Alginate is produced from brown seaweed and used traditionally for medical dressings and stitches due to its high iodine content. Alginate fiber is a biodegradable, biocompatible, and eco-friendly fiber known for its excellent moisture absorption, wound-healing, and flame-resistant properties. This viscose-type fiber was discovered in 1940s at Leeds University, and it was used to create an alginate multifilament yarn.
Alginate is a substance that occurs in brown seaweed. It is a block copolymer of α-l-guluronic acid (G) and β-d-mannuronic acid (M), the GG and MM blocks occurring in various lengths and proportions, depending on the type of seaweed. Alginate fibers usually contain a high proportion of either the G or the M monomers. Alginate fibers are composed of water-insoluble alginic acid and/or its salts, which are obtained from the cell walls of brown algae. The raw material of alginate fiber (alginic acid) is obtained from marine brown algae (Ascophyllum, Durvillaea, Ecklonia, Laminaria, Lessonia, Macrocystis, Sargassum, and Turbinaria species).
Seaweed is collected, dried and ground into a fine powder. It is dissolved in sodium carbonate and caustic soda, which produces a sodium alginate solution that is extruded into a calcium chloride bath to coagulate the fiber. Alginate fibers are produced by wet spinning technology, in which a solution of sodium alginate is extruded through a spinneret into a bath of calcium chloride solution. The fibers precipitate as the calcium alginate form. The solution is forced through a spinneret, which goes into a spinning bath containing calcium chloride, which acts as a coagulant. The fibers are precipitated in the spinning bath and then carried over the first set of rollers.
For the production of fibers, first the alginate is extracted from raw seaweed by treatment with NaOH, thereby turning the natural alginate into water-soluble sodium alginate. After several filtrations, it can be treated with calcium chloride to get a precipitate. The precipitated alginate can be dried and crushed to make a powder. Then the powder can be dissolved in water to feed into wet spinning. Alginate fibers are generally prepared by injecting a solution of water-soluble alginate (usually sodium alginate) into a bath containing an acidic solution or calcium salt solution to produce the corresponding alginic acid or calcium alginate fibers, which can be used to produce yarns and fabrics for medical applications and as drug carriers for wound healing.
The fibers are most easily produced for wound dressings as a non-woven web. They are of fairly low tenacity (only 14–18 cN tex−1) and have quite low elongation (about 2–6%), so they are difficult to process by conventional textile machinery into yarns for weaving or knitting. Specially developed processes are required for making yarns from these fibers. Alginate fibers have excellent gel-forming properties, which help them to hold large quantities of water. Generally, alginate fibers are mostly used in medical textiles (particularly for wound-healing products, gels, foams, and absorbent nonwoven materials).
The most important source of commercial alginates is brown algae. Alginate is found in the cell wall and intercellular regions of brown algae. However, only three types of brown algae are sufficiently abundant or suitable for commercial extraction of the alginic acid. In order of abundance, they are laminaria (British Isles, Norway, France, N. America, Japan), microcystis (USA) and ascophyllum (British Isles). The high viscosity alginate in commercial use has a molecular weight of about 150,000 and a DP of about 750 but the average molecular weight of ordinary alginate is 15,000. Harvesting is easy because most brown seaweed grow in shallow water.
Minor fiber made of a jelly-like calcium alginate derived from certain forms of seaweed used as scaffolding in such fabrics as surgical dressings which can be dissolved away.
Properties of Alginate Fiber
Alginate fibers are fine, highly absorbent, therapeutic; promotes rapid healing and hastens blood clotting. It is flame resistant and renewable. Alginate fibers are soluble in hot water mixed with a soap alkali. Solubility is used to create the burn-out effect – the holey effect on woven fabric that is similar to that of devoré. Alginates can be used as scaffolding to support weaker yarns or delicate fabrics during manufacturing processes and are dissolved later.
