Shear relaxation behavior for degraded polypropylene melt in torque rheometer

Abstract

AbstractShear relaxation behavior for polymer melt exists in different processing techniques and influences the dimensional accuracy and production efficiency of polymer products. A micro physical and mathematical model based on microstructure of polymer chains and processing parameters was established and verified by experimental results obtained from a torque rheometer. The shear relaxation time of polypropylene degraded by di‐tert‐butyl peroxide was characterized with torque rheometer. The effects of microstructure and processing parameters on the shear relaxation time was investigated. The results showed that a wider molecular weight distribution could result in a decrease in shear relaxation time and polypropylene chains with higher molecular weight were more sensitive to molecular weight distribution. The shear relaxation time declined exponentially with shear rate and increased with internal pressure. The temperature could enhance the movement of polymer chains and reduce the shear relaxation time linearly, but polypropylene with lower molecular weight was less sensitive to temperature. The insight obtained from the mathematical and experimental results can be profoundly applied in practical process control to manufacture product with better dimensional stability and production efficiency for viscoelastic polymer.Highlights A physical and mathematical model based on microstructure and processing parameters of molecular chains was established to explore the shear relaxation mechanism. Shear relaxation time of polypropylene degraded by di‐tert‐butyl peroxide was characterized with the help of torque rheometer. The effects of microstructure and processing parameters on shear relaxation time was investigated to optimize the manufacturing of polypropylene products.