The effects of lignocellulosic fiber surface area on the dynamics of lignin oxidation and diffusion

A novel preliminary experimental approach was developed to determine the effect of maximizing pulp fiber surface area for the regulation of the oxidation and diffusion of lignin through the carbohydrate matrix. The approach entailed liquid nitrogen freezing of mature black spruce kraft pulp fibers and subsequent mechanical grinding to a fine powder to test the effect of enhanced pulp fiber surface area on the efficiencies of lignin oxidation and lignin diffusion. It was found that the liquid nitrogen ground pulp samples provided higher optical reflectance (brightness) after both oxygen and hydrogen peroxide oxidation, which appears to be from chromophoric (chemical) differences and not light scattering differences as supported by UV/Vis spectroscopy. BET (absorption) experiments indicated a dramatic difference in the surface area of the pulp as a result of the grinding, although no differences existed among the pore sizes between the samples, as determined from SEM experiments. Lignin diffusion experiments demonstrated that differences did exist in the kinetics of lignin diffusion into a bulk solution between a control and liquid nitrogen ground samples. Lignin uptake into bulk solutions was enhanced by the liquid nitrogen/pulp‐grinding technique albeit not from chemical changes in the lignin because the subsequent NMR spectra did not point to any major chemical differences as a result of liquid nitrogen freezing and grinding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 177–181, 2004     

Methylmethacrylate Grafting onto Cotton Stalk Pulp

Grafting of cotton stalk pulp with methylmethacrylate monomer using a ceric salt redox system is carried out. The effect of different variables—for example, monomer dose, reaction time, reaction temperature, acid concentration, initiator concentration, and liquor ratio—are studied. The effect of the presence of different amounts of residual lignin in cotton stalks pulp on the grafting process is demonstrated. Residual lignin percentage in the pulp plays an important role in determining the grafting rate. A sharp decrease in the grafting rate is observed by increasing the residual lignin percent in pulp from 1.64% to 4.96%. As the residual lignin percentage in the pulp is increased to 12% in pulp, the grafting reaction is nearly stopped. Optimization of the grafting conditions is clarified.     

Integrated -Omics: A Powerful Approach to Understanding the Heterogeneous Lignification of Fibre Crops

Lignin and cellulose represent the two main components of plant secondary walls and the most abundant polymers on Earth. Quantitatively one of the principal products of the phenylpropanoid pathway, lignin confers high mechanical strength and hydrophobicity to plant walls, thus enabling erect growth and high-pressure water transport in the vessels. Lignin is characterized by a high natural heterogeneity in its composition and abundance in plant secondary cell walls, even in the different tissues of the same plant. A typical example is the stem of fibre crops, which shows a lignified core enveloped by a cellulosic, lignin-poor cortex. Despite the great value of fibre crops for humanity, however, still little is known on the mechanisms controlling their cell wall biogenesis, and particularly, what regulates their spatially-defined lignification pattern. Given the chemical complexity and the heterogeneous composition of fibre crops’ secondary walls, only the use of multidisciplinary approaches can convey an integrated picture and provide exhaustive information covering different levels of biological complexity. The present review highlights the importance of combining high throughput -omics approaches to get a complete understanding of the factors regulating the lignification heterogeneity typical of fibre crops.     

枫香树材清洁制浆技术

对速生阔叶木枫香树材的纤维形态、主要化学组成、清洁制浆及绿色漂白工艺进行了一系列探讨。结果显示,枫香木纤维平均长度较长,长宽比均比杨木大,且其综纤维素和戊聚糖含量高而Klason木素含量低,是一种很有发展潜力的制浆造纸原料。采用硫酸盐法制浆,蒸煮后所得细浆得率为49.9%,卡伯值为23.0,白度为23.8%ISO,黏度为734.7 mL/g。利用环境友好型漂白法——氧脱木素技术处理该枫香树材硫酸盐浆,并在此过程中创造性地使用助剂蒽醌。四因素三水平正交试验结果表明:用碱量、氧压、温度和时间对枫香树材硫酸盐浆添加蒽醌氧脱木素后浆料的性能均有很大的影响。其中,温度对得率、卡伯值、白度和黏度等的影响最大,时间对卡伯值、白度和黏度的影响最小。枫香树材硫酸盐浆添加蒽醌氧脱木素的较为适宜的工艺为:用碱量3%,氧压0.7 MPa,温度105℃,保温时间90 min,浆浓20%,MgSO4用量0.5%,蒽醌用量0.1%。在该条件下所得浆料得率90.7%,卡伯值7.0,黏度545.1 mL/g,白度51.0%ISO,脱木素选择性8.42×10-2。与相同条件下常规氧脱相比,卡伯值和白度相近,但得率、黏度和脱木素选择性都有所提高。蒽醌在枫香树材硫酸盐浆氧脱木素过程中可保护碳水化合物,提高脱木素选择性,是一种良好的氧脱木素助剂。     

