One of the most widely used methods to produce microcellular poly(methyl methacrylate) (PMMA) at the laboratory scale is the gas dissolution foaming process. Currently, this technique allows producing small samples with simple geometries. In addition, it requires very long saturation times (even more than 20 hours for a sample 4 mm thick). These facts make this foaming technique a good method to test formulations and materials at the laboratory scale but with low possibilities of being scaled up to mass production.
One interesting alternative based on similar principles to the pervious explained technology is the bead foaming technology. Foams made of beads are formed by a large number of expanded beads which are welded together by heat giving rise to a perfectly defined three-dimensional material. One important characteristic of this technology is that allows obtaining foams with complicated geometries. This technology is currently used at industrial scale to produced EPS , EPP or ETPU. Moreover, due to the small size of the precursors (also called micro-pellets) used, the saturation time is drastically reduced (less than 2 hours for a 1 mm thick micro-pellet).
In this work, PMMA microcellular beads have been produced using a one-step gas dissolution foaming process in an autoclave using CO2 as blowing agent. The influence of foaming conditions such as saturation temperature and saturation pressure on the cellular morphology and bead density has been analysed. Different saturation temperatures (50 ℃, 55 ℃ and 60 ℃) and saturation pressures (10 MPa, 15 MPa and 20 MPa) have been used. Different grades of PMMA have been also analysed.