Reasons leading to the brightness ceiling in mechanical pulp peroxide bleaching were investigated with spruce thermomechanical pulp. During peroxide bleaching, new phenolic guaiacyl units, alpha-carbonyls and catechols were shown to be formed. All those are known precursors that can be converted to new coloured structures. High chemical charges, especially alkali, enhance formation of these precursors, and thereby limit brightness development. Contrary to the previously reported results on hardwood chemithermomechanical pulp, nitrogen pressurization had no beneficial effect on final brightness of spruce thermomechanical pulp, although it may slightly reduce formation of some colour precursors. The lower chromophore formation is probably obscured by the reduced lignin dissolution. During peroxide bleaching, naturally formed peracetic acid has no significant role in brightness development.
The acid hydrogen peroxide system has the potential to significantly reduce the specific energy consumption in the production of softwood thermomechanical pulps (TMPs). A drawback of the chemical system is discoloration of the pulp during refining. The work presented in this study evaluates the possibility to regain the lost brightness by washing, chelating and sodium dithionite or hydrogen peroxide bleaching of the treated pulps.A washing or chelating procedure can reduce the metal ion content of the chemically treated TMPs considerably, though brightness can be increased by a maximum of two ISO units. The amount of iron can be further reduced to a level similar to that of untreated pulps by performing a reducing agent-assisted chelating stage (Q(Y)) with dithionite. The discoloration cannot,, however, be completely eliminated. The brightness decrease-of the treated pulps is thus not only caused by higher iron content in the pulp, but is also dependent on the type of iron compound and/or other coloured compounds connected with the acid hydrogen peroxide treatment.Oxidative bleaching with hydrogen peroxide (P) is more effective than reductive bleaching with sodium dithionite in regaining the brightness lost during the energy reductive treatment. By using a Q(Y) P sequence, a hydrogen peroxide charge of 3.8% was needed to reach an ISO brightness of 75% for the chemically treated pulps. The corresponding hydrogen peroxide charge for the untreated TMP reference was 2.5%.
The physical location of flocculants and nanoparticles in laboratory prepared paper sheets was investigated by confocal laser scanning microscopy (CLSM) using fluorescently-tagged cationic polyacrylamide flocculant and fluorescently-tagged anionic colloidal borosilicate nanoparticles. Results suggest that flocculant did not coat individual fibres, but instead was associated with fibrils on the fibre surface and with deposited filler aggregates. Nanoparticles were found to be associated with the sites containing pre-adsorbed flocculant, and in the presence of starch, they were evenly distributed throughout the paper sheet. Semi-quantitative analysis of CLSM images of paper sheets was also performed. General guidelines for extracting quantitative information from images were established. Relative area covered by flocculant and nanoparticles was estimated and appeared to correlate with changes in retention aid doses.
A novel multi-element foil (MEF (TM)) pulp screen rotor has been developed to provide decreased power consumption, increased capacity and improved contaminant removal efficiency. The new rotor is based on multi-element air foil technology used in the aircraft and high performance race car industries to provide high lift at relatively low speeds. In pressure screens, the high lift design enables increased capacity even when operating with very narrow slotted screen cylinders and the low speed results in low power consumption. The rotor configuration, angle-of-attack and flap angle, were optimized in a series of computational and pilot screening trials. The performance of the optimized MEF (TM) rotor was evaluated and it was shown that the rotor provided a 26% power reduction over the state-of-the-art single foil rotor at the same capacity In mill trials at a deink fine screening system, a prototype MEF (TM) rotor was shown to provide a 43% energy reduction over the existing rotor while maintaining capacity and efficiency.
Traditional air-cooled carryover probes, while excellent for research and longer term studies, do not lend themselves readily for use by mill operators. The main objective of this work was to develop and calibrate an un-cooled short-time probe technique that could quickly estimate the deposit accumulation rate in a recovery boiler The deposits on the probe surface were photographed after exposure, and the photos were analyzed with image processing software. The degree of particle coverage on the probe surface was converted to correspond to the long-term air-cooled probe results. A reference series for the short-time probe was created. This can be easily used by the boiler operators simply by comparing the short-time probe surface after the measurement with the reference image series, and converting the obtained degree of particle hit coverage to carryover concentration in the flue gas. New information on the particle size variations was obtained from the short-time probe images.
Fractionation and the alkaline peroxide treatment (APT) of rejects were used to produce pulps for value-added grades using TMP from the latency tank of a newsprint mill. Hydrocyclones were able to selectively fractionate and remove undeveloped fibres from a blend of long, medium, and short fibres. Savings of 18% in reject refining specific energy were achieved when hydrocyclone rejects were treated with alkaline peroxide before refining. When newsprint TMP was processed in the hydrocyclone fractionation system followed by APT and reject refining, the treated pulp was suitable for making a lightweight coated (LWC) grade with substantially less reinforcing chemical pulp. The overall specific energy consumption was also similar to 15% less than that of a typical commercial TMP for LWC grades. With the implementation of technologies involving fractionation and the alkaline peroxide treatment of rejects, an existing newsprint refining installation could be maintained and used to produce pulp for value-added grades with minimal capital investment.