Location of Lignin-Bonded Pectic Polysaccharides

The hypothesis that galactose and arabinose pectic substances are disributed with lignin throughout wood cell walls was tested by analyzing a high-yield loblolly pine kraft pulp that had been separated into middle-lamella-rich and secondary-wall-rich fractions. The fractions were first treated with a polysaccharidase enzyme mixture to obtain “enzyme lignins.” The structures of the galactose and arabinose oligomers remaining attached to the lignin were determined by methylation analysis. The 1→4 linked galactose structure, characteristic of pectic materials, was present in significant amounts in the middle-lamella-rich fraction, but to only a very small extent in the secondary-wall-rich fraction. In contrast, the pectic arabinan 1→5 linked structure was a significant proportion of the arabinose from both fractions. The 1→5 linked arabinose structure can arise from a linkage of arabinoxylan to lignin through the 5 position of the arabinose substituent as well as from pectic structures. After partial acid hydrolysis, approximately half the remaining arabinose in the secondary-wall-rich fraction was attached as monomeric units to lignin through the 5 position.     

THE EFFECT OF LIGNIN CONTENT OF WOOD FIBERS ON PULP SCREENING/SEPARATION

An experimental investigation of the effect of lignin content of wood fibers on pulp screening is conducted. A non-uniform lignin distribution may exist in wood pulp due to variations in wood chip characteristics, and/or cooking conditions in a digester. Pulp screening was conducted in a modified Williams Freeness tester at different fiber lignin contents and pulp consistencies. The study indicated a large drop in pulp accepts fraction, thus a substantial fiber loss, with an increase in lignin content. The fiber loss was more significant at higher consistencies of pulp. This study suggests that the fiber lignin content should be considered an important process variable affecting the efficiency of pulp screening processes.     

Molecular Weight of Lignin Fractions Leached from Unbleached Kraft Pulp Fibers

The molecular weights of lignin fractions leached from an unbleached kraft pulp were found to increase from 230,000 to 410,000 as washing of the pulp proceeded. The free diffusion coefficients for both a spherical and a disk-like conformation were calculated and were found to be seven orders of magnitude higher than the observed intrafiber diffusion coefficient. Also the change in the free diffusion coefficient with molecular weight was far less than the 100-fold polydispersity observed previously. A comparison of the molecular dimensions with the pore size indicated that a flat, disk-like conformation, rather than a spherical conformation, is appropriate for the lignin macromolecule.     

Enzymatic activation of wood fibres as a means for the production of wood composites

The incubation of wood fibres with a phenoloxidase (laccase) results in the oxidation of the lignin crust on the fibre surface which finally is released from the fibre surface into the incubation medium. During this reaction, the lignin is highly oxidized, as can be seen from its high carboxyl content. When fibres treated with the enzyme are pressed together under conditions usually employed during the process of making fibre boards, boards are obtained which meet the required standards for German medium density fibre board (MDF). The enzymatically activated fibres in the wood composites made by this process are bound together in a way which is closer to the situation in the naturally grown wood than any other process used today in the present production of wood composites.     

Fibre fractionation using air‐sparged hydrocyclone

Fractionation of mechanical wood pulp into two or more streams on the basis of fibre length has been investigated to recover valuable long fibres from virgin or recycled wood pulp. An air‐sparged hydrocyclone was used to fractionate the pulp at feed mass concentrations (consistencies) of 0.15% and 0.30%. The extent of fibre fractionation, as affected by feed flow rate, air flow rate, ratio of overflow to underflow rates, was studied. As well, the effects of pore size of the air sparger and cyclone length are presented. It was found that at low consistencies of the pulp feed, the overflow stream from the hydrocyclone had a significantly longer average fibre length than that of the feed pulp. The feed pulp consistency, feed flow rate, air flow rate and the ratio of overflow to underflow flow rates had a direct effect on the fractionation performance.     

