Environmentally friendly pulping and bleaching of bagasse

Depithed Sudanese bagasse was examined for its suitability for pulp production. Bagasse fibre dimensions, morphological and chemical characteristics are reported. The pulping trials were carried out with soda–AQ and alkaline sulphite–AQ (AS–AQ) methods and soda method as reference. The AS–AQ pulping gave the best results in yield, degree of delignification, mechanical and optical pulp properties. Blending of bagasse and bamboo alkaline sulphite–anthraquinone pulps in different ratios gave well-balanced pulp strength characteristics with good tensile and tear indices, widening the range of different end products from bagasse pulp. Totally chlorine free bleaching (Q₁O/PQ₂P) of the best unbleached bagasse pulps gave bleached pulps of 76.9% ISO brightness, suitable for use in writing and printing grades of paper.     

Optimization of formic/acetic acid delignification of Miscanthus × giganteus for enzymatic hydrolysis using response surface methodology

A Box-Behnken experimental design and response surface methodology were employed to optimize the pretreatment parameters of a formic/acetic acid delignification treatment of Miscanthus × giganteus for enzymatic hydrolysis. The effects of three independent variables, namely cooking time (1, 2 and 3 h), formic acid/acetic acid/water ratio (20/60/20, 30/50/20 and 40/40/20) and temperature (80, 90 and 107 °C) on pulp yield, residual Klason lignin content, concentration of degradation products (furfural and hydroxymethylfurfural) in the black liquor, and enzymatic digestibility of the pulps were investigated. The major parameter influencing was the temperature for pulp yield, delignification degree, furfural production and enzymatic digestibility. According to the response surface analysis the optimum conditions predicted for a maximum enzymatic digestibility of the glucan (75.3%) would be obtained using a cooking time of 3 h, at 107 °C and with a formic acid/acetic acid/water ratio of 40/40/20%. Glucan digestibility was highly dependent on the delignification degree.     

Alkaline sulfite–anthraquinone (AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching of pulps

Alkaline sulfite–anthraquinone (AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching of resulting pulps was investigated. Wheat straw was supplied by the Ferdosii University Experimental Station in Northeastern Iran, cleaned and chopped into about 3–5 cm long pieces. In the AS/AQ pulping experiments, the active alkali charge on oven dry wheat straw, heating time to maximum cooking temperature, AQ dose and liquor to straw ratio were kept constant at 16%, 60 min, 0.1% and 4/1, respectively. The alkali ratio, Na₂SO₃/NaOH, calculated as NaOH, was varied from 20/80 to 80/20. Cooking time at maximum temperature was varied from 30 to 90 min and maximum cooking temperature was adjusted between 152 and 160 °C. Reference soda and soda/AQ pulps were produced.AS/AQ and soda/AQ pulps with kappa numbers below 15 were produced easily. Cooking of corresponding soda pulps under comparable conditions stopped at a kappa number of 25. The characteristics of unbleached AS/AQ, soda/AQ and soda pulps were compared. AS/AQ and soda/AQ pulps had similar tensile strength but tear was in favor to AS/AQ. The latter had much higher yield and brightness.TCF bleaching of AS/AQ pulp was performed in O Q (OP) or O Q (OP) P sequences. Oxygen delignification (O) resulted in a delignification degree of approximately one third. Followed by a chelating treatment (Q) and a subsequent (OP) stage under drastic conditions a brightness of 82.7% ISO was achieved in an O Q (OP) sequence. The sequence O Q (OP) P, with 2% H₂O₂ in the final P stage, improved brightness from 77.2% ISO after the OP stage to 83.6% ISO. Bleaching led to only small losses in tensile and burst strength but enhanced tear strength. Short beating in a Jokro mill was sufficient to attain good pulp strength. The results of this study indicate that AS/AQ pulping and TCF bleaching is a convincing alternative to produce high-quality pulp from wheat straw for writing and printing paper.     

