Comparison of hot-water extraction and steam treatment for production of high purity-grade dissolving pulp from green bamboo

The performance of hot-water extraction (HWE) and steam treatment (ST), followed by kraft pulping were compared for production of high purity-grade dissolving pulp from green bamboo. With the same prehydrolysis intensity (represented by the P-factor), the fractionation efficiency of HWE is far lower than that of ST. Because of lower removal of non-cellulosic components, the solid residue from HWE (even at approximately double the prehydrolysis intensity, P-factor = 1,379) required more active alkali (AA) during kraft pulping to obtain a cellulose purity equivalent to that achieved by the ST (P-factor = 756)-kraft process. To reach equivalent hemicellulose removal, HWE required more severe intensity than ST. However, FTIR and SEM characterizations of solid residue confirmed that intensified HWE resulted in significant lignin condensation. Antagonistic effects of hemicellulose removal and lignin condensation extent on subsequent kraft pulping were therefore more apparent in HWE than that in ST. Under the same kraft pulping conditions, lignin condensation from a severely intensified HWE process (P-factor = 2,020) caused greater cellulose yield and viscosity loss than that found for ST. Finally, at a given residual pentosan or lignin content, the cellulose yields from all HWE-kraft pulps were about 3 % lower than those from ST-kraft pulps. Consequently, based on an optimally setup chlorine dioxide bleaching stage, a cellulosic pulp with alpha-cellulose content of 97.6 % and viscosity of 927 mL/g was successfully produced from a ST-kraft pulp (P-factor = 756, AA = 19 %).     

The effect of eucalypt pulp xylan content on its bleachability,refinability and drainability

Currently, bleached eucalypt pulps are largely used for printing and writing (P&W) and sanitary (tissue) paper grades. Among the many pulp quality requirements for P&W and tissue paper production the xylan content is one of the most significant. For P&W papers, increasing xylans improve pulp refinability and strength properties but negatively affect bulk and drainability. For tissue paper, xylans are purportedly advantageous during paper drying in the Yankee cylinder but negatively affect paper bulk and may increase dusting during paper manufacture. On the other hand, bleachability is a very important parameter for both P&W and tissue grade pulps since bleaching cost is the second most significant in eucalypt bleached kraft pulp production. The aim of this study was evaluating the influence of eucalyptus pulp xylan content on its bleachability, refinability and drainability. A sample of industrial unbleached eucalyptus kraft pulp containing 15.6?% xylans was treated with various alkali charges at room temperature in order to obtain materials with different xylan contents. The pulps were bleached to 90 % ISO brightness with the O–D_HT–(EP)–D sequence and evaluated for their refinability and drainability. By increasing the alkali concentration in the range of 10–70 g/L pulps of 14.5–5.9 % xylans were produced with no significant impact on cellulose crystallinity. The decrease of xylan content significantly decreased pulp bleaching chemical demand, water retention value and refinability and increased pulp drainability.     

Ionic liquid extraction method for upgrading eucalyptus kraft pulp to high purity dissolving pulp

High purity cellulose from wood is an important raw material for many applications such as cellulosic fibers, films or the manufacture of various cellulose acetate products. Hitherto, multi-step refining processes are needed for an efficient hemicellulose removal, most of them suffering from severe cellulose losses. Recently, a novel method for producing high purity cellulose from bleached paper grade birch kraft pulp was presented. In this so called IONCELL process, hemicelluloses are extracted by an ionic liquid–water mixture and both fractions can be recovered without yield losses or polymer degradation. Herein, it is demonstrated that bleached Eucalyptus urograndis kraft pulp can be refined to high purity acetate grade pulp via the IONCELL process. The hemicellulose content could be reduced from initial 16.6 to 2.4 wt% while persevering the cellulose I crystal form by using an optimized 1-ethyl-3-methylimidazolium dimethylphosphate-water mixture as the extraction medium. The degree of polymerization was then reduced by a sulfuric acid treatment for subsequent acetylation of the pulp, resulting in a final hemicellulose content of 2.2 wt%. When pre-treating the pulp enzymatically with endoxylanase, the final hemicellulose content could be reduced even to 1.7 wt%. For comparison, the eucalyptus kraft pulp was also subjected to cold caustic extraction and the same subsequent acid treatment which led to 3.9 wt% of residual hemicelluloses. The performance in acetylation of all produced pulps was tested and compared to commercial acetate grade pulp. The endoxylanase-IONCELL-treated pulp showed superior properties. Thus, an ecologically and economically efficient alternative for the production of highest value cellulose pulp is presented.     

