熔融缩聚合成聚乳酸及原位聚合改性的研究
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摘要
资源危机和生态问题引发了全世界对于可持续发展材料的研究热潮,聚乳酸以其良好的生物相容性和可降解性成为高分子材料研究的热点之一。
制备聚乳酸较成熟的工艺是丙交酯开环聚合,但开环聚合法工艺路线长,产物成本高,限制了聚乳酸的广泛应用。如何控制工艺路线,降低材料成本,是聚乳酸广泛应用迫切需要解决的问题,本文以耐热级L-LA为原料,直接熔融缩聚合成较高分子量聚乳酸,减少了制取中间产物丙交酯的过程,研究聚乳酸的低成本合成技术,以实现聚乳酸类产物的应用。
直接熔融缩聚合成的均聚物聚乳酸分子量较低,质脆,热稳定性差,本文选用亚磷酸三苯酯(TPPi)对其进行扩链增粘,碱处理后经MAPP接枝的植物纤维对其进行原位聚合改性,期望在降低聚乳酸成本的同时,提高其性能。
本文首先对催化剂种类、催化剂用量、乳酸的预聚合条件、聚合时间、聚合温度、TPPi的扩链工艺等反应条件对聚乳酸分子量的影响进行了研究,为植物纤维原位聚合改性PLA可降解材料提供理论数据。在确定制备高分子量聚乳酸的熔融缩聚最佳工艺条件之后,将处理和未处理的植物纤维在乳酸预聚合后加入到反应体系中,之后的聚合工艺条件不变,制得植物纤维原位聚合改性的PLA可降解材料。采用红外光谱(IR)、凝胶渗透色谱(GPC)、拉伸测试机、示差扫描量热仪(DSC)、热失重(TGA)、扫描电镜(SEM)等,探讨了植物纤维的加入、接枝处理、含量对基体聚乳酸的重均分子量和结构,材料的力学性能、热性能和降解性能的影响,并结合材料颜色的变化情况发现,植物纤维经过接枝处理后、加入质量分数为乳酸预聚物的0.2%时,产物颜色较浅,各项性能较优,其拉伸强度、断裂伸长率、开始热分解温度较纯PLA分别提高了14.07%、21.35%、9.75%,但冲击强度却较纯PLA仅提高了1.32%。通过对材料热降解和水降解的研究发现,改性植物纤维的加入使得材料的降解性能较纯PLA有所下降。
Polylactic acid (PLA) has been the research focus of macromolecule chemistry with its wonderful biologic compatibility and biodegradable properties.
The conventional produce of PLA is a ring-opening polymerization, but this method limits its widespread application because of the long route and the high cost. How to control the process route and reduce material costs are the main factors to expand the application of PLA. Using L-LA that resists heat as raw material, we studied on the synthesis of polylactic acid by low-cost technology to realize its widely applications.
PLA prepared by direct melt polycondensation is still limited in applications due to its low molecular weight, intrinsic brittleness, and poor thermal stability. Accordingly, we study on the effect of triphenyl phosphite (TPPi) enhancing the intrinsic viscosity of PLA, and the modification of PLA by in situ polymerization process with the plant fibers that graft MAPP after alkali treatment as modifier. Expect for the costs of PLA are reduced, while the performance of PLA.are improved.
First of all, the melt condensation polymerization conditions for the polylactic acid had been discussed such as types and dosage of catalysts, prepolymerization, the reaction time and temperature, TPPi, which was the fundamental theory for the preparation of the modification of PLA by in situ polymerization process with the plant fibers. After the optimum conditions of high molecular weight Poly(lactic acid)(PLA) polymers by melt polycondensation were confirmed, the modified and unmodified plant fibers were added to the reaction system behind the prepolymerization of lactic acid, then the polymerization conditions remain unchanged. Then several instruments such as infrared spectrum (IR), gel permeation chrom- atography (GPC), tensile testing machine, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscope(SEM) and so on had been employed in this study. The effect of the addition of modified and unmodified plant fibers and their content on the molecular weight and structure of polylactic acid and properties of the composites including mechanical properties, thermal properties and degradation properties was discussed. Besides, the color of the composites was investigated. The results showed that when the content of plant fibers modified with MAPP is 0.2%, the product’s color was shallow, meanwhile, the properties of the product was superior. At the moment, the tensile strength, the elongation at break, the temperature of starting thermal-decomposition increased by 14.07%, 21.35%, 9.75% than pure PLA, respectively. But the impact strength reduced by 5.26%. According to study on the thermal and water degradation of product, the degradation character- istic of product decreased with the addition of modified plant fibers. Whereas the ma- terial’s vicat softening temperature is approximately 38℃, it could be used as the fixed material of bone fracture.
