Thermal properties of directionally oriented polymer fibrous materials as a function of fibre arrangement at mesoscopic level

Thermal properties of directionally oriented fibrous materials have been investigated in this research with the purpose of considering the influence of fibre arrangement at mesoscopic level. The range of various distributions of fibres in the fibrous materials was obtained by applying different twist intensity during spinning of cotton fibres. From various twisted cotton yarns the knitted fabrics were produced under controlled conditions, so as to obtain as similar as possible constructions. This made possible to obtain the heterogeneity of the porous fibrous structures coming from the mesoscopic level. Thermal conductivity and heat transfer coefficient of the materials were investigated. The results obtained indicate the arrangement of fibres (or their compactness, orientation and migration), which, in turn, was determined by twist intensity (mesoscopic scale), as the key factor influencing thermal properties. Yarn compactness and fibre migration, determined by lateral forces imposed by the twist inserted in yarn, affected variations in structural parameters of the knitted fabrics, and thus influenced their thermal properties. Fibre orientation manifested itself in surface geometry of the yarn was also proved to have a considerable influence on heat transfer properties.