原位X射线研究拉伸过程中间规聚丙烯晶体熔融与晶体取向关系

Relationship Between Crystal Orientation and Stress-induced Crystalline Melting of Syndiotactic Polypropylene Under Uniaxial Deformation via in situ Wide-angle X-ray Scattering

间规聚丙烯熔体(sPP)淬冷至液氮温度并保持5 min,于20,40,80,120℃下等温退火10 h,制备出具有不同片晶厚度的样品.在室温条件下,利用原位X射线在线研究sPP样品拉伸过程中应力诱导的晶体熔融和晶体取向关系.结果表明,在单轴拉伸过程中,应力导致的晶体熔融和晶体取向同时发生,即两者在同一应变、同一应力下同时发生,这一特性不受片晶厚度的影响.随着片晶厚度的增加,晶体熔融和取向需要的临界应力不断增大,在所研究范围内,该临界应力的增加和片晶厚度基本呈线性关系.另外,随着片晶厚度增大,样品的弹性模量、屈服强度和应变硬化模量均有一定程度的增大.

Melt of syndiotactic polypropylene（sPP） was quenched to liquid nitrogen and held for 5 min,then the quenched samples were put into vacuum oven at 20,40,80,120 ℃ for 10 h to prepare samples with different lamellar thicknesses.Relationship between crystal orientation and stress-induced crystalline melting under uniaxial stretching was studied with the combination of micro-tensile tester and in-situ wide angle X-ray diffraction（WAXD） measurement.Based on these results,＂stress-induced melting＂ always occurs simulta-neously with crystal orientation in spite of different lamellar thicknesses.Critical stress for stress-induced melting illustrated a linear correlation vs.lamellar thicknesses.Furthermore,with the increase of lamellar thickness,the mechanical properties of sPP samples,such as elastic modulus,yield stress and modulus of strain harden changed obviously.