Regenerated Protein Fibers

Keywords

Milk protein • Casein • Solubility • Alkaline solution • Stability • Cross-linking • Aldehyde • Carboxylic acid • Allergy • Cytotoxicity

The milk protein casein was made into fibers on an industrial scale as early as the 1950s and was available in the commercial names such as Lanita produced from Snia and Fibrolane produced from Courtalds [07Hea]. Trade names of casein fibers also varied by the country where the fibers were produced. For example, casein fibers were marketed as Aralac and Caslen (USA), Lactofil (Holland), Cargan (Belgium), Tiolan (Germany), Silkool (Japan), and Fibrolane (England) [51Tra]. Traditionally, casein fibers were produced by dissolving casein in alkaline solutions, extruding and coagulating using sulfuric acid and sodium sulfate and later cross-linked with aluminum sulfate and formaldehyde, and finally treated with metal salts such as zinc [69Sal]. Although most reports do not provide the properties of the fibers, it has been suggested that casein fibers had dry tenacity of 0.8-1.0 g/den, wet tenacity of 0.4-0.5 g/den, and elongation of 30-50 % [69Sal]. However, the fibers were soluble to weak alkali and to enzymes and therefore not practically useable. In addition, yellowing of the fibers was observed when fibers were treated with alkali at 70 °C for 40 min, but the fibers were stable under acidic conditions. Casein fibers were reported to have good uniformity, less impurity, and superior spinnability, but the fibers had poor cohesion and frictional resistance necessitating a pretreatment before the fibers could be made into yarns of 136 tex. The protein fibers were dyed with reactive dyes and found to have uniform dyeability.

In a more recent study, casein was mixed with soy proteins and made into fibers. Proteins were dissolved using urea and sodium sulfite, mixed in various ratios, and extruded into an acidic coagulation bath saturated with sodium sulfate [11Sud]. It was found that casein contents higher than 50 % were necessary to obtain fibers with improved morphology and thermal stability. However, tensile properties of the
fibers were not studied. In another recent study, casein fibers were dissolved in aqueous alkali and wet spun into a coagulation bath [12Yan]. Fibers obtained at 30 % casein concentration had strength of about 1 g/den, elongation of 13 %, and modulus of about 87 g/den. However, the fibers were unstable in water and therefore cross-linked with citric acid to improve stability. After cross-linking, the fibers retained about 50 % of their strength after treating in PBS at 37 °C for 12 days. Fibers also had good strength retention in acidic and weak alkaline solutions. However, casein fibers were found to be cytotoxic, probably related to the allergenic nature of milk proteins. It has been recently reported that casein fibers are produced on a commercial scale (http://www. reuters. com/article/2011/10/06/ us-germany-fashion-milk-idUSTRE7953MG20111006). However, the fibers are blends with other polymers and amount of casein in the fibers, the use of cross­linkers, if any, or the stability of the fibers under various conditions is not known.

References

[51Tra] Traill, D.: J. Soc. Dyer. Color. 67(7), 257 (1951)

[69Sal] Salzberg, H. K.: Encycl. Polym. Sci. Technol. 11, 688 (1969)

[07Hea] Hearle, J. W.J.: Mater. Sci. 42(19), 8010 (2007)

[11Sud] Sudha, T. B., Thanikaivelan, P., Ashok Kumar, M., Chandrasekaran, B.: Appl.

Biochem. Biotechnol. 163(2), 247 (2011)

[12Yan] Yang, Y., Reddy, N.: Int. J. Biol. Macromol. 51(1-2), 37 (2012)