Volume 35, Issue 2

The objective of this study was to understand the influence of bleaching on % residual lignin, water retention value, brightness and morphological properties of Subabul heartwood and sapwood pulps. The second aim was to compare the properties of unbleached and bleached handsheets with respect to tensile index and fractography. Screened wood chips of Subabul were subjected to kraft cooking (165 °C, 3 hours) followed by ECF bleaching and refining. When unbleached handsheets were compared, higher tensile index was found for sapwood sheets (29.8 N.m/g) than heartwood sheets (12.8 N.m/g). Therefore, it is recommended to use unbleached sapwood sheets for packaging grade applications. The bleached pulps have exhibited negligible residual lignin (0.1 %), higher water retention value (∼21) and higher brightness (88 %) compared to unbleached pulps. Subsequently, the bleached heartwood sheets revealed higher tensile index (∼7 fold) and higher modulus of elasticity (∼2.7 fold) compared to unbleached heartwood sheets. For printing grade applications bleached sapwood and bleached heartwood pulps are equally recommended, because no differences were observed in their pulp and sheet characteristics.

Although fibrous suspensions are finding increasing use in many applications, holistic studies investigating their material properties are essentially non-existent due to a lack of simple and reliable measurement techniques. To address this, geotechnical techniques have been considered for the characterisation of an extruded suspension of poplar fibres. Use of such characterization techniques was thought suitable since the extruded fibres share many physical similarities with fibrous peats, and since both materials are primarily derived from plants. In the present study, oedometer and direct shear tests were employed to evaluate the compressibility, permeability and friction properties of poplar fibres. Triplicates of each test were carried out for two differently prepared poplar fibres at several different initial water contents. All measurements were found to be in good agreement with the values typical of fibrous peats, justifying direct cross-over of geotechnical techniques as an alternative method for characterising and modelling fibrous suspensions in manufacturing applications.

Polylactic acid fibrils (PLAf) were employed as a fiber component in papermaking. The addition of 5 wt % of PLAf to bleached kraft birch pulp increased the tensile index of the resulting 100 g/m 2 paper sheets by 20 % in comparison to sheets produced without PLAf. By heat-treating the paper sheets containing 5 wt % PLAf, a 35 % higher tensile index in comparison to sheets produced without PLAf was achieved. SEM imaging showed that the heat-treatment caused the PLAf to melt, which formed a film on the fiber web. The PLAf was ultrasonicated in an attempt to make its surface more hydrophilic and anionic and thus more compatible with cellulose. Chemical additives (cationic polyacrylamide, polyethylene imine and polyethylene glycol) were added to the PLAf/cellulose pulp mixture in order to increase the binding between the ultrasonicated PLAf and cellulose. Ultrasonication caused the PLAf length to decrease and the PLAf surface charge changed by 36 %, indicating that the PLAf became significantly more anionic. Neither ultrasonication of PLAf nor the chemical additives improved the paper sheets’ stretchability. Polyethyleneimine as an additive in an amount of 1 % increased the tensile index of heat-treated sheets made with 5 wt % of PLAf by 19 %.

The hypothesis is that it should be possible to modify papermaking conditions in line with the softening properties of high yield pulp fibres and achieve similar strength properties to conventional chemical pulp based paper. We therefore investigated the rheological and physical properties of high yield pulp based papers during hot-pressing. Our results confirm that increased temperature combined with sufficient pressure enables permanent densification by softening of lignin, producing very high tensile strength. This treatment also significantly improved the wet tensile strength in comparison to bleached kraft pulp without using wet strength agents. The high yield pulps used here were spruce based thermomechanical pulp, chemi-thermomechanical pulp, and high temperature chemi-thermomechanical pulp, and birch-aspen based neutral sulphite semi chemical pulp, with spruce-pine based bleached kraft pulp as reference. Rapid Köhten sheets of 150g/m2150\hspace{0.1667em}\text{g}/{\text{m}^{2}} and 50 % dryness were hot-pressed in a cylinder-press at 20–200 °C, 7 MPa, and 1 m/min. The mechanical properties showed great improvements in these high yield pulp papers, with tensile index increased to 75 kNm/kg and compression strength index to 45 kNm/kg; levels close to and better than bleached kraft. Wet strength increased to 16 Nm/g compared to 5 Nm/g for bleached kraft.

