Effect of temperature and strain rate on the compressive behaviour of supramolecular polyurethane

Abstract

Abstract. Supramolecular polyurethanes (SPUs) possess thermoresponsive and thermoreversible properties, and those characteristics are highly desirable in both bulk commodity and value-added applications such as adhesives, shape-memory materials, healable coatings and lightweight, impact-resistant structures (e.g. protection for mobile electronics). A better understanding of the mechanical properties, especially the rate and temperature sensitivity, of these materials are required to assess their suitability for different applications. In this paper, a newly developed SPU with tuneable thermal properties was studied, and the response of this SPU to compressive loading over strain rates from 10 −3 to 10 4 s −1 was presented. Furthermore, the effect of temperature on the mechanical response was also demonstrated. The sample was tested using an Instron mechanical testing machine for quasi-static loading, a home-made hydraulic system for moderate rates and a traditional split Hopkinson pressure bars (SHPBs) for high strain rates. Results showed that the compression stress-strain behaviour was affected significantly by the thermoresponsive nature of SPU, but that, as expected for polymeric materials, the general trends of the temperature and the rate dependence mirror each other. However, this behaviour is more complicated than observed for many other polymeric materials, as a result of the richer range of transitions that influence the behaviour over the range of temperatures and strain rates tested.

Mechanical characterisation and modelling of a thermoreversible superamolecular polyurethane over a wide range of rates

“…In the first heating, an additional broad endothermic dip was observed starting at 40 °C. This was not observed in subsequent cycles, and may be associated with phase separation within the cast material which has insufficient time to reform equilibrium in subsequent loops given the cooling and heating rates imposed [24]; evidence of an additional structure in the 'raw' specimens is shown in the SAXS data below.…”

“…The nature of these noncovalent interactions permits the material, in common with other supramolecular polyurethanes [21][22][23], to be addressable as a result of its inherent thermo-responsive character of the supramolecular interactions, thereby delivering dramatic viscosity changes over well-defined and tuneable temperature ranges, as well as leading to the capability to recover a significant degree of their mechanical strength after damage. As a result of the non-covalent interactions within the network being relatively weak, the recognition motifs within the polymer can assemble or dissociate relatively easily as a consequence of the low thermal activation energy, making it, in common with other supramolecular polyurethanes and polyureas, easy to process at relatively low temperatures [24][25][26].…”