Milk or Casein Fiber: Properties, Manufacturing Process, Benefits and Uses

Last Updated on 02/06/2021

Milk or Casein Fiber:

Milk fibers are regenerated protein fibers made from a chemical substance and casein, which is derived from milk after the butterfat is removed. Casein fibers are made using a viscose process, the same process used to produce viscose rayon. It takes 100 pounds of skim milk to make 3 pounds of milk fiber.

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.

milk fiber
Fig: Milk fiber

Under the microscope, milk fiber cross‐sections appear similar to the beanlike shape of soybean fibers, though this shape is slightly less pronounced in milk fibers. The elongated air bubble inclusions seen in soybean fibers are not found in milk fibers. While silk fibers are translucent, smooth, or pseudoopaque, milk protein fibers, such as soybean protein fibers, are flattened with somewhat ribbon‐like characteristics.

History of Casein or Milk Protein Fiber:
According to Euroflax Industries, milk protein 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. Whoa. For a longwhile! 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?

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 It was 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.

Characteristics of Milk Fiber:
In milk fiber,the natural protein humectant factor is present, which makes the skin delicate and smooth…

  1. It absorbs moisture very well as it is hygroscopic in nature.
  2. It is antibacterial and antifungal as amino acids present in the fiber.
  3. It is glossy and luxurious in appearance, feel and comfortability, just like silk..
  4. It is very easy to dye and can be dyed under normal temperature.
  5. It can be blended well with other different fibers, such as tencel, cotton, bamboo fiber, modal fiber.

Properties of Milk Fiber
The fiber is naturally white, smooth surfaced, with faint striations. Cross section is bean shaped to round with dappled shape due to pitting. It can be spun into extremely fine filaments of 20–30μ in diameter.

Physical and chemical properties of casein fiber:

  • Tenacity, dry: 9.7–8.0 cN/tex (1.1–0.9 g/den)
  • Elongation: 60–70%
  • Specific gravity: 1.3
  • Effect of heat: Turns yellow if heated at 100°C itself for long time, at 150°C it decomposes.
  • Moisture regain: 14%
  • Effect of sunlight: Very little, like wool.
  • Effect of acid: Weak acid – no effect. Strong mineral acid – decomposes.
  • Effect of alkali: Sensitive to alkali. Sodium bicarbonate and disodium hydrogen phosphate have little effect. Strong alkali disintegrates.
  • Organic solvents: Stable to dry-cleaning solvents.
Cross section view of milk fiber
Fig: Cross section view of milk fiber
Magnified view of milk fiber
Fig: Magnified view of milk fiber

Production Process of Milk Fiber:

Raw material for the production of casein fiber is skimmed milk. The skimmed milk is treated with acid when the casein is obtained (coagulates) as curd. It is then washed dried and powdered. 35 liters of milk can give one kilogram of casein.

Flow chart of milk fiber manufacturing
Fig: Flow chart of milk fiber manufacturing

The casein made as explained above is dissolved in caustic soda solution and allowed to stand to reach a predetermined viscosity (ripening). This solution is pumped to spinnerets and under pressure, the filaments are extruded into a coagulating solution.

Example of coagulating solution (recipe):

  • 2 parts Sulphuric acid
  • 5 parts Formaldehyde
  • 20 parts Glucose
  • 100 parts Water

During coagulation, the filaments are stretched to some extent. During the spinning operation, the molecules are aligned to some extent but are not crystallized hence they are weak and soft, if handled will break and also water can enter the fiber and push the molecules apart hence it has got little use in textiles. To make it stronger, the casein is cross linked which will hold the molecule together. Cross-linked casein acquires an increased resistance to the effect of water, retaining a higher degree of tensile strength and resistance to swelling.

Milk protein fiber production line application processing system cannot do without the cooperation of the link. Shanghai is home on R and D Technology Co., Ltd. milk silk protein fibers, also engaged in spinning, dyeing and finishing of technical research, raw material quality, technology is complete, customers can better support the promotion of milk fiber.

In case of milk the content of 2.8–3.2 wt% of protein is of value for production of casein fibers. As a first step, casein has to be isolated from the milk by coagulation and filtration. Coagulation, for example, can be achieved by pH reduction through addition of acid or by addition of proteases (rennin, chymosin). The filtered casein then is dried and a powdery product is formed. The casein is then dissolved in caustic soda solution and the spinning dope becomes extruded into an acidic precipitation bath (e.g. sulphuric acid). To stabilise the coagulated protein structure, tanning agents and cross-linkers (e.g. formaldehyde and glutaraldehyde) are added.

Steps of milk fibre production
Fig: Steps of milk fiber production

Five amino acids represent the major components of casein: Glutamic acid/glutamine (15.6%), proline (10.5%), leucine and isomers (9.4%), valine (7.2%) and aspartic acid/asparagines (6.7%).

Milk protein fiber can be used, in theory, cationic dyes, direct dyes, acid dyes, reactive dyes, neutral dyes, generally more than the actual cationic dye and reactive dye used is suitable for pure milk protein fiber and its products, such as staple fiber, yarn line, knitted fabrics, woven fabrics and garments. Period in order to milk protein fiber textiles as an example of pure cationic dyes and reactive dyes on the usage described as follows.

