| With the widely using of plastics, the reprocessing of plastic waste and its environmental pollution has attracted more and more attention by peoples, it has also become a global problem. The development of degradable plastics was an effective way to solve the pollution of plastics. Starch-based plastics were made by mixing starch with polyolefin. As the starch was safe, cheap, wealth of sources and degradable, people pay great attention to starch-based plastics. The native starch were modified, in order to expand its application and improve its compatibility with polyolefin, to improve the content of starch in the starch-based plastics and reduce the content of non-biodegradable polyolefin, which can alleviate the pressure of the environmental pollution problem. Therefore, the research on starch modified technology was very important.The method of single factor experiment was used to investigate the non-food cassava starch modified with an acetic anhydride as esterifying agent,p-toluenesulfonic acid as catalyst. Using degree of substitution(DS) and reaction efficiency(RE) as the index, the results show that the optimum conditions for preparing cassava acetate starch are as follows: mass fraction of acetic anhydride was15%, mass fraction of catalyst was 1.5%, the reaction time was 3h, the reaction temperature was 45 ℃, and liquor ratio was 1:3. FT-IR confirms the reaction of esterification. SEM shows that the esterification occurred not only on the surface of starch granules, but also occurred in the internal of starch granules. XRD shows that esterification destroyed the crystal structure of starch, and the crystallinity decreased 8.03% compared to native starch. DSC shows that the esterification of starch improved the melting properties, and the melting temperature decreased by 22.3℃ compared to native starch.Based on the study of esterification cassava starch, starch-based plastics were prepared, blending polypropylene(PP) with different DS of starch, and different content of starch. By means of testing on tensile property, flexible property, water absorption and morphology, the influence of DS, percentage of starch on property of materials was studied. Studied on the materials with 25% starch, it was found that tensile strength, flexible strength, elongation at break, all increased with DS increased,while flexible modulus, the water absorption decreased. The esterification starch-based plastics with the DS of 0.105 exhibited better comprehensive properties.Research on the esterification starch-based materials with the DS of 0.105, it was found that tensile strength, flexible strength, elongation at break, all decreased with the increasing of starch content, while flexible modulus, the water absorption increased. The results of SEM showed that the combination status of two phases in esterification starch-based plastics were improved, compared with raw starch-based plastics. It also showed that the increasing of starch content was inimical to its dispersion in blend system.Based on the single esterification modification, esterification and cross-linked composite modified starch were prepared. Starch-based plastics were prepared by blending polypropylene(PP) with different degree of cross-linked composite modified starch, and different content of composite modified starch. Using tensile strength, elongation at break as the measure index, to explore the influence of the cross-linking degree of composite modified starch and the content of composite modified starch on the tensile properties of the plastic. The influence of the esterification, cross-linked blending modified starch on the tensile properties of starch-based plastics, and the influence of the esterification and cross-linked composite modified starch was compared at the same time. Studied on the plastics with 30% starch, it was found that the tensile strength increased with the increasing of cross-linked degree of esterification and cross-linked composite modified starch, it’s higher than single esterification modified starch-based plastics. The elongation at break increased with the increasing of cross-linked degree of esterification and cross-linked composite modified starch. At low cross-linked degree, the elongation at break of composite modified starch-based plastics was lower than single esterification modified starch-based plastics. While at high cross-linked degree, the elongation at break of composite modified starch-based plastics was higher than single esterification modified starch-based plastics. All things considered, The composite modified starch-based plastics with sedimentation volume 0.9m L exhibited better comprehensive properties, it’s more suitable for further study. Studied on thecomposite modified starch-based plastics with 0.9mL sedimentation volume, it was found that tensile strength and elongation at break all decreased with the increasing of starch content. When the content of esterification and cross-linked composite modified starch was 35%, the strength of the plastic was 33.27 MPa, it’s higher than30% single esterification modified starch, which the strength was 32.71 MPa. When the content of composite modified starch was 35%, the elongation at break was 7.21%,its higher than 2.83%, which the content of single esterification modified starch was30%.These results shows that the esterification and cross-linked composite modified starch is more conducive to improve the content of starch in plastic, compared to single esterification modified starch. Using 15% esterification starch with 0.095 DS,and 15% cross-linked starch with 0.9mL sedimentation volume, blending with 70%PP, made into esterification, cross-linked blending starch-based plastic I, using 30%esterification and cross-linked composite modified starch, blending with 70% PP,made into esterification and cross-linked composite modified starch-based plastic II,It was found that the strength of plastic II is 41.26 MPa, its higher than plastic I, which the strength is 40.15 MPa, the elongation at break of plastic II is 4.8% higher than plastic I. |
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