Effect of xylan in hardwood pulp on the reaction rate of TEMPO-mediated oxidation and the rheology of the final nanofibrillated cellulose gel

alkali-washed nanofibrillated cellulose (NFC) samples, obtained from hardwood kraft pulp, with different amounts of retained xylan were prepared to study the influence of xylan on the water-retention properties of NFC suspensions. In this study, NFC was produced using an oxoammonium-catalyzed oxidation reaction that converts the cellulosic substrate to a more highly oxidized material via the action of the nitroxide radical species 2,2,6,6-tetramethylpiperidine-1-oxyl. Reduction of the xylan content in NFC was achieved by cold alkali extraction of kraft pulp. The pulps were then oxidized to a set charge under constant chemical conditions, and the reaction time was determined. The xylan content of the feed pulp was found to have a large negative influence on the oxidation rate of the pulp, as the oxidation time shortened when xylan was removed, from 220 min (for 25.2 % xylan content) to 28 min (for 7.3 % xylan content). Following fibrillation by homogenization, the swelling of the NFC was determined by a two-point solute exclusion method. The distribution of hemicellulose over the fibril surface was observed by atomic force microscopy. Xylan was found to be distributed unevenly over the surface, and its presence increased the water immobilized within flocs of NFC, i.e., so-called network swelling. The swelling of the NFC had a large impact on its rheology and dewatering. Comparison of the morphological and swelling properties of the suspensions with their rheological and dynamic dewatering behavior showed that reducing the xylan content in NFC results in a weaker gel structure of the nanocellulose suspension. The results indicate that most of the water is held by the swollen structure by means of xylan particles trapped within the hemicellulose layer covering the fibril surface. Samples with high xylan content had high shear modulus and viscosity and were difficult to dewater.     

Possibilities for Optimization of Industrial Alkaline Steeping of Wood-Based Cellulose Fibers

Steeping of cellulosic materials in aqueous solution of NaOH is a common pre-treatment in several industrial processes for production of cellulose-based products, including viscose fibers. This study investigated whether the span of commonly applied process settings has the potential for process optimization regarding purity, yield, and degree of transformation to alkali cellulose. A hardwood kraft dissolving pulp was extracted with 17–20 wt% aq. NaOH at 40−50 °C. The regenerated residue of the pulp was characterized regarding its chemical composition, molecular structure, and cellulose conformation. Yield was shown to be favored primarily by low temperature and secondly by high alkali concentration. Purity of xylan developed inversely. Both purity of xylan and yield varied over the applied span of settings to an extent which makes case-adapted process optimization meaningful. Decreasing the steeping temperature by 2 °C increased xylan content in the residue with 0.13%-units over the whole span of applied alkali concentrations, while yield increased by 0.15%-units when extracting with 17 wt% aq. NaOH, and by 0.20%-units when extracting with 20 wt%. Moreover, the yield-favoring conditions resulted in a narrower molecular weight distribution. The degree of transformation via alkali cellulose to cellulose II, as determined with Raman spectroscopy, was found to be high at all extraction settings applied.     

Upgrading of paper grade pulps to dissolving pulps by nitren extraction: yields,molecular and supramolecular structures of nitren extracted pulps

Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure of selected pulps were further studied by solid state ¹³C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps. Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction. The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the resultant dissolving pulps still have the cellulose I structure. All laboratories are members of the European polysaccharide network of excellence EPNOE.     