The focus of this study is the development of a methodology to mechanically separate or fractionate micro-fibrillated fibre suspensions (MFC) into different size classes. We extend the principle outlined by Madani et al. (2010) and create a continuous separation in an annular gap undergoing spiral Poiseuille flow (solid body rotation superimposed on pressure driven flow). Achieving hydrodynamic stability of this flow was the main scientific challenge for scale-up. This work is presented in two different studies. In the first study, we perform a series of batch-wise centrifugation tests to develop the criteria for motion of the individual classes of particles which compose a Eucalyptus MFC suspension. Here, we suspend the MFC in a weak gel and demonstrate a linear reduction in average particle size with increasing centrifugal force; motion is initiated in heavier particles before the lighter ones. In the second study, we use this batch-wise data to design a continuous prototype and we successfully demonstrate a continuous separation with performance similar to that achieved in the batch-wise tests.

Pulp and paper industry in the world have been growing fast. As a result, there has been a massive request for pulp and paper raw materials. The raw materials used in papermaking can be classified into three groups: wood, non-wood, and recycled wastepaper. The Non-wood raw material is an important fiber resource in the regions where forest resources are limited. The current usage of non-wood plant fibers, as rice straws, corn stalks, cotton stalks, and bagasse would play a chief role in increasing papermaking raw materials. Using of non-wood plant fibers in the paper industry associated with some problems, including collection, transportation, storage and handling, washing, bleaching, papermaking, chemical recovery, supply of raw material and the properties of finished paper. Recently, a high-tech innovation in all the fields of papermaking has made non-wood more reasonable with wood as a raw material for papermaking. Although till now, use of non-wood fibers for pulp and paper manufacture was focused in countries with limited wood supply, it is now showing a growing effort even in countries with acceptable wood source due to environmental concerns. Consequently, the future of non-wood plant fibers as pulping and papermaking raw material looks bright.

The objective of this investigation is to analyze and model tensile index. Two approaches are used, one based on training and validation data, while the other novel approach tests models using all possible combinations of data points. This approach is focused on small data sets which have here been obtained from nineteen pulp samples at different refining conditions in a full-scale TMP production line with a CD-76 refiner as a primary stage. From each pulp sample twenty handsheet strips for tensile index measurements were performed. Initially, specific energy and the external variables (dilution water feed rates and plate gaps) are used as predictors in a modeling approach based on an adjusted R2{R^{2}} approach. Thereafter, the resulting models are compared with a combination of specific energy and internal variables (primarily consistencies) obtained from temperature measurements inside the refining zones using a soft sensor concept. It is found that specific energy and internal variables as predictors outperform the external variables when estimating tensile index.

The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress Py{P_{y}} and shear yield stress τy{\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of τy/Py{\tau _{y}}/{P_{y}} were also examined and the variation of τy/Py{\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

A composite filler was developed by pre-flocculation of fiber fines and precipitated calcium carbonate (PCC) particles with flocculants such as cationic polyacrylamide (cPAM) and bentonite. The composite filler was compared with a conventional loading method in terms of physical properties of handsheet and filler retention. The handsheets using the composite filler showed higher strength properties than that using a conventional loading at a similar paper ash content level, implying that paper ash content can be increased maintaining same level of paper strength. Optical properties such as opacity and brightness of the paper with the composite were quite similar with the paper with the conventional loading. Filler retention of the composite filler was slightly higher than that of the conventional loading even though retention aids were not used for the composite filler. Paper formation of the composite filler was better than the case of the conventional loading. However, the sheet with the composite filler showed lower bulk than that with the conventional loading. Conclusively, the composite filler technology by pre-flocculation of fines and filler has a potential to be utilized to produce a high loaded paper.

Surfactant residues in foam forming are related to the circulation of surfactant in the foaming process, but they may also affect the properties of the foam-formed product. In this work, residues of an anionic surfactant, sodium dodecyl sulphate (SDS), in foam-formed products were studied. Two different methods were applied for the determination of SDS: ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) and solvent extraction spectrophotometry. The dry matter content of the sample before the drying step has a significant effect on the SDS residue. Another factor that has a significant effect on the SDS residues is the amount of precipitated dodecyl sulphate (DS). It was found that SDS does not degrade in the drying phase and will remain in the salt form in the final product. SDS residue decreased when the temperature of the fibre suspension was increased. Theoretical values for SDS residues were estimated from the original surfactant concentration and the amount of water remaining in the product before the drying phase. When all the surfactant was in soluble form, measured SDS residues were close to the theoretical values, which indicates that SDS was not permanently adsorbed onto softwood cellulose fibres.

