| Poly lactic acid(PLA)has good chemical stability,feasibility of production processes , excellent biocompatibility and biodegradability.It is harmless and unaccumulative because the PLA gradually biodegrades into water and carbon dioxide in the body.The fiber made from the polylactic acid has high tensile strength and good flexibility. Furthermore,lactic acid monomer can be produced from agricultural starch wastes.Therefore, the polymer is one of the most promising biodegradable materials. However, one of the biggest problems of PLA lays in its extremely high price,because the polymer is conventionally obtained by a ring-opening polymerization process from lactide, such as dimmer of lactice acid which is very expensive,so its application is limited.In this paper, we used the direct melt-solid state polycondensation method with D,L-lactic acid so as to reduce the cost of polylactic acid and to expand its application. The influence of catalyst types ,catalyst quantity,reaction temperature and time on molecular weight were studied. And the best reaction condictions were found,meanwhile the craftwork had been chosed best .The best condiction of melt polymerization is as followed: SnCl2 was chosed as the appropriate catalyst and was 0.5% ,180℃, reacting 7.5h with the atmosphere of acridine;meanwhile the pressure was reduced properly.This molecular weight of PLA had been achieved 84383..Then the PLA's condiction of solid-state polycondensation : the reaction temperature has been rosen step by step at the atmosphere of acridine;130℃,5 hour and 145℃,10 hour;the whole time is 15 hour.The molecular weight has been achieved 303779,and was 3.6 times than the former.The polymer samples were characterized with IR, 1HNMR, 13CNMR, DSC and TG.Because of PDLLA'noncrystal,L-lactic acid was used as monomer to synthesize PLLA by the former means.The molecular weight of PLLA was 325857.Then,melt-filature of PLLA was studied primarily.The process built a foundation to produce PLLA fibre by means of melt-filature.
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