Optimizing twisted yarn structure for natural fiber-reinforced polymeric composites

Natural plant fibers need to be spun into yarns to produce textile preforms for structural composites. The twist in the spun yarn causes fiber misalignment. This paper reports the construction of a two-ply yarn from such twisted yarn with improved fiber alignment to maximize the mechanical performance of resulting composites. This is achieved by twisting two twisted singles yarns in the opposite direction. The level of opposite-direction ply twist as a percentage of the twist in the initial singles yarn has shown a significant influence on the tensile and flexural properties of the final composites. The maximum performance is achieved when the ratio between the ply yarn twist and the singles yarn twist was approximately 0.3, which coincides with the ratio for achieving maximum Krenchel fiber orientation factor for the two-ply yarn as predicted by a geometrical model. This ply yarn twist/singles yarn twist ratio can be used as a design guideline for natural fiber yarns used as reinforcement for load-bearing composites.