Introduction to Common Wool Scouring Agents

In the next series of posts, we are going to go over the results and method that we’ve developed to wash wool in small batches for the home processor. Unhappy with our results by other methods, we set out to find out which scours worked better in our favor and a way to wash wool that depended on listening to your fleece and not the instructions on the bottle. We found too often that we were left with overall sticky fiber, tinged tips, or “pockets” of lanolin left in the fleece where there should be none. This has been quite an interesting series of experiments and fully changed how we approach our wools. Knowing James Perry, also known as LongDrawJames, had his PhD in Sustainable Surfactant Chemistry, we decided to work with him to develop the testing methods and gather his insight. We collaborated on this blog series and below are his writings for the scours we chose to test. None of the materials listed were sponsored and this was a fully unbiased and curious approach.

How Scouring Works

At its fundamental basis, when we scour wool, we aim to do two things – firstly, to remove contaminants such as feces, urine remnants, dirt, and suint (sheep sweat) and secondly, to remove the lanolin. This is an important step in processing wool and very few applications would need lanolin left in the fleece. You should also seek to clean your wools to lengthen the lifespan and ease of use on your processing tools. Lanolin and other contaminants can be incredibly hard to clean off of the teeth of most processing tools. Generally speaking, the suint, or sweat, is made up of salts and other water-soluble organic molecules. Lanolin is a complex natural mixture of greases and oils, containing mostly long-chain triglycerides as well as sterols. Lanolin is naturally water repellent, giving it purpose in aiding the fibers to prevent felting and soaking on the sheep. This means that water alone cannot remove it from the surface of the fibers.

In order to remove the lanolin, we generally employ detergent formulations. Within these detergents, the active chemical compounds which emulsify the grease are called surfactants, a conjunction of surface-active-agents. Surfactants are what are known as amphiphilic molecules, meaning they have a part of their molecule which is hydrophobic, unable to mix with water, and a portion of their molecule that is hydrophilic, which does mix with water.  They are able to lower surface tension between phase boundaries, which means they can allow two liquids which normally would not mix to be granted the ability to mix. Oil and water are a great example. In the case of wool scouring, they allow the lanolin, a hydrophobic grease, and the water to mix.

There are four general types of surfactants and they are named depending on the nature of their hydrophilic group – anionic (negatively charged), cationic (positively charged), amphoteric (both positive and negatively charged), and non-ionic (uncharged). The most important surfactants for wool scouring here are anionic and non-ionic surfactants as these are designed to give optimum performance in the areas we need.

Anionic surfactants are by far, the most widely used surfactants worldwide, making up around 70% of the world’s surfactant use. They are used in almost every single cleaning product. The most common surfactants of this class are Linear Alkylbenzene Sulfonate (LAS) and Sodium Dodecyl Sulfate (SDS), also known as Sodium Lauryl Sulfate. They are mostly used in applications where dirt and stain removal is most important, with LAS tending to be used more in clothes detergents and SDS being used more in personal care as it is much milder to the skin. The major downside of these surfactants in operation is their lack of resistance to hard water. Hard water contains lots of dissolved calcium, which interacts with the surfactants and forms insoluble calcium salts that render the surfactant useless for cleaning. This means you need to add more surfactant than you’d normally need to get the same level of cleaning to account for the amount of surfactant “deactivated” by the calcium. If you are sustainability minded the other major downside of these detergents is their production methods. LAS is produced exclusively from crude oil fractions, and SDS is produced from C12 fatty alcohols derived from palm and coconut oils which have an intensive environmental impact.

Within wool scouring, it is actually the non-ionics which offer the best solutions for lanolin removal as they excel at emulsifying oils and greases. Generally, the most commonly used non-ionics are Nonylphenol Ethoxylates (NPE) and Alcohol Ethoxylates (AE). AE are generally also made from C12-C14 alcohols and a molecule called Ethylene Oxide which is used to introduce the Ethoxylate, a wetting agent and emulsifier. NPE is derived from crude oil. NPE is more of an industrial detergent and is being banned in many countries due to its carcinogenic degradation products and aquatic toxicity. The toxic effects of NPE are a good lesson that biodegradable doesn’t always mean better.

Wool Scouring Formulas on the Market

There are a number of formulations available today as specialist wool scouring agents, as well as some detergents not designed for scouring that people swear by. The four we see most commonly discussed are Orvus Paste, Dawn Dish Soap, Unicorn Power Scour, and Kookaburra Wool Scour.

