Gas Diffusion in Closed-Cell Foams

An experimental toolbox for the physical characterization of thermal insulating polymeric foams

Recent advancements in polymer science and manufacturing technologies triggered new developments of porous materials used for mitigating heat losses, such as thermal insulating polymeric foams. The major bottleneck in the optimization of these products, however, remains the absence of analytical methods able to scrutinize their large design space reasonably quickly and cost-effectively. This manuscript targets the paucity of data for polymeric foams by illustrating, at a proof-of-principle level, that several well-established analytical methods including optical microscopy, pycnometry, dielectric spectroscopy, thermogravimetric analysis, and nuclear magnetic resonance can be exploited for an extensive, yet logistically efficient, characterization of these materials. The purpose of this study is thus introducing an experimental platform for the characterization of market foam products and for the development of new polymeric foams with pore sizes that are particularly relevant for industrial and residential thermal insulation. Since this work introduces several new methodologies, it may be used as a guide for both laboratory users and specialists in the field, who may further improve the herein proposed experimental concepts.

Gas Diffusivity Through EPS Foams

A simple multiscale model was developed and used to predict gas diffusivities through expanded polystyrene foam at near standard temperature and pressure conditions. The technique involves measuring gas diffusivities at various length scales then combining them using an electrical analogy for parallel resistances to construct an effective property. A commonly used experimental technique, the continuous flow method, was used to obtain diffusivity data for argon through polystyrene films and foams. Although a simple Fickian mathematical model was able to predict diffusivities through films, a simple ‘coarse’ multiscale model that accounts for the morphological features was developed for the foam.

Gas Diffusion in Polyolefin Foams during Creep Tests. Effect on Impact Behaviour and Recovery after Creep

A method to obtain the effective diffusion coefficient of the gas contained in closed cell polyolefin foams under static loading is presented. This property is obtained from pressure decrease with time using an analytical solution of the diffusion equation. The effect of density, type of base polymer, crosslinking and sample size on the diffusion coefficient is analysed.

It has been shown that the impact behaviour of low density closed cell polyethylene based foams deteriorates after compressive creep periods and that this reduction of the cushion capabilities is directly related with the diffusion coefficient of the foams.

Moreover, the recovery of the foams after creep showed a peculiar non-homogeneous behaviour, which has been analysed. Gas diffusion during creep is the main responsible for this particular behaviour.