The Role of Polytetrahydrofuran (PTHF) as Reactive Plasticizer on the Processing and Performance of Hydroxyl-Terminated Polybutadiene (HTPB)-Based Polyurethane Elastomers

Abstract

Despite better processing and flexibility, conventional plasticizers, being unbound additives, tend to migrate, which adversely affects the structural integrity of the end product by modifying mechanical properties. This study aims to investigate the potential of polytetrahydrofuran (PTHF) as a reactive plasticizer to enhance the processing and performance of HTPB-based polyurethane elastomers (PUE), providing a balance between improved flexibility, desired mechanical properties, and also a remedial solution to overcome the plasticizer migration issue. Optimization of processing parameters and chemo-rheological cure kinetics was evaluated through chemo-rheological analysis at a wider temperature range of 50°C–80°C. Cure kinetics due to the polymerization reaction was also monitored by periodically observing the disappearance of the characteristic NCO peak using Fourier-transform infrared spectroscopy (FTIR). The impact of different molar ratios of PTHF/HTPB (ξ) on the performance of the synthesized PUE has also been evaluated. The polymerization temperature was set to 60°C, supported by minimal viscosity build-up and a lower activation energy of 30.4 kJ mol⁻¹. The pot life increased by 86% when ξ was 0.20 as compared to the control sample and reduced by 47% for PUE at ξ = 0.10 when the curing temperature increased from 50°C to 80°C. With increasing ξ, the tensile strength increased to 2.73 MPa when ξ was 0.15 and then declined afterward, and elongation at break increased from 505% to 764%. The molar ratio (ξ) at 0.15 was optimized and presented excellent results in terms of higher pot life and a good balance of mechanical properties.