Hybrid Ti₃C₂T_<i>x</i> MXene and Carbon Nanotube Reinforced Epoxy Nanocomposites for Self-Sensing and Structural Health Monitoring

Herein we present the transformative effects of multiwall carbon nanotube (MWCNT)-MXene hybrid nanofillers on the mechanical, electrical, and piezoresistive properties of the resulting epoxy nanocomposites. The utilization of the MWCNT-MXene hybrids significantly improves the dispersion of fillers within the epoxy matrix, effectively eliminating the agglomeration of individual fillers and improving the stress transfer efficiency. With just 1 wt % MWCNT-MXene hybrid, we observed improvements in the Young’s modulus and the flexural modulus, which increased by 31 and 28%, respectively, when compared to neat epoxy. Furthermore, the fracture toughness of these composites was 84.5% higher than that of neat epoxy, primarily attributed to crack deflection and filler debonding mechanisms. The hybrid composites exhibited increased piezoresistive sensitivity during tensile, flexural, and fracture tests due to the creation of a percolating network of MWCNT and MXene nanoplatelets. Our findings have implications for the development of advanced hybrid materials, holding promise for applications in strain sensors and self-sensing structures

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.</p

Energy efficient out-of-oven manufacturing of natural fibre composites with integrated sensing capabilities and improved water barrier properties

Bio-based and eco-friendly materials have gained a great amount of attention, thanks to the increased awareness of sustainable development and global environments. The use of natural fibres in composites can reduce greenhouse gas emissions and the carbon footprint compared to many synthetic fibres. However, some challenges and concerns remain in natural fibre-reinforced plastics, such as the high moisture absorption and high energy consumption during their manufacturing stage. To tackle these challenges, this study developed an energy-efficient out-of-oven manufacturing method based on a conductive biopolymer nanocomposite film to fabricate natural fibre-reinforced composites with integrated multifunctionalities throughout their life cycle. The smart nanocomposite layer works as an autonomous self-regulating heating element to cure the laminates at the desired temperature without the risk of overheating. Extremely high energy efficiency has been achieved with a significantly reduced energy consumption (a 95% reduction compared with traditional oven curing), which has been attained through the direct heat conduction from the surface layer to the laminates. The embedded nanocomposite surface film on the cured laminate subsequently becomes an integrated multifunctional layer, providing integrated real-time deformation and damage sensing capabilities with enhanced water barrier properties to prolong the service life of natural fibre composites.</p

Toward self-powered sensing and thermal energy harvesting in high-performance composites via self-folded carbon nanotube honeycomb structures

The development of high-performance self-powered sensors in advanced composites addresses the increasing demands of various fields such as aerospace, wearable electronics, healthcare devices, and the Internet-of-Things. Among different energy sources, the thermoelectric (TE) effect which converts ambient temperature gradients to electric energy is of particular interest. However, challenges remain on how to increase the power output as well as how to harvest thermal energy at the out-of-plane direction in high-performance fiber-reinforced composite laminates, greatly limiting the pace of advance in this evolving field. Herein, we utilize a temperature-induced self-folding process together with continuous carbon nanotube veils to overcome these two challenges simultaneously, achieving a high TE output (21 mV and 812 nW at a temperature difference of 17 °C only) in structural composites with the capability to harvest the thermal energy from out-of-plane direction. Real-time self-powered deformation and damage sensing is achieved in fabricated composite laminates based on a thermal gradient of 17 °C only, without the need of any external power supply, opening up new areas of autonomous self-powered sensing in high-performance applications based on TE materials.</p