| Poly (lactic acid) (PLA) was in situ grafted to starch in one step by using solution method and get the starch grafted PLA copolymer. Starch was first dissolved in the strong polar solvent -- dimethyl sulfoxide (DMSO), potassium text-butoxide was put into the react system as initiator, initiated L-lactide to ring opening copolymerization. After crude products were purified by extraction, the starch reacted to L-lactide was testified via FT-IR, NMR, XRD analysises, when the copolymerization temperature was 75℃and time was 4 h, material ratio was starch: lactide: potassium text-butoxide = 10:75:3, the graft percentage (GP) could reach to 83%.Starch-g-PLA copolymer Synthesized by swelling method, stach was firstl swelled by adding a small mount of DMSO to activate the hydroxyl groups on starch, then potassium text-butoxide was put into the react system as initiator, initiated lactide to ring opening copolymerization. The influence of polymerization temperature, polymerization time, feed molar ratio, solvent type and volume on the graft percentage was examined and it was found that when the copolymerization temperature was 120℃and time was 3 h, 10 mL DMSO as the swelling solution, material mole ratio was starch: lactide: potassium text-butoxide = 10:100:2, the grafting percentage of product was reached to 376%, changing the material ratio different grafting percentage from 115% to 376% was getted. The water absorption of the product after grafted reaction were found decresed sharply through the DSC and TG analysis, It was found that the product had good thermal stability below 200℃and there was no obvious curve in DSC scane from room temperature to 200℃.The starch/PLA composite was perpared by solution blending method, and the grafting copolymer which graft percentage was 83% was put in the starch/PLA blends, the fact that PLA's crystallinity asscended gradually compared to which did not add it was attested by DSC analysis, when the mount of graft copolymer was 7%, the crystallinity of PLA in the composite reached to 39.19%; In PLA/starch blending, the TG curve shown two phases weight loss characterization, but the TG curve which added grafting copolymer was presented regularity changes with the increasing amount of graft copolymer, when the contain of the copolymer up to 10%, TG curve of the composite was shown a homogeneous phase weight loss characterization, starch in the composite was getted better uniform distribution compared to the starch/PLA blends.The PLA/starch blending composite was prepared by melt blending, and graft copolymer which grafting percentage was 200% synthesised by swelling method was added. When the mount of the graft copolymer was not more than 3.3%, the tensile strength and impact strength of the composite were improved, however, when the contain of the graft copolymer exceeded the critical value, the mechnical properties of the comostie was decrease. The PLA/starch composite was found obvious two phase structure by SEM, but when it came to the PLA/starch/starch-g-PLA composite, the more amount of the graft copolymer, the more improvement of the two separate interfaces was achieved.The PLA/DMSO plasticized starch composite was prepared by melt blending method, it wsa found that when the content of DMSO is small (such as 1.7%, 3.3%), the tensile strength and impact strength of the composite were improved, flexural strength and elastic modulus decreased, when the DMSO content keep increasing, the tensile strength was decreased, but the impact stength was found increasing persistently and the flexural strength and elastic modulus decreased as the increasing DMSO, the brittle materials was significantly improved. In the PLA/starch blending composite, the crystallinity of PLA was increased by adding more starch, crystallization temperature and melting temperature were found significantly lower then pure PLA and the crystallinity of PLA was higher than PLA when the mount of DMSO was 3%. It was found that PLA/starch composites show a clear two-phase weight loss, after added DMSO the weight loss curves of composite materials were gradual converted to homogeneous weight losses. The PLA/starch was found apparent phase separation by SEM, when the starch was plasticized by DMSO, the form of starch in the PLA martrix gradually changed, followed by plastified in the starch surface, breaking up, the hole in the middle of the starch gradually increased, eventually was plastified thoroughly and the particles were completely destroyed.Compared to the PLA/starch/starch-g-PLA composite and the PLA/DMSO plasticized starch composite, the later system was found have better mechnical properties.The compatibilization mechanism of starch-g-PLA was migrated to the interface during blending, and formed a transition layer to strengthen the cohesive of the interface, which was similar with the dispersant in the suspension polymerization. But the mechanism of DMSO in starch was destroy the Granular structure and crystal structure of starch, the starch was gradually ruptured from the internal hole, and then the particle was destroyed and plasticized thoroughly, the DMSO plasticized starch could distributed more evenly in polylactide matrix.
|
PDF Full Text Request