Bleached Chemithermomechanical Pulp Research Articles

Investigation of the photo-oxidative chemistry of acetylated softwood lignin

Lignin was isolated from a spruce bleached chemithermomechanical pulp (BCTMP) with a mild acid hydrolysis and acetylated. Nonacetylated and acetylated lignins were impregnated onto cellulosic testsheets and photolyzed by two different light sources. Optical reflective studies indicated that the irradiated lignin underwent a two-phase photodiscoloration process with the acetylated lignin exhibiting reduced color formation. To examine the chemical processes initiated by irradiation, the photolyzed nonacetylated and acetylated lignins were extracted from the cellulosic testsheets and analyzed by using nuclear magnetic resonance (NMR). The results indicated that the photobehavior of the acetylated lignin exhibited substantially decreased reactivity during the light irradiation. The extent of lignin acetylation prior to photolysis was shown to be a very important parameter in controlling the overall photoreactivity of the acetylated materials. Aliphatic hydroxyl groups in lignin were observed to extensively degrade during photolysis, whereas the amounts of C5 condensed phenolics, guaiacyl phenolics, acids, and p-hydroxyphenyl increased.

Metso supplies BCTMP line to China

Metso Paper will supply a bleached chemithermomechanical pulp (BCTMP) line for mechanical pulp production to Shandong Bohui Paper Co Ltd in China. The value of the order has not been disclosed. Visit www.filtsep.com for the latest filtration industry news

METSO SUPPLIES BCTMP LINE TO CHINA

Metso Paper will supply a bleached chemithermomechanical pulp (BCTMP) line for mechanical pulp production to Shandong Bohui Paper Co Ltd in China. The value of the order has not been disclosed. This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.

Photoyellowing Inhibition of Bleached High Yield Pulps Using Novel Water-Soluble UV Screens

To address the deficiencies of benzophenone UV screens for preventing brightness reversion in high yield mechanical papers, we synthesized a new series of such materials with enhanced water solubility and compatibility with the lignocellulosic substrate. A series of 2,4-dihydroxybenzophenones (DHB) were synthesized containing various Mannich bases at the C3 position of one of its rings. They possess the UV-screening ability of o-hydroxylbenzophenones, and they also contain tertiary nitrogen atoms that may function as radical scavengers. Aqueous solutions of the hydrochloride salt of 3-(dimethylaminomethylene)-2,4-dihydroxylbenzophenone (1), when applied on bleached chemithermomechanical pulp (CTMP) sheets, were significantly more efficient in preventing photoyellowing than the original DHB applied on the sheets from ethanol–water solutions. This confirmed our original hypothesis that increasing the compatibility of the UV screen with the lignocellulosic matrix would increase its efficiency in preventing photoyellowing. Compound 1, however, was found to be somewhat more effective than its hydrochloride salt toward preventing photoyellowing. This was attributed to the synergistic action of the free tertiary aminic center attached on the molecule with its UV-screening ability. To comprehend further the various parameters that influence the photoyellowing inhibition performance of these compounds and DHB with bleached CTMP pulp fibers, a series of handsheets were prepared at different pH. The interactions of the protonated compound 1 with pulp fibers were then evaluated by studying their kinetics of absorption and desorption to and from the fiber matrix. This part of our study found that the adsorption of protonated Mannich derivatives of DHB onto pulp is most likely governed by a cation-exchange mechanism involving the cationic amine group with the sulfonic and carboxylic acid groups located on the surface of the fibers. The pH the paper sheet was made from was also found to affect profoundly the adsorption and retention characteristics of these compounds onto the lignocellulosic matrix.

Photoyellowing inhibition of bleached high yield pulps using novel water-soluble UV screens.

