The thermal conductivity of textiles

A review of fire performance of plant-based natural fibre reinforced polymer composites

Natural fibre from plant-based reinforced polymer composites (NFRPCs) offers an attractive solution for various applications due to their cost-effectiveness, sustainability, and favourable properties. These materials provide high strength and stiffness while remaining lightweight, which is especially advantageous in weight-sensitive applications. However, their susceptibility to high flammability poses a significant challenge for applications requiring robust fire resistance. Consequently, researchers and engineers face the primary task of enhancing flame retardancy and thermal stability in NFRPCs. This paper provides a comprehensive review of the flammability and flame retardancy aspects of NFRPCs, delving into critical elements such as modification methods, the interfacial bond between natural fibres and the polymer matrix, fibre type, loading ratio, fibre orientation, polymer type, and composite structure. Understanding these factors is crucial for improving material fire resistance. The paper explores various flame-retardant strategies for NFRPCs, including additives, coatings, treatments, and nanomaterial hybridization. Detailed insights into mechanisms and characterization techniques related to thermal and flame retardancy are provided, covering aspects like thermal degradation, char formation, gas-phase reactions, fire testing methods, universally accepted standards, and specific flame-retardant requirements for NFRPCs in diverse applications such as automotive, aerospace, marine, and civil construction. The discussion on future directions emphasizes the development of innovative flame-retardant materials, improving composite design and fabrication improvements, and assessing fire performance and environmental impact.

Exploring keratin composition variability for sustainable thermal insulator design

In pursuing sustainable thermal insulation solutions, this study explores the integration of human hair and feather keratin with alginate. The aim is to assess its potential in thermal insulation materials, focusing on the resultant composites' thermal and mechanical characteristics. The investigation uncovers that the type and proportion of keratin significantly influence the composites' porosity and thermal conductivity. Specifically, higher feather keratin content is associated with lesser sulfur and reduced crosslinking due to shorter amino acids, leading to increased porosity and pore sizes. This, in turn, results in a decrease in β-structured hydrogen bond networks, raising non-ordered protein structures and diminishing thermal conductivity from 0.044 W/(m·K) for pure alginate matrices to between 0.033 and 0.038 W/(m·K) for keratin-alginate composites, contingent upon the specific ratio of feather to hair keratin used. Mechanical evaluations further indicate that composites with a higher ratio of hair keratin exhibit an enhanced compressive modulus, ranging from 60 to 77 kPa, demonstrating the potential for tailored mechanical properties to suit various applications. The research underscores the critical role of sulfur content and the crosslinking index within keratin's structures, significantly impacting the thermal and mechanical properties of the matrices. The findings position keratin-based composites as environmentally friendly alternatives to traditional insulation materials.

Thermoconductive, Moisture-Permeable, and Superhydrophobic Nanofibrous Membranes with Interpenetrated Boron Nitride Network for Personal Cooling Fabrics

Space cooling occupies a large portion of total building energy consumption, aggravating the energy crisis and restricting human sustainable development, thus an efficient and energy-saving personal cooling technology is in high demand. Recently, thermally conductive fillers, such as boron nitride (BN), are usually enriched to fibrous materials to construct thermal management textiles. However, these fabrication processes are complex and time-consuming, and the resultant materials fail to transmit moisture and resist liquid water. Herein, we develop a facile and scalable methodology to construct highly thermoconductive breathable superhydrophobic nanofibrous membranes to enhance the thermal management of textiles for personal cooling. The strategy causes boron nitride (BN) to be linked with each other along nanofibers, and thus the membranes contain well interpenetrated BN network and remain porous structure simultaneously, improving their thermal conductivity without sacrificing the moisture permeability. In addition, the membranes possess good resistance to water penetration and intriguing superhydrophobicity due to the synergistic effect of the hydrophobic polymeric matrix and improved roughness. As a consequence, the resultant membranes demonstrate outstanding hybrid active-passive cooling performance with ultrahigh in-plane thermal conductivity of 17.9 W m^-1 K^-1, cross-plane thermal conductivity of 0.29 W m^-1 K^-1, and high water vapor transmission (WVT) rate of 11.6 kg m^-2 day^-1, as well as excellent water repellency with water contact angle of 153° and high hydrostatic pressure of 32 kPa, indicating promising utility for the next generation of cooling fabrics.

Theoretical and Experimental Studies on Thermal Properties of Polyester Nonwoven Fibrous Material

Polyester nonwoven fibrous material is widely used in construction and automobile industries for thermal insulation purposes. It is worthy and meaningful to understand the effect of structural parameters on the thermal property. Fiber orientation, as one of the most vital parameters, has a significant effect on thermal property. However, there has been little quantitative analysis focusing on this aspect. This paper theoretically and experimentally analyzes the thermal conductivity of samples with varying fiber orientation. Existing models were selected to predict the thermal conductivity of polyester nonwoven samples. Two different apparatus were applied to carry out the experimental measurements. The relative differences between the predicted and measured results were compared. One commonly used model was modified for accurate prediction. It was shown that some existing models under- or overestimate the thermal conductivity compared to the measured values. The results indicate that the modified model can accurately predict the thermal conductivity of polyester nonwoven materials within a 0.2% relative difference.

