Itzhak Shalev

Heat and Moisture Transfer Through Nonwoven Fabrics: Part I: Heat Transfer

A theoretical model is demonstrated that provides a reliable prediction of thermal transmission through nonwoven structures. The validity of the model is confirmed in experiments that measure the thermal conductivity of various nonwoven barrier fabrics. The model is used to characterize the relative contribution of heat transfer mechanisms to the total heat transmission. It also provides a good explanation of the roles played by fiber and fabric variables in determining the thermal insulation of nonwoven barrier materials.

Protective Fabrics: A Comparison of Laboratory Methods for Evaluating Thermal Protective Performance in Convective/Radiant Exposures

Two laboratory methods used to evaluate the ability of fabrics to provide protective insulation against high intensity thermal exposures are compared. These procedures are ASTM D4108-82, a method that uses a single laboratory gas burner as the heat source, and a more versatile method that combines two gas burners and quartz heaters to provide a different mixture of radiant and convective heat. Comparisons are based on a series of tests made on a large group of specialized fabrics that might be used in the construction of protective apparel. Among the fabrics tested are samples made with flame resistant cotton, rayon, and wool, fabrics from glass and ceramic fibers, and fabrics from polyaramids, cross-linked phenolics, modacrylics, polybenzimidazole, and stabilized acrylic fibers. Differences in materials comparisons caused by the test procedure are discussed, especially the difference made by the balance of radiant to convective energy provided by the heat sources. Correlations are made with fiber and fabric properties. Special emphasis is placed on observing the performance of alu minized samples.

Analysis of Heat Transfer Characteristits of Fabrics in an Open Flame Exposure

Experiments measured the transfer of heat through protective fabrics when the exposure is to a convective source (open flame). An instrumented calorimeter located on the opposite side of the fabric measured the heat transferred. Heat flux data were used to compute a burn protective index based on data on the tolerance of human tissue, developed by Stoll. Among the materials analyzed were fabrics made with flame-resistant cotton, rayon, and wool; fabrics from glass and ceramic fibers; and fabrics from polyaramids, novoloids, modacrylic, polybenzimidazole and stabilized acrylic fibers.

Heat and Moisture Transfer Through Nonwoven Fabrics Part II: Moisture Diffusivity

The geometric moisture diffusivity model developed by this research indicates that fiber volume fraction and shape coefficient are the most important structural parameters affecting water vapor diffusivity through nonhydrophilic nonwoven fabrics. Water vapor diffusivity decreases with increasing fiber volume fraction and decreases as the flatness of the fiber cross section increases. Although structural properties such as fiber fineness and fabric thickness affect optical porosity, their effect on water vapor diffusivity through nonhygroscopic nonwoven materials is small.

Predicting the Thermal Protective Performance of Heat-Protective Fabrics from Basic Properties

Novel experimental techniques were developed to measure changes in the weight, thickness, density, heat capacity, heat conductivity, and infrared (IR) transmission of protective fabrics occurring during a thermal protective performance (TPP) test. Comparisons are made between polybenzimidazole (PBI), aramid, a PBI/aramid blend fabric, and flame-retardant (FR) cotton fabrics in the 250 g/m 2 (7.5-oz/yd 2 ) weight range. This research analyzes changes in fabric heat transfer properties produced through mechanisms of pyrolysis, char formation, and shrinkage. Fiber character is shown to play a decisive role in determining the direction and extent of change in thermophysical properties. Retention of air volume is found to be critical to prolonged thermal protection performance. Experimental data indicate that air and fiber conduction dominate in intense exposures to a mixture of radiant and convective thermal energy; direct radiant transmission is not an important contributor to the total heat transferred in these exposures. The ability of fabrics to maintain surface fibers is thought to have significant impact in blocking convective heat transmission. The degradation behaviors of different materials are compared and related to their thermal protective performance.

Tissue Softness Evaluation by Mechanical Stylus Scanning

A mechanical stylus surface analyzer (MSSA) system and the corresponding software were used to conduct standard surface analysis procedures. The MSSA instrumentation measures surface characteristics of soft bathroom tissue products. This paper describes the applicability of MSSA and how human tactile response may be modeled through characterization of surfaces. The concepts of passive and active touch as related to human perceived softness are reviewed. In particular, parameters pertinent to these kinds of tactile exploration are mentioned, as well as how they can be used to build a better model of human tactile response. A novel frequency analysis parameter called the frequency index for tactile sensitivity (FITS) is based on tissue paper surface analysis results from MSSA and provides the basis for the human response model. Included is a review of subjective human softness evaluation data for select tissues gathered to represent actual human responses. The MSSA and optical image analysis (OIA) data were collected on the same tissues, and the FITS parameter was found using MSSA. Also, MSSA data were used to reproduce an old standard parameter for evaluating tissue softness called the human tactile response (HTR) index. Since it is not possible to exactly reproduce HTR, the reproduced parameter calculated in this study is called HTR equivalent (HTR_EQ). Finally, standard deviation of luminance (SDL) and loosely bonded surface fibers (LBSF) parameters are determined for select tissues using OIA. Correlation results of the human data with FITS, HTR—EQ, SDL, and LBSF are discussed; FITS correlates best with the human response data and, together MSSA and FITS, has the ability to model human response to the softness of tissue paper products.