SynopsisCellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose 11) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose 11, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70aC, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.
SYNOPSISCarbanilation reactions of cellulose samples (bleached cotton linters and Avicel ) with phenylisocyanate in dimethylsulfoxide (DMSO) were carried out at 60°C in the presence of various pyridine derivatives. The molecular weight distributions of the resulting cellulose tricarbanilates ( CTCs) were measured by high-performance size exclusion chromatography. When pyridine or its derivatives were included in the reactions, the CTCs had reduced degree of polymerization (DP) values compared to those of CTCs prepared without the additives. The cellulose depolymerization was promoted by pyridines with electron-donating substituents and was not favored by pyridines with electron-withdrawing substituents nor with groups at positions ortho to the pyridine ring nitrogen atom. For the 3-, 4-, and 3,4-substituted pyridines, there was a linear relationship between log (weight-average CTC D P ) and the pK, (in water) of the pyridine derivative. For 2-and 2,6-substituted pyridines, the DP-pKa relationships were different, probably because of steric effects of the different substituents ortho to the pyridine nitrogen atom. The optimum DMSO : pyridine solvent ratio for cellulose depolymerization during carbanilation in DMSO : pyridine mixtures was 3 : 1. All three components, phenylisocyanate, pyridine or its derivatives, and DMSO, are required for the depolymerization reaction. It is suggested that the depolymerization may be a consequence of cellulose oxidation by DMSO and/or cleavage of glucosidic bonds of partially carbanilated celluloses by reactions promoted by an enhanced solvent effect of DMSO.
Oxygen-delignified kraft pulps from both mature and young eucalypt wood samples were treated with chlorine (C), chlorine dioxide (D) or a mixture of the two reagents, and were subsequently extracted with alkali (E), optionally reinforced with oxygen (EO). C(EO) and D(EO) treatments were also carried out without interstage washing. The levels of Chlorinated phenols in the filtrates were estimated by an in situ acetylation technique. The 14 major Chlorinated phenols consisted of 3 catechols, 4 guaiacols, l syringol, 2 Vanillins, 2 syringaldehydes and 2 acetosyringones. Chlorinated phenolic aldehydes were the most prevalent components in the bleaching filtrates; 2,6-dichlorosyringaldehyde was the major analyte from C treatments and 2-chlorosyringaldehyde from D treatments. The amounts of Chlorinated phenols were higher in the filtrates following C treatments than in the filtrates from D treatments, and increased in the order C(or D) < E < EO < EO without interstage washing. There was a poor correlation between the levels of Chlorinated phenols and the adsorbable organic halogen (AOX) Contents of the different bleaching filtrates. The levels of Chlorinated phenols differed significantly between pulp samples, with higher levels obtained from the two young E. globulus samples than from mature mixed eucalypt samples. The Chlorinated phenol levels correlated well with the yields of Vanillin and syringaldehyde from nitrobenzene oxidation of the pulps. The difference in Chlorinated phenol levels from the eucalypt pulp samples is rationalised in terms of differences in the amounts and/or structure of the residual lignin in the pulps.
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