Infrared Absorption Spectra of Cellulose Pulps of Palm Tree

Palm leaves are used for the production of different cellulose pulps; their properties are investigated, the resulting pulps were bleached by a multistage process, the effects of the addition of solvent during the pulping process on the chemical structure of the pulps are discussed. The strength properties of the paper which is produced from unbleached and bleached pulps increased with increasing cellulose percentage and decreasing lignin content in the pulp. Infrared absorption spectra were recorded for different unbleached and bleached pulp in the frequency range 200–4000 cm^-1 by using the alkali halide disk technique; the factors which affect the experimental technique were calibrated through these studies. The structural units within pulping yield (holocellulose, hemicellulose, cellulose, lignin, and ash) were interpreted within the pulp network structure by the infrared absorption spectra, where different samples of unbleached, bleached soda, and kraft pulps were also elucidated by IR spectra, after preheating at different temperatures and with using different ratios of organic solvents. The addition of organic solvents decreased or increased the crystallinity indices, depending on the type of solvent and the pulping temperature. It was also found that, at the same pulping temperature (155°C) and with the same percent of organic solvents in the pulping liquor, the asymmetry indices also the mean hydrogen bonding strength (A _OH/A_CH) of the unbleached soda pulps (organosolv or nonorganosolv pulping) were less than that of unbleached kraft pulps, except for the pulps obtained by pulping with dioxan at 155°C. The mean hydrogen bond strength of the bleached pulps decreased or increased, depending on the type solvent used and the pulping temperature.     

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.     

Characterization of the Residual Kraft Pulp Lignin In Situ by Sulfite Treatments

Abstract

The O₂ delignification of kraft pulps from Norway spruce was shown having a significant impact on the reactivity of the residual pulp lignin as revealed from their responses to sulfite treatments at pH 7.5. A substantial higher ratio of lignin sulfonation to the phenolic hydroxyl group content of residual pulp lignin was observed for the O₂ -delignified kraft pulps (～ 0.8) as compared to a value of ～ 0.3 for the unbleached samples and ～ 1 for the spruce wood lignin. Under the prevailing sulfite treatment conditions, the sulfonation would be largely attributed to the phenolic lignin component and the etherified structures containing an α -carbonyl or -unsaturated group. The contribution from the latter units, evaluated by a borohydride pretreatment of pulps prior to the sulfite treatment, can only account for approximately 15% of the sulfonation observed for the O₂ -delignified sample. Thus, the nature of phenolic structures in the O₂ -delignified pulps was more similar to that of the wood lignin than that of the kraft pulps.     

氧脱木素过程中超氧阴离子自由基的控制

In this study, the superoxide anion radicals were generated by the auto-oxidation of 1,2,3-trihydroxybenzene and determined by UV spectrophotometry, and the reaction was found to be facilitated by anthraquinone-2-sulfonic acid sodium salt. The bamboo kraft pulps were treated by the 1,2,3-trihydroxybenzene auto-oxidation method or the 1,2,3-trihydroxybenzene auto-oxidation combined with anthraquinone-2-sulfonic acid sodium salt to show the ef- fect of the superoxide anion radicals during the oxygen delignification of bamboo kraft pulp and the enhancing affect of anthraquinone compounds as an additive on delignification. The results indicated that the superoxide anion radicals could react with lignin and remove it from pulp with negligible damage on cellulose, and the anthraquinone-2-sulfonic acid sodium salt could facilitate the generation of superoxide anion radical to enhance delig- nification of pulps. The oxygen delignification selectivity could be improved using the 1,2,3-trihydroxybenzene auto-oxidation system combined with anthraquinone-2-sulfonic acid sodium salt.     

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.     

Mechanistic Differences Between Kraft and Soda/AQ Pulping. Part 1: Results from Wood Chips and Pulps

Abstract

Soda pulping catalyzed by anthraquinone (AQ) or 2-methylanthraquinone (MAQ) can produce hardwood chemical pulps similar to kraft pulps in all respect but for bleachability. Results accumulated in our laboratory suggest that the residual lignin in pulps from anthraquinone catalyzed processes is less reactive toward bleaching chemicals than that in kraft pulps. Analyses of pulps by periodate and permanganate oxidations suggest that the residual lignin from the non-sulfur processes contained more condensed structures than kraft residual lignin. The low reactivity of these structures is believed to be responsible for the lower brightness of bleached soda-AQ (SAQ) pulps. Pulping and bleaching trials with hardwood chips demonstrated that shortening of the cooking time and/or increasing the alkalinity is one strategy for improving bleachability of SAQ pulps. When sugar maple (Acer saccharum) chips were SAQ cooked for 1.0 and 2.0 h at 165°C, the higher kappa number pulp produced after 1.0 h of cooking bleached to a significantly higher brightness with a small increase in the chlorine dioxide application.     

