Thermal Degradation Studies of a Polyurethane Propellant Binder

Abstract

The thermal oxidative aging of a crosslinked hydroxy-terminated polybutadiene (HTPB)/ isophorone diisocyanate (IPDI) based polyurethane rubber, used as a polymeric binder in solid propellant grain, was investigated at temperatures ffom 25°C to 125°C. The changes in tensile elongation, polymer network properties and chain dynamics, mechanical hardening and density were determined with a range of techniques including modulus profiling, solvent swelling, NMR relaxation and Oz permeability measurements. We critically evaluated the Arrhenius methodology that is commonly used with a linear extrapolation of high temperature aging data using extensive data superposition ahd highly sensitive oxygen consumption experiments. The effects of other constituents in the propellant formulation on aging were also investigated. We conclude that crosslinking is the dominant process at higher temperatures and that the degradation involves only limited hardening in the bulk of the material. Significant curvature in the Arrhenius diagram of the oxidation rates was observed. This is similar to results for other rubber materials

Diffusion of plasticizer in a solid propellant based on hydroxyl-terminated polybutadiene

“…This is probably caused by the polymeric matrix, which is responsible for the mechanical properties of the propellant, that is already formed and has the usual trend of hardening by loss of plasticizer and oxidation [2,[14][15] .…”

“…This phenomenon affects the mechanical properties such as hardness, elongation at break, maximum stress and others [8][9][10][11][12][13][14][15][16] . The main mechanisms that govern aging are attributed to loss of plasticizer by diffusion and oxidation of the polymeric matrix [1,12] .…”

Condition monitoring of a thermally aged hydroxy‐terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) elastomer by nuclear magnetic resonance cross‐polarization recovery times

“…A sample containing no antioxidant oxidizes ϳ3 orders of magnitude faster than the stabilized material confirming the action of the antioxidant. 1 The resulting resin was thermally cured for 1 week at 65°C to obtain sheets of 2 mm thickness using Tefloncoated molds to allow for removal after curing. The sheets were cut into strips 6 mm wide and 150 mm long.…”

“…1 Because of considerable unsaturation of their polymer structure, they are highly susceptible to oxidation. Oxidation of the binder is associated with a loss in its mechanical properties that can adversely affect the performance of the propellant.…”

“…A time-temperature superposition study of tensile-elongation at break has been completed for a pure HTPB/isophorone diisocyanate (IPDI) elastomer. 1 To predict the performance of a propellant, however, one must understand how the binder ages when incorporated in the propellant. The binder comprises ϳ10% of the propellant by weight.…”