Mechanical and rheological testing to develop thermoplastic elastomer-polyborodimethylsiloxane blends for personal impact protection

To claim ‘wearability’, clothing for protection against impact injury must not only act locally as a rigid shell under impact in order to satisfy drop-weight tests, but also flex freely with normal movement and offer permeability and light weight. Previous materials used carrier textiles coated with ‘dilatant’ but mechanically weak polyborodimethylsiloxane (PBDMS) compounds. We outline a procedure for developing blends of PBDMS with thermoplastic elastomers which, while minimizing the force transmitted in standard drop-weight tests on monolithic plate, can also be injection moulded into more wearable 3D shell structures. The first successful blends were developed by trial-and-error, involving the melding and testing of many plate specimens. The new procedure uses dynamic mechanical thermal analysis and time-temperature superposition to calibrate Zener-solid models for specific conditions within the service temperature and impact-speed envelope. Each model material is then subjected to a virtual drop-weight impact test to estimate the peak transmitted impact force. These results guide the selection of blends suitable for further development, correlating well with those obtained using the previous, more laborious procedure. When distributed within a suitable blend, PBDMS contributes considerably greater impact force attenuation than bulk uniaxial tests indicate