Alginate fibers show poor resistance to UV. Fiber solubility depends on the degree and type of crosslinking with multivalent metal ions. Ion exchange, absorption and gel swelling properties of alginate fibers are very important for using them as wound dressings. Generally, the properties of alginate fibers are generated by their fiber-forming material structure. Standard calcium alginate fibers are characterized by the following properties:
Elongation at break: 10–14% under normal conditions; 25% wet
Typical absorbency (at 0.9% saline): 18 g/100 cm2
Moisture regain: 20–35
Specific gravity: 1.779
Effect of alkali: Calcium alginate readily soluble in dilute alkali
Effect of moisture: Calcium alginate is not soluble in water
Effect of organic solvents: Not soluble
The main properties of alginates, which are particularly important to their application, are:
Alginates have some unique properties such as non-toxicity, biocompatibility, biodegradability and hydrophilicity and have a relatively low cost.
Alginates have the ability to create permanent gels as a result of their reactions with calcium salts. This ability is used, for example, in processing into medical materials.
Alginate fibers are produced mainly for medical use (especially as wound dressings), so the alginates used should be characterized by appropriate properties, such as molecular weight, polydispersity and an appropriate participation of individual blocks. Taking into consideration demands put in front of fiber-forming polymers and the demands concerning fiber tenacity, it is recommended that they should have a high molecular mass and low polydispersity. To ensure an appropriate functionality of the fibers from the point of view of using them in wound dressings, it is necessary for the presence of a fraction with lower molecular weight to partake.
Alginates were found useful also as carriers controlling drug release, in tissue engineering and in artificial pancreas construction.
Production of Alginate Fibers
Alginate fibers were produced by a conventional wet spinning technique using a multifunctional laboratory extruder. The manufacture of alginate fibers consists of the following steps. Seaweed is collected, dried and milled.
Raw material is sea weed which contains alginic acid which is a polymer of d-mannuronic acid of molecular weight in excess of 15,000, which accounts of the one-third its weight of many dried sea weeds. The dried seaweed is powdered and (stored) is treated with a solution of sodium carbonate and caustic soda where by the alginic acid is converted to sodium alginate. Resultant solution allowed to stand and all undissolved matters are allowed to settle and removed. The viscous solution of sodium alginate is purified by sedimentation then bleached and sterilized by the addition of sodium hypochlorite. The alginic acid is then precipitated by acidification, which is later washed and reconverted to the pure sodium salt. The sodium alginate salt is made into a thick paste, dried and milled to make sodium alginate powder.
A dilute solution of sodium alginate is made, filtered, then spun by the viscose spinning method into a coagulation bath (wet spinning) containing certain polyvalent cation salts (Ca++, Al+++, etc.) or inorganic acid solution; about 0.02 N hydrochloric acid, emulsified oil and a small quantity of a cationic surface agent. The water soluble sodium alginate is thus precipitated in filament form as an alginic acid metal salt, e.g., calcium alginate or alginic acid. The filaments are drawn together, washed, lubricated, dried and wound. The alginic acid is again converted to sodium alginate by neutralization with soda ash.
This solution is extruded through spinneret into coagulating bath containing hydrochloric acid, calcium chloride and a little surface active agent. Streams emerging coagulate into calcium alginate fibers which are washed, oiled, dried and wound onto bobbins or cut (sometimes stretched to break the fibers by varying the relative feed rates which control the degree of stretch-breaking effect) to the required staple length suitable for non-woven products. As calcium or hydrogen ions are exchanged with sodium ion, the reaction proceeds until the sodium alginate is converted to calcium alginate or alginic acid.
Spinning process
Alginate can be wet spun in apparatus similar to those used for spinning regenerated cellulose fibers. The precipitation (coagulation) bath can be situated horizontally or vertically (fiber moving upwards or downwards). Further manufacturing operations (drawing, washing, drying, etc.) can be realized continuously or periodically as separate operations. A typical spinning process may be as follows: a 6.4% by weight aqueous sodium alginate solution is extruded through a jet containing 20 holes into a bath containing 5% salt of calcium chloride, a 0.2% acetic acid and 0.05% cetylpyridinium chloride (cation active compound) at 40°C. By this process, it is possible to obtain alginate fibers which do not adhere to one another without addition of emulsified oil to the bath. The threads produced are 37% stretched by passing them over godets and reeled into skeins. They are then washed in a 0.1% solution of calcium chloride at 80°C and then dried at room temperature and conditioned (Fig. 6.7).