Optimisation of oxygen delignification in production of totally chlorine-free cellulose pulps from oil palm empty fruit bunch fibre

The effects of oxygen delignification on prehydrolysed-soda pulps produced from oil palm (Elaeis guineensis) empty fruit bunch fibre were statistically investigated by employing response surface methodology (RSM). Polynomial estimation models of five response variables namely yield, Kappa number, α-cellulose, viscosity and brightness were developed, each model comprised of four-independent variables: reaction temperature, reaction time, the alkali charge, and initial Kappa number. The calculated optimum condition (95 °C reaction temperature, 60 min reaction time, 2% alkali charge, and initial Kappa number of 6.6) is capable to produce pulp with 98.1% yield, Kappa number 2.4, 97.38% α-cellulose, pulp viscosity 13.8 cPs and ISO brightness 67.1%, which were proven close to the predicted values calculated from estimation models. The results indicated that oxygen delignification which is used as the first stage of bleaching sequence has the ability to both delignify and increase pulp brightness without substantial reduction in viscosity and α-cellulose, that appeared to be beneficial for subsequent TCF bleaching.     

Multi-stage Bagasse pulping by using alkali/Caro’s acid treatment

Bagasse delignification by using separate alkali and Caro’s acid treatments is considered as a promising process to prepare high-yield bagasse pulp. This could be achieved via two-stage technique (NaOH/Caro’s acid) and three-stage technique (NaOH/Caro’s acid/NaOH). The two techniques were practiced at low temperatures and atmospheric pressure. Three-stage techniques provide a possibility to produce chemical pulps, which have the advantages of both mechanical pulp (high-yield pulp), and chemical pulp (good strength properties). At moderate concentration of Caro’s acid used (3.0, 4.5% based on raw materials), three-stage technique has higher delignification selectivity than that of two-stage technique Three-stage techniques produced pulps of higher breaking length and burst factor than that produced by two-stage techniques. Tear factor of pulps produced by two-stage techniques has the superiority.     

Evaluation of grape stalks as a bioresource

The compositional characteristics of grape stalk in terms of lignin, sugars, ash, extractives and tannins contents were established. The biomass composition of grape stalk is 34% lignin, 36% cellulose, 24% hemicellulose and 6% tannins. The tannins, analysed by solution ¹³C NMR, were essentially of procyanidin type and the dichloromethane extractives fraction, characterized by GC-MS, was mainly composed of fatty acids. Different processes for the pretreatment of grape stalk were compared. Due to the high content of lignin and tannins, dilute sulfuric acid and ethanol organosolv pretreatments resulted in a low degree of delignification. However, a wet oxidation process permitted a significant reduction of the Klason lignin content of the pulp with a good carbohydrate recovery and improved enzymatic digestibility.     

Upgrading of hemp core for papermaking purposes by means of organosolv process

Non-wood raw materials for paper production have been maintained constant during last decade. In Europe, fibres from non-wood resources proceed mainly from flax and hemp crops. Hemp core is considered a by-product of the process, mainly used in equestrian sector. The application of these fibres for papermaking process gives a significant added value to the sector.New technologies in cooking processes like organosolv pulping gives advantages compared with traditional Kraft cooking. Hemp fibres obtained by means of organosolv process have been compared with eucalyptus Kraft pulp to determine if physical and mechanical properties of final pulps are similar.Efficiency of the organosolv cooking experiments was evaluated by means of yield, percentage of uncooked sample, kappa number and viscosity.To analyze the suitability of pulp samples for papermaking applications, different evaluation of mechanical properties as morphological characterization were done. Controlling cooking conditions of hemp core, similar properties of eucalyptus Kraft fibres are obtained.     

Delignification of wheat straw using a mixture of carboxylic acids and peroxoacids

Wheat straw was pulping by an Organosolv process using a mixture of acetic acid/formic acid/water (AA/FA/water). In order to make easier the bleaching step, it was possible to improve the delignification in an efficient and selective manner by using peroxoacids in acidic organic medium. First a solution of peroxoacids was synthesized by adding hydrogen peroxide in a mixture of acetic acid/formic acid, without any inorganic acids as catalyst. Then this mixture was added to the unbleached pulp. Several parameters (temperature, extraction alkaline, reaction time …) were investigated.This simple and innovative way to use peroxoacids allows to overcome problem due to the control of their stability in aqueous medium and proves to be perfectly complementary to the cooking method in a carboxylic acid medium. Low kappa numbers and high viscosity were obtained. Strength properties of the pulp after the peroxoacids step were improved.     

