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This paper used Material Studio soft to build the polymer of polylactic acid and the modifier of polylactic acid, and to optimize the polymer built by geometry optimization of the polymer and molecular dynamics simulation; through Amorphous Cell module of simulation software we build the blends structure model of PLA with modifier,and make molecular dynamics simulations for the structural model, while make the simulations of compatibility for PLA blends by blends module of the software, combined with two modules,we get that PLA with Starch or polyethylene or polyvinycl alcohol has better compatibility in theory,but with humic acid or glycerin, in theory, it has relatively poor compatibility;before the molecular simulation,this paper prepared humic acid with content of 85.06% basing on the experimental theory of "alkali-soluble and acid precipitation",and measured the molecular weight with 863 by freezing point depression method, and designed the molecular structure by the data got from the industrial, elements, and functional group analysis of humic acid, and used the structure to make simulation for the substitute of humic acid.Reference to the conclusions of theoretical models, this paper studied the compatibility, mechanical properties thermal stability and degradation impact on PLA with the modifier humic acid, starch or polyvinyl alcohol while using the polyethylene glycol as a plasticizer. Throug the study of using humic as the modifier of PLA by Hack torque rheometer we know that the compatibility of PLA with humic acid as modifier is poor,it is not conducive to the plastics processing; through the mechanical testing, DMA and thermal re-analysis,we know that PLA blends with polyethylene glycol, polyvinyl alcohol or starch has good compatibility, it is consistent with the molecular simulation, starch can maintain thermal stability of PLA,but greatly reduces the mechanical properties and flexibility composite thin films,polyethylene glycol and polyvinyl alcohol reduce the PLA thermal stability and mechanical strength,but greatly improved the flexibility of poly-lactic acid; degradation experiments have unearthed buried degradation is more similar with natural degradation process than water-soluble degradation, PLA has poor hydrophilic, polyethylene glycol can not effect the degradation rate of PLA, but with the starch or PVA, the degradation rate of composite thin films has greatly increased; the study has shown that when PLA, starch, PVA and PEG has the mass ratio of 80:20:10:10, the biodegradable PLA composite films have the best performance.
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