DMA of polyester-based polyurethane elastomers for composite rocket propellants containing different energetic plasticizers

Abstract

The aim of this work is to evaluate the effect of several types of plasticizers on the glass–rubber transition temperatures (Tg) of polyester-based polyurethane binders, using dynamic mechanical analysis (DMA). The polyester polyol commercially named Desmophen® 2200 (D2200®) has been investigated for use as binder for composite propellant applications due to its good ballistic properties and also due to its potential glass–rubber transition temperature when mixed with polar energetic plasticizers. Therefore, it is important to evaluate the behavior of D2200® with different energetic plasticizers. In the present work, this inert polar binder was mixed individually with several different plasticizers and cured with a polyisocyanate commercially named Desmodur® N3400. The plasticizers used were: nitrate ester methyl trimethylol ethane trinitrate (TMETN), N-(n-butyl)-N-(2-nitroxyethyl) nitramine (Bu-NENA), bis-(2,2-dinitropropyl) formal and bis-(2,2-dinitropropyl) acetal mix 1:1 (BDNPF-A), nearly monodispersed low molar mass azido-terminated glycidyl azide polymer (GAP-A), ethylene glycol bis-(azidoacetate) (EGBAA) and 1,2-bis-(2-azidoethoxy) ethane (TEGDA) or BATEG, bis-azido-triethylene glycol, in an amount of 35 mass/%. The cured elastomers were characterized using torsion DMA at several frequencies, and the loss factor curves were described with exponentially modified Gaussian (EMG) distribution functions. Increasing deformation frequency in DMA increases Tg, and an apparent activation energy was correlated with plasticizer performance. The plasticizer ability to decrease Tg follows the order: TEGDA > butyl-NENA > GAP-A > EGBAA > BDNPF-A > TMETN. The ability of each energetic plasticizer could be related to its molecular structure, as well as to its molar mass and interaction possibilities with the polymer chains.