Lipophilic Extractives in Eucalyptus globulus Kraft Pulps. Behavior during ECF Bleaching

Abstract

The composition of E. globulus kraft pulp lipophilic extractives and their behaviour during an ECF (DEDED) bleaching sequence were investigated. Sterols; fatty acids, including several α‐ and ω‐hydroxyfatty acids; and long‐chain aliphatic alcohols are the major lipophilic extractives of the unbleached pulp. During the bleaching, about 80% of the aliphatic extractives are removed from pulp (ca. 70% of the sterols, 70% of the fatty acids, and 90% of the long‐chain aliphatic alcohols). The decrease of sterols is mainly due to the degradation of β‐sitosterol by chlorine dioxide, while the decrease of fatty acids and alcohols is essentially assigned to their extraction and elimination with the alkaline filtrates. The major chemical transformations in pulp extractives composition and structure occur in the last bleaching stages.     

Study of the Fate of Lipophilic Wood Extractives During Acid Sulphite Pulping Process by Ultrasonic Solid-Liquid Extraction and Gas Chromatography Mass Spectrometry

Abstract

Lipophilic extractives in dissolving pulp are still a big concern for pulp industries due to their detrimental effect on the quality of pulp. Since lipophilic extractives remaining in pulp are trapped in low-accessible fiber structures, effective extraction methods need to be established for studying their fate in the process. A simple, ultrasonic, solid liquid extraction established in this study was found to be more effective in capturing extractive residues in all “elemental chlorine-free” bleaching stages. Its efficiency was dependent on the extraction temperature, time, and solvent composition. A linearly correlated removal pattern of sterols and unsaturated fatty acids by the bleaching sequence was observed. It was further found that the bleaching combination did not fully remove lipophilic extractives. This study suggests an opportunity to explore ultrasonication-based extraction as an effective extraction procedure prior to gas chromatography mass spectrometry analysis for monitoring extractives in pulp.     

Behavior of Eucalyptus Kraft Pulp Extractives Components across ECF Bleaching and Their Impact on Brightness Reversion

Abstract

This study investigated the chemical composition of the dichloromethane and acetone extracts of eucalypt pulp across D(EP)DP and AZDP bleaching sequences by gas chromatography-mass spectrometry (GC-MS). The bleaching stages led to the partial removal and to several oxidative transformations of fatty acids and sterols, the main lipophilic extractives found in the unbleached pulp. The pulp samples were bleached to 90–91% ISO by D(EP)DP and AZDP sequences and their brightness stability and chemical characteristics determined. The effect of aging on brightness was investigated. The AZDP bleaching sequence resulted in pulps of higher brightness stability. Furoic structures representing the main acid degradation products of HexA are suggested as the actual intermediates that cause yellowing by forming colored compounds. The AZDP process removed larger amounts of HexA across bleaching.     

Lipophilic Extractives in Populus × euramericana “Guariento” Stemwood and Bark

Abstract

The lipophilic extractives in stemwood and bark from three different heights of Populus × euramericana “Guariento” were analyzed. The bark samples, especially from 4 and 8 meters height, contained much more extractives than the stemwood samples. The lipophilic extractives identified by Gas Chromatography–Mass Spectroscopy (GC-MS) were composed of five component groups (i.e. triglycerides, steryl esters, free fatty acids, sterols, and free fatty alcohols both in the stemwood and bark). Besides ferulic acid esters, α-amyrin and its esters, 4-hydroxycinnamic acid esters of fatty alcohols were also identified in the stemwood and bark. Small amounts of alkanes and oligomeric or polymeric material with higher molar mass than triglycerides were present only in the bark. Glycerides, mainly triglycerides, were the largest component group of the lipophilic extractives. The high proportion of short-chain fatty acids released after alkaline hydrolysis are beneficial when removing pitch particles or fatty acid soaps by dispersing and washing during pulping and papermaking.     

Formic Acid-Peroxyformic Acid Pulping of Fagus sylvatica

Abstract

Beech (Fagus sylvatica) wood samples were subjected to two-stage treatments following the philosophy of the Milox process. By means of incomplete, second-order, factorial designs, the effects of selected operational variables on the composition and on the technical properties of pulps were assessed for optimization purposes. Under the best conditions assayed, a pulp with 5.5% lignin, 86.3% cellulose and 4.3% xylan was obtained at 46.6% pulp yield. The selected pulp showed good technical properties (kappa number = 25, SCAN viscosity higher than 1000 mL/g, R-10 test for alkaline resistance = 88.9%, R-18 test for alkaline resistance = 91.8%), showing potentiality to be used as feedstock for dissolving pulp production after TCF bleaching.     

