Halfa, also known as Stipa tenacissima, is grown in North Africa and south Spain. Due to its short fiber length, paper of halfa remains bulk and takes the block letters well. In this study halfa was evaluated for bleached pulp production. Two cellulose pulps with different chemical compositions were pulped by conventional Kraft process: one from the original halfa material and the other from halfa pretreated by diluted acid. The pulp produced from halfa pretreated by diluted acid was bleached by elemental chlorine-free sequences, DEPD and DEDP. Yield, Kappa number, brightness and α-cellulose contents of bleached and unbleached pulps were evaluated. The results show that during the chemical pulping process, treated halfa was easily cooked than that original halfa. Treated halfa pulp also showed very good bleaching, showing brightness level of 94.8% ISO, yield 93.6% and α-cellulose content 96.8% with DEDP bleaching sequence compared to 83.2% ISO brightness level, 92.8% yield and 95.1% α-cellulose content for bleached pulp with DEPD bleaching sequence. On the other hand, the physicomechanical properties of pulp were not notably reduced by the bleaching process. Breaking length, tear and burst index of paper sheets were acceptable. Therefore, this halfa material could be a worthwhile choice for cellulosic fiber supply. 相似文献
In this work, Eucalyptus camaldulensis was evaluated as the raw material for chemical pulp under different pulping and bleaching conditions. The pulping was carried out at different H‐factors, and at different effective alkalis. The resulting pulps were then oxygen delignified and bleached using various dosages of bleaching chemicals in a D0EpD1 sequence. The effect of independent variables (pulping or bleaching variables) on dependent variables (pulp properties) was analysed based on the multivariable least square method via MATLAB software. An agreement was found between the results predicted from the models and the experimental data. To obtain a kappa number of 15, the optimum pulping conditions were a temperature of 155°C, a time of 225 min, and an EA of 23%. Also, the hexenuronic acid (HexA) content of cooked pulp was significantly decreased in the chlorine dioxide bleaching stages, and was only marginally related to the final HexA content of bleached pulps. 相似文献
A study of electrochemical bleaching of cellulose pulp was carried out in an electrolyte cell composed of a horizontal graphite anode and a parallel stainless screen steel cathode, using NaCl as electrolyte. Variables studied were: current density, sodium chloride concentration, pulp concentration, pH and temperature. The rate of bleaching was found to increase with increasing current density, salt concentration and temperature. The rate of bleaching was found to decrease with increasing pH and pulp concentration. Energy consumption ranged from 0.1 kWh kg?1 (pulp) to 1.75 kWh kg?1 (pulp), depending on current density and degree of bleaching. The quality of electrochemically bleached pulp was found to compare favourably with that of chemically bleached pulp. 相似文献
To promote the efficient utilization of lignocellulosic materials, one-step fractionation by formic acid-based organosolv process under pressure has been studied for converting lignocellulose in its main components. Lignin and hemicelluloses were selectively dissolved, while cellulose was not obviously degraded. Under optimized conditions (85% formic acid, a liquor-to-solid ratio of 7:1, and a temperature of 145°C for 45 min), this process provided a high efficient way to separate the main components of bamboo, obtaining 42.2% cellulose pulp, 31.5% lignin, 8.5% hemicellulose-rich fraction, 3.56% furfural and 3.80% acetic acid. Cellulose pulp with satisfying viscosity could easily be bleached to a high brightness of over 87% ISO with a short bleaching sequence, and had an acceptable paper strength properties. The recovered lignin fraction contained a small amount of carbohydrates and a considerable part of proteins and p-hydroxycinnamates. Additionally, the organic substances in hemicellulose-rich fraction obtained was composed of 95% carbohydrates, most of which was monosaccharides, as well as 5% lignin. 相似文献
A rapid and mild nitric acid pulping of rice straw was developed and different grades of pulp were produced. A satisfactory nitric chemimechanical rice straw pulp was obtained in a yield of 80% by two stage pulping. In the first stage 5% HNO3 was used at 80°C and a 6:1 liquor ratio for 30 min, followed by a second alkali stage, 3% NaOH at 95°C for 30 min. The pulp had a satisfactory strength and high opacity and it was bleached by an HP sequence to a 67% general electric brightness (GE). Semichemical pulp of 65% yield was produced by cooking with 10% HNO3 and 10% NaOH at 20:1 liquor ratio. The pulp had superior strength and it was bleached to a 61% GE by a chlorination-alkali extraction hypochlorite (CEH) sequence. Nitric bleached chemical pulp of 48% and 82% GE was produced by cooking with 6% HNO3 and 7% NaOH at 10:1 liquor ratio and bleached by a CEH sequence. The chemical pulp is of higher yield and strength than soda pulp. Newsprint that fulfils all the requirements was produced on an experimental paper machine from a furnish composed of 80% bleached nitric chemimechanical rice straw pulp, 10% bleached softwood pulp and 10% clay. 相似文献
