Relationship between microstructure and mechanical properties of polyether block amide foams

• Published in: Polymer engineering and science 2021-07, Vol.61 (7), p.1971-1981
• Main Authors: Ernault, Estève, Diani, Julie, Hallais, Simon, Cocquet, Clio
• Format: Article
• Language: English
• Subjects: Amides; Analysis; Engineering Sciences; Fineness; foam; Foamed materials; Holes; Injection molding; Mass ratios; mechanical behavior; Mechanical properties; Mechanics; Mechanics of materials; Microstructure; Observations; Plastic foam; recovery; Segments; shape ratio; Stress relaxation; Stress-strain curves; Viscoelasticity
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.25712

The mechanical behaviors of five polyether block amide foams, obtained by mold‐opening foam injection process, were investigated with regard to their microstructures. The materials vary in mass ratios of hard versus soft segments, and/or in process packing time. The resulting microstructures have been characterized in terms of cavity size and shape ratios, by analyzing scanning electron microscope images after careful sample preparation. The foam mechanical responses have been characterized in compression at small and large strain. At small strain, the initial linear part of the stress–strain curve is enhanced firstly by the hard segment mass ratio and secondly by the fineness of the microstructure. Similar results have been obtained at large strain. The foam viscoelasticity at large strain has been characterized by stress relaxation and strain recovery tests, relevant for foam applications. Reduced packing time and pressure have been shown to lead to the presence of undesired large cavities. The morphological defects appear to have a negligible impact on the macroscopic mechanical behavior of the foams at infinitesimal strain, but lead to critical inconsistency at large strain. Furthermore, the mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness. This study tends to identify the impact of hard/soft segment ratio and packing time and pressure of mechanical behaviour of Poly ether‐block‐amide foams. Five foams have been characterized thanks to differential scanning calorimetry, scanning electron microscopy and compression tests at small and large strain. Mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness.