Effect of mixing rate on molecular structure parameters of polybutadiene rubber based on rheology

The rheological properties of polymers before and after mixing are of primary concern because of the damage to the original molecular weight of polymers during processing. In order to reveal the correlation between mixing speed, rheological properties of polymer melts, and their molecular weight parameters, different grades of polybutadiene rubber (BR) at different mixing speeds were prepared in this study. Furthermore, the selected samples were subjected to the dynamic melt viscoelasticity test using a rubber process analyzer (RPA). The molecular weight changes of BR after mixing were observed on a rheological basis to analyze the effects of mechanical shear and thermo-oxidative aging on the molecular weight and distribution of the rubber. The measured values were directly compared with those obtained from gel permeation chromatography (GPC). The results showed that lower mixing speeds did not significantly affect the number-mean molecular weight (Mn), while the Z-mean molecular weight (Mz) and the weight-mean molecular weight (Mw) were increased, and the molecular weight distribution (MWD) was expanded. In addition, a transition state between thermo-oxidative aging and mechanical shear was further demonstrated. The behavior of the rubber was further elucidated and validated through large-amplitude oscillatory shear (LAOS) tests and thermal stability tests, demonstrating that the gel is a manifestation of the molecular weight coalescence of rubber and associating it with the mixing process of BR. According to the results of the RPA tests, melt rheology characterization is an environmentally friendly and fast way to provide information about the molecular structure of the BR.