title: Effects of dry heat and saturated steam on the physical properties of chitosan.
abstract: Heat may be employed to facilitate the processing of chitosan and to confer sterility on chitosan-based medical products. In this study, changes were analyzed of the physical properties of purified chitosan heated at 60 to 160 degrees C under specified conditions for periods ranging from 0.5 to 4 h. Two forms of heat were used for processing: dry heat generated by a convection oven and saturated steam generated by an autoclave. Dry heat at < or = 80 degrees C resulted in less rigid chains with lower glass transition temperature, improved aqueous solubility, and slightly higher [eta]. At higher temperatures, dry heat produced chromophores, which may be related to interchain crosslink formation involving the NH2 groups. The [eta] and aqueous solubility of the samples decreased with temperatures > or = 120 degrees C. The coloration of the samples intensified from yellow to brown with increasing temperatures and duration of heat exposure. Chitosan heated at 160 degrees C for > or = 2 h was insoluble in the 0.2 M acetic acid/0.1 M sodium acetate solvent. The rate and extent of the thermal reactions were increased in the presence of saturated steam; the autoclaved samples became insoluble after 2 h of heating at 115 degrees C and after 1 h at > or = 120 degrees C. On the other hand, the physical changes induced by dry heat at < or = 120 degrees C were not affected significantly by heating the chitosan samples under anoxic conditions.
authors.affiliation: Department of Pharmacy, National University of Singapore, Singapore. phalimly@nus.edu.sg
authors.forename: L Y
authors.initials: LY
authors.lastname: Lim
authors.forename: E
authors.initials: E
authors.lastname: Khor
authors.forename: C E
authors.initials: CE
authors.lastname: Ling
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D001704:Biopolymers; D002686:Chitin / Q000031:analogs & derivatives* / Q000737:chemistry; D048271:Chitosan; D013696:Temperature
chemical_list: D001672:Biocompatible Materials; D001704:Biopolymers; D002686:Chitin; D048271:Chitosan