Poly acrylic acid (PAA) is a polymer with the formula (CH2-CHCO2H)n. It is a derivative of acrylic acid (CH2=CHCO2H). In addition to the homopolymers, a variety of copolymers and crosslinked polymers, and partially deprotonated derivatives thereof are known and of commercial value. In a water solution at neutral pH, PAA is an anionic polymer, i.e., many of the side chains of PAA lose their protons and acquire a negative charge. Partially or wholly deprotonaated PAAs are polyelectrolytes, with the ability to absorb and retain water and swell to many times their original volume. These properties - acid-base and water-attracting - are the bases of many applications.
The dominant application for PAA is as a superabsorbent. About 25% of PAA is used for detergents and dispersants.
Polyacrylic acid and its derivatives are used in disposable diapers. Acrylic acid is also the main component of Superadsorbent Polymers (SAPs), cross-linked polyacrylates that can absorb and retain more than 100 times of their own weight in liquid. The US Food and Drug Administration authorised the use of SAPs in packaging with indirect food contact.
Detergents often contain copolymers of acrylic acid that assist in sequestering dirt.Cross-linked polyacrylic acid has also been used in the processing of household products, including floor cleaners. PAA may inactivate the antiseptic chlorhexidine gluconate.
The neutralized polyacrylic acid gels are suitable biocompatible matrices for medical applications such as gels for skin care products. PAA films can be deposited on orthopaedic implants to protect them from corrosion. Crosslinked hydrogels of AA and gelatin have also been used as medical glue.
Other applications involve paints and cosmetics. They stabilize suspended solid in liquids, prevent emulsions from separating, and control the consistency in flow of cosmetics. Carbomer codes (910, 934, 940, 941, and 934P) are an indication of molecular weight and the specific components of the polymer. For many applications PAAs are used in form of alkali metal or ammonium salts, e.g. sodium polyacrylate.