Aerogel Embedded High-performance Fibrous Materials

Vlákenné materiály jsou široce používány jako tepelné izolátory v různých aplikacích pro úsporu energie. Jejich tepelně izolační vlastnosti jsou omezeny, pokud je tloušťka materiálu omezena na několik milimetrů. V dnešní době je stále častěji kladen důraz na vývoj vysoce výkonných tepelně izolačních materiálů pro úsporu energie, zvýšení pohodlí, snížení nákladů a složitosti těchto systémů. Aerogel, který vykazuje vynikající tepelnou izolaci s extrémně nízkou tepelnou vodivostí, byl shledán jedním z nejatraktivnějších tepelně izolačních materiálů. Cílem této práce bylo vyvinout vysoce výkonný aerogel spojený s vlákennými materiály pro tepelnou izolaci a prověřit jeho výkon.Vrstvená nanovlákenná síťovina /aerogel /netkané materiály byly připraveny použitím laminovací metody s práškem s nízkým bodem tání jako tepelně spojujícím materiálem. Byl zkoumán účinek aerogelu a tepelného lepidla na tepelnou izolaci a propustnost vzduchu. V úvahu byl vzat sériový model pro tepelný odpor, byly porovnány a analyzovány teoretické předpoklady a naměřené výsledky. Bylo navrženo, že by měly být vzaty v úvahu nové techniky kombinující aerogel s vysoce porézními textiliemi s menším využitím pojivových materiálů.Nový aerogel obalený vlákenným materiálem bez použití jakéhokoliv pojivového materiálu, který spojuje částice aerogelu, byl vyvinut pomocí techniky laserového gravírování a laminovací metody. Pro měření tepelného výkonu byly použity termální kamera, zařízení Alambeta a KES-FT-II Thermolab. Byla provedena tlaková zkouška ke zkoumání kompresního zotavení, které určuje udržitelnost tepelné izolace. Dále bylo použito laboratorně vyráběné dynamické zařízení pro přenos tepla pro zjištění konvektivního tepelného chování těchto vícevrstvých materiálů, jakož i netkaných textilií obalených aerogelem, při různých rychlostech proudění vzduchu a zahřívání. Byly porovnány teplotní křivky v reálném čase z měření předehřátých podmínek. Byly vypočteny a posouzeny hodnoty teplotních rozdílů a konvektivního součinitele přestupu tepla za podmínek kontinuálního ohřevu. Zjištění by mohla přispět k novému vývoji pružných vysoce výkonných textilních materiálů se zabudovaným aerogelem pro průmyslové i oděvní aplikace.Pružné polyuretanové a polyvinylidenfluoridové nanoporézní membrány kombinované s aerogelem na bázi oxidu křemičitého byly připraveny elektrostatickým zvlákňováním. Tepelné vlastnosti a propustnost vzduchu byly hodnoceny a porovnávány. Byl učiněn závěr, že nanovlákna s aerogelem jsou vhodná pro tepelnou izolaci za chladného počasí. Tepelně izolační nosiče obsahující nanovlákna by mohly případně snížit hmotnost a objem tepelně ochranného oblečení.Pro provedení a vyhodnocování všech statistických výsledků byl v této práci použit statistický a analytický software Matlab_R2017a. Dosažené výsledky jsou významné a mohou být použity pro další studium v oblasti tepelných vlastností vysoko pevnostních vlákenných materiálů s aerogelem, které mohou být využity například pro tepelnou izolaci budov či ochranné oděvy.Fibrous materials are widely used as thermal insulators in various applications. Their thermal insulation ability is restricted when the material thickness is limited to few milli-meters. Nowadays, development of high-performance insulation materials to save energy consumption, increase comfort, decrease cost and complexity has drawn increasing attention. Silica aerogel, exhibiting superior thermal insulation performance with extremely low thermal conductivity, has been well acknowledged as one of the most attractive thermal insulating materials. The objective of this thesis was to develop aerogel embedded high-performance fibrous materials for thermal insulation application and investigate their performance.Layered nanofibrous web/silica aerogel/ nonwoven materials were prepared via laminating method by using low melting powder as thermal binding material. The effect of aerogel and thermal adhesive on thermal insulation performance and air permeability was examined. A series model was considered for thermal resistance, the theoretical predicted and measured results were compared and analysed. Results revealed that novel techniques to combine silica aerogel with high porous textiles with less use of binding materials should be considered.A novel aerogel-encapsulated fibrous material without using any binding material to bond aerogel particles was developed by using laser engraving technique and laminating method. Thermo Camera, Alambeta device and KES-FT-II Thermolabo were employed to measure thermal performance. Compression test was performed to examine the compression recovery which determines the sustainability of thermal insulation ability. Moreover, a laboratory-made dynamic heat transfer device was used to figure out convective thermal behaviour of these multi-layered materials as well as aerogel treated nonwovens under different airflow velocity and heating conditions. The real-time temperature curves of different materials were compared. The temperature difference and convective heat transfer coefficient under continuous heating condition were calculated and investigated. The findings could contribute to new developments in flexible aerogel-embedded high-performance textile materials for both industrial and clothing applications.Flexible polyurethane and polyvinylidene fluoride nanoporous membranes embedded with silica aerogel were prepared by electrospinning technique. Thermal properties and air permeability were evaluated and compared. It was concluded that nanofibers embedded with aerogel are good for thermal insulation in cold weather conditions. Thermal insulation battings incorporating nanofibers could possibly decrease the weight and bulk of current thermal protective clothing.Statistical analysis software, Matlab_R2017a were used to conduct all the statistical results in this study. The findings are significant and can be used for further study in the areas of aerogel embedded high-performance fibrous materials for thermal insulation in building, industrial and protective textile fields

