Binder selection for second generation glass fiber nonwovens and composites

In this study, the focus was on the surface treatments of thermochemically recycled glass fibers for nonwoven second-generation epoxy matrix composites. The fibre-matrix interfacial shear strength was in the core of the experimental part. The addressed research questions were the following: (i) Can sufficient interfacial properties be achieved by applying only a binder without a sizing? How does (ii) the chemical formulation or (iii) the molecular weight of the binder, and (iv) the solid content of the binder polymer affect the interfacial properties? The methodology of the study focused on interfacial fibre-matrix adhesion studies with the microbond method using an automated high-throughput microbond tester. Within the selected binders, polyurethane-based treatment resulted in the most consistent interfacial behavior independent of the amount of binder, whereas the epoxy-based binder resulted in plasticization of the interphase which the resizing diminished. Increasing the solid content
and the number average molecular weight of the binder decreased the interfacial strength which was assumed to be due to a weak interfacial layer generated by the high local concentration of comparably small molecular weight binder components at the fiber-matrix interphase.