Adaptive textiles for thermal management using wool fibers

Abstract

Adaptive textiles are well recognized for responding to various environmental stimuli such as changes in humidity, temperature, pH, electrical field, solvents and light. These functions facilitate them for working as sensor, actuator, artificial muscle and functional material. Therefore, this can be classified as "Very smart textiles". The current commercial manufacturing method of developing adaptive textiles for clothing comfort utilizes phase change materials, various responsive synthetic materials, conductive materials, wearable attachment, coating application and artificial intelligent technologies which can sense and control environmental temperature and humidity in the microclimate of human body. However, this method generates high amount of carbon footprint along with processing complexity and the scientific merit of this practice is also questionable. However, up to now, it is rather hard to find publications reporting research and development using bio-based materials. Wool fibers has stimuli-responsive shape memory ability. Upon water/sweat stimulation, they undergo shape change in length and width direction, making them ideal raw materials for developing adaptive textiles using natural fibres. Wool knitwear is generally considered as winter clothing materials for keeping the body warm. An investigation into water-gradient responsive wool knitwear for developing adaptive textiles and thermoregulation ability has excellent potential to rediscover the wool biopolymer as a clothing material all over the year. This study aims to explore the thermoregulatory performance of wool-based knitwear using the water-driven shape memory effect (SME) of wool biopolymer. In this study, a knitted structure has been prepared using 100% descaled wool yarn, and their thermal management property has been examined and compared under various water gradient levels. This study presents the findings that water actuation of wool knitwear enables pore size change effect significantly impacts body thermoregulation by the clothing. Moreover, two commercially popular knitted structures, such as Single Jersey and Double Knit, have been prepared from 100% wool yarn. Their smart heat and moisture regulation behaviour due to SME have been investigated and compared to detect the fabric structural effect on SME and thermoregulation performance. This study presents the findings of SME of wool in the form of fibres, yarns, and fabrics stimulated with water using an optical camera and light microscope. It has been found that the water stimulated fabrics to exhibit 20% more area change compared to the dry sample. Moreover, the water gradient responsive, unique pore actuation behaviour of the fabrics has been noted for both structures. The thermal regulation performance of the samples at different water gradients such as 0,25,50,75 and a100 percentage of water absorption have been investigated by measuring air permeability, thermal conductivity values, water vapour transmission through the samples under different environmental temperatures and humidity and IR characterization using FLIR-IR camera and ATR-FTIR spectroscopy. The evidence suggests that SME, technical structure, and unique pore actuation ability of the fabrics plays a crucial role in improving fabric thermoregulation performance stimulated with water. The Single Jersey structure is the most suitable for maximum pore actuation, cool touch, and air permeability. Besides, in harmony with the air permeability values, the water vapour transmission for single jersey fabrics is increased significantly compared to double knit structure from the dry samples to wet samples of different water gradient for each set of ambient condition. Furthermore, Single Jersey demonstrates the lower surface temperature both in dry and wet conditions than the double knit in thermal images, indicating that the single jersey sample can provide a better radiative cooling effect than double knit samples. The quantitive analysis of the IR transmission of dry and wet samples also supports thermal images for single jersey fabric. However, the double-knit fabric shows the only better thermal property in terms of thermal conductivity measurement. These overall results illustrate that wool knitwear and a single jersey structure may offer a promising clothing material to the wearer all over the year. This material can give a similar response upon contact with body sweat/water and the humid environment. Besides, woolen knitwear is established as textiles for both hot and cold because of their superior water-actuated shape-memory performance. Herein, a robust and sustainable bio-based woolen respirator with the superior ability of cooling management are demonstrated using simple knitting and melt-blown technology. The as-prepared respirators provide excellent protection from airborne particulate along with a high level of cooling, compared with a commercial mask. Moreover, it exhibits a high rating during wear trial. This provides a new insight to develop high quality sustainable respiratory mask with an excellent cooling performance from functional biomaterials.