Superabsorbent resin

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Overview: Superabsorbent Polymer (SAP) is a new type of functional polymer material capable of absorbing water in amounts ranging from several hundred to over a thousand times its own weight. Due to its molecular structure, which allows for a certain degree of cross-linking, the water within the molecular network cannot be easily extracted using simple mechanical methods; as a result, it possesses strong water-retaining properties. Over the past 20-plus years, superabsorbent polymers have been widely used in many areas such as sanitary product materials, leading to a rapid increase in production. Brief development history: In the 1950s, Goodrich Company developed a production technology for cross-linked polyacrylic acid. During this period, Paul J. Flory developed the theory of particle network absorption for cross-linked polymer electrolyte water-swelling polymers, laying a theoretical foundation for the development of such polymers. In 1961, C. R. Russell and others at the Northern Research Station of the U.S. Department of Agriculture began researching the synthesis of superabsorbent polymers starting with starch grafted with acrylonitrile. In 1973, UCC Company used superabsorbent polymers as soil moisture retention agents, and later expanded their use to areas such as nursery cultivation in agriculture and horticulture. Although the use of water-absorbing polymers as liquid storage materials in personal care products was proposed as early as 1966, it was in Japan that superabsorbent polymers were first applied to sanitary materials. In 1978, high-absorbency polymers were industrialized in Japan. In 1979, Sanyo Kasei Industrial Company was the first to successfully add superabsorbent polymers to women’s sanitary pads. In 1979, Sanyo Kasei Industrial Company established a factory in Nagoya, Japan, with an annual production capacity of 1,000 tons of superabsorbent polymers; the products were sold to countries in Europe and the United States. Thereafter, companies such as National Starch Company, Atocem Company, Nippon Catalyst Company, Kao Company, Sumitomo Seika Company, Showa Denko Company, Nippon Steel Corporation, the German company Stockhausen, and the French company Atochem successively produced acrylic polymers using various cross-linking methods. In 1983, superabsorbent polymers were applied to baby diapers. Since the gel formed by water-absorbing polymers after absorbing water has a certain degree of strength and is relatively soft, it provides greater comfort when in contact with the skin, causes no irritation to living organisms, and has good ammonia absorption properties as well as a certain inhibitory effect on the breakdown by urease; therefore, it is suitable for use in sanitary products such as sanitary pads and diapers. Therefore, it developed rapidly in the 1990s. In 1985, there were only 13 production companies worldwide, and by 1995 this number increased to 50. Currently, about 90% of the production of superabsorbent polymers is used in sanitary products, especially in baby diapers (pants). Characteristics of superabsorbent polymers: Typical acrylic superabsorbent polymers are slightly cross-linked and partially neutralized acrylates. The product is in the form of a white powder with an extremely high water absorption capacity. Upon addition of water, it swells rapidly by absorbing water, endowing the entire solution with gel-like properties; 1 gram of this polymer can absorb more than 1000 grams of water. Superabsorbent polymers are polymer electrolytes, and their water absorption capacity is affected by salts and pH value. A polymer that can absorb 1000 grams of pure water per gram will have a water absorption capacity of only 50–70 grams per gram when absorbing 1% saline solution. The urine absorption capacity ranges from 20 to 40 milliliters per gram. Swollen polymers possess a certain level of water-retention capacity; the water absorbed under certain pressure can still be retained to a large extent. This differs significantly from the water-retention properties of wood pulp. As a result, over the past decade or so, these polymers have been used as a substitute for wood pulp in baby diapers and other sanitary products, which has led to rapid development in this field and a significant increase in production volumes. As can be seen from Table 7.1.1 below, acrylate has better properties, which is why its production volume is the highest.

Production status abroad: Thanks to the successful incorporation of superabsorbent polymers into women’s sanitary products and baby diapers, these products quickly became popular in the Japanese, American, and European markets, thereby opening up new opportunities for the use of SAP. At the same time, it was quickly expanded to other application areas. SAP’s production capacity and output are increasing year by year. In 1980, the global production capacity for SAP was less than 0.5 million tons per year; it reached 750,000 tons per year in 1995, and by 2004 it had reached 1.47 million tons per year. It is expected to reach over 1.6 million tons per year by 2010. In terms of production volume, the global production of SAP was 207,000 tons in 1989, 846,000 tons in 1996, and 1.02 million tons in 2000. Domestic production status: Foreign SAP manufacturers have recognized the huge potential market for SAP in China, given its large consumer base and rapid economic development, and as a result they have begun to set up SAP facilities in this country. Nippon Catalyst built a 30,000-ton/year superabsorbent polymer plant in Zhangjiagang, Jiangsu, which came online in 2004. Japanese company San Dia Polymer built a 30,000-ton/year SAP plant in Nantong, Jiangsu, which came online in 2005. The domestic SAP industry itself is still small in scale and has low production levels; both the quantity and quality of its products are not competitive with imported ones. The total production capacity of domestic facilities is less than 20,000 tons per year, with output at around 5,000 tons per year; most of this product is used in agriculture and other applications, while the SAP used in sanitary materials is largely imported from abroad. Ruijin Co., Ltd. in Zhongshan, Guangdong, which has a large production capacity, produced only a few thousand tons in 2002. Baoding Kehan Resin Factory has a production line with an annual capacity of 3,000 tons. Tangshan Boya Chemical Plant also has a production facility with an annual capacity of 3,000 tons. The capacity of the remaining units ranges from 100 to 5,000 tons per year. There is no 10,000-ton SAP plant in the country yet. The output is generally in the range of several hundred tons. The main manufacturers include Wuxi Jiabao Sanitary Materials Company, Jiangsu Guoda Polymer Materials Co., Ltd., Wuxi Hailong Sanitary Materials Company, Shanghai Gaoqiao Petrochemical Pujiang Plastic Factory, and Heilongjiang Beian Xuguang Chemical Plant, among others. Due to the sharp rise in the price of acrylic acid, which serves as a raw material for SAP in recent years, domestic SAP manufacturers have found it difficult to cope with the situation and have thus had to reduce production or even cease operations. Coupled with foreign large companies building large-scale SAP facilities in China, it has made it even more difficult for these domestic SAP manufacturers to survive.