| Polylactic acid (PLA) is a kind of green materials, but also a renewable plant resources for the new biodegradable synthetic raw materials. In vivo or in the soil, the role of microorganisms in the poly-lactic acid degrades to lactic acid, the last metabolites into carbon dioxide and water. Because of its good chemical inertness, easy to machining, good biological compatibility and biodegradable properties, in the body can be gradually degraded into carbon dioxide and water, and there has not pollution to the environment, the polylactide and its copolymers has been attached great importance to both at home and abroad in the pharmaceutical and medical supplies applications and development. The significance of polylactic acid application is not only reflected in environmental protection, for recycling economy and building a conservation-oriented society will also have a positive effect. This paper studies the preparation and kaolin terminal carboxyl-modified polylactic acid/polylactic acid compound material preparation.(1) Preparation and polylactic acid lactide. This article uses two-step, condensation and then depolymerization. Lactic acid esterification dehydration will first generate lactic acid oligomer, and then subjecting lactic acid oligomers at higher temperatures catalytic depolymerization to give lactide. First of all, the preparation of lactide monomer is lactic acid monomer, zinc oxide as catalyst, under pressure is 0.095 MPa, the temperature heats up to 180?, dehydration reaction 3h, and discusses the influencing factors of lactide synthesis. Experimental lactic acid monomer obtained at 140? conditions, the catalyst mass percentage of zinc oxide was 1.5%, the reaction time was 3 hours to obtain a high molecular weight polylactic acid. Preparation of polylactic acid is lactide monomers, stannous octoate as catalyst, under the pressure is 0.095MPa, the temperature was gradually raised to 160?, polymerization 5h, and investigate the effect of polylactic acid synthesis factors. Experiment when n (lactide)/n (stannous caprylate)= 5000, time of 5 h of polymerization, the polymerization temperature between 170-180?, the relative molecular mass can be obtained for 65000 of polylactic acid. FTIR and 1H-NMR data show that the annular lactide ring-opening reaction happened under stannous caprylate catalyst.(2) Chain expansion and modification of the carboxyl terminated poly-lactide. In extender chain of poly (lactic acid) (PLA), the 2-oxazoline (1,3-PBO) type chain extension agent attracted researchers pay close attention to, with its good terminal stability, and high selectivity polymerization product advantages. The terminal carboxyl group of polylactic acid copolymer P (LA/SA) was synthesized with lactide as raw material, stannous caprylate as the catalyst and succinic anhydride as modifier by direct melt polycondensation. The polyesteramide (PEA) was synthesized using 1,3-PBO (2,2-(1,3-phenylene)-bis(2-oxazoline)) chain the terminal carboxyl group of polylactic acid copolymer. Finally, kaolin and PEA melting compound was modified under stress conditions. FTIR and 1H-NMR data show that the carboxyl reaction with 1,3 - PBO generate the target product successfully. The terminal carboxyl group of polylactic acid copolymer P (LA/SA) was synthesized with lactide as raw material,and using 1,3-PBO(2,2-(1,3-phenylene)-bis(2-oxazoline))chain stannous caprylate as the catalyst, ang the best condition is under the condition of 150 ? and 0.098MPa (LA/SA). The polyesteramide (PEA) was synthesized the terminal carboxyl group of polylactic acid copolymer with the n (lactide)/n (1, 3-PBO) is 1:2.4, n (succinic anhydride):n (lactide)= 1:9.5, and the reaction time of 1h. The heavy molecular weight of PEA was up to 240000. The glass transition temperature data show that after the chain extension of polylactic acid and heat-resistant properties of the composites were modified to improve. The tensile strength test shows that the mechanical properties of composite materials for promotion.SEM photo shows that the experiment successful insert PEA particles between kaolin lamella.(3)Preparation of Composite kaolin modified polylactide. This experiment prepared kaolin/PLEA nanocomposites by in situ polymerization method. First preparing a low molecular weight terminal carboxyl group of the polylactic acid P (LA/SA), then prepared kaolin/dimethyl sulfoxide intercalation compound,and the prepared PLEA/kaolin composites at a certain temperature under reduced pressure in situ polymerization chain extender 45 min. Then compeared the composite material with PLEA. The study found that the experiment will be successful synthesis of kaolin modified polylactic acid-based composite materials with 1,3-PBO chain extender. Finally confirmed that when the ratio of the m (P (LA/SA)):m (Kaolinite/dimethyl sulfoxide) is 1.2, the good Polymerization temperature is 160 ?, and the reaction time is 12h, the kaolin/PLEA composites performance is improved obviously, after the kaolin modified kaolin/PLEA complex heat resistance was improved, enhanced toughness. |
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