微尺度下压力对聚丙烯剪切黏度影响研究

利用高精度RH10毛细管流变仪开展微尺度下聚丙烯（PP）流变实验研究。选用内径分别为0.25、0.5、1.0 mm的口模，研究剪切速率3×10²~5×10³ s^-1范围内，温度为210、220、230℃时PP黏度变化。结果表明：在相同的剪切速率与温度下，相比于1.0 mm口模中PP熔体黏度，0.25、0.5 mm口模中PP熔体的黏度增大；3种口模内体现黏度与温度关系的Arrhenius公式拟合系数不同，揭示了微尺度下PP剪切黏度的尺度依赖性。分析认为在微小直径口模内PP熔体压力的增加是黏度变化的原因之一，并基于Barus公式提出用于量化微尺度下PP黏度的等效压力概念。

Effect of pressure on the shear viscosity of polypropylene at a micro scale

The viscosity of a polymer has a significant effect on both the fabrication process and the final profiles of polymeric parts with micro-features.Using an advanced twin-bore capillary rheometer,the shear viscosity of polypropylene (PP) melts in a microdie has been investigated at 210,220 and 230 ℃.The experiments were performed over a shear rate range of 3 × 102 to 5 × 103 s-1,and dies with diameters of 0.25,0.5 and 1.0 mm were employed.The results indicated that the viscosity values of the PP melt in the 0.25 and 0.5 mm dies were higher than those in the 1.0 mm die for the same shear rate and temperature.The diversity of the fitted coefficients of the Arrhenius equation-which demonstrates the relationship between the viscosity of a polymer melt and its temperature-revealed the geometrical dependence of PP viscosity at the micro scale.The analysis indicated that the increases in the pressure drops partially contribute to the viscosity deviations of the PP melts in the micro dies.Based on the Barus equation,an equivalent pressure was proposed as a means of evaluating the combined contributions of the factors that affect the shear viscosity of PP at the micro scale.