Mechanical Properties of Needle-Punched Fabrics in Relation to Fiber Orientation

Needle-Punching process is a mechanical method by which entanglement of fibrous webs can be enhanced. Fiber entanglement together with fabric weight can be held responsible for the variations in the mechanical properties of nonwovens. In this work, mean fiber orientation angle and fabric weight measurements were used for prediction of bending and tensile properties of needlepunched fabrics. Samples of needled nonwoven fabrics in four groups with different fabric weights were produced using appropriate carding/cross-lapping machines. The samples of each weight group were needled at various punch densities and needle penetration depths. The orientation of the fibers in the samples was determined using Radon transform method. Bending stiffness and breaking strength of the samples in both machine-direction and cross-machine direction were determined using two simply supported beam system and strip method, respectively. The results indicated that an increase in the amount of punch-density generally leads to variation in orientation angle of the fibers in the samples. It was observed that an increase in the amount of punch-density led to an increase in mean fiber orientation angle in all samples along the machine-direction. This is due to the displacement of the fibers by the needling process. Additionally, fiber orientation pattern of the samples enormously changed due to the changes in needle penetration depth. Multiple regressions based on least square method were used to estimate the mechanical properties of needlepunched fabrics. The results pointed to the paramount importance of the degree of fiber orientation and fabric weight as two influential factors controlling the mechanical properties of needle punched fabrics.