Cyclic Gas Dissolution Foaming as an Approach for Simultaneously Reducing Cell Size and Relative Density in Nanocellular PMMA

Abstract

A new approach to produce nanocellular polymers combining small cell sizes with low relative densities is presented herein. This production method, based on gas dissolution foaming, consists of performing a double saturation and foaming cycle. Thus, nanocellular polymethylmethacrylate (PMMA) has been produced through a first saturation at different saturation conditions (6, 10, and 20 MPa and −32 °C), at constant foaming conditions (60 °C for 1 min). Then, the nanocellular PMMAs obtained from the previous step were again saturated at different saturation conditions, 10 MPa 24 °C, 31 MPa 24 °C, 35 MPa 22 °C, and 6 MPa −15 °C and foamed at different temperatures (40, 80 and 100 °C) for 1 min. This new approach allows the cells created in the first saturation and foaming cycle to further grow in the second cycle. This fact permits producing nanocellular polymethylmethacrylate sheets combining, for the first time in the literature, cell sizes of 24 nm with relative densities of 0.3.

Production of Cellular Polymers Without Solid Outer Skins by Gas Dissolution Foaming: A Long-Sought Step Towards New Applications

“…Although several methods which concern multiple stages based on the gas dissolution foaming have been developed [35,37,[42][43][44], none of these previous approaches has proved to be a general and versatile approach to hinder the formation of the non-foamed skin during the gas dissolution foaming process, being limited in terms of geometry or expansion, or introducing complex additional steps without providing remarkable results.…”