Detailed properties and application of sodium alginate printing and dyeing auxiliaries

　　Sodium alginate, also known as sodium alginate, kelp gum, fucoidan and alginate, is a natural polysaccharide carbohydrate extracted from kelp. Widely used in food, medicine, textile, printing and dyeing, papermaking, daily chemical products, etc., as thickener, emulsifier, stabilizer, adhesive, sizing agent, etc. Since 1980s, the application of sodium alginate in food has been expanded. Sodium alginate is not only a safe food additive, but also a base material of bionic food or therapeutic food. Because it is actually a natural cellulose, it can slow down the absorption of fatty sugar and bile salt, reduce serum cholesterol, triglyceride and blood sugar, and prevent modern diseases such as hypertension, diabetes and obesity. It can inhibit the accumulation of harmful metals such as strontium, cadmium and lead in the intestine. It is precisely because of these important functions that sodium alginate has been paid more and more attention at home and abroad. Japanese call the food rich in sodium alginate "longevity food", while Americans call it "wonderful food additive".

　　Alginate is a natural polymer existing in brown algae and a natural polysaccharide extracted from brown algae or bacteria. It is similar to glycosaminoglycan GAGs in extracellular matrix, and has no subacute/chronic toxicity or carcinogenic reaction. It can be used as an edible food additive and a scaffold material for medical purposes, and has good biocompatibility [10]. Alginic acid is composed of guluronic acid (G segment) and its stereoisomer mannuronic acid (M segment), which are passed through α -1,4 glycosidic bonds are linked to form an unbranched linear block copolymer. Alginate can easily combine with some divalent cations to form a gel. Moreover, its mild sol-gel process and good biocompatibility make alginic acid suitable as microcapsules for releasing or embedding drugs, proteins and cells. When the carboxyl group at the 6 th position is combined with sodium ion, Sodium Alginate is formed. There are many classification methods of sodium alginate. Structurally, it can be divided into three types: high G/M ratio, medium G/M ratio and low G/M ratio. From the viscosity, it can be divided into low viscosity, medium viscosity and high viscosity sodium alginate. In terms of purity, it can be divided into three levels: industrial, edible and medical. Different qualities of sodium alginate have great influence on the structure of colloidal beads. Generally speaking, sodium alginate with high G/M ratio and low viscosity is suitable for preparing colloidal beads. Besides,When the colloidal beads are used in the field of bioengineering, medical grade sodium alginate should be selected. Sodium alginate is a high viscosity polymer compound. It is different from starch, cellulose and so on in that it has carboxyl groups and is β The aldehyde group of -D- mannuronic acid is a polyuronic acid formed by glycoside bond. Its functional properties are as follows:

　　(1) Strong hydrophilicity, which can be dissolved in cold water and warm water to form a very viscous and uniform solution.

　　(2) The formed true solution has softness, uniformity and other excellent characteristics which are difficult to be obtained by other analogues.

　　(3) It has a strong protective effect on colloid and strong emulsifying power on oil.

　　(4) When metal salts such as aluminum, barium, calcium, copper, iron, lead, zinc and nickel are added to the solution, insoluble alginate will be generated. These metal salts are buffers such as sodium and potassium phosphates and acetates, which can inhibit and delay solidification.

　　(5) Generally, the pH value is 7, which is neutral and can be adjusted between 4 and 10.

　　(6) It is a linear polymer electrolyte, which can be made into tough fibers (alginate fibers) or films, and has the function of preventing cracking.

　　(7) Low adhesion, suitable for warp sizing and demoulding. Sodium alginate has been listed as a safe food additive in Europe, America and Japan. As a kind of seaweed gum, it can improve the properties and structure of food with its inherent physical and chemical properties. It is low in heat and nontoxic, easy to swell and high in flexibility. When added to food, its functions are solidification, thickening, emulsification, suspension, stability and prevention of food drying. The most important function is gelation, that is, the formation of edible gel, close to solid, to maintain the shape of the molding. Therefore, it is an excellent food additive. It can not only increase the nutritional content of food, improve the quality of products, increase the variety of colors, but also reduce the cost and improve the economic benefits of enterprises.