Volume 33, Issue 4

The use of infrared radiation for heating the web in the through air drying process was investigated in lab scale. The hypothesis was that infrared radiation should be a more efficient method to transfer drying energy to the wet web compared to hot air, but that a certain air flow is still required as a transport medium for the evaporated water. A trial program comprising handsheets made of two types of bleached chemical pulps, five grammages (15, 22, 30 and 60 g/m²), and dried with five radiator power levels was performed on a lab scale through air drying equipment. Drying times of the samples were determined from temperature data recorded with an infrared camera. The use of infrared radiation shortened drying times, especially for low grammage samples. The shortening of the drying time ranged between 10 and 45 %. The most substantial shortenings were obtained for the lowest grammages and the highest radiator power level. However, the increase of power did not linearly shorten drying time. After an initial shortening at the lowest power level, the positive effect of the IR heating decreased as the power was further increased.

In end-use, containerboard is subjected to a variety of loading histories, such as seconds of loading/unloading, hours of vibration, days of creep load. The fundamental question is whether the commonly measured static strength represents “strength” under these conditions. Another question is, since those time-dependent failures are notoriously variable, how to describe the probabilistic aspect. This study concerns the characterisation of these different facets of “strength”. In our earlier work, we have investigated the theoretical framework for time-dependent, probabilistic failures, and identified three material parameters: (1) characteristic strength, Sc{S_{c}}, representing short-term strength, (2) brittleness/durability parameter, ρ , and (3) reliability parameter, β . We have also developed a new method that allows us to determine all these parameters much faster than typical creep tests. Using the new method, we have started investigating effects of basic papermaking variables on the new material parameters. Among the samples tested, the parameter ρ varied from 20 to 50, and β from 0.5 to 1.0. This suggests that, even within the current papermaking practice, there is a wide operating window to tune these new material parameters. The future work is, therefore, to find specific manufacturing variables that can systematically change these new material parameters.

Filler pre-flocculation has been extensively studied in the past to increase filler content while maintaining the physical strength properties of paper. However, optical properties of paper could be negatively affected due to the filler pre-flocculation. In this work, two kinds of precipitated calcium carbonate (PCC) fillers with different particle sizes, namely PCC1 (4.2 μm) and PCC2 (7.7 μm), were used to investigate the effects of filler pre-flocculation on the strength and optical properties of paper. Results showed that pre-flocculated fillers with smaller particle size (PCC1) could improve the tensile strength of handsheets more effectively, since the tensile index was increased by 22.9 %. Meanwhile, for a given floc size, the handsheets with PCC1 flocs exhibited a better light scattering ability comparing to the ones filled with PCC2 flocs. The improved light scattering ability of handsheets filled with 24 μm PCC1 flocs compared to 24 μm flocs produced with PCC2 can be attributed to the complex micro void structure of flocs. This finding can be used as a guidance for the selection of filler particle size when using filler pre-flocculation to optimize the mechanical and optical properties of paper.

When studying the properties of cellulose nanofibrils (CNF) enriched fiber products, it is essential to be able to determine the retention and the spatial distribution of the CNF inside the end-product. That is, to determine how much and where the CNF has been attached. As the CNF and cellulose fibers share the same density and chemical composition, labeling of the CNF is required to distinguish them from each other. In this work, we have applied iron and iron-cobalt -labeling. Labeling with iron is more desirable because of the carcinogenic and toxic properties of cobalt chloride. The benefits of our labeling method are the possibility to determine the retention of the labeled nanocellulose using inductively coupled plasma optical emission spectroscopy (ICP-OES), and to define the spatial distribution using X-ray micro-computed tomographic (XμCT). With XμCT we were able to measure fairly large samples (2 cm × 5 cm × 5 cm). Our study found that the retention of iron-labeled CNF was about 95 % and that of iron-cobalt labeled CNF was 84–94 %. Labeling of CNF improves the contrast of X-ray images. Labeled CNF is attached to fiber network also in the inner structures of the sample. Furthermore, when making thick porous structures using cationic starch, there might be agglomerates in the sample that cannot be visually detected by looking the sample.

