Minimizing Viscosity Loss during Totally Chlorine-Free Bleaching of Hardwood Kraft Pulp

Abstract

By applying increasing amounts of ozone (Z stage bleaching) on eucalyptus oxygen-delignified pulps, it was observed that both lignin and hexenuronic acids (HexA) are attacked early during the treatment. While the HexA were progressively removed, however, the oxidized lignin tended to stay in the pulp. An acidic stage (A stage) at pH 3 and a temperature of 90 to 95°C removed a high proportion of the HexA, which eventually reduced the ozone requirement. In spite of the negative impact of the A stage on the DP of cellulose, totally chlorine-free sequences containing A led to pulps of higher viscosity. Increasing the temperature in A to 120°C did not seem to have an effect other than increasing the rate of the hydrolysis reactions. A very efficient metal removal was observed when a chelating agent was added in A (A Q ). Some trials showed that splitting the Z stage in a ZEZE-like process (E for alkaline extraction) minimized the impact on pulp viscosity, and that A Q PZE-like sequences can reach a quality comparable to some commercial elemental chlorine free (ECF) pulps.

Effect of hot calendering on physical properties and water vapor transfer resistance of bacterial cellulose films

“…Aiming to increase the brightness of the films, BC suspension was treated with ozone, an environment friendly bleaching agent used in the bleaching of vegetal pulp fibers. Due to the relatively low selectivity of ozone, carbonyl groups are introduced in the cellulose chain, which can lead to cellulose depolymerization [27]. In fact, Table 1 shows that after ozone treatment, BCO exhibits 10 % lower DP v (41.7 % lower intrinsic viscosity) than that of the untreated BC.…”

“…In fact, Table 1 shows that after ozone treatment, BCO exhibits 10 % lower DP v (41.7 % lower intrinsic viscosity) than that of the untreated BC. Most of this depolymerization is likely to take place in the intrinsic viscosity determination process itself, since the carbonyl groups introduced in the cellulose chain may lead to its cleavage under the alkaline conditions used in the essay [27]. Calendering at 100°C had a marginal effect on the DP of BC, BCO, and VC films.…”

“…Regarding the influence of the film structure on water vapor permeability, an important property for food packaging applications, the following aspects were observed: the calendered VC (VC_HC6), exhibits higher WVTR than the before calendering (BC), in spite of the higher porosity of the latter; the ozonated BC (BCO, before and after calendering) exhibits higher WVTR than the nonozonated BC (BC, before and after calendering), despite its lower porosity. Based on literature [27,37], the BC submitted to ozone bleaching should have higher carbonyl and some carboxyl content than the BC, and the vegetal fibers have amorphous material (hemicelluloses). Both features lead to higher water affinity, which probably justifies the observed behavior.…”

Use of UV resonance Raman spectroscopy for assessing the brightness stability of ozone TCF bleached pulp

“…Moreover, in subsequent alkaline extraction stage, part of the carbohydrates C=O groups initiate β-elimination and alkaline rearrangements that ultimately result in chain scissions, lowering the pulp degree of polymerization (DP) (Lewin and Herman, 1997) and giving rise to unsaturated substances (Perrin et al 2014;Zhou et al 2011). Thus, the effect of Z stages on brightness stability can be both beneficial by destroying chromophores and chromogens and detrimental by generating heat-sensitive degradation products (Pouyet et al 2013;Röhrling et al 2002). Some of the chromophores still present in bleached chemical pulps have been identified and quantified (Rosenau et al 2004(Rosenau et al , 2011.…”

“…The UVRR spectroscopy was used with a 244 nm laser wavelength to understand the role of the bleaching chemistry on both the nature of the residual substances in ECF and TCFz bleached pulps and their role in brightness reversion. In this work, the ECF sequence was that currently applied in the Fibre Excellence-Saint Gaudens kraft pulp mill DEpDD and the TCFz sequence A(ZEo)(ZEo)(ZP) was designed and optimized according to the principles recently developed to minimize the decrease of the cellulose DP (Pouyet et al 2013).…”