Thermal Textile Pixels: The Characterisation of Temporal and Spatial Thermal Development

This study introduces the concept of a thermal textile pixel, a spatially and temporally defined textile structure that shows spatial and temporal thermal contrast and can be used in the context of thermal communication. A study was performed investigating (a) in-plane and (b) out-of-plane thermal signal behaviour for knitted structures made of three different fibre types; namely, polyamide, wool, and metal containing Shieldex yarn, and two different knitting structures: plain knit and terry knit. The model thermal source was a Peltier element. For (a), a thermography set-up was used to monitor the spatial development of thermal contrast, and for (b), an arrangement with thermocouple measuring temperature development over time. Results show that the use of conductive materials such as Shieldex is unnecessary for the plain knit if only heating is required, whereas such use significantly improves performance for the terry knit structures. The findings demonstrate that the textile pixel is able to spatially and temporally focus thermal signals, thereby making it viable for use as an interface for thermal communication devices. Having well-defined thermal textile pixels opens up potential for the development of matrices for more complex information conveyance.

Thermal Conductivity of Protein-Based Materials: A Review

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical residues or brittleness. With the fast development of cutting-edge flexible materials and bioelectronics processing technologies, the market for biocompatible materials with extremely high or low thermal conductivity is growing rapidly. The thermal conductivity of protein films, which is usually on the order of 0.1 W/m·K, can be rather tunable as the value for stretched protein fibers can be substantially larger, outperforming that of many synthetic polymer materials. These findings indicate that the thermal conductivity and the heat transfer direction of protein-based materials can be finely controlled by manipulating their nano-scale structures. This review will focus on the structure of different fibrous proteins, such as silks, collagen and keratin, summarizing factors that can influence the thermal conductivity of protein-based materials and the different experimental methods used to measure their heat transfer properties.

Effects of fabric thickness and material on apparent 'wet' conductive thermal resistance of knitted fabric 'skin' on sweating manikins

Currently, no published standard and research work have addressed the basic requirements on knitted fabric 'skin' on sweating manikins. In this study, we performed 252 experiments to investigate the influence of fabric thickness and material on the apparent 'wet' conductive (or effective) thermal resistance of the fabric 'skin' using a 'Newton' manikin. Four types of cotton fabric 'skin' (fabric thickness: 0.38, 0.54, 0.92 and 1.43mm) and three types of polyester fabric 'skin' (fabric thickness: 0.41, 0.54 and 1.0mm) were selected and their 'wet' conductive thermal resistance was determined. Empirical equations were also developed for each fabric 'skin' to predict wet fabric 'skin' surface temperatures. It was found that both fabric thickness and material significantly affected the apparent 'wet' conductive thermal resistance. Clothing total evaporative resistance determined using thin fabric 'skin' (e.g., CO1, CO2) was normally lower than that determined using thick fabric 'skin' (e.g., CO4). Besides, synthetic fabric 'skin' tended to have a larger apparent 'wet' conductive thermal resistance than the cotton fabric 'skin' due to a smaller amount of moisture contained. Hence, there is a great need to standardize the fabric 'skin' to eliminate the influence of fabric 'skin' on the measurement of clothing evaporative resistance by means of a sweating manikin.

Radiative human body cooling by nanoporous polyethylene textile

Thermal management through personal heating and cooling is a strategy by which to expand indoor temperature setpoint range for large energy saving. We show that nanoporous polyethylene (nanoPE) is transparent to mid-infrared human body radiation but opaque to visible light because of the pore size distribution (50 to 1000 nanometers). We processed the material to develop a textile that promotes effective radiative cooling while still having sufficient air permeability, water-wicking rate, and mechanical strength for wearability. We developed a device to simulate skin temperature that shows temperatures 2.7° and 2.0°C lower when covered with nanoPE cloth and with processed nanoPE cloth, respectively, than when covered with cotton. Our processed nanoPE is an effective and scalable textile for personal thermal management.

A Facile Approach to Evaluate Thermal Insulation Performance of Paper Cups

Paper cups are ubiquitous in daily life for serving water, soup, coffee, tea, and milk due to their convenience, biodegradability, recyclability, and sustainability. The thermal insulation performance of paper cups is of significance because they are used to supply hot food or drinks. Using an effective thermal conductivity to accurately evaluate the thermal insulation performance of paper cups is complex due to the inclusion of complicated components and a multilayer structure. Moreover, an effective thermal conductivity is unsuitable for evaluating thermal insulation performance of paper cups in the case of fluctuating temperature. In this work, we propose a facile approach to precisely analyze the thermal insulation performance of paper cups in a particular range of temperature by using an evaluation model based on the MISO (Multiple-Input Single-Output) technical theory, which includes a characterization parameter (temperature factor) and a measurement apparatus. A series of experiments was conducted according to this evaluation model, and the results show that this evaluation model enables accurate characterization of the thermal insulation performance of paper cups and provides an efficient theoretical basis for selecting paper materials for paper cups.

New secrets of spider silk: exceptionally high thermal conductivity and its abnormal change under stretching

Two new significant discoveries are reported: i) the dragline silk of N. clavipes spider has an exceptionally high thermal conductivity: up to 416 W/m·K that beats most materials; ii) contrary to normal materials, its thermal conductivity increases with strain (19% increase under ∼20% strain). These new findings will revolutionize the design of polymer fibers to increase their thermal conductivity by orders of magnitude.