This paper discusses the usage of thiourea dioxide to modify the residual terminal amino groups of amino acid in laccase. The effect of modified-laccase/glutamate treatment on the microstructure and properties of old newspaper deinked pulp was investigated by means of fourier transform infrared spectroscopy and headspace gas chromatography. Results showed that after the modified-laccase/glutamate treatment, the content of carboxyl groups in pulp increased remarkably by 20.8 %. Microscope images showed the fiber filamentation was more obvious, and fibrils content on the fiber surface increased. The fiber quality analyse indicated that fiber coarseness decreased notably but length and width changed a little. The paper physical analysis showed that the paper strength properties had improved remarkably while whiteness decreased slightly.

The gelatinization of cationic starch during a heating-holding-cooling cycle in a batch cook was monitored by measuring 1 H NMR spin-spin relaxation rates R 2 on-line. The effect of storage time and temperature (8, 20 and 60 °C) on cationic starch retrogradation was also studied. Clear differences were measured between the gelatinization and retrogradation behavior of potato starch and cereal starches (wheat and barley). The potato starch gelatinized completely when cooked at 95 °C at normal pressure, whereas cereal starches gelatinized only partially. Partial gelatinization lead to rapid retrogradation upon cooling. For fully gelatinized starch, the beginning of retrogradation was slower and began at a lower temperature. NaCl and Na 2 SO 4 did not have a significant impact on the gelatinization of wheat starch but did affect retrogradation. The results show that NMR-relaxometry is suitable for following starch gelatinization on-line from a batch cook and that it can be used to determine whether gelatinization is complete. This technique can thus be a useful tool in paper mills for the on-line quality control of starch solutions.

We propose that a testing procedure we call wet-peel significantly augments conventional wet paper testing when comparing wet-strength resin efficacy or the influence wood pulp fiber surface treatments on wet paper strength. A thin layer of wet-strength resin is sandwiched between a pair of thin, wet regenerated cellulose membranes to form a laminate, which is a physical model for fiber-fiber joints in paper. In the wet-peel method, the ninety-degree wet-delamination force gives a direct measure of adhesion in the wet cellulose-cellulose joint. Wet-peel measurements offer: 1) comparisons of wet-strength polymers at the same content of polymer in the laminate joint without the influences of varying fines contents, formation or paper density; 2) measurements of both the wet-strength of cured, dried joints, and the strength of never-dried joints (i. e. analogous to wet-web strength); 3) demonstrations of the influence of fiber surface chemistry modifications including oxidation and the presence of firmly bound polymers; and, 4) the evaluation of more exotic joint structures including layer-by-layer assemblies, microgels and colloidal polyelectrolyte complexes.

To investigate the dispersibility of dried cellulose nanofibers (CNFs), various additions (glycerol, octanol, glycol, and sodium perchlorate) were added to CNFs prior to drying. Glycerol was the only species to show any significant effect on re-dispersibility. The sedimentation was slower, and the transmittance of the solution was comparable to that of its undried counterpart. Increasing the amount of glycerol showed a clear trend with regard to dispersibility. The mechanical properties of films were maintained for samples that were dried and redispersed in the presence of glycerol.

Hydrogen bonding among fiber microfibrils is the primary cause of fiber hornification, wherein NaOH/urea aqueous solution precooled to −13 °C can disassemble inter- and intramolecular hydrogen bonds. Whether hornified fibers treated with this process can significantly improve fiber swelling ability and physical properties of the resulting paper sheets remains a problem. In this investigation, the 6th cycle fiber was pretreated with this procedure, and the water retention value of the fiber before and after treatment and the physical properties of the resulting paper sheets were studied. The results indicate that the lignin decline, complete swelling of flat fiber, filling of cellulose film between the interfiber network, and decreasing crystalline region all contribute to the increase in water retention value. The water retention value of repaired fiber is equivalent to that of virgin pulp, and hornification reverses by 89 %. In addition, the cellulose film filling among the fiber network constructs a similar reinforced concrete structure, which causes the tear, burst, and tensile index of the resulting paper sheets to increase by 145 %, 98 %, and 43 %, respectively.