Rhoades, G. V. (1979) The effect of the structural parameters of polyester resins on the mechanical properties of polyester moulding compounds. (PhD thesis), Kingston Polytechnic, .
Abstract
A detailed study of the effect of polyester resin structural parameters on the mechanical properties of sheet moulding compounds has been carried out. The investigation involved the synthesis and mechanical testing of a series of unsaturated polyester resins and the incorporation of these resins into sheet moulding compounds (SMC) with their subsequent testing. Two main structural parameters were varied, firstly the degree of unsaturation of the resin (i.e. maleic:phthalic ratio), and secondly the amount of diol excess added to the reaction vessel during the resin synthesis thereby varying the hydroxyl value of the resin. It was found that the properties of the resins, both structural and mechanical, were interdependent. Altering the maleic:phthalic ratio was found to effect the hydroxyl value, notch sensitivity, shrinkage, and modulus of the resin. Low resin hydroxyl values were found to give SMC with low tensile strength and low fracture toughness. Unusually high hydroxyl values enhanced the toughness but the SMC did not show the expected increase in tensile strength. Surprisingly the toughness of SMC appears insensitive to the notch sensitivity of the resins despite the relatively wide range of resins used and their range of notch sensitivities. It was concluded that debonding was the predominant mechanism by which failure occurred in these composites and that the bond strength was enhanced by the use of a matrix resin with a suitably high hydroxyl value. A high hydroxyl value being dependent on the dial excess and the maleic:phthalic ratio of the resin.
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