Enzymatic hydrolysis of mercerized and unmercerized sisal pulp

Enzymatic saccharification of sisal cellulosic pulp has been investigated. Brazil leads global production of lignocellulosic sisal fiber, which has high cellulose content, an important property for producing glucose via saccharification. Hence, sisal pulp can be a good alternative for use in biorefineries. Prior to enzymatic hydrolysis, the starting pulp [85 ± 2% α-cellulose, 15 ± 2% hemicelluloses, 1.2 ± 2% insoluble lignin, viscometric average molar mass (MMvis) 19,357 ± 590 g mol^?1, crystallinity index (CI) 74%] was pretreated with alkaline aqueous solution (mercerization, 20 g of pulp L^?1, 20% NaOH, 50 °C). The changes in the properties of the cellulosic pulp during this pretreatment were analyzed [α-cellulose content, MMvis, CI, pulp fiber dimensions, and scanning electron microscopy (SEM)]. The unmercerized and mercerized (97.4 ± 2% α-cellulose, 2.6 ± 2% hemicelluloses, 0.3 ± 0.1% insoluble lignin, MMvis 94,618 ± 300 g mol^?1, CI 68%) pulps were subjected to enzymatic hydrolysis (48 h, commercial cellulase enzymes, 0.5 mL g^?1 pulp); during the reactions, aliquots consisting of unreacted pulp and liquor were withdrawn from the medium at certain times and characterized (unreacted pulp: MMvis, CI, fiber dimensions, SEM; liquor: high-performance liquid chromatography). The changes in pulp properties observed during mercerization facilitated access of enzymes to cellulose chains, and the yield of the hydrolysis reaction increased from 50.2 (unmercerized pulp) to 89.0% (mercerized pulp). These initial results for enzymatic hydrolysis of sisal pulp indicate that it represents a good alternative biomass for bioethanol production.     

Xylan enriched viscose fibers

In this study, a new xylan enriched viscose fiber was developed. A high molecular weight xylan with a degree of polymerization of 150–200 was added during a late stage of the viscose production process. The xylan deriving from a cold caustic extraction (CCE) of an eucalypt paper pulp was introduced to the process after xanthation and thus neither objected to any degradation conditions during alkalization nor to the xanthation step. About 90 % of the added xylan was transferred to the final fiber. A xylan content of up to 7.5 % was achieved. Fiber properties like strength showed a comparable level to the reference fibers while the water retention value was clearly raised due to the higher content of hemicelluloses. The hemicellulose distribution over the fiber cross section was investigated by enzymatic peeling. Even though a segregation of the different polysaccharides was observed, the goal of a good blending of CCE-xylan into cellulosic fibers with new interesting features was achieved.     

Dissolving-grade birch pulps produced under various prehydrolysis intensities: quality,structure and applications

Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties.     

Quantification of a tightly adsorbed monolayer of xylan on cellulose surface

The successive extraction and re-adsorption of a linear β-(1 → 4) xylan extracted from microfibrillated birch pulp was investigated using solid-state CP/MAS ¹³C NMR spectroscopy, specific surface area measurements, and atomistic molecular dynamics (MD) simulations. The NMR spectra confirmed that when in contact with cellulose after re-adsorption, the xylan molecules altered their conformation from the classical left-handed threefold structure found in the bulk to a different one, presumably a cellulose-like twofold system for quantities up to the equivalent amount of extracted xylan. Combining these observations with specific surface area measurements and the surface occupied by a xylosyl residue, it was possible to show that the re-adsorbed xylan in the modified conformation occurred only within the first adsorbed layer in direct interaction with the cellulose surface. It is only when an excess xylan was added and after full cellulose surface coverage, that the subsequent deposited layers took the classical threefold organization. Following the variation of xylan conformation in terms of sequential xylan addition allowed quantifying the surface of cellulose accessible for a tight adsorption of xylan, not only for microfibrillated birch cellulose, but for other samples as well. The MD simulations confirmed that xylan in threefold conformation had a weaker affinity for the cellulose surface than its twofold counterpart, thus supporting the hypothesis of the twofold conformation for xylan at the cellulose surface. The MD simulations also showed that in contact with cellulose, the adsorbed xylan was mainly organized as an extended molecular chain aligned parallel to the cellulose chain direction.     

Sulfur-free dissolving pulps and their application for viscose and lyocell

In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E) both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high molecular weight xylan of the CCE-treated pulps even took part in fiber forming.     

Catalyzed sulphite and semichemical pulping

Very high yield sulphite pulps were produced by cooking black spruce wafers in pulping liquors at pH 7 or 10, containing 0.1% (on O.D. wood) of soluble anthraquinone (SAQ). These pulps had better strength properties relative to controls prepared without SAQ, breaking length and burst index being greater, on average, by 20%. Other improvements included: increased pulping rate, lower lignin contents at comparable pulp yields, and higher carbohydrate content at the same level of residual lignin in pulp (this resulted in an increase of total pulp yield by 2%). Results of cooks in liquors ranging in pH from 4 to 10, and under variable conditions of time (20–60 min) and temperature (120–160°C) suggested that: firstly, AQ does not act as a pulping catalyst at pH 4, and secondly, the sulphonate contents of AQ-catalyzed pulps are lower than those of the uncatalyzed controls. In the light of the lower sulphonate content, the higher strength is unexpected.     