Thermal protection properties of aerogel-coated Kevlar woven fabrics

This paper investigated the thermal properties of aerogel-coated Kevlar fabrics under both the ambient temperature and high temperature with laser radiation. It is found that the aerogels combined with a Kevlar fabric contribute to a higher thermal insulation value. Under laser radiation with high temperature, the aerogel content plays a vital role on the surface temperature of the fabrics. At laser radiations with pixel time 330 μs, the surface temperatures of the aerogel coated Kevlar fabrics are 400-440°C lower than that of the uncoated fabric. Results also show that the fabric temperature is directly proportional to pixel time. It can be concluded that the Kevlar fabrics coated with silica aerogel provides better thermal protection under high temperature

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

Sound Absorption Properties of Natural Fibers: A Review

In recent years, in an attempt to substitute the conventional synthetic sound absorption material, natural fibers and their sound absorption properties have been increasingly studied. This is due to the fact that conventional synthetic fiber has potential health risks for human beings and significant environmental impact. In this review, existing and newly emerging natural fiber sound absorbers are summarized and highlighted in three categories: raw material, fiber assembly and composite. The sound absorption mechanism, several widely used prediction models and the popular acoustic characterization methods are presented. The comparison of sound absorption properties between some natural sound absorbers and glass fiber is conducted in two groups, i.e., thin material and thick material. It is found that many natural fibers have comparable sound absorption performance, some of them can be the ideal alternatives to glass fiber, such as kapok fiber, pineapple-leaf fiber and hemp fiber. Last, the conclusion part of this review gives an outlook regarding the promotion of the commercial use of natural fiber by means of theoretical study, efficient and environmentally friendly pretreatment and Life Cycle Assessment

Study on the sound absorption behavior of multi-component polyester nonwovens: experimental and numerical methods

This study presents an investigation of the acoustical properties of multi-component polyester nonwovens with experimental and numerical methods. Fifteen types of nonwoven samples made with staple, hollow and bi-component polyester fibers were chosen to carry out this study. The AFD300 AcoustiFlow device was employed to measure airflow resistivity. Several models were grouped in theoretical and empirical model categories and used to predict the airflow resistivity. A simple empirical model based on fiber diameter and fabric bulk density was obtained through the power-fitting method. The difference between measured and predicted airflow resistivity was analyzed. The surface impedance and sound absorption coefficient were determined by using a 45 mm Materiacustica impedance tube. Some widely used impedance models were used to predict the acoustical properties. A comparison between measured and predicted values was carried out to determine the most accurate model for multi-component polyester nonwovens. The results show that one of the Tarnow model provides the closest prediction to the measured value, with an error of 12%. The proposed power-fitted empirical model exhibits a very small error of 6.8%. It is shown that the Delany–Bazley and Miki models can accurately predict surface impedance of multi-component polyester nonwovens, but the Komatsu model is less accurate, especially at the low-frequency range. The results indicate that the Miki model is the most accurate method to predict the sound absorption coefficient, with a mean error of 8.39%

Preparation and Characterization of Electrosprayed Aerogel/Polytetrafluoroethylene Microporous Materials

This paper presents the preparation of aerogel/polytetrafluoroethylene (PTFE) microporous materials via needleless electrospray technique, by using an aqueous dispersion of polytetrafluoroethylene as the basic spinning liquid. Different contents of aerogel powders were applied to the spinning liquid for electrospraying to investigate the effect on the structural characteristics and various properties of the materials. Cross-section, surface morphology, and particle size distribution of the electrosprayed materials were examined. Surface roughness, hydrophobicity, and thermal conductivity were evaluated and discussed. The results showed that the electrosprayed aerogel/PTFE layers were compact and disordered stacking structures composed of spherical particles with a rough surface. As the aerogel content increased, the electrosprayed materials demonstrated increased surface roughness and improved surface hydrophobicity with a contact angle up to 147.88°. In addition, the successful achievement of thermal conductivity as low as 0.024 (W m−1 K−1) indicated a superior ability of the prepared aerogel/PTFE composites to prevent heat transfer. This study contributes to the field of development of aerogel/PTFE composites via electrospray technique, providing enhanced final performance for potential use as thermal and moisture barriers in textiles or electronic devices