纸质出版日期:1992-4-20
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用超高分子量聚丙烯的对二甲苯溶液中冷却析出的结晶沉积压制成的结晶垫,经热拉伸制备了不同拉伸倍数的薄膜.与用低分子量聚丙烯制备的结晶垫或熔融结晶物不同,超高分子量聚丙烯的结晶垫显示出极高的拉伸变形性能,因而制得了高达69倍的拉伸样品.WAXD照片表明在未拉伸的结晶垫中,微晶的c轴沿结晶垫法线方向择优取向,但仅经2-4倍的拉伸,微晶即发生破裂,且产生的较小的折叠链微晶已转向沿拉伸轴方向取向;晶区取向因子在拉伸过程中迅速增加并在较低拉伸倍数下即接近于理想取向.但非晶区取向因子在整个拉伸领域中增加缓慢.随拉伸倍数的增大,晶粒尺寸D110及D040逐渐减小;而长周期L逐渐增加.这表明在高倍拉伸样品中存在着折叠链被从片晶中拉出并部分形成伸直链结晶的转变.
A superdrawn technique called crystal real drawing has beea applied to obtain the oriented isotactic polypropyIene (i-PP) films.Orystal mat of ultrahigh moIecular weight i-PP(Mw-4×106) obtained by crystallization from its dilute xylene solution,exhibits a dramatlcally high de-formability compared to both the low toolecular weight mat and the mek-crystallized forms.such cryatsl mats are prepared to a series of samples with the various draw ratios and the highest draw ratio can be achieved up to 69.An X-ray diffraction photograph shows that the c-axis of the lamellar crystals in the original mat orient preferentially in the normal direction of the mat plane,and such crystals had already been split and c-axis orientation had been turned to parallel with the draw direction in the draw ratio range of 110 and D040 decrease as the draw ratio is in-creased,but the long period L found to becomelarger with the draw ratio raise up to the high value.These results indicate that lamellar crystals are deformed through a chain folds unrave-ling and then partially recrganized into a fully straight crystalline structure.
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