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Apr 13, 2018Keywords:
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Chemical reactivity and supramolecular susceptibility of hardwood celluloses towards succinic anhydride
Abstract
In order to understand the chemical reactivity and the relative susceptibility of Iα and Iβ cellulose allomorphs of some tropical hardwoods with coupling agents bearing succinic moiety, their cellulose fibers were isolated and esterified by succinic anhydride molecule heated at 120 °C for 4 h in dimethylformamide(DMF)/pyridine(Py) used as swelling solvent. The morphological structure of Testulea gabonensis (T. gabonensis), Julbernardia pellegriniana (J. pellegriniana), Aucoumea klaineana (A. klaineana) and Tieghemella africana (T. africana) fibers were characterized by the MORFI® apparatus. The fibers were the longest for T. africana (769 μm), J. pellegriniana (717 μm) and T. gabonensis (700 μm) while those from A. klaineana were the shortest (624 μm). No difference was found between T. gabonensis, A. klaineana and T. africana fibers width which varied from 24.0 to 24.2 μm while J. pellegriniana cellulose exhibited the smallest width (18.6 μm). The cellulose fibers of T. gabonensis, T. africana and J. pellegriniana displayed the better reactivity as revealed by their respective weigh per cent gains: 16.57 ± 1.11%, 14.16 ± 0.67% and 12.96 ± 0.77% compared with A. klaineana (11.85 ± 0.62%). The latter exhibited the lowest decrease of crystallinity among those cellulose esters. Nevertheless, solid state 13C NMR showed a strong reactivity of amorphous cellulose and chains exposed on crystal surfaces than interior crystallite chains. Any evidence of Iα and Iβ allomorphs esterification was found in those cellulose fibers with the exception of T. africana which displayed a decrease of Iα and Iβ allomorphs without a preferential reactivity of Iα cellulose. The trend of heterogeneous phase esterification of cellulose fibers with succinic anhydride in DMF/Py at 120 °C for 4 hours to be merely controlled by amorphous phase and chains exposed on crystal surface was discussed.
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Keywords: Cellulose allomorphs, Esterification, Solid state NMR, X-ray diffraction
