Classification of Superabsorbent Polymer···

Introduction
Superabsorbent polymer (super absorbent resin) is developing rapidly, and the types are increasing day by day, and the source of raw materials is quite rich. Due to the hydrophilic groups on the molecular structure of the superabsorbent polymer, or the low crosslinking degree or partial crystallization in the chemical structure. The structure is not the same, so it has formed its own characteristics while giving it high water absorption performance. From the perspectives of raw material sources, structural characteristics, performance characteristics, product shapes and production processes, the superabsorbent polymer are classified to form a variety of classification methods.

1. Classification according to the source of raw materials.
With the continuous deepening of research on superabsorbent polymer, the traditional super absorbent resins are classified into starch series, cellulose series and synthetic resin series, which cannot meet the classification requirements. Therefore, Professor Zou combined his own research results and proposed six series of classifications. Starch series: including grafted starch, carboxymethylated starch, phosphated starch, starch xanthate, etc.; cellulose series: including grafted cellulose, carboxymethylated cellulose, hydroxypropylated cellulose, Xanthogenated fiber cords, etc.; Synthetic polymer series: including polyacrylates, polyvinyl alcohols, polyoxyalkylenes, inorganic polymers, etc.; Protein series: including soy protein, silk protein, gluten, etc. ; Other natural products and their derivatives: including pectin, alginic acid, chitosan, heparin, etc.; Blends and composites: including blending of super absorbent resin, super absorbent resin and inorganic gel Composites, superabsorbent polymers and organics, etc.

2. Classification according to the hydrophilization method.
The superabsorbent polymer has a large number of hydrophilic chemical groups in the molecular structure, and the hydrophilicity of these groups greatly affects the water absorption and retention properties of the superabsorbent resin, how effectively obtaining the organizational structure of these chemical groups on the chemical structure of the superabsorbent polymer and giving full play to the effectiveness of the hydrophilic point where each chemical group is located has become the focus of research on superabsorbent polymers. Therefore, it can be classified from the hydrophilization method. Polymerization of hydrophilic monomers (such as polyacrylates, polyacrylamides, acrylic-acrylamide copolymers, etc.); carboxymethylation (or carboxyalkylation) of hydrophobic (or poorly hydrophilic) polymers (Such as starch carboxymethylation reaction, cellulose carboxymethylation reaction, polyvinyl alcohol (PVA)-maleic anhydride reaction, etc.); hydrophobic (or poorly hydrophilic) polymer graft polymerization hydrophilic monomers (such as starch grafted acrylate, starch grafted acrylamide, cellulose grafted acrylate, starch-acrylic acid-acrylamide graft copolymer, etc.); polymers containing cyano, ester, and amide groups hydrolysis reaction (such as hydrolysis after starch grafting acrylonitrile, hydrolysis of acrylate-vinyl acetate copolymer, hydrolysis of polyacrylamide, etc.).

3. Classification according to the cross-linking method.
The cross-linking control of the superabsorbent resin is an important aspect to control its spatial organization state. The density of its crosslinking point directly affects the water absorption and water retention capacity of the superabsorbent polymer. Therefore, according to the different ways of forming crosslinking points, the following classifications can be made. Cross-linking agent for network reaction (such as multi-reactive functional group cross-linking agent water-soluble polymer, multivalent metal ion cross-linking water-soluble polymer, water-soluble polymer cross-linking with polymer cross-linking agent Etc.); Self-crosslinking network reaction (such as self-crosslinking polymerization reaction of polyacrylate, polyacrylamide, etc.); Radiation irradiation networking reaction (such as polyvinyl alcohol, polyoxyalkylene, etc. crosslinking by radiation irradiation ); The water-soluble polymer is introduced with a hydrophobic group or a crystalline structure (for example, polyacrylic acid is esterified with an alcohol containing a long chain (C12 to C20) to obtain an insoluble super absorbent polymer, etc.).

4. Other classification methods.
According to the classification of products, super absorbent resin can be divided into powder, fiber, film, microsphere and so on. According to the preparation method, the super absorbent resin can be divided into synthetic polymer polymerization cross-linking, carboxymethylation, starch graft copolymerization, cellulose graft copolymerization, etc. In terms of degradation performance, SAR can be divided into non-degradable types (including sodium acrylate, methyl methacrylate and other polymerized products), and degradable types (including starch, cellulose and other natural polymer graft copolymerization products).

Keywords: superabsorbent, superabsorbent polymer, SAP

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