Studies on Multilayer Nonwovens Containing Flax Fibres Designed for Electromagnetic Radiation Barriers

Abstract

The barrier properties against electromagnetic radiation of multilayer needle-bonded nonwovens containing flax (F) fibres and polypropylene (PP) fibres and manufactured in different technological conditions have been investigated. Single-fibre webs of longitudinally arranged fibres put into layers one onto another to comprise a multilayer structure of seven single-fibre webs. The number of F fibre webs in the lap influenced the percentage of flax fibres evaluated by mass. Each kind of the laps was needled at the density 80, 120, and 200 cm–2. As a result, 18 samples of needle-bonded nonwovens of similar morphological and comfort properties but different bulk electrical resistance were prepared. The maximum bulk electrical resistance at dry conditions, of the order of 7·1014 Ω, was characteristic for the samples made entirely of PP fibres, while the minimum resistance, of the order of 1010 Ω, was characteristic for the samples made entirely of F fibres. Insert of flax fibres into the nonwoven structure at amount ~14 % resulted in 20 – 100 times decrease of electrical bulk resistance. At the amount of flax fibre ~ 43 % the electrical resistance at dry conditions was about 200 – 2000 times lower in comparison with the resistance of single PP nonwoven. In spite of such a dramatic change of resistance, none of the samples exhibited barrier properties in the electromagnetic wavelength range from 3.1 mm to 4.3 mm. Further reducing fibre resistance is needed. Fibre arrangement in the nonwovens needs to be optimised, as well. The analysis of the problem is continued.