Screening of Ophiostoma Species for Removal of Eucalyptus Extractives

Abstract

Ophiostoma species have been demonstrated to metabolize wood extractives and be useful to the pulp and paper industry. In order to have new isolates for the Asian market, Eucalyptus camaldulensis logs were harvested from forest sites in central Taiwan and 28 strains of the Ophiostoma genus were isolated from them. These strains were subsequently inoculated onto Eucalyptus wood chips to evaluate their effects on weight losses of wood and the amounts of acetone extractives degraded. At the same time, Gas Chromatography-Mass Spectroscopy (GC-MS) analysis was conducted and by using calibration curves and a database of GC-MS mass spectra, changes in lipophilic compounds were analyzed. Fatty acids, hydrocarbons, sterol compounds, sterol esters, and triglycerides were significantly reduced after two weeks’ inoculation by the fungal strains. The results show that six of the strains were capable of reducing the lipophilic fractions by more than 60% in a two-week treatment. DNA of the most effective strains were analyzed and found to be a variant of Ophiostoma querci.     

GC/MS characterization of effluents front the ozone bleaching of eucalypt kraft pulps

Concerns regarding the possible environmental effects of organochlorine by‐products from bleaching of pulp with chlorine‐based compounds have led to the pulp and paper industry developing new bleaching sequences. Ozone, oxygen and hydrogen peroxide are the main reagents in these Totally Chlorine Free (TCF) bleaching processes.

In this study, eucalypt kraft pulps from a variety of Australian wood sources were subjected to bleaching sequences comprising oxygen, ozone and hydrogen peroxide/alkali extraction stages. The aqueous liquid effluents from each stage were analyzed by GC/MS for aldehydes, ketones, alcohols, carboxylic acids and other by‐products. Pentafluorobenzyl oxime derivatives of the aldehydes and ketones were analyzed by electron impact GC/MS. The major carbonyl compounds detected were formaldehyde, glyoxal, dimethylglyoxal and acetone. An homologous series of n‐aldehydes corresponding to cleavage of ω‐3, 6, 9 and 12 unsaturated fatty acids also was detected. Aromatic aldehydes were identified in the oxygen stage and high consistency ozone stages, but not in any medium consistency ozone or post‐ozone bleach stages. In all stages a series of saturated alkyl carboxylic acids from formic to octacosanoic acid was detected. Formic and acetic acids were present in the highest yield. Only trace quantities of unsaturated fatty acids were detected. Details of these and other compounds detected are discussed.     

Distribution of Anionic Groups in TMP Suspensions

Abstract

The distribution of anionic groups in fibres, fines, the colloidal fraction, and the dissolved fraction of thermomechanical pulp (TMP) suspensions was determined. The influence of extraction, alkaline treatment, and peroxide bleaching of spruce TMP were also studied.

Spruce TMP was extracted with hexane, treated with alkali, or bleached with peroxide. Suspensions were made at pH 5.5 or 8, and fractionated into long fibres, large fines, small fines, a colloidal fraction, and a dissolved fraction. The surface and total charge of the fractions were determined separately by polyelectrolyte titration. To determine the origin of the charges, the contents of fatty acids, resin acids, and acidic units in polysaccharides in the different fractions were determined by gas chromatography.

Extraction of TMP with hexane prior to fractionation increased the measured total and surface charge of the fibres. The removal of wood resin probably uncovered some anionic groups on the fibre surface, or improved the penetration of the polymers into the pores of the fibres. The total charge, determined with polybrene titration, of the fines and the colloidal fraction was lower when the resin had been removed, while the surface charge, determined with poly-DADMAC, was not greatly affected.

Alkaline treatment of the TMP increased both the total charge and the surface charge of the fibres and fines, mainly because of demethylation of pectins. Alkaline treatment also increased the total and surface charge of the dissolved substances, due to the release of pectic acids into the water phase. Alkaline peroxide bleaching further increased the total and surface charge of fibres and dissolved substances, most likely due to oxidation of lignin. The total charge and the surface charge of the colloidal substances, consisting mainly of wood resin, were only slightly affected by alkaline treatment and peroxide bleaching.

