Effect of Workwear Fabric Characteristics on the Changes in Tensile Properties of Sewing Threads after Sewing

During sewing at high speed, the needle thread is subjected to repeated tensile stresses, heat, bending, pressure, torsion and wearing. These stresses act on the thread repeatedly and the thread passes 50–80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam. As a result both the sewing thread and the yarns in the fabric get abraded/ severed during the seaming process. A number of researchers observed that there could be 30% to 40% strength loss in the cotton needle thread after sewing. The extent of damage becomes more critical if the fabric being used is of a dense, thick and heavy construction. A number of studies have been carried out on thread strength loss after sewing, but the impact of fabric characteristics on thread strength loss is still unexplored. In this paper, the effect of weight and fabric composition of workwear fabrics, on the changes in the tenacity, breaking elongation and initial modulus of the needle thread has been studied. The tenacity and breaking elongation loss increase with increase in fabric weight for staple threads and remain unchanged for core spun threads. The loss in initial modulus increases for polyester threads as fabric weight increases, and decreases for cotton thread. When sewn on polyester-cotton fabric of same weight, the cotton thread shows decrease in tenacity and breaking elongation loss, whereas loss in initial modulus increases. The polyester core spun threads show exactly opposite change, i.e. tenacity and elongation loss increase and loss in initial modulus decreases when sewn on polyester-cotton fabric.