Polyacrylic acid which produced by acrylic acid can be further modified to produce superabsorbent polymers (SAPs) and other polyacrylic acid homopolymers or copolymers used as detergents, dispersants/antiscalants, anionic polyelectrolytes for water treatment, and rheology modifiers.
Acrylic acid (AAc, IUPAC: prop-2-enoic acid) is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus with the formula CH2=CHCO2H which is a colorless liquid above its freezing point of 13°C (56°F) with a distinctive acrid odor. It is corrosive to metals and tissue and prolonged exposure to fire or heat can cause polymerization. If polymerization takes place in a closed container, violent rupture may occur because the polymerizaiton of acrylic acid is exothermic. The inhibitor (usually hydroquinone) can greatly reduce the tendency to polymerize. It is miscible with water, alcohol, ether, benzene, chloroform, and acetone, but incompatible with strong oxidisers, strong bases, strong alkalies and pure nitrogen. It may polymerize (sometimes explosively) when contacting with amines, ammonia, oleum and chlorosulfonic acid, iron salts and peroxides.
Acrylic acid is a carboxylic acid, of which the primary use is in the production of acrylic esters. It has been traditionally used as the raw material for acrylic esters – methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate which were originally used to produce solvent-based acrylic resins but environmental concerns about solvent use led to the development of water-based acrylics. Acrylic acid can readily react with a wide variety of organic and inorganic compounds which results in it’s considered as a very useful feedstock to manufacture many low molecular compounds, such as propionic acid, unsaturated fatty acids, heterocyclic compounds, and Diels-Alder addition products. As a vinyl compound and a carboxylic acid, acrylic acid is used widely for polymerisation, including production of polyacrylates. It is also a monomer for polyacrylic and polymethacrylic acids and other acrylic polymers.
SAPs are cross-linked polyacrylates with the ability to absorb and retain more than 100 times their own weight in liquid. They have experienced very strong growth, primarily in baby diapers (nappies) and incontinence products.
A new application for SAPs is soaker pads used in food packaging. In 2007, the US Food and Drug Adminstration authorised SAPs in packaging with indirect food contact for poultry, meat, fish, fruit and vegetables.
Acrylic acid and esters are flammable, reactive, volatile liquids based on an alpha-, beta-unsaturated carboxyl structure. Incorporation of varying percentages of acrylate monomers permits the production of many formulations for latex and solution copolymers, copolymer plastics and cross-linkable polymer systems. Their performance characteristics—which impart varying degrees of tackiness, durability, hardness, and glass transition temperatures—promote consumption in many end-use applications. Major markets for the esters include surface coatings, textiles, adhesives, and plastics.
Crude acrylic acid (CAA) is made by the oxidation of propylene. About 55% of the CAA is converted to acrylate esters. The remaining 45% is purified to 98–99.5% purity to glacial acrylic acid (GAA), which, in turn, is converted to polyacrylic acid, which is used to produce superabsorbent polymers (SAPs) and other polyacrylic acid copolymers. In 2016, global glacial acrylic acid consumption was estimated to account for about 45% of total crude acrylic acid consumption, of which 79% was consumed for superabsorbent polymers. Growth in GAA consumption is forecast at about 5% per year during 2016?21. Growth in demand for crude acrylic acid is forecast at 4.5% per year during 2016?21, driven by growth in superabsorbent polymers at 5.5% and acrylate esters at about 4%.