Optimization of the mechanical performance of TDI-based polyurethanes <i>via</i> orthogonal design and response surface methodology

The mechanical properties of polyurethane elastomers are primarily determined by their formulations and synthetic processes. Here, we present an in-depth investigation into the optimization of the mechanical performance of a toluene diisocyanate (TDI)-based polyurethane using orthogonal design and response surface methodology (RSM). The utmost mechanical performance with a tensile strength of 14.67 MPa and an elongation at break of 1160% was achieved. The model reliability in predicting the mechanical strength was validated with a reasonable accuracy error of 2.2%. The correlation between mechanical properties of the TDI-based polyurethane and factors including NCO/OH ratio (<i>R</i>-value), chain extension coefficient, crosslinking coefficient, and curing temperature was elucidated through a combination of Fourier transform infrared (FTIR) and Raman spectroscopy with RSM. A net positive interactive effect among the <i>R</i>-value, chain extension coefficient, and curing temperature was observed. Additionally, a volcano-shaped relationship was identified between tensile strength and the crosslinking coefficient, while a similar non-monotonic trend was found between elongation at break and curing temperature. Through multiple characterization experiments including equilibrium swelling measurements, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), the relationship between elastomer crosslink density and mechanical properties was systematically examined. This work provides valuable insights for the rational design of high-performance polymer materials.