Mechanical Properties of Unsaturated Polyester-Isocyanate Hybrid Polymer Network and Its E-Glass Fiber-reinforced Composite

Abstract

In this research, a conventional propylene glycol-based unsaturated polyester is synthesized and modified with diphenylmethane-4,40-diisocyanate (MDI), which leads to the formation of a hybrid polymer network (HPN). The effect of this modification on the mechanical properties is studied experimentally. The optimum molar ratio of MDI to unsaturated polyester which had the highest toughness is found to be NCO/OH 1/4 0.45 using compression testing. In the second stage of the research, E-glass-reinforced unidirectional composites are produced with pure unsaturated polyester (UP) and an optimum amount of HPN. Tensile and bending tests are applied to the neat unsaturated polyester, the HPN resins, and to the composites prepared from these resin matrices. For pure polyester, the tensile strength at rupture is 27 MPa with a Young’s modulus of 920 MPa, whereas the tensile strength and the modulus of HPN are 42 and 860 MPa, respectively. In unsaturated polyester composites, a tensile strength of 500 MPa and a Young’s modulus of 27,800 MPa are obtained while in HPN composites, the tensile strength and the modulus are 685 and 26,300 MPa, respectively. Hence, an increase in toughness is achieved for both resin matrices and composites by the use of MDI. The bending strength and the modulus of elasticity are 60.7 and 2464 MPa for UP resin, and 65.7 and 2871 MPa for the HPN resin. The corresponding values for UP composites are 858 MPa and 29.8 GPa, and are 1141 MPa and 37.5 GPa, respectively for the HPN composite.