茂金属聚乙烯和低密度聚乙烯共混物的流变行为

研究了茂金属催化乙烯丁烯1共聚物mPE和LDPE共混物的流变行为.测定了一系列共混物的稳态剪切粘度和动态粘弹性,用改进Cross模型拟合实验数据.mPE的零切粘度η₀较小,从牛顿型转变为非牛顿型所需的剪切速率较大,转变应力较高,在挤出加工剪切速率范围内熔体粘度高,对剪切敏感性差,这是由于它有较低的重均分子量、窄的分子量分布(M_w/M_n=21)所致.对于对数加和规律,共混物η₀在mPE/LDPE为50/50和25/75时有强烈的正偏差,这是由于共混物自由体积减小所致.共混物的转变应力τ^*和非牛顿指数n随LDPE加入量增大而降低,表明共混物对剪切的敏感性提高,加工性得到改善.G'和G”的一致性说明mPE和LDPE共混是相容的.

Rheological Behavior of Metallocene Catalyzed PE and LDPE Blends

The rheological behavior was studied for blends of metallocene catalyzed ethylene/1-butene copolymer(mPE) and low density polyethylene(LDPE). Steady-state viscosity and dynamic viscoelasticity were measured by using a DSR-200 rheometer with parallel plate geometry. Non-linear fitting with the modified cross model was conducted successfully. Due to lower molecular weight and narrower molecular weight distribution(Mw/Mn=2.1), mPE has a lower sensitivity to shear, shown by a lower zero shear viscosity, higher values of shear rate and shear stress at the transition from Newtonian to non-Newtonian behavior, higher viscosities in shear rate range from 100 s-1 to 102 s-1. Zero shear viscosities of mPE/LDPE 50/50 and 25/75(mass ratio) blends have a large positive deviation from log-additivity rule, due to a decrease of the free volume fraction in these blends. The transition stress and non-Newtonian index decrease with increasing LDPE fraction in blends, which indicate that the blends have high sensitivity to shear and improved processability. The single correlation between G' and G＂ corresponds to the behavior expected for a miscible blend.