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.     

Pulp from oil palm fronds by chemical processes

To enhance the use of the abundant biomass generated by the palm oil industry in Malaysia a study was conducted in view of exploring the papermaking potential of this industrial byproduct. Fiber strands from the frond of oil palm trees were examined relative to their physical and chemical characteristics and their response to chemical pulping such as sulfite, soda-sulfite and soda processes. Morphologically, the frond fibers are comparable to those of hardwood. They contain high content of holocellulose but low in lignin. Chemical pulps of 45–50% yield produced either by soda-sulfite or soda process exhibit acceptable papermaking properties comparable to those of hardwood kraft pulps. The study showed that frond pulp might be used as a reinforcement component in newsprint production using softwood thermomechanical fibers.     

Comparison of various pulping processes for producing pulp from vine shoots

The results of characterization for four different vine shoot varieties, grown using two different methods, revealed no significant differences in composition among vine varieties or between growing methods. The holocellulose content of vine shoots (67.14%) is lower than those of other non-wood raw materials (e.g. wheat straw, sunflower stalks, cotton stalks, etc.), but similar to those of pine and higher to those of olive trimmings. On the other hand, their lignin content (20.27%) is similar to those of eucalyptus and the non-wood raw materials. Also, their contents in cold-water, hot-water and 1% soda solubles, and ethanol–benzene extractables, are higher than for pine and eucalyptus.Soda, kraft, ethanol and ethylene–glycol pulping processes have low yields (29–47%) relative to the pulping processes applied to olive trimmings and wheat straw. Kraft pulp is that exhibiting the best properties, including a higher α-cellulose content (73.74%) than pulp from wheat straw or olive trimmings, but a higher lignin content (17.18%). Also, kraft pulp provides paper with the highest breaking length, burst index and tear index (viz. 1316 m, 1.63 kN/g and 1.59 mN m²/g, respectively); these values, which are intermediate among those for olive trimmings, wheat straw and sunflower seeds, are low and can be substantially improved by appropriate refining of the pulp.     

Improving the value of sugarcane bagasse wastes via integrated chemical production systems: an environmentally friendly approach

Xylitol production by chemical or enzymatic routes generates massive amounts of hydrolyzed sugarcane bagasse as a residue. This biomass is a renewable feedstock for the production of added-value chemicals from its lignocellulosic constituents. In this work, chlorine-free, α-cellulose pulp and acetic acid were produced from hydrolyzed bagasse. Soda/AQ and oxidative processes were developed to remove lignin from the biomass. Lignin-rich liquid effluents (mixed black liquors) were converted into acetic acid via wet peroxide oxidation (WPO). Transition metals (Fe, Cu, and Mn) present in the liquor were used as homogeneous catalysts. Experimental results demonstrate the technical feasibility of converting hydrolyzed sugarcane bagasse into α-cellulose, chlorine-free pulps, and acetic acid via environmentally friendly integrated processes.     

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.     

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.     

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。      

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.     

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.     

Paper from olive tree residues

An experimental design was performed to study the influence of process variables (135–175 °C for temperature, 60–120 min for pulping time and 15–25% for active alkali) on the properties of pulps (yield, Kappa index, viscosity, 1% NaOH solubles, alcohol–benzene extractives holocellulose, lignin and α-cellulose contents and brightness) and paper sheets (stretch index, burst index, and tear index) obtained from olive trimming residues. Obtaining pulps with acceptably high physical and chemical properties entails operating at a temperature of 175 °C for 90 min and 25% of active alkali. The paper sheets obtained from olive trimming residues pulps that were produced in different degrees of refining are characterised for their stretch index, burst index, and tear index. An increase in the different parameters for the paper sheet upon increasing the degree of refining is found. All pulps reached between 33 and 39 kN m/kg in the stretch index, between 1.5 and 2 kN/g for the burst index and 0.7–2.5 N m²/g for the tear index and not in excess of the refining degree (<45 °SR).     

