Understanding cellulose hornification provides crucial information regarding drying of pulp, paper, and other cellulosic materials as well as recycling them. By measuring drainage, fiber width, and water retention value of hardwood and softwood pulps before and after sheet forming and after different drying procedures at different achieved levels of solids, the hornification was evaluated. The water retention value was also measured for the pulps when dried from acetone to observe what happens when hydrogen bonds are not available in the liquid phase. The drainage and fiber width decreased with increasing solids content; the fibers became increasingly stiff with increased water removal. Water retention measurements indicated that hornification is a stepwise process with large drops in fiber flexibility as soon as the fibers are being processed and later after a certain amount of water has been removed. In sum, the fibers must achieve a certain solids content to show hornification, and hydrogen bonds in water draw the cellulose surfaces together to create hornification. The mechanism of hornification is believed to be driven by hydrogen bonds and related to the distance between cellulose chains inside the fiber wall. Other types of bonds are probably also present and help with the irreversibility of hornification.

Dewatering and air flow in high vacuum suction boxes was examined. The work was mainly numerical and was based on, and compared with, previously published experimental results of vacuum dewatering from laboratory equipment and from a pilot paper machine. A previously published numerical model for wet pressing is used as the basis for this work. The aims of this study were to find new fitting parameters that allows the previous model to be used for vacuum dewatering instead of pressing, and to examine two extensions to the original model. The results indicate that the new vacuum dewatering model for moisture can predict the dewatering behavior for several different experimental data series both from laboratory equipment and a pilot paper machine using the same set of fitting parameters. Two different numerical models for air flow through the paper sheet, during vacuum dewatering, were developed based on postulating that the decrease in moisture permeability is accompanied by a simultaneous increase in air permeability. The models for air flow can also be fitted to experimental data and predict the magnitudes of air flow during vacuum dewatering. The data sets for air flow exhibit a certain degree of operator dependence though, so that one set of fitting parameters is not enough for obtaining good agreement with all data sets.

The addition of nano-and micro-fibrillated cellulose to conventional softwood Kraft pulps can enhance the product performance by increasing the strength properties and enabling the use of less raw material for a given product performance. However, dewatering is a major problem when implementing these materials to conventional paper grades because of their high water retention capacity. This study investigated how vacuum dewatering is affected by different types of additives. The hypothesis was that different types of pulp additions behave differently during a process like vacuum suction, even when the different additions have the same water retention value. One reference pulp and three additives were used in a laboratory-scaled experimental study of high vacuum suction box dewatering. The results suggested that there was a linear relationship between the water retention value and how much water that could be removed with vacuum dewatering. However, the linear relationship was dependent upon the pulp type and the additives. Additions of micro-fibrillated cellulose and dialcohol cellulose to the stock led to dewatering behaviors that suggested their addition in existing full-scale production plants can be accomplished without a major redesign of the wire or high vacuum section.

This investigation used numerical models to describe forming section sheet dewatering at the high vacuum suction boxes. Three different fabric structures were examined with numerical models for single-phase flow of air and for two-phase flow of air and water. This was done to evaluate how forming fabric structure influences sheet dewatering. The numerical models were compared with an experimental study of the same fabrics investigated on a laboratory suction box. The small differences in dewatering rate in the experimental study could be simulated with the models, which confirmed the validity of the models. This implies that these numerical models can be used to describe new fabrics and how they will respond in the papermaking process.

An innovative creping simulator for tissue has been developed to meet the requirements set by both industrial needs, such as speed and process step duration, and research ambitions, such as flexibility for modifications and efficient operation. Some of these factors can be difficult to achieve with the previously introduced simulators. Lower speeds and much longer process step times can jeopardize results when, for instance, the drying time of chemicals is longer and the speed of creping is slower than in a tissue mill. The newly developed simulator has been used to investigate the effects of paper grammage, creping angle, temperature of dryer, speed and the horizontal force experienced during tissue creping. Results show good agreement with results of industrial-scale tissue production, with the exception of shrinkage which was greater. It was observed that the grammage influences the final thickness and the shrinkage of creped sheets, and that creping speed affects the creping frequency, thickness and shrinkage. The temperature of the surface of a sled mimicking the Yankee cylinder was shown to influence creping frequency and thickness. The horizontal friction force during creping appears to increase if drying temperature is lowered.