Suitability of Hybrid Willow as a Source of Pulp

Hybrid willow (Salix spp.) is a potential source of pulp as demonstrated by its fibre morphology, chemical composition and pulping kinetics. Fibre length and cell wall thickness measurements on one and two years old clones ranged from 0·49 mm to 0·70 mm and 2·5 μm to 3·6 μm respectively. Fibre length variation by annual growth layer varied from 0·5 mm in the first growth layer to about 1·1 mm in the last growth layer and the maximum growth rate occurred in the first two to three years for fourteen years old clones. The clones were producing more fibre fraction as indicated by volumetric composition. The UV absorptfvities of milled wood lignin was found in the range of 12·17 -14·31 Lg^?1cm^?1 at 278 nm and the presence of syringyl and guaiacyl lignin was observed. ¹³C-NMR results of acetylated milled wood lignin showed clonal structural variations during lignification process and the Klason lignin content of one and two years old clones ranged from 20·8% to 26·1%. Bulk kraft delignification of mature wood resulted in 5–6% higher yield than juvenile wood from the same clone and the pulping activation energy ranged from 98 kJ.mol^?1 to 120 kJ.mor^?1.     

Optimization of beech wood pulping in catalyzed acetic acid media

Fagus sylvatica wood samples were treated in HCl‐catalyzed, acetic acid solutions. The effects of selected operational variables (catalyst concentration, reaction time and liquor to wood ratio) on pulp yield, composition of pulps and composition of pulping liquors were assessed using incomplete, second‐order, centred, factorial designs. Pulp composition was measured by the contents in cellulose, xylan and lignin. The concentrations of glucose, xylose and furfural in pulping liquors were also considered as experimental variables. Under selected conditions, pulps with 5.8% to 7.5% Klason lignin (kappa numbers in the range 25 to 33), 77.2% to 85.3% cellulose and 3.3% to 6.1% xylan were obtained at 45.8% to 50.0% pulp yield. The selected pulps showed good SCAN viscosity (723 to 814 mL/g) and alkaline resistances which were affected by the acetyl group content of samples (6.6 to 7.6 weight percent).     

Quantification of Lignin and Hexenuronic Acid in Bleached Hardwood Kraft Pulps: A New Calibration Method for UVRR Spectroscopy and Evaluation of the Conventional Methods

Abstract

Lignin content determination is an important task when pulp bleaching is studied. However, none of the conventional methods were developed for bleached pulps and therefore they are accurate mainly for unbleached pulps. This article describes a new, rapid method to determine lignin and hexenuronic acid contents of bleached hardwood kraft pulps based on UV resonance Raman (UVRR) spectroscopy. The lignin contents of pulp samples were determined from the aromatic band heights of the UVRR spectra. Therefore the measurements gave the content of aromatic lignin in pulp, and did not include extensively oxidized lignin structures. The method was applicable for hardwood kraft pulps with lignin content less than 1%. The measured lignin content correlated linearly with the kappa number. The lignin content (% on pulp) equaled 0.15κ+0.16. The constant 0.16 was presumably caused by the incomplete oxidation of the lignin in the kappa number determination. Klason lignin or total lignin determinations were not accurate for these kinds of pulps. Hexenuronic acid content was simultaneously determined from the UVRR band height of unsaturated C?O and C?C structures. The linear correlation of this band with hexenuronic acid indicated that the content of other unsaturated structures was constant in all the pulps, was proportional to the hexenuronic acid content of the pulps, or was insignificantly low. When compared to conventional methods, the UVRR spectroscopic method is fast, requires little sample and pretreatment, and the procedure has good repeatability. In addition, the accuracy of this technique increases with decreasing lignin content (<1%) making it a very attractive method for bleaching studies.     

