Manufacturing carbon nanofibers toughened polyester/glass fiber composites using vacuum assisted resin transfer molding for enhancing the mode-I delamination resistance

Polymer composite materials reinforced by continuous fibers have excellent in-plane strength but are usually weak against delamination. This paper presents an experimental study of using carbon nanofibers (CNF) to improve the interlaminar fracture properties of polyester/glass fiber composites, Surfactant-treated CNF were dispersed in polyester resin and then the CNF-resin suspension was infused to impregnate a glass fiber preform using vacuum assisted resin transfer molding (VARTM). The manufacturability of using VARTM for thick and large CNF toughened composite parts has been experimentally investigated. The influence of CNF concentration on the CNF filtration in the glass fiber preform, the resin viscosity, and the micro-void formation has been examined. By choosing appropriate manufacturing parameters, we were able to use VARTM process to infuse the surfactant-treated CNF/resin matrix into the glass fiber preform and successfully manufactured the CNF toughened polyester/glass fiber composite specimens for mode-I delamination tests. The critical energy release rates of mode-I delamination (G(IC)) were characterized for several composite specimens with 1 wt% CNF concentrations and for those with pure resin. Significant improvement in the G(IC) was consistently observed as 1 wt% CNF were added to toughen the polyester resin. Microscopy pictures showed that the fracture surfaces of the 1 wt% CNF toughened polyester/glass fiber composite samples were more complex than the fracture surfaces of regular polyester/glass fiber composites. (c) 2005 Elsevier Ltd. All rights reserved.