Shrinkage is phenomenon of getting squeezed when fabric is processed with any chemical or even with simple water. The reason behind the fabric shrinking can be tracked by studying the weaving. During weaving yarn is coated with sizing material to avoid breaking and strengthen the fiber. Usually this material is natural starch This starch produce a constant tension in yarn fiber. Not only in denim but also in all cotton fabrics this tension is present in yarn fiber. This also gives a rigid and harsh feel to fabric.
after stitching denim garment, in washing the first job is to remove this starch for two reasons
- To make the garment wearable by removing starch to make it little soft.
- It will allow the next chemicals to work evenly on the fabric, that cannot be done in presence of starch coating.
When this starch is removed the fiber relaxes and comes back to normal tension. This results to reduce the volume of fabric as it get squeezed to minimum. This shrinkage is very important to know with exact dimensions before cutting and sewing of garment. Shrinkage tests are conducted on fabric before cutting so one get accurate dimensions after washing.
Before wash, swatches from different fabric rolls are cut and traced of 25 cm2 dimensions with the help of textile markers (irremovable ink). Then washing standard is taken and according to that standard washing process is proceeded. After washing process the drawn pattern is re-measured and shrinkage of those panels is taken. Samples are prepared according to that report. A shrinkage report is prepared on bases of those readings . Warp and weft shrinkage is determined separately according to the above described method.
Denim fabric have a verity of weave such as cross hatch, right and left hand twills, broken twill, open end, slub denim etc. in addition to that there a number of percentage combinations with synthetic fibers. These synthetic fibers like nylon are always used in weft position as warp is to dyed. Cotton and other natural fibers have more shrinking tendency than the synthetic fibers like polyesters. As we discussed the shrinkage is maximum for pure cotton of other natural fibers and for blended fabrics it depends to the percentage.
In fabric reference, shrinkage is maximum in stretch denim. The special elastic material used in denim to produce stretch is very much sensitive to chemicals used for shading matching. Especially sodium hypochlorite damages this material to dead (addition of caustic soda to bleach bath is very helpful to prevent this damage) . Also the temperature provided in different operations like hot bath or drying process do effect the material a lot and reduces the elasticity. All these conditions are very important while dealing with stretch denim.
Denim shrinks more in high temperature treatments, washed in hot water or dried in a hot dryer will favor to more shrinkage. And vise versa it will be minimum to low temperature bath and drying in less hot dryer.
Denim has a special character to adjust with the body shape due to its diagonal weave. It expands with wear and then returns to the original shape when washed.