Effects of thermoplastic preforming binder on the properties of S2-glass fabric reinforced epoxy composites

The effect of a thermoplastic polyester binder on the thermophysical and mechanical properties of an S2-glass/epoxy-amine system was investigated. The purpose of the polymeric binder is to bond the individual fabric layers together during preforming prior to composite fabrication. This paper will address the significance of the binder chemistry, i.e., the compatibility of the binder with the matrix polymer, on the composite properties. The peel strength of preforms consolidated with various concentrations of binder was evaluated using the T-peel test. The highest peel resistance was obtained from preforms that have full coverage of the binder on the glass fabric. Further increase of the concentration of the binder does not change the peel strength. Scanning electron microscopy (SEM) on peel test fracture surfaces revealed mostly adhesive-type failure between binder and fiber. Double cantilever beam (DCB) and short beam shear (SBS) test results of the composite showed that the presence of about 2.6 wt% of the polyester binder reduces the Mode I interlaminar fracture toughness and apparent interlaminar shear strength of the S2-glass/SC-15 epoxy-amine system by about 60% and 25%, respectively. Moreover, the Tg of the matrix polymer within the interlaminar region decreases about 6°C due to the presence of the binder. The dissolution of the polyester binder within the reacting matrix resin is limited for the standard cure cycle.