Extraction and Characterization of Hemicelluloses and Cellulose from Oil Palm Trunk and Empty Fruit Bunch Fibres

Abstract

The cell walls of oil palm trunk fibre and empty fruit bunch (EFB) fibre were initially extracted with 5% NaOH at boiling for 2 h, which removed 17.3% and 15.2% hemicelluloses, respectively. Further extraction of the delignified palm trunk and EFB fibre was conducted with 10% NaOH at 20°C for 16 h and 24% KOH-2% H₃BO₃ at 20°C for 2 h. This resulted in the release of 11.9%, 13.5%, 12.7% and 14.9% residual hemicelluloses, respectively. The cellulose content, isolated by 24% KOH-2% H₃BO₃ from the two fibre samples, was found to be 41.3-41.7%, most of which was relatively free of associated lignin and hemicelluloses. The hemicelluloses, extracted with 5% NaOH from the lignified palm trunk fibre and EFB fibre, contained relatively high amounts of xylose, and minor arabinose and rhamnose than the hemicelluloses, extracted with 10% NaOH and 24% KOH-2% H₃BO₃ from the delignified fibres. While the hemicelluloses, extracted with 10% NaOH and 24% KOH-2% H₃BO₃ from the delignified palm trunk and EFB fibre, contained slightly more galactose, glucose, and mannose than the hemicelluloses, extracted with 5% NaOH from the lignified fibres. Further studies implied that the hemicelluloses, extracted with 5% NaOH from the lignified fibres, were more linear and acidic and had a large molecular size (weight-average, 17,400-22,900), together with comparatively high associated lignins (12.0-15.7%). Which were found to be linked to hemicelluloses mainly via syringyl unit. On the other hand, the hemicelluloses, extracted with 10% NaOH and 24% KOH-2% H₃BO₃ from the delignified fibres, were more branched but less acidic and had a comparatively small molecular size (weight-average, 6,600-10,800), together with trace amounts of associated lignin (0.3-1.1%). The hemicelluloses in the cell walls of palm EFB had a higher degree of polymerizaton than the hemicelluloses in the cell walls of palm trunk fibre as indicated by the molecular-average weights, ranging from 7,200 to 22,900, and from 6,600 to 17,400, respectively.     

The use of a mixing-sensitive chemical reaction for the study of pulp fibre suspension mixing

The competitive, consecutive chemical reactions between 1-naphthol and diazotized sulfanilic acid were utilized to study the mixing of a pulp fibre suspension in a 22 L stirred tank reactor. Mixing quality was determined from the distribution between the mono and bis substituted reaction products once a correlation was made for the adsorption of the product dyes onto the suspended fibres. The technique was found to be adequate for assessing micromixing and turbulence intensity within a fibre suspension provided the measured product distribution, Xs, was between 0.4 and 0.01. Thus the mixing conditions that could be assessed depended on both the energy dissipation within the mixer and the amount of the fibre present. For the experimental conditions chosen for this study energy dissipation rates would typically have to be less than 80 W/kg and the suspension mass concentration less than 2.5%. When compared with water, a reduction in turbulence levels at both the impeller zone and a remote zone in the stirred vessel was observed for fibre mass concentrations as low as 0.5%. The turbulence decreased as the suspension mass concentration was increased. This decrease is attributed to energy dissipation by friction at fibre-fibre contact points as the fibres move relative to one another in the flow. This sink removes energy from the turbulence cascade which never shows up as small-scale fluid deformations leading to better mixing.     

Soft measurement of pulp suspension flow velocity based on wavelet transform

A soft measurement technique is presented, which the pulp suspension flow velocity (PSFV) can be obtained by analysis of pulp fibre consistency signal without using the flow sensor or flow meter. Doppler Effect in pulp fibre consistency signal, which is caused by the relative motion between pulp suspension flowing in pulp pipe and consistency sensor fixed in the pipe, is discovered on the basis of studying the structure of pulp suspension and the properties of pulp fibre consistency signal, and it is proved by wavelet transform (WT) in this paper. WT are used to analyse pulp fibre consistency signal based on Doppler Effect. PSFV can be determined by the average period of WT which is used to analyse pulp fibre consistency signal based on Doppler Effect. The corresponding tests indicate that the measurement technique is feasible with high precision and better dynamic characteristics.     

A theoretical/experimental approach to the intrinsic oxidation reactivities of C/C composites and of their components

The oxidation reactivities of two C/C composites and of their available components (fibers, bulk matrices) are determined by measurement of mass loss rate in a cylindrical oxidation reactor under dry air and at atmospheric pressure. In order to identify reactional and diffusional regimes, and to provide a safe method for the identification of the intrinsic heterogeneous reaction rates at high temperatures, a modeling approach has been developed. Diffusion of the oxidant is considered throughout the reactor for all the samples (global-scale modeling) in combination with convection and reactions. Fibers have been arranged in unidirectional bundles in which diffusion is also considered (local-scale modeling). The importance of the reaction rate relatively to global-scale and local-scale diffusion has been evaluated. When reaction is slow enough, diffusion effects can be neglected; in the converse case, the intrinsic reaction rates are extracted from the experimental data using the models. Incidentally, the comparison of the fiber and matrix intrinsic reactivities supports the idea that the composites feature a complex oxidation behavior mainly based on a weakest link process. This result is illustrated and discussed using SEM and TEM investigations.     