Orvus Paste is a detergent we see used by many home processors. Unfortunately, it is almost entirely pure SDS. Good for dirt removal, but it has poor hard water stability and does not entirely remove grease. It will do a good job on dirt and is biodegradable, though. Keep in mind that biodegradable is a label that can be put on products even if they do not reach 100% of their materials breaking down in a set timeline. The other issue is its very, very high foaming capacity which means you’ll need a lot of rinses to get it out. Orvus Paste is typically chosen because it is used to wash livestock prior to shows. The use of it to wash the animals makes sense as you would not want to remove the grease from them. Washing wool on sheep in a way that removes their natural oils can cause fleece, skin, and health damage.

Dawn Dish Soap is a formulation specifically designed to clean plates and dishes. It’s a blend of anionic and Amine Oxide surfactants that is often at around 30% surfactant loading in water. In the case of Dawn, the major anionic surfactant is SDS, the same as is found in Orvus Paste. The second surfactant is an Amine Oxide surfactant, which are technically amphoteric, but behave much more like non-ionic surfactants in their cleaning. They are usually very effective de-greasers. In Original Dawn Ultra, or Blue Dawn, you are also going to find some other additives such as a copolymer of PEG and PEI, an anti-deposition agent, as well as Methylisothioazlinone, which is a biocide that can cause acute aquatic toxicity. This makes it not biodegradable. Some formulations contain optical brighteners or enzymes such as proteases which will degrade your wool by breaking it down, so make sure you read the label if you are going to use these. You would not want to get the wrong one and have your wool damaged by it.

Unicorn Power Scour is a formulated blend of surfactants specifically designed for scouring wool. Generally speaking, this is a surfactant blend in water. Surfactants used here are mostly ethoxylated non-ionics which offer best performance for removal of greases, as well as a smaller component of anionic surfactant, which helps remove dirt. Specific identities of these surfactants are not really clarified and it is rather hard to tell which they are using, as there are so many variations which can be sought on the market. The formulation also adds a polyacrylic based copolymer which is a designated anti-deposition agent. This is specifically designed to prevent dirt and emulsified lanolin from depositing itself onto the surface of the wool fibers again and definitely something you want in a scour. Unicorn Power Scour has been labeled and tested to be biodegradable as well, but without knowing what is in the product, we cannot say how much of it is.

Kookaburra Scour is another common formulation for scouring wool. It is also a surfactant formulation in water listed as being natural and plant based. Surfactants used here for de-greasing are almost exclusively fatty acid glycol ethers, which use sugars as the non-ionic group rather than an ethoxylate. This formulation does also contain a very small amount of anionic and ethoxylated detergent and sulfated oil which acts as a surface lubricant.

The Chemistry Behind It

As mentioned previously, the major process which occurs to remove grease from wool is emulsification, meaning the oil and water phases (lanolin and water) are allowed to mix, facilitated by the surfactant. This is not a chemical reaction, but it is a chemical process as the grease itself is not chemically changed by the surfactant.

When a surfactant is dissolved into water, the molecules will remain free in solution. The free surfactant molecules assemble onto the grease using their hydrophobic tails (which are able to mix with the oil). When the concentration becomes high enough, the “pull” of the hydrophilic headgroups by the water is enough that the grease rolls off of the surface and forms a spherical structure known as a micelle. This process is known as the “roll off” method. Generally, people think of micelles cleaning greases, but in the case of detergents this is the actual mechanism of detergency.

The grease has to be fluid enough for the roll off method to work, which is why scouring is carried out at high temperature. The base melting point of lanolin is 120F/48.8C, though it is advised to go a little higher. Likewise, most non-ionic surfactants also work more efficiently at this temperature range.

At a molecular level, this is what is happening when we are scouring wool. But what does this mean on the application level?

Well, when you scour, you need to think of a few different parameters. Part of this is your water temperature, hardness, and volume. You need to have a temperature high enough that you have melted the lanolin. We chose to stick to 130-140F/54.4-60C to truly melt the lanolin and keep the water from cooling between water changes. You also need to consider how hard your water is. Many detergents, specifically anionics are going to suffer from water hardness and you may have to use more than you otherwise might if your water is hard. The bins you use will need to be large enough to accommodate your wool and enough water to give the debris space to gather away from the wool as well. This was all considered for our tests.

What detergent you use is also going to matter. It is generally personal preference as to which scouring agent you use, but we find that one with more non-ionic detergent will de-grease more effectively. We both personally like Power Scour as in our own water situations, which are both, vastly speaking, very hard, this seems to work best. We are also rather fond of the smell and its low foaming capacity that means fewer rinses. Fewer rinses means less water wasted. You will see that it is well reflected in our washing results.

Our next set of posts will be about how we accomplished our testing parameters, their results, and the scouring method that’s been developed. There will be in depth photos for that as well.