Showing papers in "Appita Journal in 2013"

Optical characterisation of size, shape and fibrillarity from microfibrillar and microcrystalline cellulose, and fine ground wood powder fractions

Abstract: Fast analysis and characterisation of small lignocellulosic particles are known to be problematic when samples contain large number of particles. New methods to quantify the size, shape and structural properties of cellulose microparticles and wood powders are needed. In this paper, we present a measurement scheme based on the flow cytometry analysis of microparticles that can, after sample fractionation, analyse cellulose and wood microparticles for their relative size, degree of fibrillation (representing the delaminated fine surface structure) and aspect ratio. Laser diffraction-based analysis is used as a reference method for particle size and the studied samples are visualised and quantified for aspect ratio and surface characteristics using an electron microscope.

Mild steam explosion followed by kraft cooking and oxygen delignification of spruce (Picea abies).

Abstract: The paper considers mild steam explosion as an initial biorefinery process step to make wood more accessible for chemicals and enzymes in subsequent extraction and isolation procedures. Wood chips were exploded at four and seven bars and the effects of the treatments were followed during both kraft cooking and oxygen delignification. The properties of the unbleached and bleached pulps, including kappa number, pulp yield, fibre length, intrinsic viscosity, chemical composition and ISO brightness, were analysed using standard methods. The findings showed a difference between treatment at four and seven bars, as the higher pressure leads to more significant visual changes as well as somewhat increased degradation of hemicelluloses. These changes however, have no apparent significant negative effect on the final pulp properties. To the contrary, a benefit of steam treatment seems that the time to reach a certain kappa number was slightly reduced with steam-exploded wood chips.

A comparison of cold and hot caustic extraction of a spruce dissolving sulfite pulp prior to final bleaching

Abstract: A magnesium sulfite pulp producer modified its pulping process to dissolving pulping in 2011 and needed a purification stage after the digester to obtain a sufficiently low hemicellulose content. The dissolving pulp was intended for viscose production and an R18 value of at least 95% and an intrinsic viscosity below 550 dm3/kg was requested. The results showed, as could be expected, a correlation between lower dissolving pulp yield and a higher degree of purification with respect to cellulose. The R18 values and the intrinsic viscosities of the dissolving pulps were found to increase with increasing sodium hydroxide concentration and/or higher temperature in the extraction stage. The pulp yield was found to be higher with higher temperature for the cold caustic extraction stage (CCE); for hot caustic extraction (HCE) the pulp yield became lower with higher temperature. The specified R18 value was easiest to reach using hot caustic extraction.

Investigation of the performance of a lint camera system in identifying lint using image analysis

Abstract: Linting is the removal of materials from the surface of uncoated paper during offset printing, and is a particular issue with sheets made from mechanically pulped fibres. Linting is a complex problem because it is a dynamic process that is influenced by both the printing press and the paper. In 2006, a video camera combined with image analysis was introduced to measure lint build-up on a blanket during printing and to separate the effect of the press variables from the effect of the paper. This paper reviews subsequent improvements that have been made to the system, and examines the suitability of the system to conduct research into the dynamics of lint or for routine quality control measurements. To do this, the lint particles identified by the camera, will be compared to the lint obtained by washing the blanket. The area distributions of lint measured when the press was running (dynamic), and halted (static) were compared to the lint measured from the washed and filtered samples. The dynamic images show a larger area on the blanket being detected as lint compared with the other two measurement methods. The dynamic images also significantly overestimated the area of large particles. The differences in the lint area distribution suggest that the dynamic measurements need to be improved further before they can be reliably used for the analysis of linting dynamics. The area of the lint removed in the static images was promising as it shows rather similar results to the lint removed by washing the blanket, suggesting that the camera is a suitable replacement for time-consuming measurements of lint by washing and image analysis.

A review on the use of zeolites to create valuable paper products and paper-like adsorbent materials

Abstract: Zeolites are used for a range of applications ranging from fillers in paper for bulk, low cost applications to gas adsorbents and catalysts due to their microporous structures and high surface activity. Current adsorption technology uses zeolites in the form of beads or pellets for gas adsorption but has issues relating to increased energy consumption due to high pressure drop as well as low recovery due to mass transfer limitations. Novel non-particulate adsorbent structures have been developed to overcome these problems. These structured adsorbents unfortunately have very low loading of zeolite, thereby limiting their usefulness. In papermaking, zeolites are used as fillers primarily to improve optical properties, bulkiness, printability, and to increase retention at the wet end. This review considers these two varying applications of zeolites. The first part of the review addresses the use of papermaking techniques to prepare zeolite sheet structures using lignocellulosic fibres as a template or substrate. The advantages of such structures along with necessary improvements and further work will be discussed. The second part of the review provides a general overview on the potential use of zeolites as fillers in papermaking for various applications. We also discuss the retention and optical properties when zeolites are used as fillers in laboratory papermaking.

Determination of the contribution of penetration, diffusion and alkali consumption in the impregnation of Eucalyptus grandis chips

Abstract: The influence of impregnation conditions on the phenomena involved in the impregnation of Eucalyptus grandis chips was studied with the aid of a new impregnation method. When pre-steaming was used, 30 minutes of penetration time was sufficient to achieve the final degree of penetration (over 95%) with white and black liquor. An impregnation time of 15 minutes was found to be sufficient to transfer the required amount of alkali into the wood for kraft cooking, provided that a high-concentrate white liquor was used. Only part of the alkali required was transferred into chips during 60 minutes of impregnation using black liquor with an effective alkali concentration of 20g NaOH/L. In addition, almost all of the alkali was consumed as it entered into the wood. This risks running out of alkali if the temperature is raised quickly to cooking temperature.