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. 相似文献
A series of methyl acrylate‐acrylic acid amphiphilic triblock copolymers (PMA‐PAA‐PMA) were prepared by solution polymerization using S,S′‐bis (α,α‐dimethy1acetic acid) trithiocarbonate (BDAT) as a reversible addition fragmentation chain transfer (RAFT) agent and methyl acrylate (MA) as the first monomer. The triblock copolymers and their common MA homopolymer precursors were characterized in terms of their compositions, molecular weights and behavior at the air–water interface using 1H‐NMR spectroscopy, thermogravimetric analysis, gel permeation chromatography, surface tension, transmission electron microscopy (TEM) and dynamic light scattering respectively. The results indicated that PMA‐PAA‐PMA was successfully synthesized through RAFT polymerization. The polydispersity index (PDI) decreased when the molar ratio [n(MA)/n(AA)] increased, the lowest PDI was obtained at 5.23 wt% RAFT and the molecular weights were consistent with the theoretical value as the RAFT agent percentage varied. The polymer neutralized by sodium hydroxide solution shows a low critical micelle concentration (CMC), which was <10?2 mol L?1 in water. The Amin values increased and showed a maximum with decreased AA chain length. TEM showed that the neutralized polymer formed a special vesicle structure with large pore structure which led to a low CMC and surface tension of water. 相似文献
Pulping of bagasse by a rapid and mild nitric acid process was successfully carried out to produce different grades of pulp. Nitric chemimechanical bagasse pulp was produced in a high yield of 91 % on pulping depithed bagasse with 4% HNO3 for a period of 30 min at 80°C, followed by alkali pulping with 2% NaOH at 95°C for 30 min. The pulp had a satisfactory strength and high opacity. On increasing the strengths of nitric acid to 7% and alkali to 7% a nitric semichemical pulp of 65% yield was obtained. The pulp had a superior strength and high opacity. The pulp was easily bleached to 71% general electric brightness (GE) with the chlorination-alkali-extraction-hypochlorite (CEH) sequence. With 15% HNO3 and 8% NaOH, nitric chemical bagasse pulp was produced. The pulp was easily bleached to a high brightness of 82% GE with one stage hypochlorite. The pulp had a higher strength than kraft bagasse pulp. A satisfactory newsprint paper was produced on an experimental paper machine with a furnish composed of 80% bleached nitric semichemical bagasse pulp, 10% bleached softwood pulp and 10% clay. 相似文献
Summary: Water‐soluble, partially hydrophobized derivatives of O‐(carboxymethyl)cellulose (CMC) were prepared by esterification of CMC in its ‘gel suspension’ form. The classical esterification method (A) using stearoyl chloride/pyridine as well as two unconventional methods based on reaction with mixed anhydrides (B) and transesterification with vinyl laurate (C) respectively, were compared in terms of the structural, molecular and performance properties of the obtained derivatives. The classical esterification and method B yielded water‐soluble simple fatty acid esters, whereas mixed acetic‐fatty acid esters were obtained by method C. In all cases, molecular degradation of CMC was observed. 1H and 13C NMR spectroscopy of the acetyl‐lauroyl derivatives of CMC with a degree of esterification DSE of 0.20 indicated a prevalence of the lauroyl groups (DSAc:DSLa = 0.03:0.17). Most of the water‐soluble derivatives exhibited excellent emulsifying efficiency. They represent polysaccharide‐based surfactants with effective anti‐redeposition properties as well as good washing power. Suitable derivatives can be prepared under mild reaction conditions by both unconventional methods which implies that they have potential as substitutes for the expensive and invasive conventional method.
Ozone gas was applied as second stage in delignification of bagasse pulp obtained with acetic acid. The kappa number was reduced from 44 to 10 with 3% ozone (based on dry pulp). Because bagasse was pulped with an aqueous solution of acetic acid (80% volume), selectivity of the ozone stage was favored and does not necessary acidulate pulp, which had pH = 1.7. Consistency of pulp for ozonation was 40% and this stage was carried out at room temperature. Physical properties of pulp were improved with ozone treatment. 相似文献