分子动力学的聚合物流动诱导结晶取向数值模拟

Numerical simulation of the flow-induced crystallization orientation of polymer based on the molecular kinetic theory

聚合物的实际成型加工过程中,熔体在充填过程中不仅要受到热历史的作用,而且要受到剪切应力的作用,所以就不可避免地发生流动诱导结晶及取向现象。本文基于悬浮液理论和分子动力学方法,建立聚合物流动诱导结晶取向的数学模型,研究了剪切作用对结晶聚合物流动诱导结晶取向的影响。模型将结晶体系假设为结晶晶粒分散于无定型基质的悬浮液,通过取向张量计算取向因子,预测剪切过程中的晶相的取向行为。使用谱方法离散求解扩散方程,并计算取向分布函数和取向张量,模拟和分析了简单剪切场下结晶聚合物的流动诱导结晶取向行为。模拟结果表明,剪切强度对聚合物熔体的取向行为有着显著的影响,较高的剪切速率有助于晶区较早的完善取向。

Properties of polymer products depend on the morphology distribution within the product, which itself depends on both the molecular properties of the polymer used and the processing conditions applied during fabrication. In the present work, the shear effect on the crystallization of polypropylene was studied through flow-induced crystallization orientation. A model was then developed to predict the orientation of crystallinity, which based on the assumption that the crystallizing system was a suspension of crystalline entities growing and spreading in a matrix of amorphous material. Drawing on Jeffery＇s model of fiber orientation, the paper linked the deformation function with the orientation factor represented by tensors to predict the orientation of crystalline during shearing process. The spectral method was used for solving the diffusion equation to calculate the distribution function and orientation tensor. The orientation behavior for a simple shear flow was simulated and the primary parameters which affect the flow-induced crystallization orientation of crystalline polymer were analyzed.