Volume 29, Issue 2

The CrillEye is a technique for qualitatively assessing loose slender and fibrillar particles created during pulping. It has also been demonstrated that the crill measurement technique can easily be used to measure the degree of fibrillation of mechanical pulp based nano-ligno-cellulose (NLC). The measurement technique is based on an optical response of a suspension at two wavelengths of light; UV and IR. The UV light contains information on both fibres and crill, while IR only contains information on fibres. The resolution on the CrillEye module is based on optical response of the pulp and on an analogue signal analysis making it concentration independent. Characterization of particlesize distribution of nano-ligno-cellulose is both important and challenging. The objective of the work presented in this paper was to study the crill values of TMP and CTMP based nano-ligno-celluloses as a function of homogenization time. Results showed that the crill value of both TMP-NLC and CTMP-NLC correlated fairly well with the homogenization time.

The objective of this work was to develop a log loading simulator of the wood room in pulp and paper industry. In the first stage the log loading process is modelled. Then the criteria for evaluating the effects of log loading on the wood room performance are defined. The motivation for the research is that log loading can be identified as playing a central role if the production and cost-effectiveness of the wood room is to be increased. The lack of reliable process measurements and changes in raw material quality, which are not measured on-line, make the data-based modelling of an industrial log loading process difficult. For these reasons, the research was performed via mathematical modelling of the process. The simulated results confirm that the same production can be obtained in many ways, but there can be differences in costs. Especially too high speed of the infeed conveyor in relation to capacity leads to several drawbacks, which typically result in increased wood loss and decreased chip quality. For this reason it is important to consider all aspects of log loading for the best performance. The results give insight into the log loading process and may help to improve the log loading process.

The purpose of this paper is to analyse the log loading process of wood room, which is typically the first processing unit in pulp and paper mills. The aim is to improve the log loading process to obtain production with a constant log flow of well de-iced logs to the debarking drum. This way it is possible to reduce costs and enhance product quality. The research was carried out utilising a log loading simulator. The parameters of the simulation model were selected on the basis of process observations on a mill. The results indicate that it is essential to adjust the process and equipment parameters, raw material properties and truck loader operation together in order to reach the target capacity with minimum costs. Especially the speed of the infeed conveyor affects all performance criteria and should be selected carefully. In addition, wood yard logistics and raw material properties have a remarkable effect on the wood room performance. The results can be utilised in mills to allow the upper level control perform in a planned way so that small wood loss and good product quality can be obtained.

The fact that industrial pulps have a lower strength than their corresponding laboratory pulps is an unsolved problem affecting in various ways the potential fibre utilisation in different mills. The loss of pulp strength has to a great extent been attributed to changes at the fibre level. In order to clarify in what way changes in fibre properties contribute to the strength losses, cooking experiments were conducted using a laboratory batch digester in which mechanical forces may be introduced. Fibre properties, i.e. fibre structure and fibre strength, of laboratory-made pulps were compared with those of an industrial pulp. It was concluded that two essentially different mechanisms may be identified; one related to the transverse fibre shape, the other to fibre damage. The latter is manifested as lower rewetted zero-span strength which reduces tear resistance and tensile strength of the pulp. The former is a collapse of the fibre, reducing the lumen area and resulting in a pulp with lower water-retaining capacity, given sheets of lower density and a pulp that has to be beaten to a higher degree to reach the desired bonding and the desired tensile strength.

The effect of screen cylinder geometry, pulp type, and rotor speed on screen capacity was investigated. Five screen cylinders with different slot geometries were tested using different ratios of softwood/hardwood kraft pulp mixtures and different reject ratios. The relationship between the rotor speed and screen slot velocity at the verge of plugging, taken here as a measure of "capacity", was found to be remarkably linear. Feed consistency and fibre length were found to have significant influences on capacity