Nanofibrillation of dried pulp in NaOH solutions using bead milling

The drying process in typical pulp production generates strong hydrogen bonding between cellulose microfibrils in refined cell walls and increases the difficulty in obtaining uniform cellulose nanofibers. To investigate the efficacy of alkaline treatment for cellulose nanofibrillation, this study applied a bead-milling method in NaOH solutions for the nanofibrillation of dried pulps. NaOH treatments loosened the hydrogen bonding between cellulose microfibrils in dried pulps and allowed preparation of cellulose nanofibers in 8 % NaOH with a width of approximately 12–20 nm and a cellulose I crystal form. Both the nanofiber suspensions prepared in 8 and 16 % (w/w) NaOH were formed into hydrogels by neutralization because of surface entanglement and/or interdigitation between the nanofibers. When the dried pulp was fibrillated in 16 % (w/w) NaOH, the sample after neutralization had a uniquely integrated continuous network. These results can be applied to the preparation of high-strength films and fibers with cellulose I crystal forms without prior dissolution of pulps.     

Mercerized cellulose biocomposites: a study of influence of mercerization on cellulose supramolecular structure, water retention value and tensile properties

In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.     

Upgrading of paper-grade pulps to dissolving pulps by nitren extraction: properties of nitren extracted xylans in comparison to NaOH and KOH extracted xylans

Different paper-grade pulps were extracted with nitren, NaOH and KOH in order to produce dissolving pulps and polymeric xylan. The yield and structure of the isolated nitren and alkali xylans were investigated by carbohydrate analysis, HPSEC and ¹H-NMR spectroscopy. In addition the effect of washing stages on the residual nickel content of the nitren xylans was investigated. By nitren extraction up to 98% of the xylan could be extracted out of the fully bleached eucalyptus and birch kraft pulps. The nitren extracted kraft xylans had DP values between 95 (birch) and 111 (eucalyptus). At most 5 mol% of the xylose units were substituted. In the case of pulps with low mannan content only marginally differences between the nitren and alkaline (KOH, NaOH) extractions occurred. The extraction of the relatively “mannnan rich” pulps of this study like softwood kraft and beech sulfite pulps revealed that the dissolution effect regarding mannans increased in the following order: nitren < KOH < NaOH. In general the nitren extractions required a lower chemical charge compared to the alkaline extractions, in order to yield similar amounts of xylans. On the other side the necessity of an effective nickel removal is a disadvantage of the nitren extractions.     

Effects of lignin and hemicellulose contents on dissolution of wood pulp in aqueous NaOH/urea solution

Four species of delignified woodchips with about 1 % lignin content (Chlorite–Woodchips) and a series of softwood pulps with different lignin contents were prepared by sodium chlorite delignification. After mechanical defibration, some Chlorite–Woodchips were directly subjected to dissolution treatment in NaOH/urea solvent; the others were first treated with NaOH solution to remove the hemicellulose to obtain NaOH–Chlorite–Woodchips or oxidized with potassium permanganate (OPP) to remove lignin completely to obtain OPP–Chlorite–Woodchips, and then subjected to the dissolution in NaOH/urea solvent. The results showed that the dissolved proportion of the Chlorite–Woodchips ranged from 36 to 46 %, the dissolved proportion of glucan was within 12 %, and most of the hemicellulose was dissolved in NaOH/urea solvent. Compared with Chlorite–Woodchips, the dissolved proportion of NaOH–Chlorite–Woodchips was lower, but their dissolved proportion of glucan was higher. After further permanganate delignification, both the dissolved proportion of the OPP–Chlorite–Woodchips and the dissolved proportion of glucan of the OPP–Chlorite–Woodchips were higher than those of the Chlorite–Woodchips. However, the dissolved proportion of glucan was still limited to only 15–30 %. The effect of the lignin content of softwood pulps on their dissolution is complicated. With the decrease of the lignin content of softwood pulp from 6.9 to 2.8 %, the dissolved proportion of pulp increased from 14 to 26 %. However, further reduction of lignin content from 2.8 to 0.3 % led to a decrease in the dissolved proportion of pulp from 26 to 12 %. The dissolved proportion of glucan followed the same tendency. These results indicated that the dissolution of wood cellulose in NaOH/urea solvent is not simply controlled by the hemicellulose and lignin contents, but also by some other factors.     