固定化白腐菌对造纸废水的生物降解研究

就具有较强木质素降解能力的白腐菌对造纸废水的降解效果及条件进行了初步研究.分别采用固定化白腐菌和悬浮态白腐菌在不同接种量下对造纸废水进行降解,对降解过程中的白腐菌生长量、pH、COD、木质素含量等废水降解指标进行测定.结果显示两种不同状态下的白腐菌均能降解造纸废水,但它们的降解程度不同.其中固定化白腐菌降解木质素效果较好,且呈现较明显规律,说明固定化的白腐菌较悬浮态的白腐菌更具有降解造纸废水的潜在能力.     

Graft copolymerization of acrylonitrile onto bagasse and wood pulps

Graft copolymerization of acrylonitrile onto bagasse and wood pulps has been studied using ceric ammonium nitrate as initiator. The effect of order of reactants addition on grafting was examined: three methods were studied. Addition of the pulp to a mixture of initiator and monomer (method A) resulted in more efficient grafting than the other two methods. The reaction produced more grafting at 50°C than at 30°C or at 40°C. The results showed that the monomer and initiator concentrations are the major factors influencing the grafting rate of acrylonitrile. Increasing the acrylonitrile or initiator concentration was accompanied by a substantial increase in graft yields. Increasing the initiator concentration is more effective on polymerization rate than the increase in monomer concentration. The extent of grafting of this monomer can best be controlled by reaction time. Water swelling of pulps significantly affected the grafting rate of acrylonitrile as well as the ceric consumption during grafting. The reactivity of bagasse pulp towards grafting of acrylonitrile is higher than that of wood pulp due to a more open structure of cellulose in bagasse pulp as well as the presence of some lignin which accelerates grafting. Ceric consumption during grafting depends on the nature of the pulp as well as the monomer and initiator concentrations, time, temperature, and the method of grafting. More Ce(IV) is consumed during grafting than during oxidation of the pulps under identical reaction conditions, due to homopolymer formation which accompanied grafting. The ceric consumption by bagasse during grafting or oxidation is somewhat greater than that consumed by wood pulp under similar reaction conditions.     

Wettability of kraft pulps-effect of surface composition and oxygen plasma treatment

Wettability and ESCA studies have been carried out using unextracted and extracted kraft pulps with different amounts of lignin. The effect of oxygen plasma treatment was investigated. The wettability was studied by placing a drop of water on a sheet made from the pulp and following the decrease in drop volume and apparent contact angle with time. The first reading is taken after about 0.1 s. Extrapolation to zero time gives the initial contact angle. The initial absorption rate was also determined. Good correlation between the initial contact angle and the oxygen to carbon atomic ratio was found for the pulps without extractives. Pulps containing extractives are very hydrophobic, but an oxygen plasma treatment renders these pulps as hydrophilic as the purest pulps. It is concluded that the oxygen plasma treatment oxidizes the lignin and the extractives but reduces the pure cellulose surface. The oxidized extractives appear to act as wetting agents. The initial absorption rate is strongly dependent on the amount of extractives in the pulp. An oxygen plasma treatment improves the absorption rate, especially if the pulp contains high amounts of extractives.     

Xylanase effects on pulp delignification

Xylanase effects on softwood pulp delignification were investigated experimentally and using mathematical models. The effect of xylanase molecular size on pulp delignification was investigated. As xylanase molecular weight decreased from 67 kDaltons to 20 kDaltons, lignin removal from pulp increased from 30 wt% to 48 wt%, respectively. The rate of xylanase-aided pulp delignification was studied using a batch system. The rate-data was fitted to a mathematical model of the batch system that enabled estimation of process parameters including xylanase and lignin effective diffusivities, lignin mass transport coefficient, and effective particle diameter for mass transport. Parameter values thus obtained were used to simulate the semi-batch delignification process, which predicted 84.6% of lignin available to UGA xylanase (MW=39,000 Daltons) would be removed in 2.5 h.