To address the deficiencies of benzophenone UV screens for preventing brightness reversion in high yield mechanical papers, we synthesized a new series of such materials with enhanced water solubility and compatibility with the lignocellulosic substrate. A series of 2,4-dihydroxybenzophenones (DHB) were synthesized containing various Mannich bases at the C3 position of one of its rings. They possess the UV-screening ability of o-hydroxylbenzophenones, and they also contain tertiary nitrogen atoms that may function as radical scavengers. Aqueous solutions of the hydrochloride salt of 3-(dimethylaminomethylene)-2,4-dihydroxylbenzophenone (1), when applied on bleached chemithermomechanical pulp (CTMP) sheets, were significantly more efficient in preventing photoyellowing than the original DHB applied on the sheets from ethanol-water solutions. This confirmed our original hypothesis that increasing the compatibility of the UV screen with the lignocellulosic matrix would increase its efficiency in preventing photoyellowing. Compound 1, however, was found to be somewhat more effective than its hydrochloride salt toward preventing photoyellowing. This was attributed to the synergistic action of the free tertiary aminic center attached on the molecule with its UV-screening ability. To comprehend further the various parameters that influence the photoyellowing inhibition performance of these compounds and DHB with bleached CTMP pulp fibers, a series of handsheets were prepared at different pH. The interactions of the protonated compound 1 with pulp fibers were then evaluated by studying their kinetics of absorption and desorption to and from the fiber matrix. This part of our study found that the adsorption of protonated Mannich derivatives of DHB onto pulp is most likely governed by a cation-exchange mechanism involving the cationic amine group with the sulfonic and carboxylic acid groups located on the surface of the fibers. The pH the paper sheet was made from was also found to affect profoundly the adsorption and retention characteristics of these compounds onto the lignocellulosic matrix.

Brightness Reversion of Mechanical Pulps Part XIII: Photoinduced Degradation of Lignin on Cellulose Matrix

An acidic dioxane extraction procedure was employed to isolate lignin from softwood bleached chemithermomechanical pulp (BCTMP). The isolated lignin was characterized spectroscopically and applied on cellulose test sheets. The treated cellulose test sheets were shown to exhibit photoyellowing properties comparable to those of BCTMP. The photolyzed lignin was re-isolated and characterized using spectroscopic techniques. UV-VIS and FT-IR studies implied elimination of the guaiacyl structure of lignin and the formation of carboxyl and/or unconjugated carbonyl groups during the photoyellowing process. The steady-state emission intensity of the excited states of guaiacyl structures decreased with increasing photolysis time, suggesting the formation of quinones during photolysis. NMR spectroscopic analysis of the photolyzed lignin indicated that the formyl, methoxyl, and uncondensed phenolics decreased in concentration as the irradiation proceeds. In contrast, condensed lignin and carboxylic acids increased as photolysis time was increased. These results are explained within the mechanism of lignin photodegradation.

Brightness Reversion of Mechanical Pulps XI: Photostabilization of High-Yield Pulps by Thiosulfinates

A series of eleven cyclic and acyclic thiosulfinates was synthesized and applied onto hardwood BCTMP (bleached chemithermomechanical pulp) testsheets. Treated and untreated testsheets were photoaged and their optical property were monitored. The results of these photoaging experiments indicated that cyclic thiosulfinates were relatively ineffective at retarding brightness reversion, whereas most acyclic additives were effective photostabilization agents for BCTMP. The use of acyclic thiosulfinates in combination with UV absorbers provided a very effective means of retarding the photoaging process of mechanical pulps.

Brightness Reversion of Mechanical Pulps. X. Photoreversion Fiber Topochemistry

The topochemistry of thiol-photostabilization of hardwood BCTMP (bleached chemithermomechanical pulp) was investigated by scanning electron microscopy (SEM). Employing advanced SEM methods, the location of unextractable sulfur across the fiber wall was determined for post-photolyzed BCTMP fibers. These studies illustrate that thio additives remove chromophores across the fiber wall.

Brightness Reversion of Mechanical Pulps VII: Photostabilization Studies of Thiol Additives for Ligniocellulosic Materials

ABTRACT The chemical mechanisms contributing to the photostabilization properties of 1-thioglycerol and 2-mercaptoethyl ether for lignocellulosic materials was studied. The thio-additives were impregnated onto woodbased fibers, photolyzed, extracted, and characterized spectroscopically. Both thio-additives were shown to yield the corresponding disulfide when the photolysis experiments were performed on bleached chemithermomechanical pulp (BCTMP). Irradiation of BCTMP fibers impregnated with 2-mercaptoethyl ether under an argon atmosphere yielded only starting material indicating that the thio-additive scavenges radicals generated after the initial photochemical reactions that contribute to the photo-discoloration of wood-based materials.

