Frontal vs. bulk polymerization of fiber-reinforced polymer-matrix composites

As frontal polymerization (FP) is being considered as a faster, more energy-efficient, out-of-autoclave manufacturing method for fiber-reinforced thermosetting-polymer-matrix composites (Robertson et al., 2018), the competition between FP and bulk polymerization (BP) is an essential component of the feasibility analysis of the FP-based manufacturing process. To that effect, we present a comparative study of FP and BP based on a nondimensional form of the reaction–diffusion equations that describe the two polymerization processes. From the nondimensional formulation of the thermo-chemical relations, we extract two parameters that involve the key quantities of the cure kinetics model, i.e., the heat of reaction, the time constant, and the activation energy. Although the analysis is general and can be adapted to a wide range of thermosetting-polymer composites, emphasis is placed on unidirectional composites made of carbon or glass fibers embedded in a dicyclopentadiene (DCPD) matrix. The competition between FP and BP is formulated in terms of the time scales involved in the two polymerization processes for the manufacturing of composites of varying sizes and fiber volume fraction values.