The use of molecular modelling in studying pitch deposition

Molecular modelling is proving to be a useful tool in understanding the fundamental interactions between molecules and surfaces. With the use of the super-computer at Australian National University (ANU) calculations on quite large molecules such as triglycerides and polymers can be made. The effect of the chemical structure of different fixatives on the interaction with the various components within pitch can be understood with the use of molecular modelling. Care is needed in choosing the most appropriate method to model the interactions. Geometry optimisation at the higher level of theory using quantum mechanics is needed. Comparison of different quantum mechanical methods yielded similar results indicating that the methods using the less computing power would be adequate in helping to gain a more fundamental understanding of the interactions that occur between various fixatives and pitch

Study of the interaction between poly(ethylene oxide) and phenol-formaldehyde resin

Interactions between poly(ethylene oxide) and phenol-formaldehyde resin play important roles in the mechanism by which the two polymers improve fibre retention in the papermaking process. these were investigated at the concentration level and shear conditions found in this process. The results indicate that the complex formed varies with pH and ionic strength over a very narrow range of conditions, and that the self association of the resin plays an important part in the quantity of resin in the complex. Because the amount of resin interacting with the polyethylene oxide appears to be related to the molecular weight, and hence chain length, of the two polymers, cooperative binding of the polymers seems to be involved. A minimum size of the network was found to be necessary for the polymers to improve fibre retentio

Wood pitch fixative evaluation by Laser particle size analysis

Wood pitch deposition onto the surface of papermaking machinery continues to be a costly problem. Fixatives - substances said to attach wood resin to wood fibre - have been used to alleviate wood pitch deposition to varying degrees of success. This paper aims to evaluate to what degree fixatives alter the colloidal wood pitch particle size. We were able to show how different wood resin fixatives alter the colloidal wood pitch particle size at three different pH values (4.75, 6.85 and 8.06). The fixatives can be divided into two categories, colloid disrupting and colloid stabilising, according to how they change pitch particle size

Evaluation of cationic polymers to control pitch deposition

A wide range of cationic polymers of varying chemical structure, charge density and molar mass were evaluated for their effectiveness to control wood resin deposition. The ability of the polymers to attach model wood resin particles to thermo-mechanical pulp fibres and to maintain the wood resin in the colloidal phase was determined at pH 4.75, 6.85 and 8.06. High molar mass poly-DADMAC, copolymer poly-(AM-co-DADMAC) and guar gum were found to be the best fixatives over the pH range investigated. The performance of poly-DADMAC was found to increase with molar mass and charge density. A conceptual model was proposed to explain the behaviour of the polymers based on their ability to stabilise the wood resin colloids, to attach the wood resins to pulp fibres and to affect the wood resin particle size

TCF bleaching of eucalypt kraft pulp with oxone

TCF delignification and bleaching of kraft eucalypt pulp using ozone and oxone under alkaline conditions has been investigated. The pulp samples were bleached in two stages of oxone (Ox) treatment using an AZOx1Ox2 sequence. Pulp brightness greater than 84% ISO was achieved. The effects of oxone charge, alkali charge, bleaching temperature and time on the bleaching response were studied. The colour removal was determined from the chromaticity coordinates (L*, a* and b*) and 98% colour removal was achieved. Accelerated ageing experiments showed excellent brightness stability with very little brightness reversion (or thermal degradation) of the oxone treated pulp. Improvements in pulp strengths compared to ozone and acid treatments were achieved along with significant HexA removal demonstrating the feasibility of oxone in TCF bleaching

Peroxide bleaching using zeolites Part 1: peroxide decomposition

Addition of certain levels of zeolite and sodium citrate to hydrogen peroxide solutions containing manganese decreased the rate of peroxide decomposition. there were differences in the ability of commercially available zeolites to reduce decomposition of peroxide. Addition of small amounts of sodium citrate to a particular zeolite system improved its ability to chelate metal ions. Sodium citrate appears to act as a transfer agent, facilitating the migration of metal ions to the zeolite. However addition of excess zeolite and citrate increase manganese induced peroxide decomposition. If the manganese-oxygen complex that decomposesperoxide under alkaline conditions was allowed to form prior to the addition of eith the zeolite or citrate then the two chelating agents were unable to interact with the complex and prevent decomposition

Peroxide bleaching with zeolites Part 2: Bleaching of pine TMP and eucalypt CCS

A combination of zeolite and sodium citrate was found to be an effective alternative to DTPA addition in alkaline peroxide bleaching of pine TMP in the presence of manganese ions, but not in the bleaching of Eucalypt CCS pulp. The addition of the zeolite had no effect on the strength properties of the TMP and CCS pulps. Some small improvements in optical properties were observed. The type of zeolite used was important. Addition of small amounts of sodium citrate to the zeolite system improved the zeolite's ability to chelate metal ions from the pine TMP fibre. Sodium citrate appears to act as a transfer agent, facilitating the migration of metal ions from the pulp fibres to the zeolite. In the presence of manganese, the alkaline conditions of the Eucalypt CCS resulted in the formation of oxidised manganese species that actively decompose peroxide. Zeolite and citrate appear to be unable to complex these metal species. DTPA, on the other hand, is effective in complexing the Mn-O species present in CCS

Use of a new novel grafted Guar Gum-copolymer as a pitch fixative

A novel fixative, guar gum-graft-poly(acrylamide-codiallyldimethylammonium chloride ) (aka GG-gp(AM-co-DADMAC)) was developed. This new grafted polymer proved to be very effective at adsorbing hydrophobic wood resin particles onto papermaking fibre surfaces and thus removing the troublesome wood resins from the water phase where they have a tendency to aggregate and form troublesome deposits. The new polymer is unique in that it takes advantage of the colloidal stabilising features of a natural product, guar gum and the wood resin fixative properties of a synthetic polymer p(AM-co-DADMAC)). GG-gp(AM-co-DADMAC was effective over the entire pH range as compared to other commercially available polymeric fixatives that were evaluated

The colloidal pKa of lipophilic extractives commonly found in Pinus radiata

This paper uses established experimental methods to determine the colloidal pKa values for a variety of weak organic acids found in a variety of lipophilic extractives of Pinus radiata at 20C and 50C. The 50C colloidal pKa values, to the knowledge of the authors, are published for the first time in this paper. The data will hopefully lead to a better understanding of how these weak organic acids interact in the 50C temperature range of modern pulp and papermaking. The colloidal pKa values for behenic, lignoceric and cerotic acids are also believed to be published for the first time in this pape

Use of wetting agents to improve flotation deinking with magnesium oxide

In the past, alkali such as magnesium oxide and calcium hydroxide have been found to be not as effective in causing fibre swelling or in alkaline flotation deinking as sodium hydroxide. The addition of a wetting agent together with magnesium oxide has been found to increase fibre swelling to near that obtained with sodium hydroxide. The chemistry of the wetting agent was found to be important. The addition of the wetting agent with magnesium oxide in deinking using a Lamort laboratory deinking cell was also found to achieve similar deinking efficiency to that achieved with sodium hydroxide as the alkali source. Similar brightness levels were achieved, but the results indicated that slightly better ink removal efficiency occurred with the magnesium oxide system. The effluent from the magnesium oxide system was also found to have a lower dissolved salts content, which is an advantage to mills where salinity is a problem