Kinetics of organosolv delignification of fibre crop Arundo donax L

Kinetics of ethanol–alkali delignification of fibre crop Arundo donax L. (giant reed) has been studied. The improved approach for determination of the reaction rate constants by accurate quantification of lignin fractions with different reactivity during standard procedure of graphical differentiation was applied. Following to a simplified model, the delignification process was considered as a complex of n-parallel irreversible first-order reactions with similar final product and analysed as a multi-component reaction system. Three kinetically distinguishable lignin fractions of A. donax were revealed and quantified in proportion of approximately 61, 23 and 16% (as initial, bulk and residual lignin, respectively) and their effective degradation rate constants were determined for different pulping conditions. The proportion of lignin fractions was different from that reported for wood, but close to another crop—wheat straw, where the initial lignin fraction was also found as a major fraction (about 90%). The values of apparent activation energy were estimated respectively as 64, 89 and 96 kJ mol⁻¹, and were generally within the range of those reported for wood kraft and organosolv pulping. The simulation of ethanol–alkali delignification using found kinetic parameters showed the high reproducibility of experimental data on lignin removal, providing thereby the adequate test on validation of the suggested kinetic approach. The data reproducibility was substantially higher in comparison with conventional consecutive kinetic model (sum of square residuals (SQR) 0.0036 versus 0.0856).     

Pulping and papermaking properties of Tunisian Alfa stems (Stipa tenacissima)—Effects of refining process

The objective of this work is to study characteristics of chemical pulps (soda cooking process) and of paper obtained from Alfa, also known as Stipa tenacissima. For this purpose, Tunisian Alfa stems, and both unbleached and bleached pulps were characterized by determining their chemical composition as well as their morphological and physical properties. Through a detailed comparison with the other pulps obtained from various species, we show that the properties of Alfa stem fibres are intermediate between those of non-wood and wood plants, and most often close to those of Eucalyptus fibres. Refining process (PFI mill device) was then applied to the unbleached and bleached Alfa pulps. The modifications of the morphological properties of the fibres and the drainability and water retention values of the pulps were studied as a function of the refining degree. Here again, Alfa fibres exhibit a behaviour similar to that of Eucalyptus fibres, as the fibre shortening is very limited during the refining process. Finally, conventional handsheets with a basis weight of 65 g/m² were prepared from the unrefined and refined pulps. Their characterization showed that Alfa based papers present low density values and quite good mechanical properties, which are significantly enhanced by the refining treatment, particularly for the unbleached pulp. This study demonstrates the high potentiality of this non-wood species for papermaking applications.     

Hydrogen peroxide bleaching of Arundo donax L. kraft-anthraquinone pulp—Effect of a chelating stage

Total chlorine free (TCF) and elemental chlorine free (ECF) bleaching sequences were applied to an Arundo donax L. (giant reed) unbleached kraft-anthraquinone pulp, using different sequences with hydrogen peroxide and chlorine dioxide stages. The evolution of ISO brightness, kappa number and pulp viscosity was observed for each stage in all bleaching sequences, as well as the process selectivity. The best results were obtained with the XOQDP sequence with a final ISO brightness of 80%. The effect of a chelating stage before the hydrogen peroxide stage was studied, and the results showed higher pulp viscosity, less peroxide consumption and higher pulp brightness, when this treatment is applied.     

Cynara cardunculus L. — a new fibre crop for pulp and paper production

The pulping potential of the thistle Cynara cardunculus L. was evaluated by studying anatomy and chemical composition of the stalks and Kraft pulp yields and properties. C. cardunculus is a perennial plant, with annual harvests, that can be grown in hot and dry climates with high productivities. The stalk of the plant has a central pith, ca. 45% in volume and 10% in weight, of small parenchyma cells, surrounded by a cortex where numerous fibre vascular bundles are imbedded. The fibres are on average 1.3 mm long, 18.8 μm wide and have a 4.8 μm wall thickness. The whole stalks have 7.7% ash, 14.6% extractives, 17.0% lignin and 53.0% polysaccharides, mainly cellulose and xylans. The pith has more lignin than the depithed stalk (20.3 vs. 13.6%). The Cynara stalks could be cooked by standard Kraft pulping to produce well delignified pulps with high yields (44–47% with Kappa 11–15), low rejects and very good strength properties, especially in relation to tensile strength. Depithing of the stalks has a positive impact on pulp yield, chemical consumption and on the pulp strength properties.     

