Abstract
A single yarn is formed by spinning short natural fibers, and a twist yarn consists of several single yarns to achieve high stiffness and strength of natural fiber composites. Generally, the amount of twist obtained by the spinning process, known as twist per inch (TPI), plays an important role in yarn properties because the twist is essential to hold the fibers together. This study investigated the effect of TPI of natural fiber yarns on resin impregnation properties, such as flow velocity and void generation, and the mechanical properties of natural fiber composites molded using VaRTM. Resin flow velocity increased with increasing TPI because capillary pressure due to the dense structure of fibers became the predominant force for tow impregnation. Mechanical properties also depended heavily on the TPI of yarns. TPI dependence on resin flow velocity was valuable in designing the complicated structure of natural fiber composite molded using VaRTM.
