PREPARATION OF LOW-MOLECULAR-WEIGHT CHITOSAN USING PHOSPHORIC-ACID

Two types of low degree of polymerisation (DP) chitosan were prepared by homogeneous hydrolysis of chitosan in 85% phosphoric acid at room t emperature for 1-6 weeks. The hydrolysates were collected by addition of excess ethanol, and were fractionated by solubility in water. The c hanges in yields of water-insoluble (higher DP) and water-soluble (low er DP) fractions were determined as a function of hydrolysis time. The hydrolysis proceeded with further deacetylation of chitosan, resultin g in degree of deacetylation of more than 90%. The water-insoluble fra ction prepared after the hydrolysis for 4 weeks (43% yield) had a weig ht-average DP (DP(w)BAR) of 16.8, and showed the 'tendon' type X-ray d iffraction pattern. The water-soluble fraction (12.5% yield) had a DP( w)BAR of 7.3, and showed the 'annealed' type pattern.