Polyborosiloxane-Thermoplastic Polyurethane for Strain Stiffening Foams with Enhanced Impact Energy Absorbance

Abstract

Soft strain stiffening foams (SSFs), which rapidly harden upon impact, have traditionally been used as shock energy absorption materials for human body protection. Even though several methods have been developed for their preparations, these methods are either inefficient or give products without the expected structures/properties. Here in this work, by foaming a blend of thermoplastic polyurethane (TPU), silanol-terminated polysiloxane, and boron oxide by expandable microspheres, polyurethane-based strain stiffening foams (SSUFs) are prepared. Characterization of SSUFs with scanning electron microscopy (SEM) shows polyborosiloxanes in SSUFs are reliably confined by a porous TPU skeleton and their cold flow is effectively restricted. Quasi-static compression tests show SSUFs have hysteresis loops pertinent to polymeric foams and are ideal for cushioning. Under impact conditions of strain rates from 3000 to 10,000 s–1, energy absorption for SSUFs monotonically increases for samples of the same density, suggesting these foams are particularly useful for high-strain-rate impact protection. For samples of different densities, impact energy absorbed monotonically increases with decreasing sample density, suggesting a cooperative effect from porous structure deformation for energy dissipation within SSUFs. The method developed in this work is simple and holds promise for the production of strain stiffening foams for human body protection purposes.