Preperation Of Films From Oxidized Starch Containing Carboxyl Group And Study On Their Structure And Performance

Starch as a natural polysaccharide,has been treated as a kind of biodegradable and environment-friendly material,which has attracted much research attention.However,starch-based films were found to present two main disadvantages such as poor water resistance and short degradation cycle,especially for starch with carboxyl groups.Therefore,the study of starch-based film materials is very important for both academic and industrial application.In this paper,oxidized starch containing carboxyl groups at C6 was prepared from potato starch by using TEMPO/NaClO/NaBr as oxidation system,and the oxidized starch was used as a matrix.The effect of two different modifiers(OTMA-POSS or potato starch),post treatment including acidification and heat treatment on the structure and properties of the films were investigated.The main results were listed as follows.(1)Oxidation process of potato starch in TEMPO/NaOCl/NaBr system was carried out and these structures were characterized by FT-IR and NMR.The results showed that the starch oxidation degree and the reactivity rate increased with the increase of the amount of oxidant and catalyst respectively.The result of FT-IR showed that there existed carboxyl groups in oxidized starch.Further characterization of NMR proved that the primary hydroxyl at C6 can be selectively and completely oxidized to carboxyl group in the alkaline reaction medium,while the oxidation of the secondary hydroxyl at C2 and C3 could not be detected.(2)Effect of the addition of OTMA-POSS and post treatment including acidification and heat treatment on the structure and properties of the CS/OTMA-POSS composite films were investigated.The results showed that the addition of OTMA-POSS improve the mechanical properties of CS-based films compared with the neat oxidized starch film,i.e.,the tensile strength CS/OTMA-POSS composite film was significantly enhanced to the maximum value of 39.20MPa which was an improvement by 18.3%as OTMA-POSS content increasing to 0.4wt%.However,the elongation at break of the nanocomposite film was not greatly improved.The results could be attributed to the ionic interaction between carboxyl group of CS chain and ammonium ions of OTMA-POSS particle.Compared with the neat oxidized starch film,CS/OTMA-POSS composite film with acidification treatment had a lower swelling ratio,better shape stability,and longer degradation cycle.The water resistance of the CS/OTMA-POSS composite film was improved after acid treatment.This was attributed to carboxylic salt group that had been changed to carboxyl group after acidification treatment,and the stronger hydrogen bonding interaction.When acidified CS/OTMA-POSS composite films were further heated at 120?,esterification was observed.The results showed that the water resistance of the CS/OTMA-POSS composite films was improved further,their shape preserving properties were increased,and degradation cycle was increased much more.Environment humidity has a great influence on the mechanical properties of the CS/OTMA-POSS composite films,i.e.,increase in humidity reduced the tensile strength of CS/OTMA-POSS composite film materials,but had not significant influence on elongation at break.Moreover the tensile strength of CS/OTMA-POSS composite film materials with acid treatment decreased too,however,elongation at break increased.(3)The introduction of potato starch(PS)to control water resistance of CS/PS composite film,post treatment including acidification and heat treatment on the structure and properties of the CS/PS composite films were researched.The results showed that the content of PS had not significant effect on mechanical properties and enzymatic degradation of CS/PS composite films,but,increased water resistance of CS/PS composite film.Also acidification treatment could improve the water resistance of CS/PS composite films,however,which had not significant effect on enzymatic degradation of CS/PS composite films.In addition,when acidified CS/PS composite films were further heated at 120?,the water resistance of the CS/PS composite films was improved further,their shape preserving properties were increased and degradation cycle was increased much further.However,there was no significant effect on the final enzymatic degradation of all the CS/PS composite films.(4)Effect of irradiation treatment on the structure and properties of the oxidized starch film(CSF)were researched.After the irradiation treatment,the FT-IR of CSF and CSF with post treatment including acidification and heat treatment had no much difference.However,mechanical properties of CSF and CSF with post treatment were improved,and enzyme degradation of CSF treated by acid and further heated at 120? were decreased,reasons for these results need further research.