Unraveling Dynamic Mechanical Deformation in Segmented Polyurethanes: From High Strain-Rate Hardening to Complete Fold Recovery; Conference paper

摘要

In light of the increased threat from terrorist activities in recent years, there is a critical need for lightweight transparent ballistic shield materials that are mechanically robust and have multi-functional properties. Transparent segmented polyurethanes (PU) in particular have shown potential for use as rigid ballistic shields and as lens materials for flexible C/B protective face masks. The performance specifications required for each application are quite different, and the current state-of-the-art PU technology can not completely fulfill the full spectra of materials survivability including the simultaneous mechanical and chemical hardening against the emerging operational threats. ARL is currently engaged in collaboration with the Institute for Soldier Nanotechnologies (ISN) to investigate and exploit new molecular mechanisms for design of novel hierarchical hybrid structures to achieve the desired physical and mechanical properties. This paper presents the experimental findings from recent studies conducted at the ISN whereby the role of molecular structures on the dynamic mechanical deformation of a model set of segmented polyurethanes was determined. The microphase morphology, thermal transitions, molecular relaxation, and mechanical deformation were investigated. The nature of chain extender significantly affected the extent of phase mixing between the hard and soft segments: incorporation of 2,2-dimethyl- 1,3- propanediol (DMPD) as the chain extender resulted in a 51 deg. C increase in the soft segment Tg relative to the analogous 1,4-butanediol (BDO)- containing PU samples. Small-angle X-ray scattering data indicated that the structure difference between chain extenders was correlated with a substantial change in interdomain structure. The BDO-containing PU samples exhibited a single, broad scattering peak that is typical of phase-segregated segmented polyurethanes.