Increasing sustainability is a critical challenge for our time. Increased plastic recycling can contribute to sustainability, but balancing high performance and recyclability is a challenge. Rubbers with permanent chemical crosslinks are widely used because of their low modulus, creep resistance, and wide temperature range. However, the permanent crosslinks make recycling impossible. It would be ideal to have the performance of a conventional rubber with the recyclability of a thermoplastic. Replacing chemical crosslinks with non-permanent, physical associations enables melt processing and recycling.
Thermoplastic elastomers (TPEs) are good candidates for this purpose, and they’re already widely used in everything from automotive ducts to shoes to medical devices. They’re crosslinked via physical associations and trapped entanglements leading to high elasticity coupled with melt processability. Their mechanical properties are governed by the interplay of the different dynamics present in the system (e.g. hard block associations and soft block mobility) as well as by their morphology. While widely used, thermoplastic elastomers are not yet able replace cross-linked rubbers in all applications as they generally have higher modulus and lower creep resistance. Additionally, irrespective of their exact chemical structure or type of association (crystal, hydrogen bonded, or glassy domains…) many soft TPEs show a reduction in toughness at higher temperatures.
Understanding how the multiple dynamics in the material contribute to the mechanical properties is critical for identifying routes to tune or improve properties. Dynamics are influence not only by temperature but also by deformation as is the case with strain induced crystallization of the initially mobile soft blocks. While there is much interest in exploring new materials based on such physical associations, currently we lack the understanding to provide guidelines on how to select the interaction dynamics to design materials with a desired property profile.
The goal of the project is to build up a physical picture for the evolution of morphology and dynamics upon deformation and to highlight the key parameters that influence the mechanical behaviors.
Focusing on a series of well-defined model TPEs, the influence of tuning composition and molecular weight on the mechanical properties as a function of temperature will be explored (i.e. tensile tests, DMTA, fracture tests, etc.). Statistical tools and models will be developed in order to describe and understand how the chain structure leads to the observed morphology and mechanical properties. The mechanical tests will be linked to how the morphology as a function of deformation and temperature to better understand the interplay between the different dynamics in the system and the mechanical response.
