The relationship between chemical microstructure, phase morphology, rheology and physico-mechanical properties of thermoplastic polyurethane elastomers synthesized with various reaction stoichiometric ratios

This research focuses on synthesizing thermoplastic polyurethane elastomers (TPUs) using a reactive mixing method in an internal mixer, aiming to overcome the viscosity-related challenges of traditional synthesis techniques. Two types of polyester polyols based on ethylene glycol (Polyester-E) and butane diol (Polyester-B) along with two diisocyanates (pure 4,4′-MDI and a mixture of 4,4′-MDI/2,4′-MDI), a butane diol (BDO) chain extender, and dibutyltin dilaurate (DBTDL) catalyst were used. The study examined one-step and two-step feeding methods to investigate how process parameters and reactant ratios affect TPU properties. Tensile testing and FTIR analysis revealed that higher hydrogen bonding index (HBI) improved mechanical strength. AFM images showed increased microphase separation with higher diisocyanate-to-polyol ratios, indicated by larger hard segment domains. DSC results confirmed reduced crystallinity and increased melting temperatures with higher hard segment content. Rheological analysis demonstrated that increasing hard segment content led to greater complex viscosity and storage modulus, suggesting improved rigidity and phase separation.