A Brief History of Super Absorbent Polymer (SAP) Chemistry

Super Absorbent Polymers (SAPs) are a class of advanced functional polymer materials capable of absorbing and retaining extremely large amounts of water—often hundreds or even thousands of times their own weight. Upon absorption, SAPs swell to form a water-containing hydrogel. Unlike traditional absorbent materials, these hydrogels can retain water even under pressure, which makes SAPs fundamentally different from materials such as tissue paper, cotton, sponges, or fluff pulp.

Before the 1960s: Traditional Absorbent Materials

Before the development of SAPs, commonly used absorbent materials included tissue paper, cotton, sponges, and fluff pulp. These materials typically could absorb no more than 20 times their own weight in water and released liquid easily when pressure was applied. Their limited absorbency and poor water retention restricted their performance in many applications.

1960s: Birth of Super Absorbent Polymers

In the 1960s, the United States Department of Agriculture (USDA) initiated research to improve water conservation in agricultural soils. Scientists developed a new resin by grafting polyacrylonitrile onto a starch backbone. This starch-grafted polymer could absorb more than 400 times its own weight in water. More importantly, the absorbed water was retained within the gel structure and was not released even under pressure. This breakthrough marked the birth of super absorbent polymer technology.

Late 1960s–1970s: Independent Research in Japan

Because Japanese companies were excluded from the USDA-developed technology, they began independent research into alternative absorbent materials. These efforts explored various raw materials, including starch, carboxymethyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA), and isobutylene–maleic anhydride (IMA). These studies significantly advanced SAP chemistry and broadened the range of possible polymer structures.

1970s: First Commercial Applications

During the 1970s, super absorbent powders were used commercially for the first time. Although SAPs were originally developed for soil amendment and agricultural water retention, their earliest large-scale commercial application was in disposable hygienic products.

1980s: Expansion into Hygiene Products

In 1982, SAPs were first used in baby diapers in Europe. Shortly thereafter, UniCharm introduced super absorbent baby diapers in Japan. This marked a major turning point, as SAPs rapidly became a core material in disposable hygiene products such as diapers and sanitary napkins.

1990s to Present: Modern SAP Technology

With ongoing technological advancements, starch-grafted absorbent polymers have largely disappeared from disposable hygiene applications. Modern SAPs are typically cross-linked acrylic homopolymers, most commonly sodium-neutralized polyacrylic acid, which offer higher absorbency, better gel strength, and improved stability.

For agricultural and soil amendment applications, SAPs are usually cross-linked acrylic–acrylamide copolymers, often potassium-neutralized, to better support plant growth and soil compatibility.

Definition and Applications of Water-Absorbing Powders

Water-absorbing powders—also referred to as hydrogels or super absorbent powders—are highly absorbent substances capable of rapidly capturing and retaining moisture from their surroundings. These materials are widely used in hygiene products, agriculture, construction, packaging, humidity control, and environmental applications. Their ability to lock in water helps prevent dampness, reduce mold growth, and regulate moisture efficiently.

Conclusion

From early low-performance natural absorbents to today’s highly engineered polymer networks, the development of super absorbent polymers represents a significant advancement in materials science. SAPs continue to evolve, offering increasingly efficient solutions for water absorption and retention across a wide range of industries.