Today, the paper industry is faced with a global deficiency of raw wood materials, so alternative sources of virgin cellulose fibres are playing an important role in paper production. Agricultural countries produce large quantities of crop farming by-products such as straw, which is an interesting alternative raw material for cellulose fibres. Straw is used in many industries because of its numerous advantages: animal food industry, biofuel industry, construction industry and as artistic material. The potential use of straw production residues is of great importance in paper and printing industry. The focus of this research is on triticale straw, which was used as a non-wood fibre source for paper production. Namely, triticale straw was converted into semi-chemical pulp and was combined with recycled wood pulp in order to produce alternative laboratory papers. The usability of this kind of laboratory papers in printing industry was analysed based on line reproduction quality. This research evaluated and analysed line reproduction quality based on four line attributes: width, blurriness and raggedness. The results of this research proved that triticale pulp in laboratory papers has equal influence on line printing quality as the recycled wood pulp.

In this study, CaCO 3 nanoparticle/pulp fiber composites were prepared by formation of ultrafine bubbles of CO 2 gas in aqueous Ca(OH) 2 solution containing beaten or unbeaten pulp fibers. Scanning electron microscopy images of the fiber/CaCO 3 composites showed that primary CaCO 3 nanoparticles with average diameters of 50–80 nm densely formed on the pulp fiber surfaces. The average sizes and morphologies of the precipitated CaCO 3 nanoparticles can be controlled by controlling the CO 2 flow rate into the pulp slurry. From dynamic drainage analysis of the CaCO 3 /pulp slurries with high shear force, retention of the CaCO 3 nanoparticles on the pulp fiber mats was ∼10 % higher for the slurry formed by the ultrafine bubble method than for that formed by mixing precipitated CaCO 3 and pulp fiber. Therefore, precipitated CaCO 3 nanoparticles stably formed on the pulp fiber surfaces in the slurry by the ultrafine bubble method. Compared with reference handsheets, handsheets prepared with the CaCO 3 nanoparticle/pulp fiber composites had higher CaCO 3 contents and had consequently higher specific surface areas and surface smoothness values. In contrast, the tensile strength and elongation at break decreased because the sheet density decreased with increasing CaCO 3 content in the handsheets.

Anatomical, morphological and chemical characteristics of kaun straw were examined to assess their suitability for paper production and the properties were compared with wheat straw and rice straw. It was found that the fiber length of kaun straw is slightly shorter than that of wheat straw and longer than that of rice straw. It has wider fiber wall thickness than that of wheat straw and rice straw. It had acceptable derived values, especially slenderness ratio, which was lower than that of wheat straw and rice straw, and higher runkel ratio and lower flexibility coefficient. Chemical analysis of kaun straw revealed satisfactory levels of α-cellulose content (35.9 %) and klason lignin content (19.3 %). The ash content in kaun straw (7.32 %) showed lower value than that of wheat straw and rice straw. In optimum cooing conditions, kaun straw produced pulp yield of 30.0 % and 41.7 % with kappa number 15.1 and 22.5 in soda-AQ and formic acid pulping processes, respectively, the values of which were lower than that of wheat straw and rice straw.

Using disposable screen-printed electrodes is a convenient way of monitoring environmental pollution, production process control etc. Usually, commercially available screen-printed electrodes are used, but more and more studies are being carried out in the field of printing electrodes on thinner, low-cost and versatile substrates, including paper. In the present research, the comparison of screen-printed electrodes printed on different paper-based materials is presented. Two unique and innovative invasive plant-based papers made from (1) Japanese knotweed, (2) Canadian and Giant goldenrod and (3) commercially available cardboard were used as a printing material for the electrodes. The selected paper substrates were characterized, and screen-printed electrodes were printed. The influence of substrates’ properties and pre- or post-treatment of the screen-printed electrodes on the electrochemical behaviour is thoroughly analyzed. The results indicate that the printing substrate (roughness) had the most significant influence on the cyclic voltammetry response. Comparing pre- and post-treatment of screen-printed electrodes, it was shown that grinding influenced the electrochemical activity significantly, while corona discharge does not have as significant influence. Besides, it was shown that the invasive plant-based papers are viable alternatives to commercially available papers and can be used as low-cost and eco-friendly alternatives for disposable screen-printed electrodes.