The anionic charge in TMP suspensions originated mainly from free uronic acids in the xylans, arabinogalactans, and pectic acids. The contribution from the fatty and resin acids was substantial only for the colloidal fraction.     

Evaluation of Prosopis juliflora as a potential feedstock for the production of sodium lignosulfonate from the spent liquor of a laboratory digester

Abstract

Chopped stems of Prosopis juliflora, an invasive xerophyte, were digested in a laboratory digester following alkaline sulfite pulping process to generate spent liquor whereby lignin underwent sulfonation to produce sodium lignosulfonate (SLS). SLS was concentrated from the spent liquor by ultrafiltration. Raw wood was featured by high lignin (23.5%), low extractives (1.0%), low wax (0.41), and low ash (2.25%) content thus making it an ideal feedstock to produce lignosulfonates with appreciable physico-chemical property and relatively high mechanical strength. Attempts were made to provide basic information on SLS structure and structural changes that might occur during pulping of P. juliflora under the present experimental conditions. Spectral and X-ray diffraction studies on as-produced SLS revealed substantial depolymerization and structural modification of lignin during sulfite pulping. The derived SLS had higher crystallinity index than the feedstock wood. Effect of average size of raw wood chip and dose of sodium sulfite in the overall yield of pulp and SLS along with the kappa number of the pulp were also analyzed. Findings from this study would serve to cultivate a better understanding of the potential of P. juliflora as a feedstock, so far unexplored, to produce SLS???a value-added product with numerous commercial applications. The use of this particular plant species in paper and pulp industry could also be considered as an effective means of integrated agro management in rural areas.     

Alkaline Pre-treatment of Hardwood Chips Prior to Delignification

Abstract

Hardwood (Betula pendula) chips were extracted having alkaline aqueous solutions with varying chemical charges (1, 2, 3, 4, 6, and 8% of NaOH on wood), treatment times (30, 60, 90, and 120 minutes), and temperatures (130°C and 150°C). The total amount of material removed was in the range 2.1–16.5% of the original dry feedstock. This fraction was characterized in terms of carbohydrates and their degradation products (mainly aliphatic carboxylic acids together with some furanoic compounds), lignin, and extractives. Low alkali charges (1–4% of NaOH) were not sufficient to neutralize all the acids formed (mainly acetic acid from the acetyl groups of xylan). In contrast, an increase in alkali charge (6% and 8% of NaOH) more intensively facilitated the alkali-catalyzed degradation reactions of polysaccharides to various hydroxy acids, which were then typically present as one of the main constituents in the dissolved organic matter, along with other aliphatic carboxylic acids (acetic and formic acids), lignin, extractives, and carbohydrates.     

Behavior of Eucalyptus Wood Xylans across Kraft Cooking

Abstract

The 4-O-methylglucuronoxylans isolated from wood, pulp, and black liquor from six eucalyptus wood species were characterized. The ¹H nuclear magnetic resonance (NMR) studies revealed that all eucalyptus wood xylans contain O-2-substituted 4-O-methylglucuronic acid (MeGlcA) groups with hexose residues (9–26%). Their molecular weight (Mw) and polydispersity varied in the range of 26,083–28,405 g.mol^?1 and 1.13–1.17, respectively. The xylan retention during pulping increased with increasing degree of MeGlcA substitution in the xylose ring. An average of 54% xylans was retained in the pulp and the remaining 46% were degraded and/or dissolved in the black liquor (39% degraded and 7% dissolved). The average Mw of the xylans retained in the pulp and dissolved in the black liquor is influenced by pulp kappa number and averaged 20,134 and 14,778 g.mol^?1, respectively, at kappa 17. The average substitution degree of uronic acids, including MeGlcA and hexenuronic acids (HexA) in the xylans isolated from pulps (kappa 17) and black liquors were 1.05 and 1.13/10 xyloses, respectively. Of the total uronic acids present in the six original woods, an average of 36% w/w was retained in the pulps.     