Studies on Hibiscus cannabinus and Hibiscus sabdariffa as an alternative pulp blend for softwood: An optimization of kraft delignification process

Hibiscus cannabinus and Hibiscus sabdariffa, agro-based residues consist of bast and wood fibers which resemble to those of softwood and hardwood, respectively. The runkel ratio of core fibers H. cannabinus and H. sabdariffa is comparable to that of Picca abies, whereas, it is much less than those of hardwood like Eucalyptus tereticornis. The slenderness ratio of H. cannabinus is much closer to P. abies in comparison to H. sabdariffa whereas, it is 7.7 and 13% less than E. tereticornis. The flexibility coefficient of H. cannabinus and H. sabdariffa are slightly lower than that of P. abies but it is 59.6 and 57.0% are more than that of E. tereticornis. It indicates that morphological characteristics of core fibers of H. cannabinus and H. sabdariffa closely resemble to that of softwood except fiber length which can be compensated by long bast fibers. Due to identical pulping conditions, H. cannabinus and H. sabdariffa can be delignified together by kraft pulping process. The optimum cooking conditions for H. cannabinus and H. sabdariffa were found to be as, active alkali 16%, sulfidity 20%, temperature 160 °C, time (at temperature) 120 min and wood to liquor ratio of 1:4.5. An anthraquinone (AQ) dose of 0.05% at an active alkali dose of 13% (as Na₂O) produces the screening rejects and kappa number similar to that obtained by using 15% active alkali (as Na₂O). The reaction kinetics study indicates that delignification is of first order. Low sulfidity AQ additive kraft pulping at constant H-factor produces better strength properties compared to non-additive kraft cooks.     

Steam explosion pretreatment reproduction and alkaline delignification reactions performed on a pilot scale with sugarcane bagasse for bioethanol production

This work was focused on the steam explosion pretreatment reproduction and alkaline delignification reactions on a pilot scale for the ethanol production, through different varieties of natural sugarcane bagasse, pretreated bagasse and delignified pretreated bagasse (cellulosic pulp). The possible chemical composition differences of the various types of bagasse, as well as the chemical composition variations of the materials in the 20 processes of pretreatment and delignification on the pilot scale were verified. The analytical results of the 20 samples of most diverse varieties and origins of natural sugarcane bagasse considering planting soils, planting periods and weather; show no significant chemical differences. It is evident that only with the chemical composition it is not possible to verify the differences between the varieties of sugarcane bagasses. The research results may offer some evidences of these varieties, but it is not a reliable parameter. The pilot process of steam explosion pretreatment and the alkaline delignification process of pretreated material showed through analytical results a good capacity of reproduction, as the standard differences were below 2.7. The average allowed in the pretreatment and alkaline delignification processes were 66.1 ± 0.8 and 51.5 ± 2.6 respectively, ensuring an excellent reproduction capacity of the processes obtained through chemical characterizations.     

Improving the use of kenaf for kraft pulping by using mixtures of bast and core fibers

Kenaf (Hibiscus cannabinus L.) is a herbaceous annual plant amenable to use as a papermaking raw material. Kraft and soda pulping of kenaf have so far been done exclusively on the bark fraction (about 34–38% of the stem) or whole stem of the plant. Using kenaf bark exploits the higher quality of its bast fibers but reduces the typically high crop yields of this plant. In any case, core kraft pulp has acceptable properties some of which (e.g. tensile index, burst index) can even surpass those of bark pulp. Pulp made from both fractions has been found to exhibit better bonding properties than bark pulp. However, too high a proportion of core fibers can result in difficult drainage, a low tear strength or poor air permeability. These problems restrict the proportion of core that can be mixed with bast fibers, hinders separation of the two fractions and raises operational costs.The primary purpose of this study was to examine the influence of the core–bark ratio on the properties of mixed kenaf pulp. We used unrefined core pulp and refined bark pulp. Based on the results for kraft sacks, obtaining kenaf paper from both fractions has some advantages. Because Gurley air porosity changed dramatically with the proportion of core pulp used, it was used to determine the maximum amount of core fibers to be added to bast fibers. A proportion of up to 34% was found to have no adverse effect on air permeability. Such a proportion allowed paper strength to be preserved with an acceptable tear index (19.8 mN m²/g) and excellent tensile index (72 N m/g). Also, energy consumption was reduced if only the bark fraction was refined. The proposed strategy thus provides increased fiber yields of kenaf per hectare per year and valorizes the core fraction.     

