EFFECT OF TEMPERATURE ON THE INTRINSIC-VISCOSITY AND CONFORMATION OF CHITOSANS IN DILUTE HCL SOLUTION

The effects of temperature on the intrinsic viscosity and on the confo rmation of chitosans in dilute HCl solution were studied. Ten chitosan s with the same degree of deacetylation but different molecular weight s were produced by alkali deacetylation of chitin which was prepared f rom red shrimp wastes. The degree of deacetylation at 83% and weight a verage molecular weight of the chitosans ranging 78-914 kDa were deter mined by infrared spectroscopy and static light scattering, respective ly. The intrinsic viscosities ([eta]) of these 10 chitosans in 0.01 M hydrochloric acid were measured at 10, 20, 30, 40, and 50 degrees C. T hen, d ln [eta]/d(1/T) and the Mark-Houwink exponents were calculated as the indices for chain flexibility and molecule conformation, respec tively. These results showed: the intrinsic viscosities decreased line arly with increasing temperature, therefore, a temperature-induced con formational transition did not occur for all 10 different molecular we ight chitosans in the temperature range studied. Values of d ln [eta]/ d(1/T) were between 633 and 1334 and increased with decreasing molecul ar weight, indicating that higher molecular weight chitosans are more flexible. Between 10 degrees and 50 degrees C, the Mark-Houwink expone nts ranged 0.64-0.76 and increased with increasing temperature, indica ting that the conformation of these chitosans were all in random coil, and a temperature-induced conformational transition did not occur. Th e alpha and alpha** Mark-Houwink exponents represent those chitosans whose molecular weights are larger and smaller than 223 kDa, respectiv ely, and were obtained by using 223 kDa as the break point in the doub le logarithmic plots of the intrinsic viscosities and weight average m olecular weight. Values of alpha* were between 0.41 and 0.54, while t he alpha values were from 0.96 to 1.07. These values for alpha** and alpha indicate that larger and smaller molecular weight chitosans wer e in random coil and rod shape, respectively. (C) 1998 Elsevier Scienc e B.V. All rights reserved.