Forming fabrics for paper manufacturing are designed with great care to enhance both process and products and are accountable for a lot of the performance of paper machines in the forming section, both with regards to energy and quality aspects. Different approaches to the design of the weave pattern and the choice of yarn materials and diameters have given the market different fabric structures. Fabric parameters that have been shown to cause differences in dewatering are caliper, void volume and permeability. To understand how the structure of the forming fabrics affects sheet dewatering selected fabrics have been tested experimentally, with dewatering equipment that simulates vacuum dewatering.

Dryness of the paper sheet was determined after dewatering and the air volume sucked through sheet and fabric was calculated. The fabrics that were chosen had similar values for all the known parameters previously shown to affect dewatering but had different structures that are defined by the open area (%) in the paper side and the wear side. Tests were performed with three fabric structures and 80 g/m2 softwood sheets. The sheets were made of both unbeaten and highly beaten pulp, and two vacuum levels were used during trials.

The results show that the fabric structure influences the sheet dewatering rate even if the caliper, void volume and permeability are the same. The air volume sucked through the structure of sheet and wire during the dewatering increased linearly with dwell time indicating that a constant air volume was reached. No significant differences were observed between the different fabrics in terms of the air volume at steady state. The conclusions are that the structure of forming fabrics affects the dewatering rate at certain conditions even with constant air volume and outgoing dryness. This is believed to be connected to (i) the fibers’ penetration of the fabric’s surface during the dewatering process or to (ii) the different resistances to in-plane and thickness- direction flow of the fabrics or to a combination of (i) and (ii). Studies of surface topography are used to explain the phenomenon and numerical simulations will be made in a later study to further evaluate this. 

Increased energy efficiency is a major concern for all companies today. Not only does the cost efficiency follow energy efficiency but also environmental and sustainability aspects motivate more energy efficient production lines. A study has been made on a pilot paper machine with the purpose to show the magnitude and time of rewetting after high vacuum suction box dewatering. The grammages used in this study were 20 and 100 g/m2 to cover both tissue and printing paper grades. Machine speed was varied from 400 to 1600 m/min and the maximum pressure drop in the suction box was 32 kPa. The pulp used was unbeaten, chemical, fully bleached softwood from Sweden. Rewetting is observed when the dewatering in the suction box is sufficiently high. No rewetting takes place when the dewatering in the suction box is limited due to insufficient pressure drop and dwell time. The time for the rewetting is in the range of 10-50 ms and in this study the maximum rewetting observed is 180 g/m2, or 6.1% decrease in dryness. The mechanisms behind the phenomenon are believed to be capillary forces caused by sufficiently low sheet moisture and expansion of the network. This study shows that rewetting is so fast that it would be difficult to prevent it without changing major machine parameters.

Tissue production is largely dependent on the creping process as creping influences the paper properties and thus the quality of the end product and the runnability of the tissue machine. The process is very complex and includes numerous variables affecting the adhesion, and ultimately the creping of the tissue paper. To perform experiments on a full scale machine, or even a pilot machine, is very costly, therefore a laboratory scale creping device is demanded, able to replicate conditions encountered on a tissue machine. In this paper new laboratory testing equipment is developed, whereby the adhesion between paper and metal surfaces (when scraping off the paper with configurations similar to the industrial process) can be studied. A new method to adhere paper to metal, used in the new laboratory creping equipment, is also developed. To evaluate the equipment, different creping angles were tested. The scraping tests show a trend in decreasing creping force for an increasing creping angle.

Creasing coated carton board or folding coated magazine paper, result in large strains in the surface layer of the paper product and might result in surface cracks, which decrease the quality of the products. A better understanding of the mechanical properties of coated layers increases the knowledge needed to reduce crack formation in coated fiberbased materials.The crack area on a coated board was measured after creasing and folding and the crack area on a coated copy paper was measured after folding. A clay pigment and a Ground Calcium Carbonate (GCC) pigment were used. The binder was either an S/B latex or an S/B latex combined with starch.