Thermal and water vapor transport properties of selected lofty nonwoven products

Abstract

The mechanism of dry heat flow through lofty nonwoven structures (i.e. thermal resistance) as occurs in quilts has been established. By contrast, there is a scarcity of published information on the water vapor transport properties. This work explores the thermal and water vapor transport properties of a number of different quilt samples with a focus on identifying fiber type effects. Both commercial product and matched laboratory samples were examined. Steady-state thermal resistance and water vapor resistance measurements confirmed that both properties are primarily determined by sample thickness and are largely independent of fiber type. Experiments were also undertaken to observe transient effects. Test samples were initially equilibrated on a ‘dry’ guarded hotplate (35 ± 0.1℃) in a low relative humidity environment (45%). The relative humidity was then rapidly increased to 85%. Compared to polyester, wool samples exhibited a large reduction in the heat flux required to maintain the hotplate temperature. This transient peak lasted for in excess of 1000 seconds. The magnitude of this transient peak in heat flux was proportional to the quantity of wool in the sample and is believed to be associated with the known exothermic nature of water vapor absorption by wool as relative humidity increases. Based on the published values of the heat of water absorption of wool it is estimated that this additional transient heat source is significant relative to a typical human resting metabolic rate and so the effect may be of practical relevance in the bedding environment.

Analysis of air gap volume in structural firefighter turnout suit constructions in relation to heat loss

“…This was surprising as the TL was also the thickest material, yet it had the greatest MTHL. 31 Although the TL consists of a thick, multi-layer construction, the MB had a higher evaporative resistance ( R et ) on the garment level, which contributed to its overall lower heat loss within the context of this particular study’s predicted test conditions and specific garment materials.…”

“…This contradicts previous literature that found fabric thickness to be the primary predictor of thermal insulation; however, the previous study assessed fabric-level test methods only. 31 Previous research also found garments with higher permeability to have lower thermal resistance through natural convection. 32 In this study, however, opposite results were found as the thick TL had the greatest air permeability and overall MTHL but did not have the lowest thermal resistance.…”

“…Surprisingly, the data indicated that as material thickness increased, so did MTHL. Fabric thickness is cited in the literature as a determinant of insulation, 12,30 and thermal resistance (R t ) has also been primarily determined by fabric thickness, independent of fiber type 31 ; however, the relationship discovered in the analysis above was not expected. These results do not follow clothing insulation principles, which demonstrate the opposite, that as fabric thickness increases, heat loss decreases.…”

Suitability of lyocell fiber for pillow fillings

“…41 Fiber effects on the water vapor transport properties of lofty structures (comforter fillings) have been previously studied. 7,31 Naylor et al 7 concluded that, under steady-state conditions, water vapor resistance is determined by thickness, independent from the fiber type, whereas shell fabric plays a minor role. In this study, the thicknesses of tested pillows were comparable (see Table 10, column h p0 ) and the measured R e values ( Table 7) are not proportional to pillow thickness.…”

“…The importance of moisture management in bedding material for the improved quality of sleep was also emphasized in a sleep study by the Joanneum Research Institute for Non-Invasive Diagnosis, 6 in which physiological and psychometric data derived from the participating subjects' heart functions during night sleep were monitored. A study conducted by Naylor et al 7 on lofty nonwoven structures from wool and polyester (PET) demonstrated that the heat resistance and water vapor permeability of a textile material are determined solely by its thickness and air content (voids) in steadystate conditions, and not by fiber type. Fiber type has a significant impact on thermal and water vapor transport properties under transient conditions.…”