Impact of the microstructure on the mechanical behavior of PEBAX foams

Five PEBAX foams provided by Arkema and obtained by mold-opening foam injection process has been studied. One one side, the microstructures have been characterized by DSC for the chemical and physical properties, and by scanning electron microscope image analysis for the structural properties. On the other side, the linear elasticity as well as the non-linear mechanical responses including stress relaxation or strain recovery have been characterized in compression.

The main results of the study are:
1) When the packing time, which characterizes the duration of mold closing after injection, is too short, large defects are randomly dispersed in the foam. These defects have a negligible impact in linear elasticity but induces a bad reproducibility of the mechanical behavior at large strain.
2) The mass ratio of soft vs. hard segments of the copolymer has a first order impact on the mechanical behavior at small and large strains. The stiffer is the material, the faster and more complete are the stress relaxation or strain recovery.
3) For identical chemical compositions, the fineness of the microstructures driven by the packing time, has a second order impact on the mechanical behavior. Actually the finer is the microstructure, the stiffer is the material, which improves the stress relaxation and strain recovery.

Lead researcher on this study: E. Ernault (Research Engineer at LMS)
The complete study may be found here: https://doi.org/10.1002/pen.25712.