Synthesis and property evaluation of polyurethane systems for structural applications

Abstract

Polyurethane (PU) foams are used as an efficient material for various structural applications because newlineof their low density, low thermal conductivity and easiness in processing. In satellite launch vehicles, newlineone of the major applications of PU foams is providing thermal insulation for cryogenic fluids/ newlinepropellants and vibration dampening of electronic packages. Presently, most of the PUs used for newlinelaunch vehicles are moulded using polyether polyol which is derived from petroleum products. newlineInvestigations have already been initiated by the researchers to find out an alternate source that has newlineeconomic and environmental advantages. Based on this, castor oil derived polyester polyol is found to newlinebe more effective due to its unique structure which can be chemically modified to polyester polyol. newlineDetailed research on PU foams from castor oil based polyester polyol is required since the PU foams newlineare mainly used for performance critical structural applications in launch vehicles. newlineIn this study castor oil-based polyester Polyol (COEP) with suitable hydroxyl value was synthesised newlinethrough polycondensation route. Using this, PU foams were moulded with different isocyanate index newlineby reacting with varying concentration of 4,4and#8223;- diphenylmethane diisocyanate (MDI). Investigations newlinewere done for structure property correlations. Using Flory Rehner relationship, crosslink density was newlineevaluated and it was found that as the isocyanate index increases from 1:1 to 1:2, cross link density newlineincreased from 0.7-0.97 moles/cm 3 . The important feature of a cellular material especially PU foam is newlinethe relative density which is defined as the ratio of density of cellular solid (and#961; f ) to the density of the newlinesolid (and#961; s ) from which it is synthesised.With this in mind, variations in mechanical properties of PU newlinefoams, which are cellular materials, were investigated for varying relative density and also cell newlineanisotropy.