Pulp and paper from kenaf bast fibers

Samples of kenaf (Hibiscus cannabinus) grown in Malaysia were examined to determine the kraft pulp and papermaking properties of their bast (or bark) fibers. Using kraft pulping process showed that bast fibers were relatively easy to cook resulting good pulp yields in the range of 45–51%. The bast pulp produced sheets with great density, tear index and dry zero-span breaking length. Kenaf bast fiber is considered promising for production of high-grade printing, writing and specialty papers.     

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.     

Variations in chemical characteristics and pulpability within jute plant (Chorcorus capsularis)

The differences in morphological and chemical characteristics and pulpability of core and bark fiber of jute at different position, top, middle and bottom were studied. The fiber length at the middle part of both bark and core was longer than the top and bottom part. With increasing height from bottom to top lignin content is decreased and α-cellulose content increased. The bark had higher α-cellulose and lower lignin than core. The bark produced nitrobenzene oxidation products with larger syringaldehyde/vanillin (S/V) ratios than the core. The yields of nitrobenzene oxidation products in bark were higher than core. The analysis of neutral sugars suggested that xylose is the predominant sugar of hemicellulose in both bark and core. The bark had higher glucose and lower xylose as compared to core. Under identical conditions of pulping, bark gave higher pulp yield and lower kappa number than core. The bark pulp showed better bleachability than core pulp. The higher tensile index in core pulp and higher tear index in bark pulp were observed.     

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.     

Xylanase pre-treatment of giant reed organosolv pulps: Direct bleaching effect and bleach boosting

The effect of enzymatic pre-treatment with xylanase preparation (endo-1,4-β-xylanase activity; EC 3.2.1.8) on properties and bleachability of organic solvent-based Ethanol-Alkali, Organocell (alkali-anthraquinone-methanol) and ASAM (alkali-sulfite-anthraquinone-methanol) pulps produced from agro-fibre crop giant reed (Arundo donax L.) has been examined and compared with traditional kraft pulp. The enzyme-assisted removal of xylan-associated lignin fragments and hexenuronic acids caused direct brightening and delignification during the enzymatic stage, while somewhat affecting the pulp strength properties. The xylanase bleach boosting substantially improved subsequent chemical bleaching of organosolv pulps by hydrogen peroxide. The savings in bleaching chemicals with simultaneous increase in brightness and degree of delignification were observed. The enzymatic pre-treatment improved the intrinsic viscosity of bleached organosolv pulps.     

The effect of different additives on the fermentation quality, aerobic stability and in vitro digestibility of pea/wheat bi-crop silages containing contrasting pea to wheat ratios

Studies were conducted to compare the effects of using two microbial inoculants, a sulphite salt‐based additive, formic acid and quebracho tannins, on the fermentation quality, nutritive value and aerobic stability of pea/wheat bi‐crop silages. Spring peas (Pisum sativum var. Magnus) and spring wheat (Triticum aestivum var. Axona) were drilled together at rates that gave high (HP/W; 3:1) or low (LP/W; 1:3) pea to wheat ratios. The peas and wheat were harvested at the yellow wrinkled pods and late milk/early dough maturity stage, respectively, and conserved in 1·5‐kg polyethylene bag, laboratory silos. The bi‐crops were conserved without treatment (control) or treated with either of two lactic acid bacteria‐based inoculants [Lactobacillus buchneri; applied at 10⁵ colony‐forming units (CFU) g^–1 fresh weight (FW) or Lactobacillus plantarum (applied at 10⁶ CFU g^–1 FW)], sulphite salts (applied at the rate of 1 ml sulphite solution kg^–1 FW), quebracho tannins (applied at 16 g kg^–1 FW) and formic acid (applied at 2·5 g kg^–1 FW). Six replicates were made for each treatment, and the silos were opened after 112 days of ensilage. The level of peas in the bi‐crop influenced the effectiveness of the additives. With the exception of sulphite salts, all the additives significantly reduced the soluble nitrogen (N) and ammonia‐N concentrations of all the silages. The ratio of lactic acid to acetic acid was generally lower in the LP/W silages than in the HP/W silages, and the additive treatments only increased the in vitro digestible organic matter in dry matter of the LP/W silages. Of all the additives evaluated, formic acid resulted in the least aerobic spoilage in HP/W bi‐crop silages. However, in the LP/W bi‐crops, additive treatment was not necessary for ensuring aerobic stability.     

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.