Effect of Binder Activation on in-Plane Capillary Flow in Multilayer Stacks of Carbon Fiber Fabrics

Binder/tackifier materials are commonly used in preforming processes to preserve the structural integrity of the preform during processing. In the following resin infusion or injection process, this additional material will influence the resin flow. While the influence on fabric permeability is thoroughly examined in scientific literature, only few studies investigate the capillary behavior. By thermal activation of the binder, the material melts and spreads across the layer’s surface or is imbibed by the rovings.

In this study, capillary rise experiments in planar direction with four different carbon fiber fabrics were performed. The tested stacks were activated at different temperature levels and compressed in a vacuum bag, one of them with additional external pressure in an autoclave. In case of no external pressure, the processing and testing conditions showed a larger influence than binder activation temperature, while autoclave-conditioned specimens showed a decreased capillary rise velocity for all levels of activation temperature. Digital microscopy images of the specimens show that molten binder can create a thin film between the layers, which prevents peripheral flow and thus forces the fluid to rise in the (angulated) capillary tubes inside the rovings.