制备聚乳酸较成熟的工艺是丙交酯开环聚合,但开环聚合法工艺路线长,产物成本高,限制了聚乳酸的广泛应用。如何控制工艺路线,降低材料成本,是聚乳酸广泛应用迫切需要解决的问题,本文以耐热级L-LA为原料,直接熔融缩聚合成较高分子量聚乳酸,减少了制取中间产物丙交酯的过程,研究聚乳酸的低成本合成技术,以实现聚乳酸类产物的应用。
直接熔融缩聚合成的均聚物聚乳酸分子量较低,质脆,热稳定性差,本文选用亚磷酸三苯酯(TPPi)对其进行扩链增粘,碱处理后经MAPP接枝的植物纤维对其进行原位聚合改性,期望在降低聚乳酸成本的同时,提高其性能。
本文首先对催化剂种类、催化剂用量、乳酸的预聚合条件、聚合时间、聚合温度、TPPi的扩链工艺等反应条件对聚乳酸分子量的影响进行了研究,为植物纤维原位聚合改性PLA可降解材料提供理论数据。在确定制备高分子量聚乳酸的熔融缩聚最佳工艺条件之后,将处理和未处理的植物纤维在乳酸预聚合后加入到反应体系中,之后的聚合工艺条件不变,制得植物纤维原位聚合改性的PLA可降解材料。采用红外光谱(IR)、凝胶渗透色谱(GPC)、拉伸测试机、示差扫描量热仪(DSC)、热失重(TGA)、扫描电镜(SEM)等,探讨了植物纤维的加入、接枝处理、含量对基体聚乳酸的重均分子量和结构,材料的力学性能、热性能和降解性能的影响,并结合材料颜色的变化情况发现,植物纤维经过接枝处理后、加入质量分数为乳酸预聚物的0.2%时,产物颜色较浅,各项性能较优,其拉伸强度、断裂伸长率、开始热分解温度较纯PLA分别提高了14.07%、21.35%、9.75%,但冲击强度却较纯PLA仅提高了1.32%。通过对材料热降解和水降解的研究发现,改性植物纤维的加入使得材料的降解性能较纯PLA有所下降。
Polylactic acid (PLA) has been the research focus of macromolecule chemistry with its wonderful biologic compatibility and biodegradable properties.
The conventional produce of PLA is a ring-opening polymerization, but this method limits its widespread application because of the long route and the high cost. How to control the process route and reduce material costs are the main factors to expand the application of PLA. Using L-LA that resists heat as raw material, we studied on the synthesis of polylactic acid by low-cost technology to realize its widely applications.
PLA prepared by direct melt polycondensation is still limited in applications due to its low molecular weight, intrinsic brittleness, and poor thermal stability. Accordingly, we study on the effect of triphenyl phosphite (TPPi) enhancing the intrinsic viscosity of PLA, and the modification of PLA by in situ polymerization process with the plant fibers that graft MAPP after alkali treatment as modifier. Expect for the costs of PLA are reduced, while the performance of PLA.are improved.
First of all, the melt condensation polymerization conditions for the polylactic acid had been discussed such as types and dosage of catalysts, prepolymerization, the reaction time and temperature, TPPi, which was the fundamental theory for the preparation of the modification of PLA by in situ polymerization process with the plant fibers. After the optimum conditions of high molecular weight Poly(lactic acid)(PLA) polymers by melt polycondensation were confirmed, the modified and unmodified plant fibers were added to the reaction system behind the prepolymerization of lactic acid, then the polymerization conditions remain unchanged. Then several instruments such as infrared spectrum (IR), gel permeation chrom- atography (GPC), tensile testing machine, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscope(SEM) and so on had been employed in this study. The effect of the addition of modified and unmodified plant fibers and their content on the molecular weight and structure of polylactic acid and properties of the composites including mechanical properties, thermal properties and degradation properties was discussed. Besides, the color of the composites was investigated. The results showed that when the content of plant fibers modified with MAPP is 0.2%, the product’s color was shallow, meanwhile, the properties of the product was superior. At the moment, the tensile strength, the elongation at break, the temperature of starting thermal-decomposition increased by 14.07%, 21.35%, 9.75% than pure PLA, respectively. But the impact strength reduced by 5.26%. According to study on the thermal and water degradation of product, the degradation character- istic of product decreased with the addition of modified plant fibers. Whereas the ma- terial’s vicat softening temperature is approximately 38℃, it could be used as the fixed material of bone fracture.
引文
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