A network alteration theory of rubbery polymers for exploring the damage and mechanochemistry

The constitutive behavior of rubbery polymers, particularly their elasticity and damage mechanisms, has been a significant area of interest for scientists due to its crucial role in engineering applications. This study suggests that the primary causes of damage and mechanochemical network alterations in these rubbery polymers are chain rupture, fluctuations in crosslinking points, and disentanglement. The proposed model suggests that both network and chain damage and mechanochemistry are consequences of instantaneous free energy effects and alterations in end-to-end vectors, which are analyzed using the Flory-Huggins lattice-like theory and rubber elasticity. This study posits that polymer damage follows a dangling and evolution of networks, which results in a constant magnitude of free energy terms but a decreasing slope (stress), ultimately leading to decreased mechanical properties. For the first time, this paper utilizes the Flory-Huggins lattice-like model to quantify conformational changes in rubbery polymers resulting from chain rupture and crosslinking point fluctuations, enabling the quantification of the mechanical dependency of mechanochemical effects in these polymers, specifically showing a scaling of the first strain invariant squared. The paper also presents and analysis a series of experiments, including hysteresis energetics, uniaxial loading-unloading tests, uniaxial and pure shear loading-unloading tests, and balloon inflation cycling, to confirm the accuracy and validity of the modeling, offering potential theoretical solutions for the design of rubbery polymers and the mitigation of damage and mechanochemistry.