking ratio of glutaraldehyde/citric acid was 1/1.In addition,it was found that citric acid could not only be used for crosslinking starch,but also enhance the fluidity of starch paste.The effect of glutaraldehyde cross-linked starch is better than that of citric acid.The effect of glutaraldehyde combined with citric acid is the best,and the two crosslinking agents have synergistic effect.Using cassava starch,glycerol,PVA,glutaraldehyde and citric acid as cross-linking agents,starch-based biodegradable films were prepared by solution blending and tape casting.The results show that the addition of crosslinking agent can significantly improve the mechanical properties and waterproof properties of the film.The combination of citric acid and glutaraldehyde enhances the mechanical properties and waterproof properties of the film to a certain extent.When starch/PVA ratio was 2/1,glycerol content was 30%(dry weight of starch and PVA),crosslinking agent content was 5% and the ratio was 1/1,the tensile strength reaches the maximum 8.55 MPa.Both of them have a synergistic effect on the elongation at break of the film,with the minimum elongation at break of203.51% and the maximum elongation at break of 250.32%.Its water absorption is stable between 80%-90%.Compared with citric acid alone,the water absorption of the composite crosslinking agent was reduced by 50%. |
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