天然纤维和退火对聚乳酸结晶及耐热性能的影响

发布时间：2018-08-12 17:32

【摘要】：聚乳酸(PLA)是可生物降解的高分子材料,其可由淀粉发酵得到的乳酸单体经聚合而成,并且因为PLA降解的最终产物为对环境无污染的水和二氧化碳,所以PLA常被用作传统石油化工基塑料的替代品,也是目前被认为最有前景和最受欢迎的环境友好材料。因为PLA有与对苯二甲酸乙二醇酯相似的透明性和优良的生物相容性等特点,所以PLA被广泛用作包装和医药材料。可是由于其本身具有结晶速率慢、耐热性能较差及价格较高等缺点,较大程度的限制了聚乳酸在更多领域的应用。针对PLA的这些缺点人们正在对其进行改性研究。其中,提高PLA结晶及耐热性效果较好的改性方法有以下两种:一是添加成核剂,二是进行退火处理。经研究发现,添加成核剂可以提高PLA的结晶速率和结晶度,并改善其耐热性能,但采用此种方法对PLA耐热性能改善的效果并不是十分理想,所以本文采取将添加成核剂和退火处理相结合的方法,希望能够更好的改善PLA的结晶及耐热性能。本文选取经过有机化处理的竹纤维(OBF)和棉花纤维(OCF)作为PLA的成核剂,选择出对结晶促进效果明显的一种成核剂和效果最好的质量配比,在加入了所选成核剂的同时,控制实验温度、时间以及介质对PLA和混合体系进行退火操作。采用傅里叶红外光谱仪(FTIR)、差示扫描量热仪(DSC)、X射线衍射仪(XRD)、偏光显微镜(POM)及维卡软化点、热变形温度测定仪等表征了成核剂和不同退火条件(温度、时间、介质)对PLA结晶及耐热性能的影响。DSC测试说明,加入OBF和OCF都可以提高PLA的结晶度,但是加入OBF的效果更为明显,在OBF添加量为1.2%时,结晶度出现极大值。且OBF的加入能够使退火所需温度降低,时间变短。退火处理可以有效改善PLA的结晶性能。POM照片表明,PLA晶体为球晶。加入OBF和OCF能够增大PLA的晶核密度,缩小晶体尺寸,加快结晶速率,说明OBF和OCF是PLA的有效成核剂;XRD测试结果说明,添加成核剂和退火处理都不改变PLA的晶型,其仍为稳定的ɑ晶型;FTIR测试结果说明,添加成核剂和退火处理不会使PLA的结构发生变化;维卡软化点、热变形温度测试结果说明,将添加成核剂和退火处理二者相结合时,可以更为明显的改善PLA的结晶和耐热性能。
[Abstract]:Polylactic acid (PLA) is a biodegradable polymer material that can be polymerized from lactate monomer produced by starch fermentation, and because the final product of PLA degradation is non-polluting water and carbon dioxide. Therefore, PLA is often used as a substitute for traditional petrochemical based plastics, and is currently considered the most promising and popular environmentally friendly material. PLA is widely used as packaging and medical materials because of its similar transparency and excellent biocompatibility with ethylene terephthalate. However, due to its low crystallization rate, poor heat resistance and high price, the application of polylactic acid in more fields is limited to a large extent. In view of these shortcomings of PLA, people are studying its modification. There are two methods to improve the crystallization and heat resistance of PLA: one is to add nucleating agent, the other is to annealing. It was found that the addition of nucleating agent could improve the crystallization rate, crystallinity and heat resistance of PLA, but the effect of this method on the heat resistance of PLA was not very good. Therefore, the method of adding nucleating agent and annealing treatment is adopted to improve the crystallization and heat resistance of PLA. In this paper, bamboo fiber (OBF) and cotton fiber (OCF) treated by organic treatment were selected as nucleating agents of PLA, and a nucleating agent and the best mass ratio were selected, which had obvious effect on promoting crystallization. At the same time, the selected nucleating agent was added. PLA and mixed system are annealed by controlling the experimental temperature, time and medium. The nucleating agent and different annealing conditions (temperature, time, temperature) were characterized by (FTIR), differential scanning calorimeter (DSC), (XRD), polarizing microscope (POM), Vicat softening point (VCR), thermal deformation temperature tester and so on. The results show that both OBF and OCF can improve the crystallinity of PLA, but the effect of adding OBF is more obvious. When the amount of OBF is 1.2%, the crystallinity of PLA can be maximized. The addition of OBF can reduce the annealing temperature and shorten the time. Annealing treatment can effectively improve the crystallinity of PLA. POM photos show that the crystal of PLA is spherulite. The addition of OBF and OCF can increase the nucleation density of PLA, decrease the crystal size and speed up the crystallization rate. The results show that OBF and OCF are effective nucleating agents for PLA. The results show that neither nucleating agent nor annealing treatment can change the crystal form of PLA. The results of FTIR test show that the structure of PLA will not be changed by adding nucleating agent and annealing treatment, and the results of Vicat softening point and thermal deformation temperature test show that when adding nucleating agent and annealing treatment are combined, the structure of PLA will not be changed by adding nucleating agent and annealing treatment. The crystallization and heat resistance of PLA can be improved more obviously.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O633.14

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