Wearable heaters are highly desirable for low-temperature environments. However, the fundamental challenge in achieving such devices is to design electric-heating membranes with flexible, breathable, and stretchable properties.
Study: Large-Scale Preparation of Micro–Nanofibrous and Fluffy Propylene-Based Elastomer/Polyurethane@Graphene Nanoplatelet Membranes with Breathable and Flexible Characteristics for Wearable Stretchy Heaters. Image Credit: s_maria/Shutterstock.com
A study published in ACS Applied Materials and Interfaces aimed to achieve an electric heating membrane with a nanofibrous fluffy texture and excellent electric-heating features. Here, an electric heating membrane was fabricated by coating a melt-blown propylene-based elastomer (PBE) with polyurethane (PU) and graphene nanoplatelet films via an easy, cost-effective, and large-scale method involving a coating-compression cyclic process.
The PU and graphene nanoplatelet film-coated PBE membranes were analyzed using scanning electron microscopy (SEM). The images revealed the uniform deposition of PU and graphene nanoplatelet films on the micronanofiber surface of PBE, forming interconnected conducting channels.
The temperature increased to 69.7 degrees Celsius when a voltage of 36 volts was applied across the PU and graphene nanoplatelet film-coated PBE membranes, indicating outstanding electric-heating features. Furthermore, the coating–compression cycles regulated the porosity of the prepared electric heating membrane.
Due to the conducting channels, the PU and graphene nanoplatelet film-coated PBE membranes exhibited favorable properties, such as regulated air permeability between 212 and 60.2 millimeters per second, 85.5% elastic recovery rate, and 53.8 softness score.
The study presents PU and graphene nanoplatelet film-coated PBE membranes as promising materials for electric-heating fabrics. Moreover, the coating–compression cyclic preparation process enables facile scale-up for industrial manufacturing.
Graphene Nanoplatelets for Wearable Devices
Electric heating membranes with light, soft, and thin properties and built-in heat sources are highly desirable in low-temperature environments to prevent dangerous effects on human health. These electric heating membranes convert electrical energy into heat, thus aiding personal thermal management.
Although such electric-heating-membrane-based wearable devices have been investigated, the insufficient flexibility and poor air permeability of conventional membranes limit their application.
Graphene nanoplatelets are two-dimensional (2D) carbon-structured materials with single or multilayer graphite planes and attractive characteristics, including high electrical conductivity, modulus, strength, thermal conductivity, and specific surface area.
Recently, functionalization based on graphene nanoplatelets was reported as a promising procedure for imparting electrical conductivity to industrially produced smart textiles. This method is adaptable to several commercially available materials, such as cotton and polyesters, since graphene nanoplatelets are produced in large amounts, suitable for the textile market.
Although graphene nanoplatelets have good potential for smart fabric applications, their primary limitation is the difficulty in binding graphene nanoplatelets to textiles and ensuring washing stability and durability. As a result, smart solutions for effectively binding graphene nanoplatelets to fabrics are required to widen their potential in wearable and textile electronics.
PU and Graphene Nanoplatelets for Wearable Devices
Several carbon nanomaterial-based micro-nanofibrous membranes have been developed using various advanced methods, such as electrospinning, melt-blown processes, and solution blow spinning. These membranes are porous and facilitate the penetration of liquids and gases.
Thermoplastic elastomers, including PU, styrene-ethylene/butylene–styrene copolymer, and PBE, have been used to prepare stretchable micro-nanofibrous membranes via the meltdown process. However, these polymers exhibit poor compatibility with inorganic graphene.
Although the coating process is a cheap and facile approach for adhering graphene onto fibers, manufacturing electric heating membranes with flexible, breathable, and elastic properties using this method remains practically unexplored.
In the present study, an easy method for the large-scale production of electric-heating membranes was reported by coating PBE micro-nanofibrous membranes with PU and graphene nanoplatelet films. The prepared electric-heating membranes were analyzed using SEM, and the resulting images revealed uniform distribution of PU and graphene nanoplatelets on PBE micro-nanofibers.
These electric-heating membranes had good air permeability, outstanding heating performance, and excellent softness, suggesting the potential of the coating–compression cyclic process for fabricating the desired elastic micro-nanofibrous membranes for potential use in wearable electric heating fabrics.
On the other hand, a slight slope in the stress-strain curves implies high elasticity and easy deformability. Additionally, the electrical resistance of designed electric-heating membranes has decreased from 2569.5 to 278.9 ohms per 5 centimeters with increasing coating, indicating an excellent electric-heating feature.
In conclusion, PBE membranes deposited with PU and graphene nanoplatelet films were presented as electric-heating membranes prepared via facile and scalable coating–compression cycles. The SEM characterization confirmed the uniform filling of gaps between the PBE micro-nanofibers by PU and the graphene nanoplatelets, regulated by the number of coatings–compression cycles to control the solid filling per unit mass.
In this study, the researchers present PU and graphene nanoplatelets film-coated PBE membranes as promising materials for application as heat sources in fabrics, such as cold-proof clothing, motorcycle riding clothing, and clothing for the healthcare sector.
Zhang, H., et al. (2022) Large-Scale Preparation of Micro–Nanofibrous and Fluffy Propylene-Based Elastomer/Polyurethane@Graphene Nanoplatelet Membranes with Breathable and Flexible Characteristics for Wearable Stretchy Heaters. ACS Applied Materials and Interfaces. https://doi.org/10.1021/acsami.2c15449