First, there were the superabsorbent polymers, those fantastical plastics that had the capability to absorb and hold up to 500 times their own weight in liquid-even under pressure. Also called 'super slurpers', they debuted commercially in sanitary napkins in the seventies and were soon being used around the world in a host of products ranging from potting soil and fragrance carriers to diapers, incontinence pads and artificial snow. It's a market that just keeps on expanding.
And now these superabsorbent polymers, or SAPs, come in green versions as well.
Curiously, the first patent for superabsorbent polymer SAP was issued in 1962 to the U.S. Department of Agriculture for use as water conservation in soil, and was, in fact, biobased. The product used starch as the basis for the polymer and then grafted acrylamide and acrylonitrile monomers along the chain with crosslinking agents. Today, however, the most common type of SAP is oil-based cross-linked polyacrylic acid or acrylamide.
The increased consumer focus on sustainability has resulted in a rapidly rising demand for alternatives to petroleum-derived superabsorbents. Various natural materials, such as cellulose, starch, chitin, and natural gums, have been used as the basis to form the main polymer chains. These have, for the most part, not yet been able to match either the cost or performance of the oil-based SAPs, leading numerous companies to explore possible routes to produce bio-acrylic acid.....