Mechanical Forces Quench Frontal Polymerization: Experiments and Theory

TL;DR

This study investigates how mechanical forces influence frontal polymerization, revealing that residual stresses can halt the reaction front and affect the quality of polymer products, emphasizing the importance of mechanical considerations in large-scale applications.

Contribution

It introduces a novel experimental approach and a theoretical model to understand the impact of mechanical forces on the propagation of frontal polymerization.

Findings

Residual stresses can quench the reaction front.

Mechanical forces cause deformation or failure in polymer components.

Theoretical model explains mechanical limitations in frontal polymerization.

Abstract

Frontal polymerization is a promising energy-saving method for rapid fabrication of polymer components with good mechanical properties. In these systems, a small energy input is sufficient to convert monomers, from a liquid or soft solid state, into a stiff polymer component. Once the reaction is initiated, it propagates as a self-sustaining front that is driven by the heat released from the reaction itself. While several studies have been proposed to capture the coupling between thermodynamics and extreme chemical kinetics in these systems, and can explain experimentally observed thermo-chemical instabilities, only few have considered the potential influence of mechanical forces that develop in these systems during fabrication. Nonetheless, some experiments do indicate that local volume changes induced by the competing effects of thermal expansion and chemical shrinkage, can lead to significant deformation or even failure in the resulting component. In this work, we present a unique experimental approach to elucidate the effect of mechanics on the propagation. Our experiments reveal that residual stresses that arise in frontal polymerization are not only a potential cause of undesired deformations in polymer products, but can also quench the reaction front. This thermo-chemo-mechanically coupled effect is captured by our theoretical model, which explains the mechanical limitations on frontal polymerization and can guide future fabrication. Overall, the findings of this work suggest that mechanical coupling needs to be taken into consideration to enable industrial applications of frontal polymerization at large scales.