Modelling of loss factor curves obtained by Torsion-DMA of HTPB and GAP based binders manufactured with different curing agents and plasticizers

Inert non-polar HTPB binder and energetic GAP binder with polar groups are the two most common used binders to create a polymeric network for solid composite rocket propellant (SCRP) formulations. One of the key parameters during the development of a new SCRP formulation is the glass-rubber transition region, which is mainly dependent on the molecular interactions between the species and can be analysed using DMA loss factor (tand= G´´/G´) in torsion mode both for binders and highly filled SCRP. The current study aims to analyse the effect of different isocyanates and different plasticizers (inert & energetic) with HTPB R45HTLO and GAP based systems by tand curves applying BLC (baseline correction) and EMG (exponentially modified Gauss) distribution. GAP binders were prepared with DesmodurTM N100 and DesmodurTM N3400 types of curing agents and with three energetic plasticizers, Butyl-NENA, BDNPF/A and BATEG. The HTPB R45HTLO binders with four different types of isocyanates (IPDI, HDI, DesmodurTM E305 and 6HMDI), with and without the common plasticizer DOA (dioctyl adipate), were also analyzed using loss factor curves obtained by torsion DMA. The evolution of tand curves as a function of measurement temperature showed distinct differences in the intensity of loss factor curves with different isocyanates in the following order HDI > IPDI >> 6HMDI > DE305. Additional series of HTPB R45HTLO+IPDI binders with four different plasticizers (DOA, DOS, DOZ and IDP) showed not such pronounced differences compared with the differences obtained with the isocyanate types. Mainly, the four plasticizers showed the same level of intensity in loss factor curves and maximum peak temperature Tg, except IDP, which provided with the lowest glass-rubber transition temperature. Energetic plasticizer BATEG shifted the glass-rubber transition region tot lower temperatures; however, together with a lack of mechanical properties in terms of elongation. The isocyanate type changed the intensity of GAP binders. Comparing plasticizers BDNPF/A and Bu-NENA, the former provided better Tg.