How does paraffin wax prevent evaporation of acrylic-based syrups dedicated to fiber-reinforced composite processing?

摘要

This study focuses on volatility and processing issues which can be faced when handling acrylic syrups designed for adhesive or composite applications. These reactive mixtures which are mainly constituted of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) can yield thermoplastic matrices through radical polymerization. However, the rapid evaporation of acrylic monomers when syrups are exposed to air raises serious manufacturing and H&S concerns, especially when relying on open-mold processes. A common strategy to prevent this phenomenon is to add paraffin wax to the syrup. However the mechanisms which rule the inhibition of evaporation have never been clearly identified so far. In this context, confocal Raman microscopy has been used to perform depth profilings to evaluate the chemical composition of wax-acrylic syrups from surface to bulk. Results show that the wax content is much higher at the surface than in bulk which leads to the formation of a solid film. This concentration gradient results from two distinct phenomena: the migration of wax at the surface and, to a lesser extent, the evaporation of near-surface MMA monomers. Thus, the capability of these syrups to impregnate reinforcing fibers is largely decreased which could be of prime concern regarding their application. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48685.