Influence of flax/polypropylene distribution in twistless thermally bonded rovings on their composite properties

Abstract Flax has a short fiber length that makes the control of fiber orientation in the composite structure very difficult, which leads to composites with inferior mechanical properties. In order to overcome this difficulty, thermally bonded roving (TBR) with a novel structure where the flax fibers are in a twistfree state and are highly oriented to the roving axis have been developed. In this study, the influence of flax/polypropylene (PP) based TBR structures on their unidirectional (UD) composite properties has been explored. In total, five sets of TBR samples with varying the flax contents (40, 50, and 60 wt% levels) and with varying degrees of flax and PP fiber mixing by changing the number of drawing passages (two times, four times, and six times) have been produced in a specially designed machine. The produced TBR samples are consolidated in a compression molding machine and the resultant unidirectional composites are tested for tensile, flexural, and impact properties. It has been observed that the tensile, flexural, and impact properties of the composite samples improve with increasing flax content and with increasing flax and PP fiber mixing in the roving structure. The present composite samples exhibit better mechanical properties compared to those reported for flax/PP composites in literature. It is mainly due to better fiber orientation and fiber‐matrix distribution in the present composite samples.