关于超高分子量聚丙烯超拉伸膜的结构性能的研究——Ⅰ.拉伸取向过程的表征

STRUCTURE AND MECHANICAL PROPERTY STUDIES ON THE SUPERDRAWN FILMS OF ULTRAHIGH MOLECULAR WEIGHT POLYPROPYLENE I. CHARACTERIZATION OF THE DRAWING/ORIENTATION PROCESSING

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D_(110)及D_(040)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 mal drawing has been applied to obtain the oriented isotactic polypropylene (i-PP) films. Crystal mat of ultrahigh molecular weight i-PP (Mg- 4 ×106) obtained by crystallization from its dilute xylene solution, exhibits a dramatically high de-formability compared to both the low molecular weight mat and the melt-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 <4. The crystalline orientation increases rapidly and approaches perfect orientation at low draw ratio. The noncrystalline orientation, however, increases much more slowly up to the highest draw ratio. For the samples with the various draw ratios, the crystalline size D110 and D040 decrease as the draw ratio is increased, 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 unraveling and then partially recrganized into a fully straight crystalline structure.