Study On Thermoplastic Elastomers For Gun Propellant

High energy, high strength gun propellant with elastomer, nitrate ester and high energetic oxidizer is the important aspect in the field of gun propellant, and the elastomer binder as the main component is the crucial research part. In this paper, upon the understanding of nitrate ester plasticized PEG(polyethylene glycol) elastomer in NEPE propellant, nitrate ester plasticized thermoplastic elastomer (PEG-TPE) for gun propellant binder are synthesized according to the strength and processing demand of gun propellant, and the properties of PEG-TPEs are studied. A novel type of interpenetrating network polymer, that is P(MMA-EA)/PEG-TPE, is synthesized. GAP based energetic thermoplastic elastomer is also synthesized. The main work as follows:For improving the strength of gun propellant with elastomer binder, a thermoplastic polyurethane elastomer is synthesized by lower molecular weight PEG as soft segment, which is different from higher molecular weight PEG in rocket propellant,4,4'-diphenylmethane diisocyanate (MDI) and ethylene glycol as hard segments. DSC, FTIR and DMA are applied to characterize the synthesized elastomers, the results show that the elastomers have structure characteristic of polyurethane structure, the elastomer tensile stress(σ_b) is 3.75MPa, elongation at break(ε_b) is 469% when hard segment is 50% in weight and the molar ratio of-NCO to-OH (R) is 1, the microstructure is homogeneous in SEM photographs.PMMA/PEG-TPE thermoplastic elastomer is synthesized by sequence interpenetrating technique to enhance the tensile stress of PEG-TPE. Theσ_b andε_b of PMMA/PEG-TPE(60/40, mass ratio, same as follows) are 24.2MPa and 4.6% whereas theσ_b andε_b of PEG-TPE 3.75MPa and 469%, showing that PMMA/PEG-TPE is a type of strong but brittle binder. The DMA analysis showed that PMMA/PEG-TPE have two individual glass-transition temperature (Tg), the lower Tg and the higher Tg are corresponding to those of PEG-TPE's soft segment and PMMA's respectively.The semi-interpenetrating polymer network of crosslinked-PMMA/PEG-TPE is synthesized using EGDMA as the crosslinking agent of PMMA, in order to improving the interpenetrating degree of PMMA and PEG-TPE polymer networks. The DMA testing shows that the crosslinked-PMMA/PEG-TPE (10/90) owns only one glass transition temperature, two glass transition temperatures of crosslinked-PMMA/PEG-TPE (30/70,50/50) shift towards to the center zone, implying the enhancement of the chains interpenetration. The ab and eb of crosslinked-PMMA/PEG-TPE(20/80) are 12.7MPa and 951%, while theσ_b andε_b of PMMA/PEEG-TPE are 6.32MPa and 450%, showing the optimization of tensile stress and toughness for crosslinked-PMMA/PEG-TPE.P(MMA/EA)/PEG-TPE interpenetrating polymer networks were synthesized by PEG-TPE and copolymer P(MMA/EA) of methyl methylacrylate and ethyl acrylate, considering that the crosslinked-PMMA/PEG-TPE is not suitable to the extrusion of gun propellant. The DMA testing shows that the P(MMA/EA)/PEG-TPE (10/90,30/70) have only one glass transition temperature. Theσ_b andε_b of P(MMA/EA)/PEG-TPE(10/90) are 14MPa and 412%, being a type of strong and tough binder and having the positive synergistic effect of mechanical properties. PEG-TPE and P(MMA/EA) can be dissolved for tested solvents, while P(MMA/EA)/PEG-TPE could only be swollen in tested solvents. The phase size contracts and the morphology is flexible from SEM photos. Thus, P(MMA/EA)/PEG-TPE is considered as a type of interpenetrating polymer networks with physical entanglement.An energetic thermoplastic elastomer (GAP-ETPE) was synthesized by melt-prepolymerization, using glycidyl azide prepolymer (GAP) as soft segments, MDI and 1,4-butanediol as hard segments for the purpose of higher energy gun propellants. The molar ratio of -NCO to -OH, hard segment content and mechanical properties, and dynamic mechanical properties are studied. Theσ_b andε_b of GAP-ETPE are 6.12MPa and 71%, when hard segment is 40% in weight and the R is 0.98. After the GAP-ETPE are plasticized by BDNPE/A, itsσ_b andε_b are 4.92MPa and 35%, respectively.A preliminary study is carried out that the pervaporation method is used to evaluate the migration properties of water, ethanol and DBP through PEG-TPE and P(MMA/EA)/PEG-TPE elastomer, in the case of PEG-TPE and P(MMA/EA)/PEG-TPE using as gun propellant coating materials.