Chemical characterization of Cedrus deodara wood extracts using water and molybdenum catalysts

The effect of the presence of some molybdenum catalysts on the amount of extractives in cedar wood has been studied. Autoclave treatment of cedar wood in the presence of some molybdenum catalysts can increase the amount of extracts. While autoclave treatment of cedar wood in water gave 2.85% extractives, the same treatment in the presence of H₃PMo₁₂O₄₀ gave 7.51% extractives. In the presence of silica-supported MoO₃, the amount of extractives was 5.50%. The extractives obtained using water were partially soluble in chloroform (40.7%). Only 27.6% of the extractives obtained using H₃PMo₁₂O₄₀ was soluble in the same organic solvent. When cedar was treated with silica-supported MoO₃, 56.4% of the extractives was soluble in chloroform. The extracts can be a source of fatty acids for biodiesel production and simple carbohydrates. The analysis of the chloroform-soluble fraction showed that the autoclave treatment of cedar wood gave 49.7% of a mixture of 2-hydroxy-1-(hydroxymethyl)ethyl hexadecanoate, 2-hydroxy-1-(hydroxymethyl)ethyl octadecanoate, and 2,3-dihydroxypropyl octadecanoate. The extractives obtained in the presence of the polyoxometalate molybdenum derivative gave 95% of the same esters of fatty acids, while those obtained in the presence of silica supported MoO₃ showed the presence of 93% of the same esters. Gas chromatography–mass spectrometry (GC-MS) of water-soluble fraction showed the presence of some simple carbohydrates, mainly ribose, xylose, and arabinose.     

Developments in Ozone-Based Bleaching of Pulps

ABSTRACT

This paper summarizes the review of developments in the area of ozone-based elemental chlorine free (ECF) and total chlorine free (TCF) bleaching of wood and non-wood pulps. Focused areas of review are reaction mechanism of ozone with carbohydrates and lignin, effect of process conditions maintained during ozone bleaching on pulp properties, effect of using different cellulose protectors, effect of alkaline extraction after ozone bleaching of pulps, effect of ozone bleaching on final bleached pulp properties, ECF and TCF bleaching sequences used along with ozone for of wood and non-wood pulps, and commercial scale utilization of ozone for pulp bleaching.     

Analysis and Fate of Lipophilic Extractives in Sulphite Pulps

Abstract

One of the major requirements of sulphite pulps, particularly those used in the manufacture of dissolving grades, is that their extractives content must not exceed certain levels, as specified by the customer. Since these levels are generally very low, the accuracy and reproducibility of extractives measurements can be poor, which in turn can lead to disagreements between pulp suppliers and their customers. In an effort to improve the reliability of extractives measurements, we have evaluated several methods for the determination of lipophilic extractives in sulphite pulps, using Soxhlet and Soxtec solvent extraction and various modes of drying the extracts including hot plate, infrared lamp, and freeze drying. Analysis of the extracts by size exclusion chromatography showed that a significant portion of the extracts was polymerized during the production process. Lipophilic extractives from ammonium sulphite pulps contain more polymerized matter than the extractives from the magnesium process.     

Totally chlorine‐free bleaching of Acetosolv pulps: a clean approach to dissolving pulp manufacture

Eucalyptus globulus wood samples were delignified in media containing concentrated acetic acid, water and hydrochloric acid (Acetosolv process) under optimized conditions, and the pulps were subjected to totally chlorine‐free (TCF) bleaching. Alkaline extractions, oxygen delignification, ozone treatment, enzymatic xylan removal and hydrogen peroxide oxidation in alkaline media were investigated as individual steps in selected bleaching sequences. Under the best conditions, fully bleached pulps with favourable characteristics for dissolving pulp manufacture were obtained. © 2001 Society of Chemical Industry     

Analyses of organic foulants in membranes fouled by pulp and paper mill effluent using solid-liquid extraction

Fouling of membranes is a serious problem in membrane technology. By characterizing the foulants in membranes it is possible to understand fouling and reduce it. However, the characterization of foulants, especially organic ones, is difficult. The purpose of this study was to find out whether there are any organic foulants such as extractives in the membranes, and if it is possible to identify them. Membranes of different materials and hydrophilicity were used in filtration of ground wood mill (GWM) circulation water during one month in an integrated pulp and paper mill, Solid—liquid extraction was employed to remove the extractives from the membranes and the characterization of them was carried out with a gas chromatograph. According to the results, there are extractives in the membranes and it is possible to characterize them. It seems that the fouling by extractives mainly comes from resin and fatty acids. In addition, some traces of lignans were found in the membranes. Moreover, the hydrophobic membranes contained more of these acids and lignans than the hydrophilic membranes.     