Significant efforts towards closed cycle papermaking operations will be required to minimize fresh water consumption and reject loads Unfortunately severe drawbacks on paper machine I-tamability and paper quality are occurring as water consumption is decreased due to a build up of dissolved and colloidal substances (DES) in process waters Adsorption of some DCS on high surface area solid sorbents is proposed to remove them from process waters prior to recycling The adsorption potential of polygalacturonic (PGA) and abietic acids. (AA) on ion exchange resins was studied These resins had different functional groups and/or porosities Optimum adsorption was achieved with a gel type (microporous) term containing tertiary amine groups Under the experimental conditions studied adsorption reached 19 mg PGA/g and 45 mg AA/g after 15 minutes Isotherms revealed that at pH 5 5 PGA was adsorbed in multiple layers while AA formed a monolayer Kinetic studies suggested that dissolved substances (PGA) could diffuse into the pores whereas this was not the case for colloidal substances. (AA)
A modified hand sheet former was used to form fibre mats under applied vacuum comparable to that experienced in a suction box. The apparatus allowed for comparison of the effects of vacuum on filler distribution and migration. Hand sheets of 60 g/m(2) final basis weight were formed using precipitated calcium carbonate (PCC), clay, or a combination of PCC and clay fillers. The PCC filler concentration increased from the top side to the wire side until a plateau was reached in approximately the bottom quarter of the sheet. Applying a vacuum during the drainage process decreased the average PCC content with the majority of the reduction from the wire side of the sheet. In hand sheets fanned with anionic clay the filler concentration increased from the top side past the sheet centre and then decreased towards the wire side, similar to the typical hand sheet distribution. Applying vacuum during forming had only a small effect on clay retention. Some sheets were formed with both filler types. In these experiments PCC was present in the lower half of the suspension and clay in the upper half or else the PCC and clay were reversed. Filler from the suspension used to create the lower portion of the sheet showed a steady increase in concentration from the centre to the wire side. Filler from the suspension used to create the upper portion of the sheet showed a concentration increase from top side to centre, and then a decrease towards the wire side. These distributions showed that filler from the upper portion of the pulp suspension migrates through the sheet and is retained throughout.
An ozone/oxygen mixture was applied as reactive gas for recovered papers deinking in a laboratory flotation column To ensure an homogeneous composition of the raw material a model pulp containing standard offset printed papers was used Results showed that the addition of ozone in the conventional flotation led to an increase of ink removal and to the reduction of the flotation rejects Additionally the destruction of optical brighteners present in the recovered papers and the reduction of effluent COD were observed during O-3/O-2 flotation
A new lab drainage test has been developed to characterize the drainage resistance of forming fabrics at different sheet basis weights. The drainage resistance profile obtained through lab drainage testing provides information about the relative change of the drainage resistance during the sheet forming process. An interface layer is formed between fabric and fibre mat during sheet forming. The interface layer has different drainage properties than the fibre mat above it. The drainage results from a pilot paper machine trial indicate that the lab drainage results correlate well with the drainage performance of a forming fabric on the paper machine. The lab drainage test can be a good tool to predict the drainage performance of various forming fabrics.
As part of a program to reduce electrical energy consumption in the refining process, the effects of alkaline peroxide treatments on second stage thermomechanical pulp properties before and after low consistency refining have been investigated. The low consistency refining stage was simulated using a "Waring Blendor". Highly alkaline peroxide treatments resulted in gains in pulp properties that would allow reduced energy input in second-stage refining. The treated pulp was more flexible and more resistant to cutting during subsequent low consistency refining. The improved properties resulted mainly from production of acid groups on the fibre surface or in the fines.
Methods combining micro scale resolution x-ray shadow graphs, computerised x-ray micro-tomography and advanced image analysis were developed to study connections between the structure of void space ...