Dissolution of softwood kraft pulps by direct derivatization in lithium chloride/N,N‐dimethylacetamide

A method for the characterization of the molar mass distributions (MMDs) of softwood kraft pulps dissolved in 0.5% lithium chloride (LiCl)/N,N‐dimethylacetamide (DMAc) by size exclusion chromatography is presented. The method is based on derivatization with ethyl isocyanate and the dissolution of samples in 8% LiCl/DMAc. In this study, the derivatization of hardwood kraft pulps did not influence the MMD. In the case of softwood pulps, however, the derivatization decreased the proportion of the high‐molecular‐mass material and increased the proportion of the low‐molecular‐mass material, which resulted in a distribution similar to the MMD of a hardwood kraft pulp. The results suggest that associations between hemicellulose and cellulose in the softwood kraft pulp were ruptured during derivatization. This led to a more correct estimation of the MMD of derivatized softwood kraft pulps than obtained by the dissolution of nonderivatized samples. This new method offers several advantages over derivatization with phenyl isocyanate: a precipitation step is not necessary, it is possible to follow the lignin distribution in the samples, and the method allows very high levels of dissolution of softwood kraft pulps up to a κ number of around 50. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 424–431, 2004     

Optimized Catalytic Bleaching Sequences for Eucalyptus Kraft Pulp

Contemporary multi-stage bleaching processes partially remove residual lignin and hexenuronic acid from cellulosic pulps. The reactions in the steps could be faster and consume smaller amounts of chemicals. Catalytic bleaching (H_cat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyl triethylenediamine (CM-DABCO), is a new discovery that has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g. through reducing the reaction time of the bleaching processes. The objective of this study was to clarify if new kraft pulp bleaching sequences with initial stage of chlorine dioxide (ClO₂; D) and an intermediate stage of H_cat could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include D₀E_(OP)H_cat(Q)P and H_catZ/DP, which attained a final brightness of 88 and 89% ISO, respectively. H_catZ/DP showed to be the best sequence for the catalytic bleaching of eucalyptus kraft pulps. This study may open new doors to future bleaching of cellulose pulps with fewer towers and decreased use of chemicals.     

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).     

Phosphorylated cation‐exchangers from cotton stalks and their constituents

Cation‐exchangers were prepared by phosphorylation of cotton stalks and their isolated constituents (lignin, soda‐anthraquinone pulp, and bleached cellulose pulp). FTIR spectra of the phosphorylated materials showed new absorption bands at 950–1200 cm^?1 of the C? O? P bonds as a result of phosphorylation. The adsorption of different heavy metal ions (lead, copper, nickel, cobalt, chromium, and cadmium) at different metal ion concentrations (50–1500 μg) by the phosphorylated cotton stalks was studied. The adsorption of metal ions by the phosphorylated cotton stalks increased by increasing their concentration. The binding capacity of phosphorylated cellulose, lignin, and soda‐anthraquinone pulp was measured at 1000 μg metal ion concentration. The adsorption of the different heavy metal ions by phosphorylated‐lignin and ‐bleached cellulose pulp was higher than that of phosphorylated cotton stalks. Thermogravimetric analysis of the raw and phosphorylated cotton stalks showed that the resistance of the phosphorylated cotton stalks to thermal degradation was higher than that of raw cotton stalks (lower rate of weight loss), despite the lower degradation onset temperature of the phosphorylated cotton stalks. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2950–2956, 2003     

裂解-气质联用分析氧漂过程中木素结构的变化

从针叶木硫酸盐原浆、氧漂浆以及氧漂后的废液中分离出残余木素,在四甲基氢氧化铵（TMAH）存在下,采用裂解气相色谱-质谱联用(Py-GC-MS)的方法研究了氧漂过程中木素分子结构的变化.对裂解产物的分析表明,木素裂解时产生多种甲基化的芳香化合物,以愈创木基型化合物为主;氧漂能够氧化和降解木素分子,产生更多的羧基化合物,氧化程度高的木素分子容易从纸浆中溶出,氧漂优先脱除沉积在纤维表面上的短侧链木素.     

