What is Milk Fiber?

Milk Fiber from China

Good question. What is milk fiber? And what do we know about it? Well, people like to spin it into yarn and made fabric from it. And it’s soft and silky. And it’s looks pretty. According to the fiber people over in China, it also is beneficial to human health, is anti-bacterial, and “has the functions of nourishing and taking care of skin.” Riiight. Now we are getting into some fantasy land spin-doctor stuff. That sounds like a marketing ploy. So let’s go digging and find out exactly what milk fiber is, and why it’s so darn special.

Ok, to start this journey, it’s important to know where milk fiber came from. According to Euroflax Industries, milk fiber was invented in 1930’s in both Italy and America and was called “milk casein.” Huh. Who knew? And here I thought it was some newfangled invention. But apparently it’s been around for a while. For a long while, actually. Crazily enough, casein was invented way before the 1930s – apparently they’ve discovered that many churches from the 14th and 15th centuries were painted with casein-based paints – the colors are still bright and unfaded even to this day! Well, apparently this milk casein stuff is great for paint. But how does that connect with milk fiber?

From the National Bellas Hess F/W 1946-47 Catalog of “Ara-Fab Fashions”: a 2-piece Aralac/rayon blend jerkin set embellished with felt motifs in kelly, blouse not included; $4.98; misses 12-22

Apparently “milk casein” fiber was used in many clothing and household items in America and Europe during the 1930s and ’40s, says Joan Kiplinger of Fabrics.net. It was a substitute for wool, which was needed by men on the front lines. However, it fell out of use after WWII ended and newer, cheaper synthetics such as nylon grew in popularity. The fiber was blended with other natural fibers and known under the brand names of Aralac, Lanatil and Merinova, for those of you checking your vintage clothing labels. While these brands’ fabrics were very similar to wool and could be dyed by the same processes, apparently there were some flaws with the milk casein fiber – namely, that it was not as strong and firm, nor as elastic as wool, and the fibers “mildewed easily” when they got damp.

However helpful this information is, we still don’t know how milk fiber, or milk casein, is made, and therefore what exactly it is. The websites selling milk fiber aren’t particularly helpful, as they simply talk about dewatering and skimming milk to make the fiber, like it’s some sort of cheese. Which it is not. Cyarn is particularly vague about this, saying simply that they:

“…manufacture the protein spinning fluid suitable for wet spinning process by means of new bio-engineering technique…

Hm, that sounds mysterious. So now it’s a protein? Ok, let’s back up a bit and find out what “casein” is. Maybe that will help us out. According to Wikipedia

Casein (from Latin caseus, “cheese”) is the name for a family of related Phosphoprotein proteins. These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 20% to 45% of the proteins in human milk. Casein has a wide variety of uses, from being a major component of cheese, to use as a food additive, to a binder for safety matches. As a food source, casein supplies essential amino acids as well as some carbohydrates and the inorganic elements calcium and phosphorus.

Ok, so now we know that “casein”, which is the protein in milk, is what is used to make the fiber. So then, is milk fiber edible? Is it just like making or eating cheese? Here’s another clue: the Wiki article mentions that fiber is made from “extruded casein.” This article from the Science in Farming website, says:

The conversion of the casein of skim milk into textile fiber is not a process that can be carried out on the farm. The casein must be made by a controlled procedure possible only in a dairy plant or a plant making casein exclusively. The conversion of casein into fiber requires the knowledge and experience of textile engineers and equipment similar to that of plants producing viscose rayon. The casein is dissolved in alkali, various other substances are added, and the solution is extruded through the fine apertures of a spinneret into a bath containing acid and dehydrating and hardening agents.

Spinneret In Action

Ok, there sounds like there are a lot of chemicals involved in manufacturing milk fiber. So definitely not like making or eating cheese, then.  Another article, Some Fibers From the Proteins, gets a little more in-depth in its explanation:

The casein is dissolved in water that contains about 2 percent by weight of alkali to make a viscous solution with 20 to 25 percent protein. The next step is to pump the filtered casein solution by a metering pump through a platinum-gold alloy disc, or spinneret, which has thousands of fine, accurately placed, and uniform holes. The solution, streaming from the holes of the spinneret, is immersed in water that contains an acid. The acid neutralizes the alkali used to dissolve the casein. The small, continuous fibers are then stretched, treated in various solutions, and collected by the spinning machinery. The tensile strength of the yarn is enhanced by stretching the fiber while it is being tanned with aluminum salts and formaldehyde. The action of the hardening baths can be accelerated by heating, and the fiber can then be stretched much more than at low temperatures. A further treatment is needed in order to make the fiber resist the boiling bath commonly used in dyeing wool.

In case your eyes just glazed over, what that brain melting paragraph just said was that the proteins from milk have to be dissolved in water and then processed through various chemicals in order to try and make them solid again. Now, there are some chemicals in there that I’m not wild about, as they sound dangerous, but according to some of the websites selling milk fiber commercially, the milk fiber industry was granted the Oeko-Tex Standard 100 green certification for international textiles in 2004. So, I wonder, how different is the manufacturing process today?

