Heat insulation characteristics of multi-layer nonwovens

Purpose This paper aims to deal with the thermal resistance of multilayer nonwovens. The effect of fibre denier, cross-sectional shape and positioning within the layers were analysed with respect to the thermal resistance. Moreover, effect of compression on thermal resistance of the multilayer nonwoven structure have also be studied. Design/methodology/approach The study involves multiple layering of thermal bonded nonwoven webs and the effect of fibre denier and positioning of different nonwovens from the hot plate. To avoid the increase in thermal resistance because of the air gaps between layers, the nonwovens were enclosed within an acrylic frame to compress them to a thickness of 12 mm. Compressional behaviour of the nonwovens were tested at a rate of 5 mm/min with peak compressive load of 50 N. Multilayer nonwoven assemblies were tested for thermal resistance with compressive pressure of 3.5 gf/cm2 and compared with that tested at zero pressure. Findings In the study, three-layered nonwoven structure, provided better thermal resistance than their single component counterparts. The structural characteristic of the multilayer nonwovens affected the conductive, convective and the radiative heat transfer. In a multi-layer nonwoven, the top most layer should have the finest fibre as possible. Second preference may be given to the middle and followed by bottom layers in terms of fibre fineness. However, fine solid fibres performed poorly in terms of compression and recovery resulting in poor thermal resistance under compressive load. Originality/value The experimental approach of controlling thickness while evaluating the thermal resistance will help in nullify the effect of air gaps between the layer interface, thus focussing on the effect of fibre denier and the positioning of nonwovens. This paper also discusses the unique properties of fine solid fibre and hollow fibres and their role in providing better thermal insulation for extreme cold weather applications.