Soda Pulping of Hardwoods Catalyzed by Anthraquinone and Methyl Substituted Anthraquinones

Abstract

Black liquor gasification (BLG) as well as the recovery of lignin and other organic compounds from pulping black liquor would be aided if an efficient sulfur‐free pulping process could be developed. This has provided new impetus for research on soda pulping with redox catalysts instead of sodium sulfide that is presently used in the kraft process. Soda/anthraquinone (AQ) pulping afforded white birch (Betula papyrifera) and sugar maple (Acer saccharum) pulps with equal if not superior strength to kraft pulps. However, the delignification rate was significantly lower for soda/AQ pulping. When AQ was replaced by 2‐methylanthraquinone (2‐MAQ) a delignification rate only slightly lower than that of kraft pulping was obtained at the same effective alkali (EA). At a kappa number of ～20, a soda/2‐MAQ pulp was produced from sugar maple at a higher yield (1.2% on chips) than for a kraft pulp. 2‐MAQ was synthesized, as a powder, at 75% yield using an AlCl₃–mediated Friedel‐Crafts reaction that is one of the methods used for commercial production of AQ.     

Characterization of Residual Lignins Isolated from Unbleached and Semibleached Softwood Kraft Pulps

Abstract

Residual lignins in an unbleached and a semibleached softwood (Pinus taeda L.) kraft pulp were isolated by enzymatic hydrolysis of polysaccharides in the pulps. After purification, the residual lignins were characterized. A dissolved lignin was also isolated from the alkaline extraction spent liquor by acidification and characterized.

Results of the characterization indicate that extensive degradation of residual lignin in kraft pulp occurred during the first two stages of bleaching. The results also strongly support the previous finding that stable covalent linkages between residual lignins and carbohydrates in pulp any be the most probable cause for the residual lignins to resist delignification during kraft pulping and prebleaching.     

Raman Spectroscopy and the Raman Microprobe: Valuable new tools for Characterizing Wood and Wood Pulp Fibers

Abstract

A brief overview of Raman spectroscopy and the photon scattering phenomena which underly it is presented, together with the rationale for applying the methodology to the study of lignocellulosics. The sequence of studies undertaken at The Institute of Paper Chemistry to apply the methods to investigation of celluloses, chemical pulps, wood and high yield fibers are then reviewed.

The program began with studies on cellulose and related model compounds. These early efforts provided a basis for interpretation of the spectra of celluloses and for investigating the effects of various process variables on the aggregation of cellulose in pulp fibers. Among the effects touched upon are the differences between kraft and sulfite pulps, the effects of refining, and the influence of press drying on pulp crystallinity. More recently studies using the Raman microprobe made possible progress in the assignment of the vibrational spectra of cellulose and established the basis for using the microprobe to investigate variability of fibril orientation in native woody tissue.

In addition our extension of the studies to include lignin are noted. These included studies of fiber sections in native wood which show the orientation of lignin in the cell wall and observations of the variability of the ratio of lignin to cellulose.

Finally, the opportunities arising from new instrumental developments are reviewed. The new multichannel detectors will greatly enhance the efficiency of acquisition of spectra and allow more comprehensive explorations of the architecture of fibers. In addition, gated detectors coupled with pulsed laser excitation will allow studies of woody tissue and of high yield pulps that would not be feasible with single channel detection and continuous laser excitation.     

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.     

