WEAVING
Journal of the TEXTILE Association
3.2 Thread differential shrinkage puckering The differential shrinkage values, both TFDS (thread to fabric) and USFDS (unstitched to stitched fabric) obtained with boiling water and dry heat tests and the AATCC pucker grades of the corresponding samples. In the case of boiling water shrinkage, the shrinkages of fabrics along warp are mostly higher than that of the threads. So, some of the values of differential shrinkages (TFDS and USFDS) along warp become zero. The dry heat shrinkage values of threads are higher than the boiled water shrinkage values. But a reverse is the case with the cotton fabric. The boiling temperature is lesser than the dry heat temperature and the threads are made of synthetic fibres are sensitive to high temperature and shrink more. The cotton fabric is more sensitive to water absorption (Table 2.4). The fabric shrinkage in boiling water is due to the relaxation of warp yarns to relieve their weaving tension. As the warp yarns shrink, the weft yarns become straightened leading to gain of dimension in weft direction. The cotton fabric does not show much shrinkage to dry heat. Fig. 3.6 shows the positive correlation between TFDS and USFDS along warp direction for the seams subjected to both boiling water (a) and dry heat (b) tests. The same trend is also observed in case of seams along weft direction. It can be inferred that the thread shrinkage is a factor causing seam pucker. In the lock stitch seam, the needle and bobbin threads are locked at the point of interlacement. In that locked condition if the threads shrink, it crush the fabric in between the two locking points causing puckering of the seam. This can happen only if the thread shrinks more than the fabric. If the fabric shrinks to the same extent or more, then the seam will not pucker. Though there is positive correlation between the differential shrinkages, i.e., TFDS and USFDS, the extent by which the differential shrinkage causing the seam to pucker varies from thread to thread. The coarser threads which can exert higher forces while shrinking induce severe pucker than the finer thread. The spun and PP core spun threads, because of their staple nature could not show higher force of shrinkage compared to the filament threads.
a
b
Fig. 3.6: Effect of thread-fabric differential shrinkage on unstitched-stitched fabric differential shrinkage in warp direction; a- boiling water; and b-dry heat
Fig. 3.7 a & b shows the negative correlation between the USFDS and AATCC pucker grades for the seams in warp direction. The same trend is also observed in the weft direction (not shown in figure). This confirms the effect of the thread shrinkage on puckering of seams. The fabric stitched with the spun and PP core spun thread have better AATCC pucker grades compared to that stitched with the filament threads. The threads SP/24/3 and PP/16/2 have zero differential shrinkage, and the seams constructed using these threads show least pucker having higher AATCC pucker grades of 4.5 each (Fig. 3.8 a & b). The seam constructed with the textured thread TP/18/1 shows severe pucker under dry heat with a AATCC pucker grade of 1.5 (Fig. 3.8 c).
a
b
Fig. 3.7: Effect of unstitched- stitched fabric differential shrinkage on pucker grades for the seams along warp; a- boiling water shrinkage; b- dry heat shrinkage
JTA : An effective marketing tool for strengthening business promotion 10
May - June 2016