酶处理对芒果原浆性质的影响

在分析芒果原浆酶处理前后的理化性质的基础上,选用合适的配方,结合酶处理技术,改进芒果打浆工艺,生产出质量稳定的芒果原浆产品,提高了芒果打浆的得浆率。      

Effect of pre-extraction on soda-anthraquinone (AQ) pulping of rice straw

The effect of hot-water and alkaline pre-extraction of rice straw on soda-anthraquinone pulping was carried out. The pre-extraction with hot water at 150 °C for 1 h dissolved 34.7% biomass and the pre-extracted liquor comprised of 16.6% sugars, 6.7% lignin, 6.6% acetic acid and other unknown products. But the pre-extraction with 1% NaOH at 100 °C for 1 h dissolved 10.2% sugars, 5.1% lignin and 10% acetic acid from rice straw. Pre-extracted rice straw was cooked by soda-anthraquinone process with varying alkali charges. The pulp from pre-extracted rice straw was low in kappa number with reduced pulp yield. The drainage resistance (°SR) improved obviously on pre-extraction of rice straw. Pulp strength properties such as the tensile index and the burst index were found to be lower, but the tear index was higher both with hot-water and alkaline pre-extraction. After bleaching, the gaps of the overall pulp yield and strength properties between pre-extracted and non-extracted rice straw became narrower. The alkaline pre-extraction showed improved yield and properties compared with hot-water pre-extracted rice straw.     

Surface chemical composition of some non-wood pulps

The surface lignin and extractives coverage of some non-wood pulps (wheat straw, reed, bagasse, bamboo and kenaf bark) were investigated by means of ESCA and compared with wood pulps. Strong enrichment of lignin and extractives on the pulp fiber surface was found for all of the pulps. At the same bulk lignin content level, the surface lignin coverage was found to be higher in the non-wood pulp than in the softwood pulp. The possible reasons for this were examined.     

不同处理对黄麻纤维木质素去除及织物性能的影响

本文研究了草酸铵、漆酶以及木聚糖酶单独或联合处理对黄麻机织布中木质素的去除作用及对织物褶皱、力学性能的影响。结果表明,漆酶单一处理仅能去除少量的木质素,联合处理可提高木质素的去除效率,以草酸铵、木聚糖酶、漆酶联合处理效果最好。在ATR红外谱图中,草酸铵、木聚糖酶、漆酶联合处理后的黄麻机织布较未处理织物在1594 cm-1、1506cm-1和1424 cm-1处的木质素芳香族特征吸收峰,1731 cm-1和1646 cm-1处的木质素羰基特征吸收峰及1242 cm-1-1031 cm-1处的半纤维素醚键特征吸收峰均有减弱,说明经草酸铵、木聚糖酶、漆酶联合处理后黄麻纤维表面木质素和半纤维素含量降低。经处理后黄麻机织布褶皱回复角提高,其中草酸铵、木聚糖酶、漆酶联合处理褶皱回复性最佳。漆酶单独处理后黄麻机织布断裂强力和断裂延伸率均提高,联合处理后断裂强力降低,断裂延伸率提高。     

Substrate selectivity and inhibitor sensitivity affect xylanase functionality in wheat flour gluten–starch separation

Addition of xylanases (EC 3.2.1.8) that varied in their substrate selectivities and/or wheat xylanase inhibitor sensitivities in dough batter gluten–starch separation of wheat flour showed the importance of these enzyme characteristics for their functionality in this process. A xylanase from Aspergillus aculeatus (XAA) with selectivity for hydrolysis of water extractable arabinoxylan (WE-AX), which is not inhibited by wheat flour xylanase inhibitors decreased batter viscosity and improved gluten agglomeration behaviour. In contrast, a xylanase from Bacillus subtilis (XBS_i) with selectivity for hydrolysis of water unextractable arabinoxylan (WU-AX), which is in vitro inhibited by wheat flour xylanase inhibitors had a negative effect on gluten agglomeration at low enzyme dosages. As expected, solubilisation of WU-AX increased batter viscosities. At higher dosages however, this enzyme also improved gluten agglomeration because of degradation of both WE-AX and enzymically solubilised AX. A mutated B. subtilis xylanase (XBS_ni) with selectivity for hydrolysis of WU-AX comparable to XBS_i but which is not inhibited by wheat flour xylanase inhibitors, increased the level of large gluten aggregates as well as the total gluten protein recovery, even at lower dosages. Because of its inhibitor insensitivity, the solubilisation and degradation of AX proceeded further. An XBS_ni dosage approximately 4 times lower than XBS_i performed as well as its inhibited counterpart. The degradation of both WE-AX and WU-AX by XBS_ni improved the gluten agglomeration behaviour to a larger extent than the XAA treatment which primarily resulted in hydrolysis of WE-AX. The results confirm the detrimental impact not only of WE-AX, but also of WU-AX, on gluten agglomeration in a dough batter gluten–starch separation process. At the same time, they provide firm evidence that xylanases are not only inhibited by xylanase inhibitors in vitro, but are also partly inhibited in the industrial process in which they are used.     

