Peroxide-bleached Thermomechanical Pulp Research Articles

Hybrid clay functionalized biofibres for composite applications

Micro-injection moulded composites of softwood fibres from two different pulping processes in thermoplastic polypropylene matrix have been studied. Surface modification of hydrogen peroxide bleached thermo mechanical pulp fibres (BTMP) from spruce (Picea abies L.) and chemical sulphate pulp fibres (BKraft) from pine (Pinus sylvestris L.) was achieved by co-precipitation of layered double hydroxide (LDH) particles that were further functionalized with sodium dodecyl sulphate (SDS) surfactant in conditions similar to wet end in paper production. Micro-injection moulded test specimens were subjected to uniaxial tension tests, water absorption, micromechanical deformation and microscopic studies. Optical micrographs show that functional pulp was homogeneously dispersed into polypropylene matrix where as the untreated fibres agglomerated during moulding. When composites were prepared with BTMP fibres the electrostatically bound SDS on fibre surface increased elongation at break by 70%. LDH particles intensified dissipation of shear energy to BKraft fibres degrading the average fibre length by 50% during moulding. Functionalization with SDS surfactant, however, increased average fibre length up to 125% in comparison to LDH modification.

Pre-flocculation of precipitated calcium carbonate filler by cationic starch for highly filled mechanical grade paper

Three commercial starches were evaluated in conjunction with colloidal silica and flocculant to retain precipitated calcium carbonate (PCC) filler. A unique feature of this study was the fact that the filler was pre-flocculated by a portion of starch (2kg starch/t PCC) and the rest of the starch was added after the flocculant but before the silica. The pulp used was peroxide bleached thermo-mechanical pulp (TMP). A statistical design methodology was employed and empirical process models were constructed based on the analysis of variance (ANOVA) results. The models were then employed to predict the retention and drainage. It was found that the high-charged cationic starch gave the highest retention and best drainage performance. The high-charged cationic starch S880 also resulted in stronger paper, probably because of the larger and stronger flocs produced and its higher affinity with the fiber and fines. Finally, pre-flocculation was found to provide stronger paper compared with a conventional starch/retention aid addition sequence.

Cost-effective brightening of thermomechanical pulp from mountain pine beetle-infested lodgepole pine

We developed a cost-effective bleaching method for overcoming the brightness ceiling of thermomechanical pulp (TMP) made from mill chips containing predominantly mountain pine beetle-infested lodgepole pine. The method involves synergistic bleaching of the TMP in the refiner with hydrosulfite (Y) and diethylenetriaminepentaacetic acid (DTPA) as the chelating agent. The synergistic, in-refiner Y+DTPA bleaching, when followed by post-refiner Y or peroxide bleaching, can provide higher brightness gain or lower bleaching chemical cost for Y- or peroxide-bleached TMP from the mill chips. Estimated cost savings for Y bleaching to 60.0% ISO brightness and peroxide bleaching to 74.3% ISO brightness are USD 5.2/ton pulp and USD 5.2-6.2/ton pulp, respectively.

Sorption of metal ions to untreated, alkali-treated and peroxide-bleached TMP

Knowledge about how different metal ions are bound to pulp fibers is very important for optimal metal management in pulping processes. A column chromatographic method was used to assess the differences in affinity of 14 metal ions to untreated, alkali-treated and peroxide-bleached thermomechanical pulp (TMP). A method of competition between cations in the column chromatographic experiments was used in the sorption experiments, with an excess of each metal ion compared to the total capacity of the pulp studied. The method is very sensitive and even small differences in affinities can be detected. By combining the results from sorption experiments with four different metal ion mixtures the following order of affinity was obtained: Pb2+ ≫ Cu2+ ≫ Cd2+ > Zn2+ > Ni2+ > Ba2+ > Ca2+ > Mn2+ > Sr2+ > Mg2+ ≫ Rb+ ≈ K+ > Na+ > Li+. All three types of pulps showed the same affinity order. Lead and copper ions were clearly most strongly bound to the pulp fibers. Within the alkali and alkaline earth metal groups the differences in affinity were quite small. The sorption of metal ions to pulp fibers takes place mainly by complexation, where the divalent metal ions are coordinated to functional groups (acid groups) in the fiber phase. Protonation constants and concentrations of acid groups were determined by potentiometric titration. A model with two carboxyl groups and two phenolic hydroxyl groups satisfied best the experimental data. By treatment with alkali and peroxide new acid groups were created and the total binding capacity of hydrogen ions increased from 137 μeq/g for untreated pulp to 187 and 228 μeq/g for alkali-treated and peroxide-treated pulp, respectively.

Application of Advanced Wet-End System Using Carboxymethyl Cellulose to Mixed Pulp Slurries for Wood-Containing Paper Production

A pulp modification technique using carboxymethyl cellulose (CMC) at the wet end was applied to mixed pulp slurries containing softwood bleached kraft pulp (SBKP), deinked pulp (DIP), and hydrogen peroxide-bleached thermomechanical pulp (TMP). Introduction of anionic sites by adsorption of the added CMC molecules on the fibers was confirmed by an increase in negative charge of the mixed pulp fibers. Sizing degree of the handsheets prepared with 2% aluminum sulfate and 0.2% rosin dispersion size was clearly improved by 0.1% CMC addition. On the other hand, we observed no significant differences in rosin size content between the handsheets prepared with and without CMC. These results indicate that some mechanisms other than enhancement of rosin size retention may have brought about the clear improvement of sizing performance by the CMC addition. Changes in distribution of rosin size components or some structural changes of rosin size components in the handsheets by the CMC addition may be candidates for sizing development. The CMC addition technique at the wet end is, therefore, also applicable to mixed pulps containing DIP and TMP.

