Toward an understanding of the effects of nanocellulose during the free-radical polymerization reactions. Kinetic aspects of suspension-free radical polymerization of methyl methacrylate (MMA) in the presence and absence of nanocellulose

The aim of the present study is to examine the evolution of monomer conversion during suspension free radical polymerization of methyl methacrylate (MMA) at 80 °C, both in the presence and absence of nanocellulose obtained via TEMPO oxidation. The main focus of this work is on the kinetic aspects of MMA polymerization, particularly the diffusive step of the termination reaction and its impact on polymeric radicals. Experimental conversion evolutions are tracked using gravimetry. In addition, we employed an existing mathematical model to describe the effects of nanocellulose during polymerization, using the Einstein diffusion equation, geometric considerations and an approach that accounts for termination between short and long polymeric radicals. This model explains the evolution of monomer conversion regarding the effects produced by nanocellulose during the free radical polymerization reactions, focusing on factors that affect the diffusive termination step as difficulties for the short polymeric radicals reacting with the long radicals and the decrease of the segmental mobility. Our experimental results exhibit a premature autoacceleration with the presence of nanocellulose during polymerization reactions. Based on the adjustments made to the model, the theoretical results suggest that this reaction behavior is due to the impact of nanocellulose on the termination stage, which hinders a successful termination collision between short and long polymeric radicals while decreasing the segmental mobility of long radicals. Therefore, at higher nanocellulose content, the termination coefficient is reduced further.