Thermal aging of hydroxy-terminated polybutadiene/isophorone diisocyanate (HTPB/IPDI)-based polyurethane was studied as a function of NCO/OH ratio (1.0 and 0.85). Samples were aged in air ovens at 50, 60, 65, and 70 ºC for periods of time from 1 to 34 weeks. Changes in chemical (swelling testing and FT-IR spectroscopy) and mechanical (tension testing and hardness) properties were evaluated throughout the aging assays. Correlation between equilibrium swelling ratio and elastic modulus, coupled with changes in FT-IR spectra, indicated oxidative cross-linking as the dominant mechanism for both molar ratios investigated. However, determination of Arrhenius activation energy resulted in values of (82 ± 10) kJ.mol-1 and (156 ± 30) kJ.mol-1 for 1.0 and 0.85 NCO/OH ratios, respectively, thus revealing faster oxidative degradation kinetics for higher urethane linkage networks.

Abstract: Copper chromites are well known as burning rate catalysts for the combustion of composite solid propellants, used as a source of energy for rocket propulsion. The propellant burning rate depends upon the catalyst characteristics such as chemical composition and specific surface area. In this work, copper chromite samples from different suppliers were characterized by chemical analysis, FT-IR spectroscopy and by surface area measurement (BET). The samples were then evaluated as burning rate catalyst in a typical composite propellant formulation based on HTPB binder, ammonium perchlorate and aluminum. The obtained surface area values are very close to those informed by the catalyst suppliers. The propellant processing as well as its mechanical properties were not substantially affected by the type of catalyst. Some copper chromite catalysts caused an increase in the propellant burning rate in comparison to the iron oxide catalyst. The results show that in addition to the surface area, other parameters like chemical composition, crystalline structure and the presence of impurities might be affecting the catalyst performance. All evaluated copper chromite samples may be used as burning rate catalyst in composite solid propellant formulations, with slight advantages for the SX14, Cu-0202P and Cu-1800P samples, which led to the highest burning rate propellants.

Abstract: Thermal aging of hydroxy-terminated polybutadiene (HTPB) stabilized with 2,6-di(tert-butyl)hydroxytoluene (BHT) was carried out at 60ºC from 1 to 11 weeks. Samples of 200 mL were stored in sealed 500-mL Erlenmeyer flasks under atmospheric pressure or vacuum and periodically withdrawn for physical and chemical analysis, infrared spectroscopy characterization and measurement of HTPB/IPDI (isophorone diisocyanate) reactivity, expressed as pot life. Mechanical properties of the cured polyurethane, prepared from aged HTPB, were assayed by uniaxial tension tests. Despite the unchanged chemical structure, an increase in HTPB/IPDI binder reactivity was observed, being correlated with BHT depletion measured as color change (yellowing). Aging of HTPB showed no interference on mechanical properties of the cured polyurethane.

Abstract: Synthesis and characterization of energetic ABA-type thermoplastic elastomers for propellant formulations has been carried out. Following the working plan elaborated, the synthesis and characterization of Poly 3-bromomethyl-3-methyl oxetane (PolyBrMMO), Poly 3- azidomethyl-3-methyl oxetane (PolyAMMO), Poly 3,3-bis-azidomethyl oxetane (PolyBAMO) and Copolymer PolyBAMO/AMMO (by TDI end capping) has been successfully performed. The thermoplastic elastomers (TPEs) were synthesized using the chain elongation process PolyAMMO, GAP and PolyBAMO by diisocyanates. In this method 2.4-toluene diisocyanate (TDI) is used to link block A (hardandmono-functional)) to B (soft and di-functional). For the hard A-block we used PolyBAMO and for the soft B-block we used PolyAMMO or GAP. This is ajoint project set up, someyears ago, between the Chemistry Division of the Institute of Aeronautics and Space (IAE) - subordinated to the Brazilian Ministry of Defense - and the Fraunhofer Institut Chemische Technologie (ICT), in Germany. The products were characterized by different techniques as IR- and (1H, 13C) NMR spectroscopies, elemental and thermal analyses. New methodologies based on FT-IR analysis have been developed as an alternative for the determination of the molecular weight and CHNO content of the energetic polymers.