Ma, Hao, et al. Journal of reinforced plastics and composites, 2014, 33(7), 687-696.
Four sisal yarns with four different twists were prepared in this work, and the mechanical properties of unimpregnated and resin-impregnated sisal yarns were studied. Unidirectional sisal yarn prepreg was prepared by a filament winding machine, and the composites were prepared by a hot press with a pressure range of 0.3~40 MPa, a temperature range of room temperature to 300℃, and a curing temperature of 140℃. The fiber volume fraction of the composite was controlled at about 65%.
· Untwisted fibers exhibit higher tensile strength due to fracture of the fiber cell wall, while twisted fibers show higher tensile modulus as reorientation of cellulose microfibrils improves fiber modulus.
· As the fiber twist level increases, the tensile strength of unimpregnated sisal yarns initially increases before decreasing at a critical twist level (90 tpm), while resin-impregnated sisal yarns show a continuous decrease in tensile properties.
· Low twist angles result in better tensile properties due to strong bonding force between fibers and the polymer matrix.
· Additionally, both tensile and flexural properties of sisal yarns reinforced composites decrease with increasing fiber twist level due to difficulties in resin impregnation and poor fiber-matrix interface. Rao's model can be used to predict the young's modulus of sisal fiber reinforced composites.
