Study On Cross-linked Cassava Starch Applied To Starch-based Plastics

Plastics is widely used in our life, which brings severe pollution to ourenvironment at the same time. Also petroleum, raw materials of plastics, is goinginto exhaustion stage which causes pressure on development of plastics.Developing degradable plastics is one of the most effective way to solve theseproblems. Starch with the advantage of safety, low cost, a wealth of sources anddegradable also helps starch-based plastics attract much more attention. Themodification method of starch is vital to starch-based plastics. And crosslinkingmethod plays an important role in these modification methods.The method of single factor experiment was used to investigate the non-foodcassava starch modified with an environmentally friendly cross-linking reagentCL. The influence of usage of CL and NaOH, reaction temperature and reactiontime on the degree of cross-linking was studied, and the cross-linked starch wascharacterized. The results showed that optimum degree of cross-linking starch wasobtained under the condition of a0.5%concentration of CL, a1.5%concentrationof NaOH, a3h time and a50℃temperature, which obtained cross-linked starchwith sedimentation volume1.0mL. The results of SEM showed that the granulesof cross-linked starch had some dents on their surfaces; It was confirmed that thecross-linking reaction was happened because the absorption peak of ether bondwas founded at1241cm-1in the FTIR spectroscopy of cross-linking starch; Theresults of XRD showed that the crystallinity decreased by16.94%after cross-linking reaction, which indicated that cross-linking reaction changed somecrystalline region to some extent.Based on the study of crosslinking cassava starch, starch-based plastics blendedwith polypropylene (PP) were prepared with variety of degree of cross-linkingstarch, raw starch, different starch content. By means of testing on tensile property, flexible property, impact property, water absorption and morphology, the influenceof degree of cross-linking starch, percentage of starch on property of materials wasstudied. Research on the materials with starch30%, it was found that tensilestrength, flexible strength, elongation at break, impact strength all decreased withsedimentation volume increased, while tensile modulus, flexible modulus, theequilibrium water absorption increased. The cross-linked starch-based materialswith1.1mL sedimentation volume exhibited better comprehensive properties. Theresearch on raw starch-based plastics and cross-linked starch-based plasticsshowed that tensile strength, flexible strength, elongation at break, impact strengthall decreased with the increasing of starch, while tensile modulus, flexiblemodulus, water absorption increased. The property of blended plastics with25%cross-linked starch was close to the property of pure PP plastic, whose tensilestrength makes up71.15%of PP plastic and better than the property of blendedplastics with20%raw starch. The results of SEM showed that the combinationstatus of two phases in plastics of cross-linked starch-based plastics improvedcompared with raw starch-based plastics. It seemed that the decreasing of starchin plastics benefited to its dispersion.