Production, cellular structure and thermal conductivity of microcellular (methyl methacrylate)–(butyl acrylate)–(methyl methacrylate) triblock copolymers

Abstract

Microcellular foaming of a (methyl methacrylate)-(butyl acrylate)-(methyl methacrylate) triblock copolymer was carried out by means of supercritical C0 2 in a single-step process. The experiments were performed at 40 C using a pressure of 300 bar (30 MPa) during 24 h. The depressurization times were modified from 2 to 30 min, leading to cell sizes from 10 to 100 \im, and relative densities from 0.11 to 0.17. It was found that the key parameter to control cell size and density was depressurization time: longer depressurization times generated larger cell sizes and lower densities. The thermal conductivity of these materials was measured using the transient plañe source technique, and it was found that this decreased as the density was reduced. Various models for the prediction of thermal conductivity by conduction were tested. It was found that all the models underestimated the experimental results due to a significant contribution of radiation heat flow for these materials.

Polymer nano-foams for insulating applications prepared from CO2 foaming

“…Nanometric cell sizes wer not obtained, but the cell size decreased by more than one decade compared with the iso-density MAM foams in Reglero-Ruiz and colleagues' study [16]. This foaming batch process was carried out in another study by Murray and colleagues [128], for 1.5mm thick plaques of ABS.…”

“…The authors [16] had already shown that the foaming of MAM copolymers led to low-density foams with micro-cells, whose growth was not restrained. However, MAM copolymers can also act as nucleating agents in a polymer/copolymer blend.…”

“…Reglero-Ruiz and colleagues [16] studied the foaming of Altuglas° MAM copolymer (30/40/30 wt %). According to these authors, MAM copolymers have very high affinity with CO 2 , that could increase, in a nanostructured assembly, the nucleation rate.…”

“…The heat transfer within cellular materials is composed of four distinct mechanisms [16]: -conduction via the gaseous phase, -conduction via the solid phase, -the radiation phenomenon, -gas convection, that can be ignored when the cell size is less than 3 mm [17].…”

On thermal conductivity of micro‐ and nanocellular polymer foams

“…Both models considered conduction through the gas and solid phases in the foam. Bauer proposed a more comprehensive model by including convective heat transfer [5], which was later shown only significant when the pore size was greater than 3 mm [14]. The radiation effect was included in a few models, as discussed in [6, 7].…”