Kinetic modeling of enzymatic saccharification using wheat straw pretreated under autohydrolysis and organosolv process

The enzymatic saccharification kinetics of untreated wheat straw, pretreated solids obtained by a sequence of autohydrolysis (solubilization of hemicellulose) and organosolv (solubilization of lignin) were studied together with two pure cellulose model substrates, filter paper and Avicel. Two kinetic models for glucose production were compared and its kinetic constants calculated. According to the obtained results, enzymatic saccharification of the autohydrolysis pretreated solids (APS) proved to be more effective than when the organosolv pretreated solids (OPS) were used. The maximum extent of the enzymatic conversion of cellulose to glucose was 90.88% and 64.04%, for APS and OPS respectively, at 96 h. This result was probably due to an increase in accessible area for APS and a possible inhibition by phenolic acids deposited on the surface of OPS, acting as a barrier for enzymatic saccharification. Initial saccharification rate for APS and OPS was 0.47 g/(L h) and 0.34 g/(L h), respectively. Models based on first and second order cellulase deactivation kinetics satisfactory predicted the behavior of glucose production, however the second order model had a higher accuracy than the first order one. Visualization of structural modification induced by enzymatic saccharification at 12 h for the pretreated solids was done using scanning electron microscopy.     

Chitosan-filled polypropylene composites: The effect of filler loading and organosolv lignin on mechanical,morphological and thermal properties

In this work, the effect of organosolv lignin on properties of polypropylene (PP)/chitosan composites was investigated. Mechanical and thermal properties of the composites were analyzed by means of ASTM D 638-91, ASTM D 256, thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Tensile strength and elongation at break of the PP composites decreased upon the presence of chitosan filler, but Young’s modulus improved. Impact strength was found to increase with the maximum value at 30 php of filler loading. At a similar loading, treated PP/chitosan composites were found to have higher tensile strength, elongation at break, Young’s modulus as well as impact strength than untreated composites. Furthermore, the presence of organosolv lignin imparted a plasticizing effect. Thermal properties of the treated PP/chitosan composites were better as compared with the untreated PP/chitosan composites; although the chemical treatment did not alter the thermal degradation mechanism. In addition, the obtained results were comparable to results from previous studies. This finding implied that the organosolv lignin could be a potential reagent to replace its synthetic counterpart.     

Delignification of Eucalyptus globulus saplings in two organosolv systems (formic and acetic acid): Preliminary analysis of dissolved lignins

Organosolv delignification of 2–3 years old Eucalyptus globulus with formic or acetic acid produced bleachable grade pulps with kappa number values of 20–35. Pulp yields for the acetic acid treatment (45–55%) were higher than for formic acid (32–46%) although also they showed the greater kappa number.Delignification was modelized by means of the accomplishment of respective factorial designs of experiments. Data were successfully fitted by mathematical models for prediction of pulp yield and kappa numbers from the process variables.Recuperation of the dissolved lignin, by means of water precipitation, allowed the recovery of about a 20% of the initial raw material (about 80% of lignin).Chemical and spectroscopic analyses for the determination of the contents of main functional groups in lignin were made and C9 formulae calculated, as follows: C₉H_7.58O_2.34(OCH₃)_0.80(COOH)_0.18(OH_Ar)_0.35(OH_R)_0.58 and C₉H_6.14O_1.55(OCH₃)_1.09(COOH)_0.18(OH_Ar)_0.52(OH_R)_0.58 for the products obtained with formic acid and acetic acid, respectively.