Effect of PLA coating on the physical, morphological and mechanical properties of natural fiber yarns

Abstract

This study investigates the effect of a PLA-based coating on the morphology, cross-sectional area and tensile response of flax and jute yarns intended for sustainable Textile Reinforced Mortar systems. The coating was prepared using 5% PLA dissolved in 95% acetone and applied by yarn immersion. Uncoated and coated yarns were characterized through linear density, density measurements, SEM image analysis and tensile tests. The results show that the PLA treatment increased the linear density and cross-sectional area of both fibres, confirming polymer deposition on the yarn surface. SEM observations showed a more compact and regular morphology after coating, with reduced fibre separation and a more continuous external surface. This effect was more evident for jute, which initially showed a more irregular structure. Tensile tests indicated that coated yarns reached higher maximum forces than uncoated yarns, suggesting improved cohesion among elementary fibres. However, when the results were normalized by the increased cross-sectional area, the tensile stress decreased. Therefore, the coating mainly improves yarn compactness and load-bearing capacity rather than the intrinsic tensile strength of the fibre material.