Isolation of pectic acids from bleached TMP water and aggregation of model and TMP pectic acids by calcium

Pectins are important structural elements in spruce fibres. Alkaline peroxide bleaching of spruce thermomechanical pulp (TMP) causes degradation and demethylation of pectins, yielding high-charge-density pectic acids. The pectic acids in fibres contribute strongly to the negative fibre charge, and the dissolved pectic acids increase the cationic demand of bleached TMP water. In this study, a method to isolate pectic acids from peroxide-bleached TMP pulp water is presented. The pectic acids were isolated and purified in good yield using a polyacrylate resin to remove lignin, a cellulose filter to remove galactoglucomannans (GGM), and an anion exchange resin to separate pectic acids from neutral carbohydrates. Salts and residual low-molar-mass carbohydrates were further removed from the isolated pectic acids by dialysis. The isolated pectic acids (>80% purity) had a low molar mass and a wide polydispersity (5.9 kDa, MW/MN 3.3). The aggregation and precipitation of the isolated pectic acids, as well as citrus fruit pectic acids with well-defined molar masses, by Ca2+-ions were studied. The molar mass of pectic acids was a key factor determining the precipitation of Ca2+-pectates. Pectic acids below 6 kDa were not precipitated by Ca2+, while higher molar masses led first to partial and then to complete precipitation. The precipitated Ca2+-pectates may impair paper machine runnability and paper quality.

Activity of laccase on unbleached and bleached thermomechanical pulp

The introduction of value-added properties to pulp fibres is an attractive proposition. One interesting option is targeted modification of fibre surfaces by enzymatic activation. In this work, the activity of laccase on pulp and pulp fractions from thermomechanical pulp (TMP) and peroxide bleached TMP was studied on the basis of consumption of the co-substrate oxygen in the reaction and by studying the formation of radicals in the pulp material as analysed by electron paramagnetic resonance spectroscopy (EPR). Laccases obtained from Trametes hirsuta and Myceliophthora thermophila were used in the study. Laccases were found to be active on pulp material of unbleached TMP, whereas only fines from bleached TMP reacted in laccase treatment. Dissolved and colloidal substances (DCS) were assumed to have a mediating role in the laccase-catalysed oxidation of the fibre-bound material.

The influence of charge density of cationic starch on dissolved and colloidal material from peroxide bleached thermomechanical pulp

The interaction between anionically charged colloidal and dissolved material (anionic trash) from peroxide bleached thermomechanical pulp and cationic starches of different charge densities has been examined. The evaluated degrees of substitution, DS, were 0.015, 0.035, 0.05 and 0.08. For comparison, a starch of considerably higher degree of substitution, called fixative, was also evaluated. A higher amount of the cationic starch of DS 0.015 was needed than that of DS 0.035 to achieve complete destabilisation of colloidal material. However, lower dosages of the starches with DS 0.035 and 0.05 were needed than of the starch of DS 0.08. A lower dosage of fixative than of the common starch of DS 0.08 was also needed. The fixative recharged the particles upon an overdose. Measurements of residual turbidity and zeta potential indicate that the common starches destabilised the colloidal lipophilic extractives by interparticle bridging. The fixative starch of considerably higher charge density, DS 0.8, may have destabilised the colloids by the patch flocculation mechanism. The common cationic starches also formed complexes with dissolved pectic substances, which are anionically charged wood polymers consisting of galacturonic acid units. The amount of starch needed to achieve complete destabilisation of pectic substances decreased with increasing charge density, probably due to intensified electrostatic interaction. Still lower amounts of fixative were needed. An overdose of fixative restablized the pectic substances.

Lignin inhibits autoxidative degradation of cellulose

We studied autoxidation of lignin-containing and lignin-free pulps, initiated by the water-soluble radical initiator 2,2′-azobis(amidinopropane)dihydrochloride (ABAP). A fully-bleached, softwood kraft pulp, treated with 0·3 m ABAP and 140 kPa oxygen for 48 h (20% solids, pH 7, 60°C), experienced an 80% reduction in cellulose degree of polymerization (DP), and lost 40% of its zero-span tensile strength. No discolouration occurred. In contrast, there was virtually no change in cellulose DP or zero-span tensile strength, but considerable discolouration for a lignin-containing pulp (peroxide-bleached thermomechanical pulp) under the same conditions. We propose that, under these conditions, the discolouration of lignin is a manifestation of its antioxidant properties.

Polysaccharides Dissolved from Norway Spruce in Thermomechanical Pulping and Peroxide Bleaching

Abstract Methanolysis, followed by GC analysis, was used to determine the amount and composition of sugar units comprising the carbohydrates present in water samples from unbleached and peroxide bleached thermomechanical pulp (TMP). Circulation experiments were carried out in the laboratory to simulate white water system closure in mechanical pulp mills. Water samples from simulated “closed” water systems were fractionated to determine the composition of the neutral and anionic polysaccharides released from the TMP samples. Decreasing fresh water consumption from 100 to 10 m3/t, for both unbleached and peroxide bleached TMP, had little influence on the overall sugar composition of the carbohydrates in the water samples. Alkaline peroxide bleaching resulted in substantial changes in the sugar composition of the carbohydrates comprising the dissolved and colloidal substances (DCS) in the water samples. The polysaccharides released from unbleached TMP were comprised of neutral (88%) and anionic (12%) polysac...