LDPE分子结构对流变行为的影响

Effect of molecular structure on rheological behavior of low density polyethylene

采用流动双折射和动态流变实验方法研究了低密度聚乙烯(LDPE)分子结构对其流变行为的影响。熔体在突变收缩口模中流动时的等差线图显示,两种LDPE的流动特性明显不同。由动态流变实验可知,LDPE 1810D在低频剪切时复数黏度比LDPE 2426K大,拟合得到的离散松弛时间谱范围较窄,表明两者的相对分子质量及其分布差别较大;两者的复数黏度随振动频率的变化方式不同,后者复数黏度的变化说明LDPE 2426K分子中含有长支链结构。结果表明,LDPE的相对分子质量及其分布、支链长度对其流变行为有重大影响。

The effect of molecular structure on rheological properties of two kinds of low density polyethylene （LDPE） was studied in flow induced birefringence and dynamic rheological experiment. The isochromatic line of the LDPE melts （grade 1810D and 2426K） when following in the abrupt contraction die shows their remarkably different rheological properties. The dynamic rheological experiment reveals that 1810D has a higher complex viscosity at low frequency and a nan-ower range of discrete relaxation spectrum compared with 2426K, indfcating that they significantly differed in relative molecular mass and its distribution. The complex viscosity of 1810D and 2426K varies with vibration frequency in different ways; the latter＇s variation in complex viscosity verifies the existence of long chain branches in 2426K. The relative molecular mass and its distribution and the length of the branches have a vital influence on the rheological properties of the LDPE melts.