聚乙烯薄膜拉伸过程中结构变化的原位研究

In Situ Study of Structure Changes During PE Film Stretching

使用差示扫描量热分析(DSC)研究了其拉伸前后结晶动力学与热力学行为的区别,使用同步加速器小角X射线散射(SAXS)和广角X射线衍射(WAXD)研究了薄膜拉伸过程中晶体结构、尺寸和长周期的变化。结果表明,拉伸使薄膜结晶度提高;拉伸过程中,二维散射图案发生明显变化,片晶结构被破坏后高应力诱导下重新结晶,拉伸使薄膜晶体取向度和晶体尺寸明显增大;随拉伸进行,纵向(拉伸方向)和45°方向的长周期先增大后减小,而横向一直呈下降趋势。聚乙烯工业缠绕膜通常在拉伸应变1.5倍附近下使用,此时薄膜纵向上已经高度取向并形成了拉伸诱导结晶,从而在纵向上有较高的力学强度。而横向上片晶结构尚未完全破坏,仍保持着一定的力学性能,因此综合使用性能较好。

Differential scanning calorimetry(DSC)was used to study the crystallization kinetics and thermodynamic behavior of polyethylene(PE)wrapping film before and after stretching.And synchrotron small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)were used to study the changes of crystal structure,crystal size and long period during the dynamic stretching process.The results show that stretching increases the crystallinity of the film.The two-dimensional scattering pattern changes significantly during stretching.The lamella structures are firstly destroyed and then recrystallized under high stress induction.Stretching process increases the crystal orientation and crystal size of the film.During stretching progresses,the long periods of lamella structure in machine direction(MD)and the 45°direction firstly increase and then decrease,while the transverse direction(TD)shows a continuous decreasing trend.PE industrial wrapping film utilizes under a strain about 1.5,when stretching induced crystallization has formed in MD,thereby presenting a good strength in MD.Also,the lamella structure has not been completely destroyed and still maintains a certain strength in TD.Thus,the wrapping film shows a comprehensive performance under working strain.