PLLA基复合材料的结晶行为及力学性能研究

发布时间：2018-04-18 09:23

  本文选题：PLLA + 球晶形态　； 参考：《郑州大学》2015年硕士论文

【摘要】：左旋聚乳酸(PLLA)作为一种绿色可再生且可生物降解的高分子材料,近年来受到了广泛的关注和研究。然而由于结晶速率慢,结晶度低以及韧性差等限制了PLLA在很多领域的应用,如何解决这些问题一直是人们关注的焦点。材料性能都是由其内部结构决定的,因此本工作从材料的微观结构出发,研究PLLA晶体的形成以及不同尺度力学性能与结构的关系。一方面可以深刻了解体系内不同晶体的形成机理；另一方面研究微观尺度材料结构与性能的对应关系,从而用于指导PLLA的生产加工和实现材料的高性能化。本文研究了不同条件形成的PLLA球晶形貌以及对应晶区和非晶区的微观力学性能；并且研究了聚乳酸立构复合晶体形成条件及其复合改性对材料性能的影响,具体研究内容如下：(1)利用偏光显微镜观察了PLLA球晶生长过程,并且发现PLLA球晶在冰水中淬冷后形成环带同心圆或者六边形裂纹,且裂纹的形状与球晶尺寸相关,当球晶较小时,裂纹不明显,随着尺寸增加,开始形成规则的正六边形,继续增加尺寸,其形貌呈现等间距同心环裂纹；扫描电镜(SEM)结果表明：球晶区断裂处存在明显的缝隙,而在球晶生长前端裂纹不明显；并且通过纳米压痕仪测试了球晶内部不同位置以及无定形区的微观力学性能,发现晶体的硬度和模量均高于非晶区,且球晶存在生长前端,其微观性能参数均处于晶区和非晶区之间。(2)利用X射线衍射仪(XRD)、差示扫描量热仪(DSC)、动态力学分析仪(DMA)及拉伸测试技术研究了立构复合聚乳酸(SC)晶体的形成条件以及对材料性能的影响。通过对比发现溶液成型更加有利于SC晶体的形成,而热压成型则会破坏已经形成的SC晶体。非晶PLLA/PDLA复合体系在熔融升温发生冷结晶,其不仅包括聚乳酸均聚物(HC)晶体,同时也有SC晶体的存在。热处理能够提高PLLA/PDLA复合体系的结晶度但对SC晶体影响不大。并且发现在90℃退火材料的断裂伸长率最高,这可能是由于在此温度退火过程中发生了相转变。(3)采用溶液浇铸法制备PLLA/BC-g-MAH复合材料,并通过傅里叶红外光谱仪(FTIR)、DSC、热重分析仪(TGA)及拉伸测试技术研究PLLA/BC-g-MAH复合材料的结晶行为及其力学性能。结果表明：用马来酸酐(MAH)对BC进行接枝可以改善BC-g-MAH与PLLA之间的界面相容性；PLLA/BC-g-MAH复合材料结晶及力学性能随着BC-g-MAH的增加而显著提高。同时,由于结晶结构更为完善使得复合材料热稳定性能也有较大的提高。
[Abstract]:As a green and biodegradable polymer, PLLA has been widely studied in recent years.However, the slow crystallization rate, low crystallinity and poor toughness limit the application of PLLA in many fields. How to solve these problems has been the focus of attention.The properties of the materials are determined by their internal structures. Therefore, the formation of PLLA crystals and the relationship between mechanical properties and structures at different scales are studied from the microstructure of the materials.On the one hand, the formation mechanism of different crystals in the system can be deeply understood; on the other hand, the relationship between the microstructure and the properties of the microscale materials can be studied, which can be used to guide the production and processing of PLLA and to realize the high performance of the materials.In this paper, the morphologies of PLLA spherulites formed under different conditions and the micromechanical properties of the corresponding crystalline and amorphous regions are studied, and the effects of the formation conditions and their modification on the properties of the composites are also studied.The specific research contents are as follows: (1) the growth process of PLLA spherulites was observed by using a polarizing microscope, and it was found that the PLLA spherulites formed concentric circles or hexagonal cracks after quenching in ice water, and the shape of the cracks was related to the size of the spherulites, when the spherulites were small,The crack was not obvious, and with the increase of size, regular hexagon began to form, and the size continued to increase, and the morphology of the crack appeared concentric ring crack with equal spacing, and the SEM results showed that there were obvious cracks in the fracture of spherulite region.The micromechanical properties of the spherulites at different positions and amorphous regions were tested by nano-indentation instrument. It was found that the hardness and modulus of the crystals were higher than that of the amorphous regions, and the spherulites had the growth front end.The microcosmic property parameters are between the crystal region and the amorphous region.) using X-ray diffractometer, differential scanning calorimeter (DSCO), dynamic mechanics analyzer (DMA) and tensile test technique, the formation conditions of the orthotropic composite polylactic acid (SCL) crystal have been studied by means of X-ray diffractometer, differential scanning calorimeter (DSC), dynamic mechanics analyzer (DMA) and tensile test technique.And its effect on the properties of materials.It is found that the solution forming is more favorable to the formation of SC crystal, while the hot pressing will destroy the formed SC crystal.Cold crystallization occurs in amorphous PLLA/PDLA composite system at melting temperature, which includes not only polylactic acid homopolymer PLLA/PDLA] crystal, but also SC crystal.Heat treatment can improve the crystallinity of PLLA/PDLA composite system, but has little effect on SC crystal.It is also found that the highest elongation at break of the annealed material at 90 鈩，

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