Production process of milk fiber

I found a clue at the Doshi Group website, which mentions that milk fiber is a “graft copolymer of casein and AN.” They even provided this cute little chart showing how they make milk fiber. As you can see, the process is very similar to what was described in that 1940s article above. There’s the dehydrating of the milk to get to the protein, dissolving it in alkali, and the spinning and drying to turn it into fiber. But interestingly enough, there’s a little stop before spinning called “graft copolymerization.” I think this is a big clue. Let’s go find out what that mysterious “AN” is.

Ah ha! I searched for a long time to find this, because nowhere on the Internet could I find the words “AN” and “milk fiber” comingling together. But finally, I hit pay dirt. An obscure Chinese science article from Dong Hua University, Shanghai in 2000 did a study of the effects of acrylonitrile (AN) being grafted onto casein. They concluded that “AN-g-casein fiber is a new type modified ‘silk-like’ fiber for wide application.” According to The Textile School, to manufacturer milk fiber, casein and acrylonitrile are grafted together chemically. They dilute alkali and forcing these solutions through a spinneret into a coagulating bath:

A fiber consisting of a copolymer of casein protein (25%-60%) grafted with 40%-75% acrylic monomers, of which at least half is acrylonitrile, has been developed in Japan under the tradename Chinon. The casein dissolved in aqueous zinc chloride and grafted with acrylonitrile is wet or dry spun into fibers. It dyes readily with acid dyes, but basic and reactive dyes can be used also. The fiber is marketed as a substitute for silk.

Ding ding ding! So what do we know now? Modern milk fiber is a blend of casein protein and acrylonitrile, most likely to strengthen it and prevent some of the problems that the original casein fiber had. But I still have questions. Like, what’s acrylonitrile? According to Wikipedia it’s a chemical compound that’s an important monomer, or binder, for the manufacture of useful plastics. This website does a great job of demonstrating how it’s made. However, they also mention it as being a pollutant, and the Environmental Protection Agency (EPA) and the German MAK commission have classified acrylonitrile as a human carcinogen. Whoa, scary! But the American Chemistry Society clarifies things a bit:

Chances are that acrylonitrile touches everyone in some way every day. Acrylonitrile is the key ingredient in the acrylic fiber used to make clothing and carpeting…telephone and computer casings and sports equipment; and in nitrile rubber, which is used in the manufacture of hoses for pumping fuel. Acrylonitrile is used to produce plastics that are impermeable to gases and are ideal for shatterproof bottles that hold chemicals and cosmetics, clear “blister packs” that keep meats fresh and medical supplies sterile, and packaging for many other products. It is also a component in plastic resins, paints, adhesives, and coatings.

Ok, so not that scary. You don’t want to try eating acrylonitrile or being near it when it’s burning, but touching things made from it won’t immediately hurt you either. But we have learned a very important fact: acrylonitrile is a “key ingredient” in making acrylic fiber, and is the raw material in making acrylic yarn as well.

So the answer to our question, “what is milk fiber” has been answered. Milk fiber is a blend of casein protein and the chemical acrylonitrile, which is used to make acrylic. It’s made using a process that is similar to rayon/viscose, but because it’s a regenerated protein fiber and not a regenerated cellulose fiber, it reacts like wool. That means that it dyes like wool and even smells like wool when burned, according to Kiplinger.

Interestingly enough, while slogging through all of this research in an effort to discover everything I could about milk fiber, I discovered that it does in fact have antibacterial properties. While the “milk slurry” is being chemically mixed and spun together, micro-zinc ions are added. This creates zinc oxide while the product dries, making it bacteriostatic. Also, according to Doshi, they do not use formaldehyde as one of the drying agents anymore. Though I do doubt their claims that fabric made from this fiber is good for the body and can “nourish skin.” Since it’s made in a way that is similar to rayon and acrylic yarns, it does nothing more to your skin than any other fiber. If you want your skin to be nourished, I recommend using some lotion instead.

UPDATE: July 27, 2011

Since writing this blog post, the conversation about milk fiber and its relationship with AN (acrylonitrile) has exploded, even being featured on major news sites such as HuffingtonPost. Thanks so much for your interest, everyone, and I always appreciate links back to my research.

I’ve come across a couple of extra pieces of information I think are really important to know about milk fiber. The reason that milk fiber hasn’t become a huge phenomenon is because of an issue of supply and demand. Apparently it takes about 100 pounds of skim milk to make 3 pounds of milk fiber. Now, my relatives are dairy farmers, and they have one barn full of dairy cows, so I have trouble fathoming the idea of enough cows to make just one roll of milk fabric. So face it, milk fiber is always going to remain sort of exotic and harder to get.

Also, milk fiber isn’t as eco-friendly as we all first were told. According to Finn + Emma, an organic children’s clothing company that actually practices what it preaches, traditional dairy farming has a big negative impact on the environment. Combine that with the inhumane way some dairy animals are treated at mass-production farms and the eco-friendliness aspect goes out the window. Ouch. Granted, I use lots of yarns that aren’t eco-friendly, but it just goes to show that you can’t always trust the hype.