A recent article in MRS Advances employed MXene functionalization to upcycle waste textile fabrics, such as cotton, hemp, and nylon, into wearable electronics capable of thermal regulation, strain sensing, and infrared (IR) camouflage.
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Background
The textile industry generates substantial waste due to its rapid manufacturing and consumption cycles. Textile consumption has increased from 7 to 13 kg per person annually over the past two decades, leading to overfull landfills and the release of greenhouse gases during decomposition.
Upcycling waste into higher-value products offers a multi-dimensional strategy to minimize environmental pollution and promote a circular economy. Incorporating multifunctional polymers and nanomaterials into waste textiles can impart exceptional properties such as conductivity, energy storage, and anti-microbial capabilities, making them suitable for wearable electronics.
MXenes, two-dimensional transition metal carbides, nitrides, or carbonitrides, offer excellent electrical conductivity, electrochemical capacitance, and surface activity. Thus, upcycling waste garments, fiber bits, and discarded pieces using MXene presents an attractive solution to reduce the environmental footprint of the textile industry.
Methods
MXene (Ti3C2Tx) coating dispersions were formulated using single-layer MXene sheets acquired using the minimally intensive layer delamination (MILD) method and processed for MAX phase etching. The cotton, hemp, and nylon fabric pieces, along with discarded cotton gloves, were sourced commercially.
The fabrics were hand-washed with a commercial detergent for 30 minutes and cut into 3×3 cm2 patches. Subsequently, the fabrics and discarded gloves were dip-coated by soaking separately in 5 mg/mL MXene dispersion for 10 minutes. Finally, they were dried at ~60 °C in an oven for 10 minutes. This soak-and-dry cycle was repeated to obtain 3, 6, and 9 coats.
The success of MAX phase etching into MXene was validated through X-ray diffraction (XRD) analysis. Additionally, the MXene dispersions and textiles were characterized by Fourier-transform infrared (FTIR) spectroscopy with an attenuated total reflection (ATR) accessory and Raman spectroscopy.
The microstructure of the fabrics and gloves was observed through a scanning electron microscope (SEM), and their sheet resistance (R) was derived from current-voltage measurements using a multimeter with a four-point probe accessory. Their thermal performance was investigated through IR imaging and Joule heating experiments with an input of 24 volts.
Results and Discussion
FTIR and Raman spectroscopy results demonstrated the fabrics' compatibility with MXene coatings. The abundant H-bonding functional groups in cotton, hemp, and nylon served as anchors for the MXene surface terminations.
SEM images revealed a uniform MXene coating on discrete fibers of all fabrics used. The concentration of MXene deposited on each substrate was only ~2-3 wt.% of its total mass, preserving the porous character of the fabrics. Water contact angle measurements demonstrated the water absorption ability of coated textiles.
The number of coating cycles influenced the distinct fiber morphology of all fabrics. The surface coverage of MXene improved with increasing coating cycles, resulting in fewer surface cracks. Moreover, the sheet resistance of all fabrics decreased after six coating cycles. However, it became constant beyond the 9th cycle, indicating an MXene-saturated fabric surface.
IR images of MXene-coated cotton, hemp, and nylon samples, when subjected to a 24 V electrical potential at room temperature, exhibited heat signatures at ~60 °C, ~30 °C, and ~30 °C, respectively. Additionally, this temperature increased from ambient conditions within seconds, indicating the heating capability of the coated fabrics with low power consumption. These temperatures were apparent heat signatures and might not represent the real sample temperatures.
The practical application of MXene-coated textiles was investigated on a discarded cotton glove. The MXene-coated glove with six coats exhibited varying electrical resistance with opening and closing hand movements, highlighting its applicability as a strain sensor. Moreover, it remained motion-sensitive even after a year of storage under ambient conditions.
The coated fabrics were examined for IR camouflage due to the fundamentally low IR emissivity of Ti3C2Tx MXenes. Small cotton fabric pieces with six coats of MXene effectively blocked IR signatures emanating from a beaker with silicon oil at ~50 °C and a hotplate at ~70 °C covered with aluminum foil.
The MXene-coated glove also demonstrated enhanced suppression of a gloved hand’s thermal signature, suggesting improved thermal insulation of cotton fabrics.
Conclusion
Overall, the researchers demonstrated the enhanced functionality of discarded textiles through passive dip coating in colloidal MXene dispersions. Uniform MXene coatings were obtained for both natural (cotton and hemp) and synthetic (nylon) fabrics, even at low MXene concentrations, without compromising conductivity.
The MXene-coated fabrics demonstrated significant potential for Joule heating, strain sensing, and IR camouflage applications. The researchers suggest integrating waste textiles into smart wearables to reduce costs and help mitigate the expected scarcity of textile supplies in the upcoming decades.
Journal Reference
Aldren, K., et al. (2024). MXene coating on waste textiles for wearable electronics and thermal regulation. MRS Advances. DOI: 10.1557/s43580-024-00911-
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