Mechanistic Investigations into the Brightness Stabilization Effects of Hexadienol

ABSTRACT The total amounts of 3,4,5-trimethoxyacetophenone and 2,6-dimethoxyphenol formed via the photocleavage of 3,4,5-trimethoxy-α-(2′,6′-dimethoxyphenoxy)-acetophenone (1) in benzene and 3:2 ethanol/benzene, have been quantified in the presence and absence of 2,4-hexadienol, a potential photostabilizing agent for mechanical pulps. Photodegradation of 1 in ethanol/benzene solutions was shown to be reduced by the addition of hexadienol. Photolysis of bleached chemithermomechanical pulp (BCTMP) treated with trans,trans-2,4-hexadienol was shown to yield all four possible geometric isomers of the hexadienol. These results suggest that a potential mode of stabilization of mechanical pulps by the hexadienol is triplet quenching of the excited state of lignin chromophores such as the α-carbonyl groups of phenacyl aryl ethers.

Fluorescence spectroscopy of mechanical pulps III: Effect of chlorite delignification

Many paper and wood samples fluoresce, but the sources of the emission are not well understood. Fluorescence excitation and emission spectra of paper sheets prepared from thermomechanical pulp (TMP) and bleached chemithermomechanical pulp (BCTMP) showed that the emission from the BCTMP was significantly higher than that from the TMP. Removing almost all of the lignin from both pulps by means of an acid chlorite treatment did not reduce the fluorescence significantly. By means of an approximate correction for changes in sheet reflectivity caused by the chlorite treatment, the fluorescence intensity was found to increase with lignin removal. Clearly, fluorescence is not simply related to lignin content. Keywords: wood pulp, lignin, cellulose, fluorescence spectra, acid chlorite delignification.

Attempts to photostabilize paper made from high-yield pulp by application of UV screens and control of pH

Paper made from bleached chemithermomechanical pulp (CTMP) was treated with UV absorbers, e.g. 2,4-dihydroxybenzophenone and a 2-(2-hydroxyphenyl)benzotriazole derivative (Tinuvin 1130) to reduce the tendency of the paper to undergo photoyellowing. Whilst some of the UV absorbers offer some protection, their effect can be enhanced by use in conjunction with a reducing agent (sodium hypophosphite) and by lowering the pH of the paper by application of potassium dihydrogen phosphate. The best effect was obtained by using Tinuvin 1130 in combination with both a reducing agent and potassium dihydrogen phosphate. The use of hindered phenols in both the presence and absence of thiols offered little protection to the paper.

Batch and continuous anaerobic toxicity of resin acids from chemithermomechanical pulp wastewater

Chemithermomechanical pulp (CTMP) wastewaters are being treated anaerobically, in full scale operations, in spite of the presence of inhibitory compounds. These compounds are neither well identified nor are they placed in an order of priority in terms of inhibition to anaerobic bacteria. In this study batch anaerobic toxicity assays were used to quantify the relative toxicity of resin acids to the total toxicity in hydrogen peroxide bleached CTMP (BCTMP) wastewater. Resin acids are partitioned between the soluble wastewater and the insoluble fiber fractions. Therefore fiber toxicity was also compared to raw BCTMP wastewater toxicity. Resin acids were found to be toxic to anaerobic bacteria but were not found to be responsible for all the toxicity in BCTMP effluents. Toxicity associated with the fiber was soluble in methanol. The bulk of the fiber which was not methanol soluble exhibited no toxicity to the anaerobic cultures used. Batch results were compared to continuous toxicity assays using an upflow anaerobic sludge blanket reactor. The continuous reactor was relatively unaffected by short term or long term exposure to resin acids at concentrations that invoked inhibition in batch tests. Inferences from these tests indicated that batch results may be unreliable when applied to continuous systems.

