Experimental study and modeling of nanofoams formation from single phase acrylic copolymers

Abstract

Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO 2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 10 16 /cm 3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.

CO2‐blown nanocellular foams

“…The MMA‐ co ‐EMA copolymers ( T g = 96°C) were found to be more effective than PEMA ( T g = 65°C), which under similar conditions produced foams with 345 nm cells and 79% porosity . The studies concluded that homogeneous nucleation theory was consistent with the experimental trends observed, which was captured in a foaming model …”

“…Under the sorption conditions (30 MPa and 35°C), all polymers were in the amorphous state and readily foamed upon depressurization (1S process). Copolymers with T g between 85°C and 105°C produced nanofoams with cell size between 100 and 200 nm with porosities between 60 and 80% . Some higher T g polymers with high CO 2 solubility, such as MMA‐ co ‐PFMA, gave foams with 70 nm cell and 60% porosity and remarkably high cell nucleation densities.…”

“…This is the first published validation of the Knudsen effect in nanocellular foams, which confirms the expected reduction of heat transfer due to the gaseous phase by a factor 2 to 3 compared to conventional foams. The highest porosity demonstrated for nanofoams with cells of about 100 nm or less is about 85%, which is expected to be suitable to minimize the balance between solid conduction and radiation. No overall TC data have been published to date on such foams but it seems reasonable to assume that low TC foams can indeed be made from low density nanocellular foams.…”

Solid‐state microcellular and nanocellular polysulfone foams

“…The concept for these polymer blends nanofoams was similar: one phase acted as the matrix and the other dispersed phase served as a template for bubble nucleation and growth. For copolymers, nanofoams have been created mainly in PMMA‐based copolymers, such as poly(MMA‐co‐EMA) and poly(MMA‐co‐tBMA) . Polymer nanocomposites, which have some amount of nanoparticles dispersed in the polymer matrix, have been shown to generate nanofoams, such as in poly(MMA‐co‐EA) with silica nanoparticles and poly(MMA‐co‐EMA) with POSS .…”

The mechanics of solid-state nanofoaming

“…12 Scanning electron microscope QUANTA 200 FEG of Thermo Fisher Scientific (USA). 13 At least 200 cells were analysed from multiple micrographs per foamed sample. 14 −− = (2) where g V is the geometric volume of the foam, p V is the pycnometer volume and s V is a penalty volume to account for the volume of the cells at the surface of the foam.…”