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Some structural parameters, such as tortuosity, viscous and thermal characteristic lengths, are difficult to obtain through direct measurements. Existing indirect methods, i.e. acoustical method, make it possible to estimate these parameters. This paper presents an application of acoustical inversion methods for estimating structural parameters of polyester nonwoven materials. A four-microphone impedance tube was used to measure sound reflection and transmission coefficients. The inversion methods used in this research are least square and Bayesian approaches. The least square method was achieved via Nelder-Mead algorithm. The Bayesian inversion process was conducted with Metropolis-Hastings algorithm and maximum a posteriori. Inversed parameters from two methods as well as front and back sides of nonwoven fabric were compared. Moreover, inversed porosity and airflow resistivity were compared with measured values. The results show that the least square and Bayesian methods has a good agreement. Estimated parameters from Bayesian method were selected for further analysis. A sizable differences on thermal characteristic length were found by comparing the values from two sides, while the differences are relatively small for other parameters. It is also found that the inversed porosity, tortuosity are reasonable. The results suggest that the acoustical inversion methods can be used to accurately characterize polyester fibrous materials. [ABSTRACT FROM AUTHOR]

In this work, a new approach to apply silica aerogel into nonwoven textiles by using laser engraving and laminating technique was proposed. Thermal performance of the prepared composites were characterized in terms of infrared thermal images, maximum heat flux and heat retention ability. Results showed that in comparison to regular composites the air pockets lead to 0.5°C lower temperature on the fabric surface, and the aerogel-encapsulated structure results in a decrease of 1.04-1.47°C in the fabric temperature. It was also noticed the aerogel-encapsulated composites have slightly lower q value and a thermal feeling, however, samples with air pockets showed increased value in q, and the increasing rate was strongly related to the composites thickness. Composites with air pockets exhibited better ability to retain heat, the highest heat retention ability was observed from composites with aerogel-encapsulated structure. [ABSTRACT FROM AUTHOR]

This work deals with the study of acoustic performance of struto nonwovens and their relation to fabric air permeability. In order to achieve the objective of the research, sound absorption coefficient of struto nonwovens was determined via impedance tube method, the average value of sound absorption coefficient ( α̅) was calculated. Air permeability of struto nonwovens was examined by using FX3300 Textech Air Permeability Tester. Results showed that struto nonwoven exhibited good absorption ability at frequency bands 3000-6400 Hz while it was ineffective for frequency lower than 3000 Hz. Struto nonwovens with high GSM and fabric thickness showed better acoustic performance and lower air permeability. It was observed that α̅ was inversely proportional to air permeability, with correlation coefficient 0.95. It was concluded that air permeability can be used as a criterion of sound absorption behavior of struto nonwovens. A lower air permeability suggests a better sound absorption performance for struto nonwoven fabrics. [ABSTRACT FROM AUTHOR]

In this study, nanofiber web was laminated onto nonwoven fabric and silica aerogels were applied between these two layers during laminating process. The transport properties of the obtained fabrics were examined in terms of air permeability, water vapor permeability as well as thermal performance. Especially, the effect of aerogel areal density and thermal adhesive on thermal insulation properties of layered fabrics were investigated and analyzed. It was observed that air permeability and water vapor permeability of these layered fabrics were determined by nanofiber web and nonwoven substrate respectively, aerogels present in this layered structure showed limited influence on air permeability and insignificant effect on water vapor permeability. Results also indicated that thermal resistance of layered fabrics was directly proportional to areal density of aerogel with a correlation coefficient 0.91. The use of adhesive in textile structure would significantly reduce the thermal insulation performance. A series model was considered for thermal resistance of layered fabrics, and the results showed a good agreement between theoretical model and experimental values. [ABSTRACT FROM AUTHOR]