Shrinkage In Wool

FACTS ABOUT WOOL

True wool is the fleece of the sheep. The term 'wool" as used (legally) in the textile industry to include hair fibers from the angora goat (mohair), camel, alpaca and vicuna. Angora obtained from the angora rabbit is not legally classified as wool. However, the fiber will be discussed since its appearance, feel and look closely resemble soft wool. Wool and wool blends are used in all types of women's, men's and children's garments.

FACTORS THAT PRODUCE SHRINKAGE

Fiber Characteristics. The wool fiber contains an outer layer of scales. The thickness and shapes of the scales vary with the kind of animal. The edges of the scales are a factor in producing felting. Felting is the extreme shrinkage of the wool fibers. Heat, moisture and mechanical action cause the wool fiber to shrink and the edges of the scales to interlock, preventing the fiber from returning to its original position. Felting differs from relaxation shrinkage, which is shrinkage that can be restored by blocking or pressing. Relaxation shrinkage does not produce an interlocking of the scales.

FABRIC CONSTRUCTION

Soft Wools. These are made from short, staple wool fibers and are referred to as a woolen yarn. Woolen yarn is loosely twisted and has a softer and fuzzier surface. Soft wool has a greater tendency to shrink due to a greater degree of exposed surface.

Worsted Wool. Combed yarn made from long staple wool fiber is referred to as a worsted yarn. A worsted yarn has a smoother surface and poses less shrinkage problems then woolen yarn.

Stretched Fabrics. Knitted and woven fabrics that have been stretched during manufacture may exhibit relaxation shrinkage when subjected to heat, moisture and mechanical action of normal wear and routine drycleaning procedures. Looser knitted fabrics have a greater tendency to shrink.

Angora. The fiber obtained from the rabbit has the possibility of shrinkage more than any other wool fiber.

Pre-Shrinkage Treatments 
London Shrunk. Prior to making a garment, heat and moisture is used to relax the wool fabric and prevent shrinkage.

Resin. A finish is applied that will alter the scale structure of the wool fibers. The finish may produce washable wool but removes some of the softness of the wool fibers.

FACTORS THAT PRODUCE SHRINKAGE

Heat, moisture and mechanical action are the three factors that produce shrinkage. Depending upon the fiber, one or more of the factors become dominantly critical. For instance, thermoplastic fibers are more sensitive to heat; natural fibers and rayon are more sensitive to moisture.

INSPECTION

Examine wool and wool blends for evidence of shrinkage and distortion. Examine wool fabrics for matting and felting that may have occurred from home washing.

IDENTIFICATION


Test for wool by cutting a small piece from an unexposed seam and bring it to the tip of a match flame. Wool will smell like burning hair. Acrylic (with which wool is frequently mistaken) will leave a bead that cannot be crushed or pulverized. If an unexposed seam is not easily available, pick off some napped fibers from the fabric surface and roll them into a yarn to test.

PRESPOTTING


If moisture is used in prespotting, soft wool fabrics must be hung to dry before putting the garment into the drycleaning machine. Wet areas may cause localized shrinkage, matting and redeposition.

DRYCLEANING

Place knitted wools in net bags to prevent the possibility of snagging and shrinkage. The solvent should be free of moisture. If the preceding load was a moisture load, run a hard load before running the soft wool load to lower the relative humidity. Solvent temperature should be between 75 - 80° F. Higher temperatures may cause the solvent to release moisture which contributes to shrinkage. Do not put any wet spotted garments in a soft wool load. Soft wools should be drycleaned for no more than 5 minutes. Reclaim at the minimum temperatures required by the type of solvent used. Worsted wools can be run 10 minutes and reclaimed the same way as soft woolens. Mechanical action will cause shrinkage in angora fabrics. In order to avoid felting and shrinkage, soak the garment in the wheel of the machine with using a high solvent level. Do not operate the wheel but simply allow a flow of fresh solvent to come in while it is on filter circulation. The solvent in the wheel should be moisture free to avoid shrinkage. Extract and dry without tumbling. The heat of the tumbler and the mechanical action may cause shrinkage. Wetcleaning may be less time consuming when processing angora.

WETCLEANING


Soft wools and angora usually respond well to wetcleaning. Test colors for safety. Use a soaking action in cool water (100° F.) Agitate by hand and rinse at the same temperature, since any drastic change in temperature between soaking and rinsing can promote shrinkage. Fold over a hanger or lay on a towel to dry. A knit garment hung on a hanger will stretch and distort.

FINISHING


Wool knit fabrics can be measured and usually blocked to size. To stretch a knitted wool fabric, apply bottom steam and pull to desired size. Vacuum dry thoroughly. To shrink in specific areas, steam fabric and push in the knit fabric using a hand pad. Vacuum dry thoroughly. Do not put loosely knitted wool garments on steam air finishers.

SUMMARY


Wool fabrics are subject to shrinkage. Shrinking is due to the physical characteristic of the fiber, fabric construction and manufacturer's pre-shrinkage treatment. Soft wool garments require special handling just as fragile fabrics do. Shrinkage will occur in drycleaning if not handled correctly. Angora garments require even more restrictive cleaning procedures because the possibility of shrinkage is more likely.

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