After Treatment of Casein Fiber:
Cationic dyes and finishing the first treatment process, due to temperature and moisture absorption of the products are strong, so do not need special treatment. With 60oC warm water, liquid running back 10s, and then the second can of cold wash. In the special white process, the use of prescription and bleaching conditions were as follows: 5% sodium hydrosulfite (95oC with warm water even after accession); 5% of the standard soap powder (use warm water even after the accession), not alkaline, does not contain brighteners; bath ratio 1:20 ~ 30; temperature of 95 ~ 98oC, time is about 15s ~ 30s, but also according to liquor ratio, equipment and raw materials of different thickness to adjust. Note that, if so special white, raw materials without cooling; If the training is finished, then white, must be 2% to 3% of the HAC, 60oC warm water running 5s ~ 10s, cold washed twice, and then softening. Prescription and use of the whitening process conditions: 1.6% cationic brighteners (Dilute with warm water even after accession); 3% HAC (Dilute with warm water even after accession); temperature of 95 ~ 98oC; time of 15s ~ 20s ; bath ratio 1:25 ~ 30. In the dyeing process, the basic cationic dye with the general approach, but not 1227, and NaAc. To liquor ratio 1:25 to 30, for example, dyeing conditions to control the following table. Cleaning, light to be 1 or 2 times the cold wash, cold wash in the dark to be 1 or 2 times and then wash with hot water, 70oC 10s, and finally cold wash 1 or 2 times. In the post-treatment processes, the use of softener 5% to 8%; temperature 45 ~ 50oC time of 20s or so; bath ratio 1:20 ~ 25.

According to different requirements of customers can choose different softeners, such as the fabric soft, smooth, elastic anti-wrinkle, anti-contamination, etc. when requested, by the production units to decide. In the dehydration process, in order to reduce the discount video, dehydration, slower, time is shorter, usually 1 minute each time, while patients have to row together, try not to let cloth folded. In the drying process, the use of the cage drying temperature of 80oC and time is 20s ~ 30s, speed too quickly, after drying grounds lit 12 to 24 hours after the stereotypes. Using rotary drying temperature of 90oC with fast speed, the disadvantage is the easy bit like a very light, must be strictly controlled temperature.

In the setting process, the general shape of water rolling open sites, the effect is better than the cylindrical shape. Process parameters are 150oC 5% overfeed of 10%, the line speed 15m / s, the pressure head of about 4kg. Reactive dyeing of basic aspects of pre-treatment with the former, but if the dye houses using recycled water, pH value may be unstable or reactive groups dealing with different materials, can be the first treatment bath by adding 1% of the HAC, it will give the pH value of the cloth evenly from the inside out, but also conducive to color dyes.

Proven, low temperature dyeing cotton used reactive dyes more suitable, light-colored soda instead of baking soda can be used as dyeing auxiliaries, the amount can be as long as required to achieve the color, the dark can be used for dyeing auxiliary sodium sulfate and soda ash , the amount of cotton fiber dyed with similar.

Benefits of Milk Protein Fiber:
Today’s milk fibre is environmentally friendly, high strength and much more superior as compare to man made fibers. Some of the benefits of having casein fiber are as given below:

  • As it is having continues graft polymerization technique hence it is totally eco-friendly in nature.
  • It can be considered as “Green Product” as no formaldehyde is present in the product.
  • Milk protein fiber is made from milk casein instead of fresh milk. We may use acid, reactive or cationic dyes for this kind of specialty fiber.
  • pH of casein fiber is 6.8 which are same as that of human skin. Hence the products made up from them are more compatible to human skin.
  • Milk fiber contains seventeen amino acids and natural anti-bacterial rate is above eighty percent. Hence casein fiber has sanitarian function.
  • It is a new synthetic fiber having milk protein as main material based on high technical process. Casein fibre has the advantages natural fiber combined with synthetic fiber.
  • These are more comfortable, excellent water transportation and air permeability.

Some of its disadvantages are getting wrinkles easily after washing, no scope for machine washing as it is not a very hard fiber and low durability. Due to abundance of other fabrics like polyester, milk fabric never really became popular.

Uses of Milk or Casein Fiber:
Because of the healthy and bacteriostatic nature of milk fiber, it is being considered as a perfect material for manufacturing of underwear. As discussed above, milk casein proteins are considered as a main ingredient of milk protein fiber, which can lubricate the skin. The milk protein contains the natural humectant factor which can help to maintain the skin moisture, to reduce the wrinkles and to smooth the skin – which may help to realize the people of taking milk bath. At first milk fiber was used in the making of feeling for hats. Casein/wool blends are used for knitted berets. Casein/cotton or nylon blended fabrics are used for interlock outerwear, T-shirts, cardigans, jumpers etc. Common uses of milk protein fiber are point out below.

wearable dress from casein fiber
Fig: Wearable dress from milk fiber fabric

The major usages of milk fiber are as given below:

  1. T-Shirts
  2. Underwear
  3. Sportswear
  4. Ladies outerwear
  5. Sweaters
  6. Children’s garments
  7. Eye mask
  8. Socks and hats
  9. Home textiles
  10. Automobile industry
  11. Medical technology
  12. Thermal insulated seat covers
  13. Hygenic diaphragms


  1. The Substrates – Fibres, Yarn and Fabric by Mathews Kolanjikombil
  2. Textile Chemistry By Thomas Bechtold and Tung Pham
  3. Textile Fiber Microscopy: A Practical Approach By Ivana Markova
  4. Abdul Aziz “Milk or Casein Fiber: An Overview”; Accessed date: 02/06/2021
  5. Nishat Tasnim, “Eco-friendly Manufacturing Process of Casein Fiber with It’s Sustainable Features & Comfortable Uses” American Journal of Environmental Engineering 2019, 9(2): 31-35 DOI: 10.5923/j.ajee.20190902.02
  6. Mohit Saluja “An Introduction to Milk Fiber-A Review”; Accessed date: 02/06/2021

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