退火热处理对iPP片材固相拉伸强化效果的影响

对等规聚丙烯（iPP）片材在退火固相拉伸过程中的晶体转变过程进行了研究。X射线衍射（XRD）表征了结晶衍射峰，定量计算出β晶的相对含量；二维小角X射线散射（2D-SAXS）揭示了α?β 晶型转变过程；差示扫描量热仪（DSC）揭示了iPP的熔融性能。结果表明，iPP片材在固相拉伸过程中发生了晶型转移，XRD衍射曲线中出现了β晶典型衍射峰β（300），2D-SAXS图中出现了取向串晶结构；在110 ℃拉伸作用下能够产生相对高β晶含量的iPP，最高含量为6.75 %；拉伸强度的增加幅度不大但其缺口冲击韧性显著提高；对固相拉伸作用后的iPP片材进行了退火处理，表明退火温度在110 ℃前串晶结构不会受到破坏，超过110 ℃退火后串晶结构被破坏再次形成球晶结构。

Influence of Annealing Heat Treatment on Solid-state Tensile Strengthening Effect of iPP Sheets

The crystal transformation process of isotactic polypropylene(iPP)sheet during the annealing solid-state stretching process was studied.The crystalline characteristics of the resulting iPP sheet were detected by X-ray diffraction and then the relative content ofβ-form crystals was calculated quantitatively.Furthermore,two-dimensional small-angle X-ray scattering(2D-SAXS)was adopted to monitor theα-βcrystalline transformation process.In addition,the melting properties of iPP sheet were characterized by differential scanning calorimetry.The results indicated that the iPP sheet underwent a crystal transformation during the stretching process,resulting in the presence of a diffraction peak at 16.1°for the(300)reflection of theβ-form cylindrites,and the oriented cylindrical structure could be observed from the 2D-SAXS patterns.A relatively high content of β-form crystals was produced under the stretching condition at 110°C,and the highest content reached 6.75%.The mechanical results showed that the notched impact toughness of iPP sheet was improved significantly,whereas the tensile strength increased slightly.In addition,it was found that the cylindrical structure was not damaged when the solid-state stretched iPP was annealed below 110°C.However,after the annealing temperature exceeded 110°C,the cylindrical structure was destroyed and the spherulite structure was formed again.