Can a shrunk sweater be restored to its original state after washing?

Soft and waxy cashmere sweaters and warm sweaters are definitely the mainstays of winter wardrobes. However, if you wash them wrongly, a size M may turn into a size XS. And often the better the material, the smaller it shrinks. Clothes that cost hundreds or thousands of dollars can no longer be worn. It's heartbreaking. However, recently some "restoration artifacts" have begun to appear on the market - detergents specifically for washing shrunken sweaters and other wool and cashmere products, which are said to restore them to their original state after washing. Is it really that magical?

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01

Reasons why wool clothing shrinks

Related to its structure

Many consumers think that cashmere is fine wool, but it is not. The wool we usually refer to is sheep wool, and cashmere is goat wool. In addition to coming from different sheep, they also have great differences in performance and price. For example, the fiber diameter of cashmere is finer than that of fine wool, so cashmere products feel softer, smoother and more comfortable to wear; the stretchability and elasticity of cashmere are better than those of wool. Moreover, the output of cashmere is low, and it is a rare special animal fiber. A goat produces about 75 grams of hairless cashmere per year. In other words, the cashmere produced by five goats in a year can only weave an ordinary cashmere sweater. Therefore, in terms of price, cashmere products are much more expensive than wool products. The shrinkage phenomenon of wool fabrics is generally called "shrinkage", and the key reason for the shrinkage phenomenon is still the structure of the wool itself.

Schematic diagram of the structure of wool fibers at different levels. Image source: Textile Materials Science

The fiber structure of wool and cashmere contains a scale layer, the main function of which is to protect wool or cashmere from changes in properties caused by external conditions. It is this scale layer that, under the action of moisture, heat and chemical reagents, and repeatedly squeezed by mechanical external forces, causes the fiber to produce irreversible directional movement, causing the fiber aggregate to gradually shrink and become tight, intertwined and entangled with each other, and interwoven into felt. Recall that when we wash wool and cashmere products, whether by hand or machine, we are actually providing conditions for their shrinkage. Therefore, it is not surprising that wool products shrink, which is its inherent characteristic. On the contrary, wool products that do not shrink or shrink very little generally have a lower wool content. But it does not mean that the better the quality of the wool product, the more it will shrink. There are differences in the surface scale structure between sheep wool and cashmere. The scale spacing of sheep wool is small, and the scale density is also large, ranging from 16.2 to 34.9 per millimeter; while the scale spacing of cashmere is large, and the scale density is smaller than that of wool, ranging from 10.3 to 15.6 per millimeter. Based on the above data, we can know that wool has greater shrinkage than cashmere. Therefore, cashmere products with a better feel actually have a much smaller chance and magnitude of shrinkage than wool products.

SEM image of sheep wool

Cashmere Scanning Electron Microscope

02

Shrinkage recovery agent

Is it really possible to restore your beloved clothes to their original state?

There are some wool and cashmere products on the market that can be used to restore shrinkage, and there are also some related shrinkage restoration methods on the Internet. So, can these restoration cleaning agents and restoration methods really restore shrunken wool products as you wish? We have learned that the fundamental reason for the shrinkage of wool products is the irreversible directional friction of the scales on the surface of the wool. Therefore, the key to preventing the shrinkage of wool products is to reduce the friction of the scales. Therefore, in the textile industry, wool and cashmere products are usually treated with chlorination, oxidation, bio-enzyme, coating, etc. The essence is to remove the scale layer on the surface of the fiber or smooth the edge of the scale layer by chemical or biological methods, or to wrap the scale layer with a coating to achieve the effect of reducing directional friction.

Then, for the wool products that have shrunk, the key to recovering them is to untangle the wool fibers that have been entangled and felted. Generally speaking, hot water or steam is used to swell the wool first to reduce the entanglement between the scales. At the same time, the fibers and scales are softened, and then the scales are stretched by external force to untangle them and recover them. During the stretching process, an iron can be used to keep the clothes moist and at a high temperature, keep the scales soft, and make the stretching recovery effect better. Similarly, the essence of shrinkage recovery detergents is some surfactants and softeners, and the purpose is to make the fibers softer and reduce the friction coefficient of the fibers. When using these so-called recovery agents, they also need to be stretched to recover them. Therefore, without recovery detergents, the softeners commonly used at home can achieve similar effects, and even the conditioners we use daily can play this role. There is also a type of shrinkage recovery agent, which is a chemical reagent that has a slightly soluble effect on wool scales. It achieves the purpose of relieving shrinkage by dissolving entangled scales, but it causes great damage to wool products and is not recommended.

In short, shrinkage recovery is not suitable for severe shrinkage. It is difficult to grasp the correct force when ironing and pulling the fabric, and it is easy to over-pull the fabric and deform it. It is better to pay more attention to the care of wool products, especially when washing clothes.

03

Master the correct washing and care methods

Minimize the chance of damage

When washing wool and cashmere products, you must first choose the right detergent. There are special detergents for wool and cashmere products on the market. In addition, you also need to pay attention to the following when washing:

1. Wash separately, use appropriate water temperature (below 30℃), avoid using hot water, and just cover the fabric with water.

2. Use an appropriate amount of detergent to wash a normal-length wool sweater in a short time. Just pour 20ml of detergent. Men's sweaters need to be poured in more. Stir and disperse evenly with your hands, press the fabric a few times, turn it over and press it a few times again. Do not rub it repeatedly, such as rubbing the collar and cuffs slightly.

3. When rinsing, hold the fabric with both hands and squeeze out the water. After rinsing, do not twist it. Wrap the fabric with a clean towel and squeeze out the water. If you want the fabric to maintain its original texture after drying, there is another trick: after rinsing, pour a basin of clean water directly into the basin, just enough to soak the sweater, then pour in softener (about 1 bottle cap), or pour in 1 bottle cap of glycerin and stir well, and finally put the fabric in to fully soak for 10 minutes. After taking it out, squeeze out the water, lay it flat in the clothes drying basket and dry it in a cool place.

Note: Do not pick up wool products with one hand. A sweater soaked with water is very heavy and will deform! Do not twist the fabric with your hands or hang it on a regular hanger to dry, as this will deform the fabric. Always use a drying basket. Do not expose the fabric to the sun. Fabrics of different colors should not be washed together to avoid staining.

Author: Zhang Desuo, Associate Professor of the School of Textile and Clothing Engineering, Soochow University, and the National Engineering Laboratory for Modern Silk

Review | Zhang Jie, Chief Engineer, China Textile Construction Planning Institute