Molecular Mass and Molecular-Mass Distribution of
TEMPO-Oxidized Celluloses and TEMPO-Oxidized Cellulose Nanofibrils
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Abstract
Native wood cellulose was oxidized
by 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO)-mediated oxidation, and the fibrous TEMPO-oxidized celluloses
(TOCs) thus obtained were disintegrated in water to prepare TOC nanofibrils
(TOCNs). The carboxyl groups of TOCs and TOCNs were methyl-esterified,
and the methylated samples were dissolved in 8% LiCl/<i>N</i>,<i>N</i>-dimethylacetamide for size-exclusion chromatography/multiangle
laser-light scattering (SEC-MALLS) analysis to obtain their molecular-mass
(MM) values and MM distributions (MMDs). The results showed that remarkable
depolymerization occurred in TOCs and TOCNs and depended on the oxidation
and sonication conditions. Because single peaks without bimodal patterns
were observed in the MMDs for all of the TOC and TOCN samples, depolymerization
may have randomly occurred on whole cellulose molecules and oxidized
cellulose molecules in the microfibrils during these treatments. Compared
with the MM values obtained by SEC-MALLS, the intrinsic viscosities
of TOCs dissolved in 0.5 M copper ethylenediamine solution provided
lower MM values owing to depolymerization during the dissolution and
postreduction processes