SEM micrographs of samples from the refining zone of a pilot refiner stopped while under load showed that the pulp appeared as aggregates or nodules with a near random local fibre orientation They were loosely connected in rope like entities which had an orientation close to the radial direction Cross sectional images illustrated how a rolling action leading to a combination of longitudinal and transverse compassion as well as rubbing and abrasion of the single fibres, could be a very likely mechanism for transfer of stresses These images will enhance the understanding of the fibre properties as developed in high consistency refining
The potential to produce mechanical pulp from Jack Pine by combining selective refining with various' chemical treatments' of the long fibre fraction was evaluated by investigating fibre characteristics and paper properties after refining The results demonstrated that compared to fibres without chemical treatment treated fibres can be developed and strength properties can be improved to some event Moreover selective refining shows an advantage in terms of refining energy consumption and physical properties over whole pulp refining
Biopolymer nanoparticles form latex dispersions that consist of crosslinked water-swollen starch nanoparticles. The biobased latex emulsion provides an alternative binder system to petrochemical-based binders used by coated paper and paperboard manufacturers. The biolatex binders consist of a re-engineered starch biopolymer that is unique because its discrete particles are not water soluble, but form a colloid dispersion in water The swelling characteristics of a typical SB latex and biolatex colloids were studied and compared. The crosslinked structure and the role of water as a fugitive plasticizer for the biolatex nanoparticles explain the unique performance both in terms of coater mutability and optical properties of the coated paper Novel titanium dioxide-biolatex conjugate compositions were produced by incorporating titanium dioxide particles into the reactive extrusion process used to prepare biopolymer nanoparticles. Increased whiteness and brightness were observed for paper coatings containing the titanium dioxide-biolatex conjugate compositions. Nanoparticle tracking analysis provided evidence for conjugate formation. The spacing created between TiO(2) particles of biobased nanoparticle-TiO(2) conjugates is believed to be responsible for the enhanced whiteness and brightness performance.
There is a lack of experimental data on the gas composition in recovery boiler furnaces, particularly in the lower furnace and at the black liquor spraying level. Experimental determination of the gas composition in full-scale furnaces is important for the understanding of the kinetics of the gasphase reactions and the formation of different intermediates in the combustion process. The gas composition was measured in the furnace of a large recovery boiler using a new gas sampling method. The measurements were carried out from the primary air level to the upper tertiary cur level. The measurements were a part of an extensive campaign planned and carried out to support validation of models hosed on Computational Fluid Dynamics. This paper will focus on the sulphur and nitrogen species measured in the furnace and on the developed gas sampling probe. A number of reactive sulphur and nitrogen intermediates were identified and quantified in the measurements. Especially high concentrations of different intermediates were measured at the black liquor spraying level. Measured nitrogen and sulphur species include: nitrogen monoxide (NO), nitrogen dioxide (NO(2)), ammonia (NH(3)), hydrogen cyanide (HCN), hydrogen sulphide (H(2)S), sulphur dioxide (SO(2)), methyl mercaptan (CH(3)SH), ethyl mercaptan (C(2)H(5)SH), dimethyl sulphide ((CH(3))(2)S), dimethyl disulphide ((CH(3))(2)S(2)), carbonyl sulphide (COS), and carbon disulphide (CS(2)). Some of these have not been reported before in full-scale measurements.
High brightness high yield pulp (HYP) also known as BCTMP is a favourable substitute for hardwood bleached draft pulp (HW BKP) in the production of printing and writing paper grades to benefit from the unique properties of HYP such as high bulk and high light scattering coefficient However in the production of high brightness HYP strong alkaline pen-Aide bleaching conditions are usually employed causing a significant loss of bulk light scattering coefficient and yield of HYP in this study we compared the advantages of the combined peroxide/OBA brightening process (combining peroxide bleaching with the use of an optical brightening agent (OBA)) over the conventional peroxide bleaching process The peroxide/OBA brightening process can produce aspen HYP with very high brightness (e g 90 % ISO) very high CIE whiteness and very low yellowness (b*) which could not otherwise be obtained economically from the conventional peroxide bleaching process For a given brightness target the bulk and light scattering coefficient of the bleached pulp from the combined peroxide/OBA brightching process were markedly higher than those from the conventional peroxide bleaching process It was also found that substantially less dissolved organic matter (measured as COD) and anionic wish were formed in the combined peroxide/OBA brightening poet ss in comparison with the conventional perorate bleaching process resulting in higher pulp yield
Energy is the most common parameter in use to characterize refining action for chemical pulp enhancement and mechanical pulp production The extent of refining is commonly quantified by specific energy and the severity of the process is quantified by an energy bused intensity However energy is not the agent of refining Forces produce the refining result by imposing strains in fibrous' material to break molecular bonds Energy is a merely a consequence of how forces are applied This paper discusses the nature of forces in refining how they can be used to quantify refining action and how they shed light on the theoretical energy required for the processes
In this experimental study we relate refiner design and operation to pulp quality changes by low consistency refining Pint we demonstrate how refiner plate gap and specific energy are sufficient in predicting both pulp freeness and fibre length changes during refining Second we experimentally determine a predictive correlation for plate gap for the key operating and design variables Finally we demonstrate a correlation between freeness and fibre length to tensile and tear strength
Cellulose nanofibres were produced from a bleached hardwood kraft pulp by means of TEMPO mediated oxidation The objective it as to studs the potential use of these nanofibres as a retention aid and strength reinforcement agent in papermaking The results showed that 93 % of the oxidized pulp could be converted into nanofibres with carboxyl contort of about 1200 mmol/kg pulp The average nanofibre length and width were 306 and 3 6 nm respectively When 1 % of nanofibres were premixed with clay at pH 2 5 before being added to a newsprint grade pulp furnish high clay retention rate and improved tensile strength could be obtained
