Maximizing Interlaminar Fracture Toughness in Bidirectional GFRP through Controlled CNT Heterogeneous Toughening.

"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect.

Tailored Out-of-Oven Energy Efficient Manufacturing of High-Performance Composites with Two-Stage Self-Regulating Heating via a Double Positive Temperature Coefficient Effect.

The needs for sustainable development and energy efficient manufacturing are crucial in the development of future composite materials. Out-of-oven (OoO) curing of fiber-reinforced composites based on smart conductive polymers reduces energy consumption and self-regulates the heating temperature with enhanced safety in manufacturing, presenting an excellent example of such energy efficient approaches. However, achieving the desired curing processes, especially for high-performance systems where two-stage curing is often required, remains a great challenge. In this study, a ternary system consisting of graphene nanoplatelets/HDPE/PVDF was developed, with a double positive temperature coefficient (PTC) effect achieved to fulfill stable self-regulating heating at two temperatures (120 and 150 °C). Systematic studies on both single and double PTC effects were performed, with morphological analysis to understand their pyroresistive behaviors. Compared to the oven curing process, up to 97% reduction in the energy consumption was achieved by the ternary system, while comparable thermal and mechanical properties were obtained in the carbon fiber/epoxy laminates. This work presents a new route to achieve OoO curing with two-stage self-regulating heating, which can be utilized in many high-performance composite applications.