Washing Wool Fiber and Textiles

by Tom Beaudet

Scouring and Fulling

In the manufacture of textiles, water and soap are two of the most important chemical substances used. It is important that we know and understand what we are trying to accomplish when we start to wet finish a textile product, then select those products to use that will accomplish what we want to do and no more.

In the textile industry, scouring (meaning the washing and cleansing of any fiber, not just wool) is a completely separate step from fulling. Scouring in the true sense of the word in the textile industry means simply removing any foreign material from the fabric; the term scour grew up around the washing of cottons and linens, which in some cases was done at the boil. In the scouring of fiber, we want to remove any foreign material from the fiber so that we can get directly to the fiber for any additional processing we may want to do satisfactorily( it may be Sanforizing, applying repellency, bleaching, dyeing, etc.). Wool is never scoured at the boil, the term was just handy to use. Handweavers, rightly or wrongly, use the term offhandedly. Because of the water and heat involved which causes the wool fiber to swell and get active (uncurl), it is very important to minimize to the greatest degree any agitation. One of the five theories of wool felting (the end product of the term fulling) is that the dimensional change in the wool fiber caused by heat and water is one of the primary contributors to felting.

You can use the same soap to full the fabric (as a lubricant) as you do to scour (as a cleaner). I use Dawn^®, and I have used Synthrapol^®, Ivory^® etc. As long as the pH is 7-9 you are safe and it will do the job. If you are in doubt about the product you are using, use the 800 number on the Label and call the manufacturer. Tell them you want to talk to someone that will give you the pH of the product you are using. In most cases they won't be able to help you but they will give you a number to call that will. All companies producing chemicals must make available on request a statement of the contents. On that sheet the pH will be listed.

In all cases the natural waxes, oils and greases that come with the raw fiber, and any oils the mill uses for lubrication can be broken up and put into solution at some temperature and then kept in solution (emulsified) by the use of a soap so it can be rinsed away. To accomplish this all we need is a soap or detergent that will hold them in suspension after they are broken up. Water hardness is very important(some well water is tough). A water analysis will tell you what it is, then it can be softened with filtering.

Soap Versus Detergent

Soap (both dry and wet) is one of the most versatile chemicals used in the mill. As long as they are low alkaline they are fiber friendly. I have been retired from the mills for a few years now but unless some new technology has been developed that I am not aware of there is no such thing as a neutral soap or detergent. All are alkaline to some degree. Neutral is a term used to designate a washed soap, that is, a soap so carefully manufactured that it does not contain an excess of either fat or free alkali.

Soap is a salt of a high molecular weight fatty acid (containing metal). There are only two that are soluble in water, and can be used to make soap, they are sodium and potassium. They are called soft soap. The primary commercial source of high molecular weight fatty acids are animal and vegetable fats and oils. These are treated with sodium hydroxide to produce soap. The removal of byproduct(free alkaline) from the soap is called washing. No matter how carefully the removal process is, the result will still be alkaline enough to turn phenolphthalein red.

Detergents are made by adding builders to soap. For laundry purposes this is done to enhance the product for specific purposes. It may be to whiten the wash or soften the hand or reduce the wrinkles, etc. Builders are also alkaline and apt to increase the pH of the product so care should be taken when using detergents with woolens. When scouring or fulling woolens it is best to choose a soap (or detergent) with a pH of 7-9. Just giving an acid rinse after is not always so simple; unless you know what's happening you may leave the goods with a harsh hand (scratchy). That is one result you do not need with woolens. In many cases, soap or detergent specifically designed for home washing of woolens may be formulated to retard shrinking. When we full woolens we want to encourage shrinking.

In the picker room (or blending room) the various components of the lot are laid out and an emulsion of water and oil is spread throughout the blend to aid in blending of the fiber, to reduce damage going through the machinery and during the drafting processes. In spinning, an oil is fed to the rings to lubricate the travelers during the spinning operation. Some of this finds its way onto the yarn as it is being spun. All machinery is lubricated and some of this finds its way onto the yarn in the process. The yarn is handled by operators at various stages and the oils and waxes from our hands is deposited onto the yarn. For proper fulling (and any further finishing) these need to be removed with a scour prior to fulling, but this is not difficult. These oils and waxes are easily emulsified and are floated away with a mild (pH 7-9) soap. There is no reason to use soap which is highly alkaline unless the cloth got accidentally contaminated with a foreign material during processing that a mild soap will not remove. If this is the case, the person responsible for removing the contamination should know or find out what the origin of the foreign material to be removed is, what the nature of the cleaning agent (chemical and pH) used to remove it is, and how to neutralize the high alkalinity when done. We do not want to end up with a worse situation when we are done. Wool and highly alkaline chemicals (caustic) do not belong in the same room.

In most cases when Greige cloth (just off the loom) is ready to be fulled, the only foreign material that needs to be removed are lubricating oils put in by the mill to aid in drafting during manufacturing (carding and spinning). These oils are designed to be easily removed. In most cases, fiber arrives in the mill picker room clean (scoured). A few mills and some hand spinners spin in the grease. This is the subject for another article.

Soap and detergent act not only as a surfactant to allow water to get into the fibres to break down the surface tension of the water to allow a thorough wetting out of the fiber, but also it provides a lubricant for the scaly fibers to slide over one another during the felting process to reduce fibers damage and give us a much tighter mass of fibers if we want that.

The Five Factors of Felting

When wool fibers are subjected to an alkaline solution with heat, the fibers start to do some peculiar things. It starts to swell and uncurl and the scales open up. When we add the third component of agitation to the mix we then have the stage set for good fulling. In general it is agreed that there is no one factor that causes wool to felt, but rather a combination of a number of factors.

The first and most common is the interlocking of the epidermal scales on the surface of the wool fiber. As the fibers are worked against one another the scales become locked. That is logical but it does not explain why some fiber with good scale profile felts poorly.

The second is creep. Under external stresses the fiber tends to migrate, or travel, towards it's root ends pulling adjacent fibers with them.

The third is that in a low alkaline solution the wool fiber has excellent elongation and recovery properties. The theory is that under certain conditions and with a number of fibers in the same space, the fiber will stretch and recover forming a tighter and tighter mass with its neighbors.

The fourth is the natural twist of the fiber. When placed in water or in a saturated atmosphere the fiber tends to twist and revolve quite rapidly until they come to rest. When that same fiber is placed in a dry atmosphere it wants to return to it's original dry form and will twist and revolve back trying to get there.

The fifth is similar to the fourth but looks at the difference between how the cuticle and cortex of the fiber react under wet conditions. The theory is that the cortex tends to contract more than the cuticle under wet conditions and therefore causes a curl of the fiber that it gives up when dried.

It is felt that all of the above contribute to some degree to the felting quality of the wool fiber. None of the individual theories is the sole factor. For example, the first and most common theory of the scales was disproved when under controlled conditions (white room), a sample of wool fiber was descaled and still had good felting qualities.

We do know that if we stay between the pH 7-9 range with the alkaline solution and apply heat and agitation we will have the best conditions for felting wool.

For some insight into soap and washing and fulling woolens, and many other fiber related subjects, read "Introduction to Textile Chemistry", by Bruce E. Hartsuch.

Tom Beaudet has worked with three major textile companies in his career (Milliken, Albant International, and Tetko) and loved every minute of it. He has and will continue to be involved with handweaving since college, more so since he retired. He currently servies as USA Technical Advisor for Leclerc looms.

"Keep those Beaters moving, it's good for your health." - Tom Beaudet

Tom Beaudet

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Westfield, MA 01085

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