Nanofibrillated cellulose/nanographite composite films

Though research into nanofibrillated cellulose (NFC) has recently increased, few studies have considered co-utilising NFC and nanographite (NG) in composite films, and, it has, however been a challenge to use high-yield pulp fibres (mechanical pulps) to produce this nanofibrillar material. It is worth noting that there is a significant difference between chemical pulp fibres and high-yield pulp fibres, as the former is composed mainly of cellulose and has a yield of approximately 50 % while the latter is consist of cellulose, hemicellulose and lignin, and has a yield of approximately 90 %. NFC was produced by combining TEMPO (2,2,6,6-tetramethypiperidine-1-oxyl)-mediated oxidation with the mechanical shearing of chemi-thermomechanical pulp (CTMP) and sulphite pulp (SP); the NG was produced by mechanically exfoliating graphite. The different NaClO dosages in the TEMPO system differently oxidised the fibres, altering their fibrillation efficiency. NFC–NG films were produced by casting in a Petri dish. We examine the effect of NG on the sheet-resistance and mechanical properties of NFC films. Addition of 10 wt% NG to 90 wt% NFC of sample CC2 (5 mmol NaClO CTMP-NFC homogenised for 60 min) improved the sheet resistance, i.e. from that of an insulating pure NFC film to 180 Ω/sq. Further addition of 20 (CC3) and 25 wt% (CC4) of NG to 80 and 75 wt% respectively, lowered the sheet resistance to 17 and 9 Ω/sq, respectively. For the mechanical properties, we found that adding 10 wt% NG to 90 wt% NFC of sample HH2 (5 mmol NaClO SP-NFC homogenised for 60 min) improved the tensile index by 28 %, tensile stiffness index by 20 %, and peak load by 28 %. The film’s surface morphology was visualised using scanning electron microscopy, revealing the fibrillated structure of NFC and NG. This methodology yields NFC–NG films that are mechanically stable, bendable, and flexible.     

Application of Pigeon Pea (Cajanus cajan) Stalks as Raw Material for Xylooligosaccharides Production

Pigeon pea (Cajanus cajan) is a perennial plant widely cultivated in tropical and subtropical regions of many countries. The present studies aimed to produce xylooligosaccharides (XOS) from pigeon pea stalks in order to do value addition. The chemical analysis of stalks revealed 18.33?±?1.40 % hemicelluloses in addition to cellulose, protein, and lignin. Sodium hydroxide coupled with steam application enabled almost 96 % recovery of original xylan, present in the pigeon pea stalks. Enzymatic hydrolysis of xylan led to production of XOS namely, xylobiose and xylotriose. Response surface model indicated a maximum yield of xylobiose (0.502 mg/ml) under the hydrolysis conditions of pH 4.91, temperature at 48.11 °C, enzyme dose at 11.01 U, and incubation time at 15.65 h. The ideal conditions for higher xylotriose yield (0.204 mg/ml) were pH 5.44, temperature at 39.29 °C, enzyme dose at 3.23 U, and incubation time at 15.26 h. The present investigation was successful in assessing the prospect of using pigeon pea stalks as a raw material for xylan extraction vis-à-vis XOS production.     

The effect of chemical and physical characteristics of spruce SEW pulps on enzymatic hydrolysis

Conifers, which are the most abundant biomass species in Nordic countries, USA, Canada and Russia, exhibit strong resistance towards depolymerization by cellulolytic enzymes. At present, it is still not possible to isolate a single structural feature which would govern the rate and degree of enzymatic hydrolysis. On the other hand, the forest residues alone represent an important potential for biochemical production of biofuels. In this study, the effect of substrate properties on the enzymatic hydrolysis of softwood was studied. Stem wood spruce chips were fractionated by SO₂–ethanol–water (SEW) treatment to produce pulps of varying composition by applying different operating conditions. The SEW technology efficiently fractionates different types of lignocellulosic biomass by rapidly dissolving hemicelluloses and lignin. Cellulose remains fully in the solid residue which is then treated by enzymes to release glucose. The differences in enzymatic digestibility of the spruce SEW pulp fibers were interpreted in terms of their chemical and physical characteristics. A strong correlation between the residual lignin content of SEW pulp and enzymatic digestibility was observed whereas cellulose degree of polymerization and hemicellulose content of pulp were not as important. For the pulps containing about 1.5 % (w/w) lignin, 90 % enzymatic digestibility was achieved at 10 FPU enzyme charge and 24 h of hydrolysis time.     

The Degree of Disorder in Hardwood Kraft Pulps Studied by Means of LODP

The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed kraft pulp. A model explaining the LODP-results is proposed.