Vegetable fiber pre‐tensioning influence on the composites reinforcement

The automated manufacturing of several complex shape composite parts simultaneously by compression and transfer molding method faces the problem of poor elastic properties of synthetic fibers, what leads to the insufficient depth of formed part and fiber breakage. Alternative to synthetic fibers, vegetable fibers have higher elasticity and lower impact on environment, but due to the lower fiber bulk integrity and orientation vegetable fibers have lower strength. However, fiber pre‐tension processes involved in various composite manufacturing routes could enhance the fibrous reinforcement orientation and increase tensile strength. Nevertheless, the influence of this method commonly is used to increase the flexural strength of the composites and its influence on the tensile properties of the composite was not studied. Thus, the aim of this work was to investigate vegetable fiber pre‐tensioning influence on the tensile and flexural properties of the composites. It was obtained that significant enhancement of flexural performance is caused by the residual compressive forces propagated in the matrix polymer, achieved only at high values of pre‐tension (approximately at 50–70% of the ultimate strength of the reinforcement), while even minimal pre‐tension load significantly increases the tensile strength of the composite. Thus, the pre‐tension technique is particularly effective in the case of vegetable fibers reinforced composite, whose properties after pre‐tension are comparable with the properties of glass fiber composites. POLYM. COMPOS., 34:1533–1537, 2013. © 2013 Society of Plastics Engineers