高吸水性ポリマー（SAPと呼ばれる）

Super Absorbent Polymer (referred to as SAP) is a revolutionary type of functional polymer material known for its exceptional absorbency capabilities. Unlike traditional water-absorbing materials like tissue paper, cotton, sponge, and fluff pulp, SAP can absorb hundreds to thousands of times its weight and transform into a water-swelling hydrogel that retains water even under pressure.

The history of SAP traces back to the 1960s when the United States Department of Agriculture (USDA) initiated research on materials to enhance water conservation in soils. Their efforts led to the development of a resin based on grafting acrylonitrile polymer onto starch molecules, resulting in a new absorbency material capable of absorbing more than 400 times its weight without releasing liquid water under pressure.

Simultaneously, Japanese companies, not involved in the USDA’s research, began independent studies using starch, carboxymethylcellulose (CMC), acrylic acid, polyvinyl alcohol (PVA), and isobutylene maleic anhydride (IMA).

By the 1970s, SAP was commercially utilized for the first time, primarily in disposable hygienic products rather than for its original intended soil amendment applications.

The breakthrough came in 1982 when SAP was incorporated into baby diapers in Europe, followed shortly by its introduction in super absorbent baby diapers in Japan by UniCharm.

Technological advancements have since reduced the use of starch-grafted super absorbent polymer in disposable hygienic products, with most super absorbents now being cross-linked acrylic homopolymers (typically sodium neutralized) in these products.

In contrast, superabsorbents used for soil amendment applications are often cross-linked acrylic-acrylamide co-polymers (usually potassium neutralized). This evolution in SAP technology has significantly contributed to the development of highly efficient water-retaining materials with diverse applications across industries.