Kinetic and thermodynamic investigation on diffusion-limited crosslinking reaction behaviors of peroxide-induced low-density polyethylene

Crosslinking reaction behaviors can determine the network morphology and further influence macroscopic properties of polymers, while the current comprehension about crosslinking reaction behaviors of peroxide-induced low-density polyethylene (PLDPE) is quite lacking, which seriously limits its development and application. Here, for the first time, the crosslinking reaction behaviors of PLDPE are fully characterized and analyzed by combining kinetic and thermodynamic analysis. The kinetic behaviors are investigated by non-isothermal DSC and isothermal rheology methods, and thermodynamic characteristics of crosslinking reaction are analyzed by Arrhenius law and transition state theory. The results demonstrate that the crosslinking reaction of PLDPE involves complex order and autocatalysis reactions. Notably, the autocatalysis reaction is considered as the driving force of the whole crosslinking reaction. Furthermore, the autocatalysis reaction is proved to be strongly dependent on the diffusion of macromolecular chains under isothermal conditions, whereas the effect of diffusion on order reaction can be ignored. Given that, a new kinetic model incorporates the single diffusion factor to significantly describe the diffusion effect on the autocatalysis reaction during crosslinking, which grasps the complexity of crosslinking reaction mechanism. This model is able to characterize and predict the kinetic results of PLDPE crosslinking reaction very well. It provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting the diffusion-limited crosslinking reaction behaviors of polymers.