Insights into In Situ Compatibilization of Polydimethylsiloxane-Modified Thermoplastic Polyurethanes by Dynamic Crosslinking: Relating Experiments to Predictive Models

Thermoplastic polyurethane (TPU)-based biomaterials are widely investigated in fabricating biomedical implants and devices. The present study describes a dynamic vulcanization-inspired reactive melt-blending methodology to modify TPU with polydimethylsiloxane (PDMS) and ensure the selective in situ crosslinking of the PDMS phase. The influence of the peroxide crosslinker during melt-processing was assessed, and, thereupon, a complete set of dynamically vulcanized blends was prepared with varying PDMS contents (10–40 wt %). The obtained thermoplastic vulcanizates (TPVs) were characterized for their crosslink density, mechanical properties, morphology, and thermal stability; and benchmarked against the uncrosslinked, pristine blends. The fractographic examination of the blend surfaces demonstrated a remarkable improvement in interfacial adhesion and a more refined microstructure for the TPVs, while a gross phase-separation was evident in the uncrosslinked blends. The experimentally determined tensile/compression response for the dynamically vulcanized system was in good agreement with the theoretical predictions, based on the Halpin–Tsai, Coran, and Takayanagi models. The pristine blends, devoid of crosslinking, largely conformed to the lower-bound series model, implying an immiscible and uncompatibilized behavior. The analysis of stress-concentration parameters was also performed to gain further insights into the discontinuities in the stress transfer in the dual-phase blend system. Taken together, the obtained results affirmed the superior properties of TPVs and established the efficacy of dynamic vulcanization for the in situ compatibilization of the TPU/PDMS system, in good corroboration with the predictive models.