Effect of Silk Treatment on Silk/Resin Wettability
Silk is being pursued as viable alternative reinforcement to widely used glass fibers, especially for environmentally cautious industries. Although silk is known to exhibit comparable specific mechanical properties to glass fibers, only scarce commercial applications employ silk composite laminates. Foiling associated fabrication-induced defects would significantly improve silk composites' performances, and thus widen their industrial applications. One such defect is weak silk/matrix bond
... k/matrix bond induced by poor fiber/resin wettability. In this study, silk treatment effects on silk/resin wettability is investigated through contact angle measurements for different resin/silk systems with different treatments. The silk/resin affinity is used to evaluate the reinforcement/matrix bonding potential, which in turn determines the mechanical properties of the silk reinforced composites. Two silk surface treatments are explored: epichlorohydrin (ECH), methanol (MeOH), in addition to a baseline with no coating. Furthermore, three resins are investigated including a vinylester and two epoxies. Treating the silk fibers with MeOH consistently yielded an improved silk/resin affinity for all resins investigated. For instance, the complete impregnation of MeOH silk by one epoxy resin is observed to be 48% shorter compared to baseline plain silk, from 882 to 461 seconds. Furthermore, among investigated resins, the vinylester resin displayed the best silk/resin affinity for all treatments, exhibiting initial contact angles of 45.7°, 56.1°, and 51.7° for silk fibers with no sizing, ECH sizing, and MeOH sizing, respectively. Total impregnation times followed a similar trend with 21, 15, and 12 seconds, respectively. The superior affinity obtained with vinylester resin and MeOH treatment indicates the potential for an improved silk/resin bond, yielding enhanced mechanical performance for silk composites.