Chapter VIII Synthetic superabsorbents

Abstract

Publisher Summary This chapter discusses synthetic superabsorbents. The chapter reviews the physical chemistry of aqueous fluid absorption and superabsorbents. The chapter discusses the manufacture of the major commercial synthetic materials, the process of performance evaluation, and also reviews the primary applications. The chapter focuses on crosslinked sodium polyacrylate gels because this is the dominant chemistry for commercial superabsorbents. Two quite different mechanisms are employed to retain fluids in absorbent products, capillarity, and osmosis. The essential characteristic of capillary absorption is illustrated by the spontaneous rise of fluid in a small tube. A familiar example of a good capillary absorbent for aqueous fluids is cellulose fluff. Osmosis, the other mechanism for fluid transport and storage, is driven by the same thermodynamics that cause dissolution. This chapter also discusses polymer networks or gels, crosslinked systems that do not form true solutions but stop at the swollen state noted by Billmeyer. The swelling process begins with the formation of a true polymer solution. Aside from swelling capacity, another property characteristic of a gel is its toughness or resiliency. In addition to sodium polyacrylate, certain other acrylate based polymer systems have been developed as superabsorbents.