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This super-absorbent polymer (SAP) has the ability to absorb 100 to 1000 times its mass in water. Sodium polyacrylate is an anionic polyelectrolyte [2] with negatively charged carboxylic groups in the main chain. It is a polymer made up of chains of acrylate compounds. It contains sodium, which gives it the ability to absorb large amounts of water.
They differ in their properties according to their chemical composition (homo-or copolyester, contained hydroxy fatty acids). They are UV stable, in contrast to other bioplastics from polymers such as polylactic acid, partial ca. temperatures up to 180 °C, and show a low permeation of water.
Superabsorbent polymers are now commonly made from the polymerization of acrylic acid blended with sodium hydroxide in the presence of an initiator to form a poly-acrylic acid sodium salt (sometimes referred to as sodium polyacrylate). This polymer is the most common type of SAP made in the world today.
The functional properties of CMC depend on the degree of substitution of the cellulose structure (i.e., how many of the hydroxyl groups have been converted to carboxymethylene groups in the substitution reaction), as well as the chain length of the cellulose backbone structure and the degree of clustering of the carboxymethyl substituents.
In diluted alkaline media (e.g. 1M sodium hydroxide solution), hydrolysis takes place in α- and β-position of the succinimide (2,5-pyrrolidinedione) ring structures and racemization follows at the chiral center of the aspartic acid, yielding the water-soluble sodium salt of the poly(α, β)-DL-aspartic acid. The α form is formed to approx ...
Polyacrylic acid is a weak anionic polyelectrolyte, whose degree of ionisation is dependent on solution pH. In its non-ionised form at low pHs, PAA may associate with various non-ionic polymers (such as polyethylene oxide, poly-N-vinyl pyrrolidone, polyacrylamide, and some cellulose ethers) and form hydrogen-bonded interpolymer complexes. [17]
Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. When the alginic acid binds with sodium and calcium ions, the resulting salts are known as alginates. Its colour ranges from white to yellowish-brown.
Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high molecular weights only at very high conversion (i.e., >95%). Solid state polymerization to afford polyamides (e.g., nylons) is an example of step-growth polymerization.