Kraft pulping of Eucalyptus nitens wood chips biotreated by Ceriporiopsis subvermispora

Eucalyptus nitens and E. globulus are wood species used in kraft pulping in Chile and Australia. Although E. nitens adapts very well to cold regions it requires more severe cooking conditions to produce bleachable kraft pulps. An attempt was made to find out whether a pre‐treatment with Ceriporiopsis subvermispora would improve its performance during kraft pulping and the pulp properties. The biotreatment of the chips carried out for a period of 15 days resulted in 13.3% lignin loss and a limited glucan degradation (2%). The pulping of biotreated samples required lower active alkali charge to reach the target kappa number compared to the control untreated sample and exhibited better pulping selectivity. The pulp yield increased by 3% and 1.5% for the pulps of 22 and 16 kappa numbers, respectively. The biotreated pulp's strength properties were improved and were similar to those of E. globulus reference pulp. Copyright © 2006 Society of Chemical Industry     

Dispersed Resin in Bleached Kraft Pulp Mills

Abstract

Several properties of the dispersed resin in bleached kraft pulp mills have been investigated. Average concentrations of resin particles in filtrates of pulps from various points along the process stream are reported. For each sampling location, the change in particle concentration with time of pulp sample storage at 5°C has been determined. In the future, this will enable rough estimation of original concentrations when samples must be measured a few days after collection. Size distributions of resin particles were the same at all sampling points, from which it follows that, in practice, the relationship between concentration and deposition rate is relatively unaffected by size distribution. Dispersed resin particles were negatively charged throughout the mills. The low charge observed in C-stage pulps was insufficient to confer stability, which further supports the hypothesis that the dispersed resin is heterocoagulated with the fibers in this acidic stage.     

Dissolution of Ethylenediamine Pretreated Pulp with High Lignin Content in LiCl/DMSO without Milling

Abstract

Various hardwood and softwood chemical pulps, including those with relatively high lignin content (up to ca. 10.5%), were completely dissolved without milling in lithium chloride/dimethyl sulfoxide (LiCl/DMSO) after a pretreatment with ethylenediamine (EDA). Because milling of the sample is not required, degradation of the cell wall components caused by milling does not take place. After the EDA pretreatment, the crystallinity of the pulps remained as high as the original pulps, although the crystal structure changed. This is the first time that transparent solutions of underivatized pulps with high lignin content were obtained in a simple organic solvent system. Interestingly, even in the case of coarse wood meal (40–80 mesh) about 70% could be dissolved after repeating the dissolving procedure two times. The formation of a pulp–EDA or wood–EDA complex seems to be critical for the dissolution in LiCl/DMSO. The nuclear magnetic resonance (NMR) spectrum of the EDA treated pulp solution had good resolution even though the degree of polymerization (DP) of the cellulose in the pulp is very high.     

The xanthate method of grafting. IV. Grafting of acrylonitrile onto high-yield pulp

A series of pulps with different lignin content was prepared from a softwood sodium bisulfite high-yield pulp. Sodium chlorite at pH 4 served as the delignification agent. The resulting pulps were subjected to grafting with acrylonitrile using the cellulose xanthate–hydrogen peroxide redox system to initiate the copolymerization reaction. The resulting products were isolated and analyzed for homopolymer content by dimethylformamide extraction. The results indicate that the presence of larger amounts of lignin in pulp may have a favorable effect on grafting. The plots of total conversion as well as of polymer loading show a minimum centered around approximately 15% of lignin. This minimum is observed invariably at five different reaction times and it coincides with the maximum concentration of reductive groups in the pulps as well as with the maximum cation exchange capacity. The parameter of grafting efficiency has a tendency to increase with rising lignin content, reflecting the lower relative yields of homopolymer obtained with high-lignin pulps. This observation is discussed in relation to possible chain transfer reactions by lignin.     

Structure and Reactivity of Spruce Mechanical Pulp Lignins Part II. Organosolv Fractionation of Lignins in a Flow-Through Reactor

Various spruce mechanical pulps were subjected to delignification with ethanol-water (1 : 1, v / v ) containing 0.1 M acetic acid at 175°C in a flow- through reactor. A thermomechanical pulp (TMP) and the corresponding samples derived from its bleaching (BTMP) and yellowing ( YBTMP ) treatments were delignified to a similar extent, about 70% of delignification degree, as compared with spruce wood. A series of five successive lignin fractions was recovered from each pulp sample and then characterized by various analytical methods. Large structural variations were observed within these fractions. The number of phenolic structures appeared to be an important factor influencing the dissolution of lignins in the ethanol-water medium. These lignin fractions were found to be different in the amount of β-aryl ether structures and in the relative importance of main carbon-carbon bonding patterns. The results are discussed in relation to the lignin fractionation in the flow-through reactor.