Kinetic Analysis of the Cracking Behavior in Methanol-Treated Poly(methyl methacrylate)/Functionalized Graphene Composites

Structural degradation in liquid environments can hinder the applications of polymer composites as structural materials. In this work, we study the impacts of methanol on surface cracking and the propagation of pre-formed cracks in UV-irradiated poly(methyl methacrylate)/functionalized graphene (PMMA/FG) composites, followed by the uptake of three different crack-generated solvents, namely 1-butanol, cyclohexanol, and 2EA, respectively. The density of surface cracks increases with the increase in the uptake of the crack-generated solvent. The dependence of the nominal diffusivity for the surface cracking on temperature follows an Arrhenius-like law. The methanol in the composites enhances the uptake of the crack-generated solvent, accompanied by the desorption of methanol, and accelerates the initiation and propagation of surface cracks. The activation energy for the initiation of surface cracks shows an increasing dependence on the Hansen solubility distance from methanol. The progression of the pre-formed crack length with time follows a parabolic law. The nominal diffusivity of the crack-generated solvent for the propagation of the single-crack is greater in the healing zone than in the crack-free zone; the corresponding activation energies exhibit an opposite trend. Increasing the fraction of functionalized graphene and decreasing the UV-irradiation dose cause increases in the energy barriers that need to be overcome for the surface cracking and propagation of preexisting cracks.