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

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.

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

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.