Fabric Shrinkage and Procedure of Shrinkage Test

What is Fabric Shrinkage?
The term ‘shrinkage’ can simply be defined as a change in the dimensions of a fabric or garment. This dimensional change may be in a positive (growth or elongation) or negative (shrinkage) direction for fabric length, width and thickness. Although the thickness of a fabric also changes with processing and use, it is not usually considered problematic. For a cotton fabric, shrinkage relates to the loss of the length and/or width dimensions. In garment form, the shrinkage characteristics relate not only to a change in fabric dimensions, but they also can relate to other parameters, such as seam puckering, torquing and overall garment fit.

Shrinkage is the process in which a fabric becomes smaller than its original size, usually through the process of laundry. Cotton fabric suffers from two main disadvantages of shrinking and creasing during subsequent washing. However, there are fabrics which are more naturally resistant to shrinking. Synthetic fibers such as polyester or nylon are typically less prone to shrinking than others, although they are not 100% shrink-proof.

Any fabric shrinks in different states, from loom state onwards to the stage till it is finished. It can be recalled that width of warp on beam (weavers beam) is different from width in reed, width of fabric on front rest differs from width in reed, width on cloth roller differs from relaxed width and finished width is smaller than grey width. Answer for all these changes is ‘shrinkage’, of cloth width wise and length wise. In some cases fabric shrinkage is high and noticeable, e.g. 10s warp sized with 10%, 34s or 40s reed, 8 or 10 pick wheel using 2s roving as weft to produce ‘chaddars’ or thick bed sheets. When grey fabric subjected to preparatory process like desizing, scouring, bleaching or mercerizing, fabric undergo shrinkage. Thus, if a cloth is finished, we need to calculate from reverse side to arrive at width of warp on beam.

Types of Fabric Shrinkage:

1. Construction shrinkage:
After cotton fabric is constructed on a knitting machine or weaving loom, it has inherent characteristics based solely on the yarn construction variables used. These characteristics or conditions are referred to as the greige delivered state and can be tested for various specifications, including shrinkage. The type of shrinkage measured at this point is defined as construction shrinkage, which is the amount of dimensional change in a fabric based solely on the construction variables used to create the fabric. Construction shrinkage is measured after fabrication but before subsequent processes.

2. Processing shrinkage:
The dyeing and finishing processes, along with the apparel manufacturing process, affect the dimensions of a product. Some techniques have more impact than others.

These steps create processing shrinkage, which can be defined as the dimensional change that a process adds to or removes from the construction shrinkage of a fabric and thereby changes the residual shrinkage accordingly. The length and width dimensions are both affected, and the fabrics may either be stretched or consolidated. Most often, the length is stretched and the width is reduced during wet processing. Some of this shrinkage is composed of elastic shrinkage and can be easily recovered; however, some of the changes in dimensions may not be recovered because the elastic limits of the fabric as constructed have been exceeded.

3. Elastic shrinkage:
Elastic shrinkage is defined as a change in the dimensions of a fabric as a result of the fabric’s ability to freely relax from the tensions experienced during construction and other processing.

4. Drying shrinkage:
Drying shrinkage is defined as a dimensional change in a fabric when the ‘deswelling’ of fiber, yarn and construction occurs in the drying step. The structure shrinks upon itself as a result of the physics of drying. Continuous processes during dyeing and preparation for drying usually stretch the length and pull down or reduce the width, sometimes beyond their elastic limits, thereby changing the relaxed dimensions.

There are also two types of shrinkage occur during washing:

  1. Length wise
  2. Width wise

Normally a square area is drawn on the heat-set material and measured. The marked cloth is boiled in soft water in the washing wheel for 30 min, centrifuged and air dried. The dimensions of the square are measured without ironing the dried fabric and the shrinkage is determined. A well set fabric should not show more than 1% residual shrinkage.

Causes of Fabric Shrinkage:
During the spinning, weaving, bleaching, dyeing and various other finishing processes, yarns and cloth are under continuous tension. Yarns and/or fabrics are not fixed materials; they consist of separate, stretchable fibers which submit to the tension. In other words, fabrics can stretch in length and width. The tension within the yarn, which is caused by this stretching, can be eliminated when the friction within the fabric is reduced.

This reduction in friction occurs during laundering, where both water and soap act as lubricants. The lubricant, along with the mechanical action of the washing, helps the fibers relax and contract to their original length before the elongation takes place; this means that the fabric shrinks and recaptures its original equilibrium.

Fabric shrinkage is not only due to the release of strains imposed during the manufacturing process but also caused by fiber and yarn swelling produced on wetting, which brings about an internal rearrangement of the material resulting in external shortening. Shrinkage is the retraction of yarn when the external forces are removed.

Due to high tension during preparation of fabric which result in excess stretch in yarn. This type of shrinkage is known as London shrinkage. Due to swelling of fibers for fiber structure.

Working Procedure of Fabric Shrinkage Test:
The sample which is done shrinkage test, spread on table. Then a glass template put on sample fabric which is square size. There are six marks on glass template and distance between two mark is 35 cm. Marking the sample fabric by unchangeable marker. Then sample is sewn by hand sewing machine. Sample is ready for washing. Simple wash the fabric at 60˚C temp for 90 min. after washing the fabric is taken out. Dry the sample as per any of the method. It can either be Line Dry or Flat Dry or Tumble Dry. To find the dimensional change read the Shrinkage/Stretch on 3 points on the Wrap side and 3 points on Weft Side. Get the mean value of wrap-wise and weft wise readings to get the Accurate Shrinkage or Stretch.

fabric shrinkage test
Fig: Fabric shrinkage test

Shrinkage is determined as;

Shrinkage % = {(length of fabric before wash) – (length of fabric after wash)} / (length of fabric after wash) x 100

Example,

length of fabric before wash = 35 cm

length of fabric after wash = 33 cm

Now, Shrinkage % = {(35-33)/ 33} x 100

= 6%

Here, Shrinkage is 6%. Normally shrinkage is acceptable less than 5%. But it can be change in case of buyer requirement.

References:

  1. Principles of Textile Finishing By Asim Kumar Roy Choudhury
  2. Chemical Technology in the Pre-Treatment Processes of Textiles by S. R. Karmakar
  3. Woven Fabric Structure Design and Product Planning by Hayavadana
  4. Woven Textile Structure: Theory And Applications By B. K. Behera and P. K. Hari

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