Low Cost Chitosan Biopolymer for Environmental Use Made from Abundant Shrimp Wastes

Chitosan, an important biopolymer with many uses, is made by deacetylation of chitin. Classical hydrolysis at high temperatures (above 100 °C) in 50 % concentrated sodium hydroxide during several hours produces chitosan, a poly-beta-glucosamine. This chemical deacetylation step is often performed under pressure in boiling ethyleneglycol and tends to degrade polymer chain length, thus the interesting polymer properties. It is convenient to search for a more economical production pathway in order to make chitosan available for environmental applications, such as use in water suspended matter flocculation. Chitin was extracted from the exoskeletons of shrimps and its deacetylation kinetics was followed for 35 days at 20 and 35 °C. The results obtained using different techniques (conductivity, viscometry, 13 C NMR and thermogravimetry) showed that the deacetylation degree of chitin increased with the incubation time reaching 99 and 88 % at 35 and 20 °C, respectively, after 35 days. Moreover, during the incubation time, the molecular weight of chitosan showed moderate decrease compared to deacetylated chitin at high temperature. Clarification or urban waste water with chitosan biopolymer demonstrated good results at 1.5 mg/L concentrations.