Art Paper for Large Wood Relief Block Printing – A Paper Development Study

Wood relief block printing was developed in China in the seventh century and is used today for many art printing applications. The presented research project describes the development of an art paper product applicable for large wood relief block printing from laboratory scale to large semi commercial production of art paper for printing image sizes of up to 44-inch (1118 mm) by 96-inch (2400 mm) at outdoor steam roller printing events or smaller indoor printing press applications. The improvement of the paper properties from laboratory development, small laboratory paper machine and semi commercial paper machine run for the production of the final art paper showed an improvement throughout the process development for the optical and mechanical paper properties and exceeded the set values set by the artist using the art paper. The produced art paper with a basis weight of 260 g/m² and a thickness of 171 µm is produced from a mixture of 70% northern bleached hardwood Kraft pulp and 30% northern bleached softwood Kraft pulp. The ISO brightness of the art paper off-white (egg-shell) colour was at 63.2% and the ISO color value for L, a, b. at 90.8, 1.1, and 12.6 respectively. The art papers surface roughness and porosity as a parameter for ink attachment and penetration is for the top side 2179 ml/min and for the bottom side (wire side) 2326 ml/min, whereas porosity was measured at 1668 ml/min. Bending stiffness in machine direction and cross machine direction was measured at 157mN and 70 mN respectively. Burst strength was measured at 2.24 kPA·m²/g.

Evaluation of fines separation from unbleached softwood kraft pulp using microperforated hole screens

The application of a bench scale and an industrial scale pressure screen to separate cellulosic fines from an unbleached softwood kraft pulp containing 5 % (w/w) primary fines was investigated and the results were compared. In the bench scale trials different microperforated screens with hole diameters of 150 µm, 250 µm, 400 µm and 600 µm were used. Based on these results a screen hole diameter of 400 µm was selected for the industrial scale trials. In all cases, a high accept flow rate proved to be the crucial parameter for high removal efficiency of the fines material and a removal efficiency of well above 50 % could be achieved. Further of interest were the limiting factors regarding increased accept flow rates with a focus on the interrelations between pressure difference, slot velocity and reject consistency. As expected, investigation of electric energy demand showed a correlation between removal efficiency and specific energy consumption, which did not exceed 35 kWh/t(od) feed.

Assessment of Q(OP)D(PO) bleachability of softwood kraft pulp

Bleachability is evaluated as how easily a pulp sample is bleached and it depends on the structure of residual lignin and carbohydrates. Also, the bleachability varies depending on the bleaching sequence. ECF light sequences have been improved significantly in the recent years. However, we still don’t fully understand how ECF light bleach plants are optimally run. This work studies the bleachability of softwood kraft pulp in an ECF light bleaching sequence, (OO)Q(OP)D(PO). Three pulp samples with brown stock kappa number 27, 32 and 35 were bleached and studied for residual lignin, hexenuronic acid and carbohydrate content. It was found that in the bleaching stages that are highly delignifying, it is beneficial with a higher kappa number for the delignifying bleachability. However, in the bleaching stages where the objective is brightness increase, the brightness gain bleachability is improved by a lower kappa number. We also intended to determine which of the three samples had the best suited kappa number for this particular bleaching sequence. According to our results, the bleaching was most effective with kappa number around 32. Although an even higher kappa number resulted in higher yield after cooking, it seemed that this bleaching sequence cannot preserve the yield gain.

Mechanical and Hygroscopic Properties of Molded Pulp Products Using Different Wood-Based Cellulose Fibers

With an increasing interest for molded pulp product (MPP) in the industry, it is important to fully understand how the manufacturing process is different from papermaking. One specific way to differentiate the processes is to compare their resulting products. As the paper industry uses several wood fibers with various pulping processes, it is interesting to compare some of these fibers, to further progress our understanding of the MPP process. In this study, six different wood fibers were used (as received) and analyzed to obtain the sample with the lowest moisture uptake and highest tensile properties. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and fiber analysis module (MorFi) observations were performed, as well as moisture uptake measurements after sorption and tensile tests. We observed significant differences between the fibers tested. Kraft fibers (bleached softwood kraft pulp (BSKP), bleached hardwood kraft pulp (BHKP), and unbleached softwood kraft pulp (USKP)) showed smoother surfaces and less non-cellulosic molecules, such as hemicellulose, lignin, and pectin, in the SEM images. Bleached chemi-thermomechanial pulp (BCTMP) and recycled pulps (R-NPM and R-CBB) both showed non-cellulosic molecules and rougher surfaces. These results were confirmed with the FTIR analysis. With kraft fibers, MPP mechanical properties were lower than non-kraft fibers. Resulting moisture uptake is in between the recycled fibers (lowest moisture uptake) and BCTMP (highest moisture uptake). The removal of non-cellulosic molecules reduces the mechanical properties of the resulting MPP. The incorporation of non-wood molecules, as found in recycled fibers, also reduces the mechanical properties, as well as moisture uptake, when compared with BCTMP.