Fig: Schematic diagram of alginate fire spinning process
It has got good dry strength but the strength is lost when wet. It is non-flammable. Used as scaffolding to support other yarns in the manufactureof lightweight, sheer and lacy fabrics. Medical application for dressing. Flameproof characteristics has also fiber suitable for limited applications. A major use of alginate yarns are as removable linkages, e.g., in collar bindings in the production of hosiery. They may be removed from the fabrics by washing in dilute solutions of sodium carbonate or sequestering agents such as Calgon. Goods should have sufficient freedom of movement to ensure that the dissolving solution reaches the alginate threads.
For years there has been increasing demand for fibers produced from alginate. These fibers are characterized by such unique properties as, e.g., non-toxicity, biocompatibility, biodegradability, high absorption, and the ability to create permanent gels. It is possible, therefore, to extend the field of their application. Great progress in such modern technologies as nanotechnology, biotechnology and composite technologies allows alginate fibers to be used for the following purposes:
Nanofibers and nanocomposites for advanced applications.
Alginate fibers are one of the most important materials for wound management. Modern active dressings, besides their function of providing a moist wound environment, should also be adaptable to the stage of wound healing and, on this basis, be capable of stimulating the granulating process or protecting against the damage of a newly formed tissue. Introducing other polymers (chitosan, carboxymethylchitosan, keratin, branan ferulate) or special additives (silver and their salts, antibiotics, deodorizing agent) allows a more functional wound material into alginate material. The use of alginate in textile scaffolds that may be knitted, woven, nonwoven, braided, embroidered or combined, has certain specialized applications. Flexibility provides versatility, and that is why alginate fiber systems are ideal for encouraging cells to reconstruct the tissue structure in three dimensions. There is also a high potential for nanofibres from this biopolymer42 to be used in tissue engineering, as a carrier of various drugs to specific sites.
Uses of Alginate Fiber
Alginate fibers are utilized across various industries, with particularly significant applications in medicine and textiles. For example, medical dressings e.g. pink knitted fabric in plasters. Used in surgical gowns, caps, and masks. Employed as scaffolds for cell culture and tissue regeneration due to its biocompatibility. As a highly absorptive alginate that forms a gel or a non-woven alginate they can be removed from a wound without damaging the new tissue. It is also used for dental products (mouth moulds), dissolvable in knitted products (welts of socks) and vanishing markers in embroidery.
Conclusion
Alginate fiber, a natural polysaccharide extracted primarily from brown seaweed is a unique bio-based and sustainable textile material. Its biocompatibility, biodegradability, high absorbency, and flame resistance make it highly valuable in medical and technical applications. From wound dressings and hygiene products to flame-retardant fabrics, alginate fiber demonstrates how natural resources can be transformed into innovative, eco-friendly solutions. With increasing demand for sustainable and functional materials, alginate fiber is poised to play a significant role in the future of smart and green textiles.
References
[1] Kolanjikombil, M. (2018). The substrates: Fibers, Yarn and Fabric. Woodhead Publishing.
[2] Ashford, B. (2016). Fibers to Fabrics.
[3] Blackburn, R. (2005). Biodegradable and sustainable fibers. In CRC Press eBooks. https://doi.org/10.1201/9781439823781
[4] Eichhorn, S., Hearle, J. W. S., Jaffe, M., & Kikutani, T. (2009). Handbook of Textile Fiber Structure: Volume 2: Natural, Regenerated, inorganic and Specialist Fibers. Woodhead Publishing.
[5] Mather, R. R., & Wardman, R. H. (2015). The chemistry of textile fibers. In The Royal Society of Chemistry eBooks. https://doi.org/10.1039/9781782626534
[6] Woodings, C. (2001). Regenerated cellulose fibers. In Woodhead Publishing Limited eBooks. https://doi.org/10.1533/9781855737587
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