A Study of the Photoyellowing of Paper Made from Bleached CTMP

Abstract The photoyellowing of papers produced from bleached CTMP is retarded when these papers are irradiated in aqueous solutions containing reducing agents such as Rongalit C and Blankit D. Papers impregnated with the reducing agents showed some photostability when irradiated in the dry state but not when irradiated in aqueous solution. The reducing agents present in these papers also failed to significantly retard the photoyellowing under natural lighting conditions and under simulated solar irradiation. It is concluded that the migratability of the reducing agents is important if photoprotection is to be achieved and that the latter is caused by the reagents bleaching the yellow photodegradation products as well as destroying prodegradent species such as hydroperoxides.

メカニカルパルプ化技術の現状と将来 ＣＴＭＰプロセスを中心として

Technology for the manufacture of unbleached and bleached pulps from hardwoods and softwoods is well established. With softwoods, the CTMP process offers significantly improved pulp quality profiles relative to those exhibited by mechanical pulp. In the case of hardwoods, the CTMP process offers a quality improvement from a low strength filler-type pulp to one capable of contributing significantly to overall sheet strength. Peroxide bleaching results in high brightness levels at reasonable peroxide consumption levels. In addition, alkaline swelling in conjunction with bleaching provides additional improvement in density and bonding properties, particularly in the case of hardwood CTMP.Unbleached and bleached CTMP from both types of wood exhibits useful physical property profiles across a wide range of drainage characteristics. The pulp is already used extensively in a broad spectrum of products ranging from low freeness printing papers to high freeness absorbent grades. With the increasing price of fully bleached chemical pulps, there is growing interest in the use of bleached CTMP in printing and writing grades. While concerns remain regarding the brightness and brightness stability of lignified high yield pulps, these factors are not impeding the growth rate of CTMP.

Role of resin acids in the anaerobic toxicity of chemithermomechanical pulp wastewater

Chemithermomechanical pulp (CTMP) wastewaters are being treated anaerobically, in full scale operations, in spite of the presence of inhibitory compounds. These compounds are neither well identified nor are they placed in an order of priority in terms of inhibition to anaerobic bacteria. In this study anaerobic toxicity assays were used to quantify the relative toxicity of resin acids to the total toxicity in bleached CTMP (BCTMP) wastewater. Resin acids are partitioned between the soluble wastewater and the fiber fractions. Therefore fiber toxicity was also compared to raw BCTMP wastewater toxicity. Resin acids were found to be toxic to anaerobic bacteria but were not found to be responsible for all the toxicity in BCTMP effluents. Toxicity associated with the fiber is soluble in methanol. The bulk of the fiber which is not methanol soluble exhibited no toxicity to the anaerobic cultures used.

Anaerobic Treatment of Sulphur-Containing Effluents

A new method of defibring wood chips and producing chemi-thermomechanical pulp with significant capital and energy savings has been developed. The pollution load of bleached CTMP effluent varied between 40-60 kg/t for BOD5 and 120-210 kg/t for COD. The process includes a sulphite stage and the effluent contains sulphur compounds which are toxic to methanogenic bacteria. Studies have been conducted on anaerobic fixed bed reactors with upflow or downflow feed modes. It is necessary to progressively acclimate bacteria to increasing concentrations of sulphur compounds. Permanent functioning of reactors is possible with COD/S ratios near 10-12 where propionate concentrations are increasing. Upflow reactors are more efficient than downflow reactors, with a maximum loading rate of 3.5 kg COD/m3.day corresponding to 800 mg/l as S. With hybrid sludge bed/fixed bed reactors it is possible to enhance anaerobic treatment efficiency. A COD loading rate of 4.7 kg/m3.day can be maintained with a residence time of 2 days and a pollution load removal efficiency of 45% for COD (55% with complementary oxidation) and 70% for BOD5. The economics of effluent treatment give an investment cost of about 20 US$/ADt for the activated sludge process and 12.5 US$/ADt for anaerobic fixed bed treatment.