Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage
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David Ibarra
Abstract
Structural modification of eucalypt pulp lignin was investigated in a totally chlorine-free (TCF) bleaching sequence including a laccase-mediator stage. This stage was applied after two oxygen delignification stages, and was followed by an alkaline peroxide stage. After two oxygen delignification stages, two more stages with a laccase mediator and alkaline peroxide were applied. The residual lignins were enzymatically isolated from the different pulps and analyzed by spectroscopic techniques and analytical pyrolysis. The latter revealed high amounts of syringyl units (>70%) in the lignins. 13C-1H heteronuclear single quantum correlation (HSQC) NMR indicated high amounts of β-O-4′ inter-unit linkages (>75% side-chains). Changes in lignin composition and inter-unit linkages were demonstrated in the course of the bleaching sequence. Moreover, oxidative modification of the major syringyl units was shown by C2,6-H2,6 HSQC correlations and by the presence of oxidized pyrolysis markers in pyrograms. The existence of both Cα keto and carboxyl groups in the residual lignin, together with normal (Cα-hydroxylated) units, was revealed by heteronuclear multiple bond correlation (HMBC) between aromatic H2,6 and side-chain carbons. These Cα-oxidized structures represent nearly 60% of total units in the lignin isolated from the enzymatically treated pulp. Analysis of residual lignin after the final peroxide stage compared with a simple alkaline treatment revealed that most of the oxidatively altered lignin was removed by the alkali used in the peroxide stage. Thus, the kappa number decreased and the final residual lignin was more structurally related to that found before the oxidative stages, although it contained less resinols and more carboxyl group-bearing units. However, the action of peroxide is necessary to attain the high brightness required (>90% ISO).
©2007 by Walter de Gruyter Berlin New York
Articles in the same Issue
- Acknowledgement
- Subject index
- Contents Volume 61 (2007)
- Author index
- Species index (scientific names)
- Meetings
- Improvement of Pinus pinaster Ait elite trees selection by combining near infrared spectroscopy and genetic tools
- Direct method for the determination of phenolic hydroxyl groups in pulp
- Comparative effect of ozone, chlorine dioxide, and hydrogen peroxide on lignin: Reactions affecting pulp colour in the final bleaching stage
- Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage
- Analysis of wood tissues by time-of-flight secondary ion mass spectrometry
- Isolation and identification of residual chromophores from aged bleached pulp samples
- Studies on oxidative modifications of cellulose in the periodate system: Molecular weight distribution and carbonyl group profiles
- Lignin-carbohydrate network in wood and pulps: A determinant for reactivity
- Cross polarisation/magic angle spinning 13C-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process
- Fungal decay of spruce and beech wood assessed by near-infrared spectroscopy in combination with uni- and multivariate data analysis
- Paper mill sludge as a component of wood adhesive formulation
- Implementation of sorption hysteresis in multi-Fickian moisture transport
- Time/temperature equivalence in the dry wood creep response
- Neural network prediction of bending strength and stiffness in western hemlock (Tsuga heterophylla Raf.)
- Bending properties of particleboard and MDF layers
- Gold as an X-ray CT scanning contrast agent: Effect on the mechanical properties of wood plastic composites
- Lignin modification in the initial phase of softwood kraft pulp delignification with polyoxometalates (POMs)
Articles in the same Issue
- Acknowledgement
- Subject index
- Contents Volume 61 (2007)
- Author index
- Species index (scientific names)
- Meetings
- Improvement of Pinus pinaster Ait elite trees selection by combining near infrared spectroscopy and genetic tools
- Direct method for the determination of phenolic hydroxyl groups in pulp
- Comparative effect of ozone, chlorine dioxide, and hydrogen peroxide on lignin: Reactions affecting pulp colour in the final bleaching stage
- Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage
- Analysis of wood tissues by time-of-flight secondary ion mass spectrometry
- Isolation and identification of residual chromophores from aged bleached pulp samples
- Studies on oxidative modifications of cellulose in the periodate system: Molecular weight distribution and carbonyl group profiles
- Lignin-carbohydrate network in wood and pulps: A determinant for reactivity
- Cross polarisation/magic angle spinning 13C-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process
- Fungal decay of spruce and beech wood assessed by near-infrared spectroscopy in combination with uni- and multivariate data analysis
- Paper mill sludge as a component of wood adhesive formulation
- Implementation of sorption hysteresis in multi-Fickian moisture transport
- Time/temperature equivalence in the dry wood creep response
- Neural network prediction of bending strength and stiffness in western hemlock (Tsuga heterophylla Raf.)
- Bending properties of particleboard and MDF layers
- Gold as an X-ray CT scanning contrast agent: Effect on the mechanical properties of wood plastic composites
- Lignin modification in the initial phase of softwood kraft pulp delignification with polyoxometalates (POMs)
