石墨烯和剪切对聚偏氟乙烯结晶行为和结晶结构的影响

发布时间：2018-01-15 04:05

本文关键词：石墨烯和剪切对聚偏氟乙烯结晶行为和结晶结构的影响　出处：《天津大学》2016年硕士论文　论文类型：学位论文

【摘要】：本文采用熔融共混的方法制备了聚偏氟乙烯/石墨烯纳米复合材料,利用偏光显微镜、DSC以及WAXS和SAXS技术研究了聚偏氟乙烯及其复合材料在静态和剪切场作用下等温结晶过程中的结晶行为以及结晶后的结晶结构变化和熔融行为。偏光显微图像表明PVDF等温结晶生成典型的带有黑十字消光的球晶,随结晶温度的升高,开始出现环带球晶和颜色较暗的小γ型球晶。剪切作用能够使等温结晶过程中球晶的数目大量增多,球晶长满视野的时间显著减少,并且在含有石墨烯的样品中,这种效果更加明显。球晶的生长速率随着结晶温度的升高呈指数下降,在同一结晶温度,所有样品的球晶生长速率几乎相同。表明剪切作用和石墨烯都能促进了PVDF的成核过程,但是对球晶的生长影响不大。WAXS实验结果显示,PVDF及其石墨烯复合材料在不同条件下等温结晶后的晶型并没有发生改变。但是晶面的微晶尺寸发生了变化:静态等温结晶后只有(021)晶面的微晶尺寸随结晶温度的升高一直增大;(020)(100)和(110)晶面的微晶尺寸在160℃的变化趋势会发生转折。剪切使得样品在160℃结晶后(100)(110)晶面的微晶尺寸明显增加,并且纯的PVDF样品要比含有石墨烯的样品增加显著。这是由于剪切作用改变了球晶中微晶择优取向的方向,使微晶朝着有利于(100)(110)晶面方向生长,而石墨烯的存在削弱了剪切的取向作用。SAXS分析显示,PVDF以及石墨烯复合材料的片晶结构也在160℃出现了转折:长周期和片晶厚度随结晶温度的升高逐渐增大,到达160℃后,继续升高温度,转而开始下降。剪切场的存在使得等温结晶后的样品在垂直于剪切方向上的长周期和片晶厚度要比平行于剪切方向上的高,并且纯PVDF样品要略高于含有0.1wt%石墨烯的样品。说明在剪切作用下,PVDF的分子链沿着流场方向有一定的伸展,使得片晶厚度增加,石墨烯的加入对剪切效应有一定的抑制作用,分子链的取向伸展受到了石墨烯片层的阻碍。DSC结果分析表明,石墨烯的加入对PVDF等温结晶样品的熔融行为影响不大,通过HW外推法得到了183℃和195℃双平衡熔点。PVDF结晶的零生长速率温度为185.8℃,远低于平衡熔点195℃。石墨烯能促进PVDF在170℃等温结晶过程中的α→γ晶型转变速率,并且随石墨烯含量的增加而提高。
[Abstract]:In this paper, the PVDF / graphene nanocomposites were prepared by melt blending, using DSC and polarizing microscope, WAXS and SAXS studied the technology of PVDF and its composites under static and shear field during isothermal crystallization crystallization behavior and crystallization after the change of crystalline structure and melting behavior. Polarizing microscope images show that the PVDF isothermal crystallization generated a typical black cross extinction spherulites, with the increase of crystallization temperature, began to appear and banded spherulites dark small gamma type shear. The spherulite can make the isothermal crystallization process of spherulite number increasing spherulite covered with vision significantly reduce the time and in the presence of graphene samples, this effect is more obvious. The spherulite growth rate increases exponentially with the crystallization temperature decreased, at the same crystallization temperature, the growth of spherulites of all samples The rate is almost the same. That shear and graphene can promote the nucleation of PVDF, but has little effect on the spherulite growth of.WAXS PVDF and the experimental results show that the graphene composite materials in the crystal under different conditions after isothermal crystallization has not changed. But the crystallite size of crystal surface changes: static only after isothermal crystallization (021) crystallite size of crystal face with increasing crystallization temperature has been increased; (020) (100) and (110) the crystallite size crystal surface will occur in the trend turning 160 degrees. The sample shear at 160 DEG C after crystallization (100) (110) the crystallite size of crystal surface increased significantly. And the pure PVDF samples were significantly higher than those containing graphene samples. This is due to the shear effect change in the direction of spherulitic crystallites oriented, the crystallite in favor (100) (110) crystal growth direction, and the presence of graphene weakened The analysis shows that the shear orientation of.SAXS, PVDF and crystal structure of graphene composites is turning 160 degrees in the long period and the lamellar thickness increases with the increase of crystallization temperature, reaches 160 DEG C, the temperature continues to rise, began to decline. In the samples after isothermal crystallization of shear field than parallel to the shear direction in the high perpendicular to the shear direction of long period and the lamellar thickness, and slightly higher than that of pure PVDF samples containing 0.1wt% graphene samples. The shear, the molecular chain of PVDF along the flow direction of a stretch, the lamellar thickness increased, adding graphene has a certain inhibition effect on the shear effect, extend the orientation of molecular chain has been hampered by the results of.DSC analysis showed that the graphene, graphene has little influence on the melting behavior of PVDF isothermal crystallization of the sample, by HW The zero equilibrium growth rate of.PVDF crystallization at 183 and 195 degrees is 185.8 PVDF, which is far below the equilibrium melting point 195. The graphene can promote the transition rate of alpha to gamma in the isothermal crystallization process of 170, and increase with the increase of graphene content.

【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O632.21;TB332

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