Acrylic acid is used mainly in the formation of polymers. Its uses include plastics, coatings, adhesives, elastomers, paints, and polishes. Additionally, acrylic acid is used in the production of hygienic medical products, detergents, and wastewater treatment chemicals. The low toxicity of acrylic acid is due to its corrosive nature.
Acrylic acid polymer, neutralized, cross-linked belongs to a class of high molecular weight cross-linked homopolymers of acrylic acid. In general, during production of the commercially available cross-linked acrylic acid polymers, high molecular weight polycarboxylate or acrylate chains are cross-linked with each other. Typically, multifunctional cross-linking agents are used to bind the single polymer chains into a three dimensional network; the amounts used vary with the type of cross-linking agent but are generally less than 1 % w/w and the amount reacted is practically 100 %. The counterion is mainly sodium. Common cross-linked acrylic acid polymers (cross-linked polyacrylates) are 60 % to 80 % neutralized with sodium and, because of the three dimensional crosslinking, are practically insoluble in water.
They can absorb a multiple of their own weight of aqueous liquids; the amount absorbed is determined by the ionic strength of the liquid in question. Typical amounts absorbed are in the range between 30 g and 400 g liquid per gramme dry weight. After absorption of liquids, the particles swell and take on the form of a gel. In vitro studies have demonstrated that the particle size in a simulated lung fluid increased on absorption of liquid by a factor of 4 to 5 and in physiological saline by a factor of 10 (sponge effect) (Procter and Gamble Company 1994).
Cross-linked polyacrylates are generally available as granulated solids with an average particle size of 300 µm to 700 µm; the proportion of particles < 100 µm is generally limited to less than 1 % to maintain the properties of the product.
For inhalation studies, micronized particles (diameter < 2 µm) of cross-linked polyacrylates have generally been used to ensure that sufficient respirable fraction was present. Commercially available cross-linked polyacrylates contain practically no respirable dust. To make this clear in the present document, cross-linked polyacrylates and micronized cross-linked polyacrylates are always differentiated. Since the beginning of the 1980s, the main use of cross-linked polyacrylates has been in hygiene products.
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