Wetout of Glass Fiber Tows in Structural Reaction Molding I. Capillary Action and Fiber Mobility

It is the purpose of this study to examine the wetout process of glass fiber tows in structural reaction injection molding (SRIM). Wetout means complete penetration of the glass fiber bundle by liquid, whereas permeability indicates encasement of the tows with some penetration, i.e., mold filling. In this initial study the effect of capillary action is described. An expression is derived from Poiseuille's equation which predicts that the rate of mass uptake by a bundle of fibers increases as the fourth power of the theoretical capillary radius; its relationship to D'Arcy's Law is shown. Experimentally, the predictions are confirmed. It is further shown that filament compression occurs under these conditions and that the degree of axial bundle penetration is about two orders of magnitude slower than the progression of the flow front during mold filling.