Abstract
Commercial chitosans prepared by heterogeneous alkaline deacetylation
with different F-A values were fractionated into acid-soluble and
acid-insoluble fractions. The amount of acid-soluble fractions increased
with increasing time of deacetylation. The acid-soluble fractions
were characterized with respect to fraction of acetylated units (F-A),
diad frequencies, intrinsic viscosities, molecular weights and molecular
weight distributions. F-A values for the acid-insoluble fractions
were obtained using CPMAS C-13 NMR spectroscopy. As a control, the
F-A values for the acid-soluble fractions determined from CPMAS C-13
NMR spectroscopy were compared and found to be consistent with the
F-A values from H-1 NMR spectroscopy. The diad frequencies indicated
that the acetyl groups in the acid-soluble fractions of the commercially
heterogeneously deacetylated chitosans were randomly distributed.
Determination of eta, M(w) and M(w)/M(n) indicated negligible depolymerization
of the acid-soluble fractions when deacetylation was performed under
a nitrogen purge at 75 degrees C. Chemical characterization revealed
compositional heterogeneity in the chitosans, with chitin-like acid-insoluble
fractions with F-A values between 0.88 and 0.95, and acid-soluble
fractions with F-A values from 0.20 to 0.52. Copyright (C) 1996 Elsevier
Science Ltd
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