摘要
以一系列高温结晶后自然冷却的高密度聚乙烯(HDPE)为研究对象,利用同步辐射超小角X射线散射(USAXS)和示差扫描量热技术(DSC)对样品的微观结构进行了分析,并在线研究了单轴拉伸过程中的空洞化行为.结果表明,结晶温度高于110℃后自然冷却到室温的样品中存在热稳定性不同的两组片晶,等温过程形成结构完善的厚片晶,而在冷却过程会形成有缺陷的薄片晶,两组片晶的熔点分别在133和110℃附近.在30℃拉伸时,所有样品都可观察到空洞化并伴随发白现象.并且,等温结晶中形成片晶厚度越大的样品,相应的空洞化现象越明显.在拉伸过程中,空洞出现在屈服点附近,其法向方向平行于拉伸方向,后随应变的增加发生转向,法向方向与拉伸方向垂直.样品中空穴的长度为900~1200 nm.另一方面,随着冷却过程生成薄片晶比例的增加,空洞化趋势下降.此外,提高拉伸温度,样品更倾向发生塑性形变,空洞化程度减弱.
A series of high-density polyethylene samples with different microstructures obtained via isothermal crystallization at various temperatures and then cooling down to room temperature were used to explore the structural evolution and cavitation behavior during stretching by means of the ultrasmall-angle X-ray scattering and differential scanning calorimetry techniques. The samples crystallized at temperature higher than 110 ℃ then naturally cooled to room temperature possess two populations of lamellar stacks with different crystalline thicknesses. The thicker lamellae with well-organized structure were formed in the isothermal crystallization process, and chains crystallized at lower temperatures during cooling down yielded thinner defective lamellar crystallites. The melting temperatures of the two populations of lamellar stacks were around 133 and 110 ℃,respectively. When deformed at 30 ℃, the cavitation was observed in all samples and accompanied with strainwhitening phenomenon. It turned out that the cavities were more intense for the samples with thicker lamellae generated during isothermal crystallization. During deformation, the cavities first take place with the normal parallel to the stretching direction around yield point, and then changes the normal perpendicular to the tensile direction with the increase of strain. The length of cavities was calculated and the values were around 900-1200 nm. On the other hand, the extent of cavitation becomes smaller with the increasing ratio of the thinner lamellae crystallized during cooling down. Moreover, the plastic deformation of the lamellae is facilitated and the degree of cavitation become weaker with the increase of the stretching temperature.
作者
付莲莲
卢影
姜志勇
门永锋
Lian-lian Fu;Ying Lu;Zhi-yong Jiang;Yong-feng Men(College of Material Science and Engineering,Huaqiao University,Xiamen 361021;State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,Changchun 130022)
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2021年第2期204-213,I0005,共11页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号21903031)
华侨大学科研基金(基金号50Y18051)资助项目.
关键词
X射线散射
聚乙烯
空洞化
拉伸温度
X-ray scattering
Polyethylene
Caivitation
Stretching temperature