Influence of wood extractives on two-component polyurethane adhesive for structural hardwood bonding

ABSTRACT

When bonding wood for structural applications, the wood–adhesive bond is influenced by a variety of factors. Besides the physical and mechanical properties of wood species, their chemical composition, e.g. wood extractives, can play a role in bonding wooden surfaces. A two-component polyurethane system (2C PUR) was chosen to better adapt to the current adhesion problem. The influence of extractives on crosslinking was determined by Attenuated Total Reflection-Fourier Transform Infrared Spectrometer (ATR-FTIR) and on the rheological behavior in terms of gel point and storage modulus. Therefore, 2C PUR was mixed with 10% of eight common wood extractives separately. Furthermore, the mechanical properties of beech wood (Fagus sylvatica L.) bonded with extractive enriched adhesive were tested by means of tensile shear strength tests and evaluation of wood failure. These results of ATR-FTIR clearly show that the majority of crosslinking was terminated after 12 hr. Acetic acid and linoleic acid expedited the isocyanate conversion during the first 2.5 hr. The curing in terms of gel point and storage modulus of 2C PUR was accelerated by starch, gallic acid, linoleic acid, and acetic acid. Heptanal, pentanal, 3-carene, and limonene decelerated the curing. All extractives lowered the storage modulus determined after 12 hr. The bonding of beech wood with extractive–adhesive blends showed a slight decrease of the mechanical properties, with the exception of a marginal increase in the case of linoleic acid and pentanal.

In summary, it can be said that 2C PUR is sensitive to the influence of wood extractives and can therefore be partly held responsible for adhesion problems occurring when extractives in surface-wide and higher contents are available.     

A Partial Magnesium Hydroxide Substitution for Sodium Hydroxide in Peroxide Bleaching of an Aspen CTMP

Abstract

A partial substitution of sodium hydroxide (NaOH) by magnesium hydroxide (Mg(OH)₂) as the alkali source was studied in peroxide bleaching of an aspen chemi-thermomechanical pulp (CTMP). The effects on pulp properties, including pulp strength, optical property and carboxylic groups content, and process characteristics, such as oxalate and anionic trash formation, were studied. The X–ray photoelectron spectroscopy (XPS) technique was used to determine the lignin and extractives concentrations on the fiber surface. With the increased Mg(OH)₂ substitution ratio, the peroxide bleaching process gave a higher pulp yield and peroxide bleaching efficiency, produced pulps with higher light scattering coefficient and bulk, while the total oxalate, anionic trash, and chemical oxygen demand load (COD) were less. The total carboxylic groups content and the surface charge of pulp fibers were decreased. The underlying mechanism responsible for the decreased strength properties, when the Mg(OH)₂ substitution ratio was increased, is discussed.     

The Formation of Oxalic Acid During Bleaching of Kraft Pulp

Abstract

Calcium oxalate scaling is a major practical problem in a paper mill, especially in the evaporators, pulp digesters, and the bleach room. The sources of oxalic acid were determined by analysis of mill samples. In the unbleached pulp mill, the source of oxalic acid is the wood. In addition, a major amount of oxalic acid was found to be formed in the bleach room. A laboratory bleaching study was undertaken to establish a quantitative relationship betweeen bleaching conditions and oxalic acid production. Hardwood kraft pulp was bleached using three sequences. The amount of oxalic acid produced was dependent upon the available lignin content of the pulp (Kappa number) and not the oxidant concentration or reaction temperature.     

Influence of wood extractives on the photo‐discoloration of wood surfaces exposed to artificial weathering

Extracted and unextracted black cherry (Prunus serotina), red oak (Quercus rubra), and red pine (Pinus resinosa) wood specimens were exposed to artificial weathering, and their discoloration process was investigated to obtain basic understanding on the role of wood extractives in the weathering of hardwoods and softwoods. Color measurements were made with a spectrometer according to ISO 2470 standards, using the CIELAB system. Results obtained showed that the rate of whiteness was not significantly affected by extractives removed with organic solvents, but were significantly affected when organic solvent extraction was followed by water extraction. The total discoloration rate had the same pattern, and chromaticity coordinates were less affected by wood extractives. These results confirm the hypothesis that some extractives contained in wood act as antioxidants and are able to provide some protection to wood surfaces against weathering degradation. However, more work is needed to understand the chemistry and mechanism of action of these extractives so as to develop any practical use for this property. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 425–434, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20248