Optimization of Technological Parameters of Straw Fiber-Based Plant Fiber Seedling Pot Raw Materials

Straw fiber seedling pots are a promising substitute for plastic seedling pots. The mixing mode of straw fiber affects the mechanical properties of the raw material membrane of the seedling pot. To explore the processing technology of making the raw material membrane of the seedling pot with two kinds of plant fibers in a layered manner, the optimal combination of the process parameters of the raw material membrane of the seedling pot without additives in the production process was studied experimentally. Response surface methodology (RSM) was used to analyze the parameters (beating degree of unbleached softwood kraft pulp fiber, beating degree of wheat straw fiber, wheat straw fiber quality percentage content, and film grammage) with regard to the dry tensile index and Z-direction tensile index of the seedling pot body. The optimal process parameter combination with a certain dry tensile index and Z-direction tensile index of seedling pot raw material was obtained by using four factors and five levels of a quadratic regression orthogonal rotation center combination design parameter optimization experiment. The optimal technical parameters were optimized as wheat straw fiber quality percentage content 70%, film grammage 70 g/m2, unbleached softwood kraft pulp fiber beating degree 47–48 °SR, and wheat straw fiber beating degree 65–75 °SR. With the optimal conditions, the dry tensile index of the seedling bowl raw material film was between 21 and 22 N·(m·g−1), and the Z-direction tensile index was greater than 2.1 N·(m·g−1). Using wheat straw fibers and unbleached sulfite wood pulp fibers as raw materials for seedling pots, the raw material membrane of the seedling pots was made in a layered manner. The experimental study proved this feasibility. With this mixing process of raw materials, the straw fiber-based plant fiber seedling pot would meet the demands of a crop nursery after adding chemical additives. The research results provide a theoretical basis and technical support for the manufacture of the raw material membrane of the seedling pot body.

Use of fines-enriched chemical pulp to increase CTMP strength

In this study, fines-enriched pulp (FE-pulp)—the fine fraction of highly-refined kraft pulp—was benchmarked against highly-refined kraft pulp (HRK-pulp) as a strength agent in eucalyptus chemithermomechanical pulp (CTMP). Both the FE-pulp and the HRK-pulp were produced from unbleached softwood kraft pulp, and equal amounts of those strength agents were added to the original CTMP, as well as to washed CTMP, where most of the fines had been removed. The effects of the added strength agents were evaluated with laboratory handsheets. The FE-pulp proved to be twice as effective as HRK-pulp. Both HRK-pulp and FE-pulp increased the strength of the CTMP handsheets. The bulk of the handsheets decreased, however, as well as the drainability. The addition of 5% FE-pulp resulted in the same strength increase as an addition of 10% HRK-pulp, as well as the same decrease in bulk and CSF. For the handsheets of washed CTMP, the strengths were not measurable; the CTMP lost the sheet strength when the CTMP-fines content was reduced through washing. The reduced strength properties were compensated for by the addition of chemical pulp fines that proved to be an efficient strength agent. The addition of 5% FE-pulp restored the strength values, and at a higher bulk and higher drainability.

Cellulose dissolution in aqueous NaOH–ZnO: effect of pulp pretreatment at macro and molecular levels

This paper discusses the effect of hydrolytic pretreatments on pulp dissolution in the aqueous NaOH–ZnO solvent system. Eight samples were studied. They consisted of a never-dried softwood kraft pulp that was hydrolyzed under seven different conditions as well as the pulp without hydrolysis as a reference. The dissolution of the pulps was evaluated both at the macro level as well as at the molecular level based on their reactivity with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxo-piperidium (4-AcNH-TEMPO+). The fiber properties (i.e. the extent of fibrillation, amount of fines and fiber width, coarseness, and length) as well as the chemical composition (hemicellulose and cellulose contents) and the viscosity of the pulps was investigated. The results show that hydrolysis at medium consistency (10%) was successful in increasing the solubility of cellulose. Hydrolysis at high consistency (50%), on the other hand, increased the solubility only to some extent. With extended treatment time the fibers formed aggregates and their dissolution became poor. This phenomenon could be overcome by mechanically refining the fibers after the hydrolysis. Moreover, comparison of the viscosity of the pulp over the degree of oxidation revealed that the viscosity needed to decrease below ca. 400 ml/g in order for the outer layers of the fibers to dissolve. Finally, when pulps with similar viscosities where compared against each other, the ones with the higher glucomannan contents formed gels over time. This was true also for the pulp with the lowest viscosity and the highest solubility of the studied samples.

New insights into the autofluorescence properties of cellulose/nanocellulose

This work explored the fluorescence properties of nano/cellulose isolated from bleached softwood kraft pulp by TEMPO oxidation. Fluorescence spectra showed that all samples exhibited a typical emission peak at 574 nm due to the probabilistic formation of unsaturated bonds by glycosidic bonds independent of lignin. Increasing the excitation wavelengths (510–530 nm) caused red shift of fluorescence emission peaks (570–585 nm) with unchanged fluorescence intensity. Conversely, changing acid/alkaline conditions led to an increase of fluorescence intensity with no shifting of fluorescence emission peak. This can be attributed to an increase in the polarity of the solution environment but does not cause interaction of functional groups within the system identified by generalized two-dimensional correlation fluorescence spectroscopy. This study provides new insight in applying nano/cellulose with special luminous characteristics in biomedicine area such as multi-color biological imaging and chemical sensing.