Immanuel Adorjan

Cellulose solutions in N-methylmorpholine-N-oxide (NMMO) – degradation processes and stabilizers

Efficient stabilization of cellulose solutions in NMMO(1) against side reactions and their harmful effects meansprevention of both homolytic and heterolytic side reactions, which is mainlyaccomplished by trapping radicals, formaldehyde, andN-(methylene)iminium ions (5). Whileradical trapping is commonly reflected by the antioxidativeefficiency, the effectivity against heterolyticdegradationin the Lyocell dope can be expressed by the newly introduced term‘formaldehyde trapping capacity’ (FTC). Propyl gallate (PG,4), the most widely applied Lyocell stabilizer nowadays, actsas a phenolic antioxidant, and is finally oxidized to a deeply colored, highlyconjugated chromophore (11) via ellagicacid (10). It was demonstrated that 4 is alsoa quencher of formaldehyde and N-(methylene)iminium ions,both in organic solutions of NMMO and in Lyocell dope. The processes of radicaltrapping and scavenging of HCHO/5 are competitive in the caseof propyl gallate. A novel oxa-chromanol derivative, PBD (14),was designed as stabilizer for Lyocell solutions. In analogy to propyl gallate,PBD acts as a scavenger of all three dangerous species, namely HCHO,5 and radicals. Upon oxidation by radical species, PBDreleasesacetaldehyde which acts as a very efficient HCHO trap. Thus, in contrast topropyl gallate, radical trapping and HCHO trapping are not competitive. Boththeantioxidative efficiency and the capacity to trap HCHO and 5are higher for PBD as compared to propyl gallate. In preliminary stabilizertesting, mixtures of PBD and PG proved to be especially effective.

Synthesis of oxidized methyl 4-O-methyl-β-d-glucopyranoside and methyl β-d-glucopyranosyl-(1→4)-β-d-glucopyranoside derivatives as substrates for fluorescence labeling reactions

Abstract The synthetic cellulose model compounds methyl 4- O -methyl-β- d -glucopyranoside and methyl 4- O -methyl-β- d -glucopyranosyl-(1→4)-β- d -glucopyranoside and related 6- O -protected intermediates were oxidized in good to fair yields using Swern-conditions or bromine/bis(tributyltin) oxide, respectively, to afford compounds containing 6-aldehyde, 3-keto, and 2,3-diketo groups. Cellobiose and oxidized monosaccharides were then labeled with the carbonyl-selective fluorescence marker 9-(7-amino-1,4,7-trioxaheptyl)-9 H -carbazolecarboxamide (CCOA). The labeled derivatives serve as model compounds for the determination of minute amounts of carbonyl groups in cellulosic polysaccharides.

Brightness reversion of eucalyptus kraft pulp: Effect of carbonyl groups generated by hypochlorous acid oxidation

Abstract The impact of hypochlorous acid (HOCl) treatment on a fully bleached eucalyptus kraft pulp was studied with respect to the final brightness as well as the brightness reversion under humid ageing conditions. The carbonyl contents in the pulps were determined by the CCOA method where carbazole-9-carboxylic acid [2-(2-aminooxethoxy)-ethoxy] amide (CCOA) was applied as the carbonyl-selective fluorescence label. The molecular weight distribution of cellulose and hemicelluloses was analyzed as well. The amount of carbonyl groups in pulp was observed to increase significantly after the HOCl treatment, and the carbonyl distribution in pulp to shift towards the low molecular weight fraction. Plotting the carbonyl content against the post color number (PCN) of the pulps revealed a linear correlation. Additionally, the effect of the hemicellulose content was investigated, and alkaline extraction was applied to partially remove the hemicelluloses in pulp. These hemicellulose-poor samples showed a lower reactivity with hypochlorous acid and less brightness reversion at equal carbonyl content.