Measuring contact angles on single fibers enables the separation of structural factors from surface chemistry factors. Current Drop-on-Fiber (DOF) contact angle measurement methods for natural fibers generally, and for pulp/paper fibers specifically, present a number of challenges. These are manipulation and mounting of the microscale fibers, straightening natural fibers to produce repeatable axisymmetric droplet conformation, measuring the droplet volume excluding the fiber volume and also human errors due to manually performed tasks. This paper presents a novel method to measure contact angles in DOF systems and overcome the above mentioned challenges using microrobots. The proposed microrobotic platform is capable of handling natural and synthetic fibrous materials in microscale, and dispensing probe liquid droplets down to 12 nl. It measures contact angle values using computer vision and a droplet-profiledetection algorithm. It reports the contact angle values as a function of volume of the droplet. The paper validates the capabilities of the proposed platform by applying three commonly used probe liquids: deionized water, ethylene glycol and diiodomethane for measuring contact angles on glass and pulp fibers. Finally, the results are compared with a picoliter contact angle measurement approach.

A silicon wafer coated with cellulose was prepared to measure the deposition of stickies on fibers and polyvinyl acetate (PVAc) suspension is prepared as the model compound. In addition, two methods, shear force and aeration, were used to induce the agglomeration and deposition of microstickies. The model surface was characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle. The results from new methods were also compared with old methods of High-density polyethylene (HDPE) deposition and INGEDE (International Association of the Deinking Industry) Method 4. Although these methods have been used to predict the deposition of stickies onto the drying felt or other equipment, the deposition of stickies onto fibers can differ significantly due to the hydrophilic nature of the fibers. This is the first measurement method that could help to predict the deposition of stickies onto paper products, which has been shown to cause detrimental effects.

The increase of filler content in paper without significantly sacrificing the paper mechanical resistances is of high interest for papermakers. In this work, precipitated calcium carbonate (PCC) modified with silica was used as filler for papermaking. Handsheets based on a eucalyptus kraft pulp furnish with different amounts of the modified filler, ranging from 16 to 40%, were produced. For similar levels of filler content it was found that the strength properties of the handsheets produced with the modified PCC were always significantly better than those obtained with the unmodified PCC. In particular, for handsheets with a filler content of 30%, the tensile index and the Scott bond internal resistance improved by ca. 20% and 39%, respectively. Some decrease of the light scattering and opacity values was noted when using the modified PCC, but the brightness was roughly the same, for each filler level evaluated. The enhanced fibre-tofiller bonding can be due to the hydrogen bonding between the cellulosic fibres and the hydroxyl groups of the silica film coating the calcium carbonate crystals, during the sheet formation. The present results with the new modified PCC provide a possibility to increase the filler amount in the papermaking industry.

A new way as shown in the following scheme was developed to fabricate paper with high strength and grease resistance. Filter paper was impregnated in NaOH/urea aqueous solution pre-cooled to -12°C for 30 s and incubated at a fixed temperature for a period of time. Swelling and dissolution of cellulose fibers facilitated more compact structure of paper and higher strength. Various influencing factors were investigated in an attempt to improve grease resistance of the paper. The results demonstrated that the paper after treatment showed a 100% grease barrier property within 24 h, and a double increase in both tensile strength and tear strength compared with the untreated paper. Moreover, burst strength was enhanced more than three times and the stretch was improved simultaneously when the paper was performed with NaOH/urea (7%:12% weight ratio) at -12°C for 120 min. In addition, the wet tensile strength of the treated paper was close to the dry tensile strength of the untreated paper.

Nanocellulose containing materials, such as micro-fibrillated cellulose (MFC) and nanofibrillated cellulose (NFC), are potential additives which could improve strength properties of coated paper and board surfaces and thus substitute natural and synthetic cobinders, such as carboxymethyl cellulose (CMC) and polyacrylic thickeners, in pigmented coating formulations. The aim of this study is to evaluate whether MFC/NFC can be used in coating colours as sole co-binder. In this investigation, the change of rheological and dewatering behaviour of coating colours, having a single blend of pigments (ground calcium carbonate and kaolin clay) together with a latex emulsion binder, is studied when CMC is used as sole co-binder and during its partial and finally total replacement with MFC/NFC. The findings suggest that even though all coatings show viscoelasticity, MFC/NFC is seen to relate to the gel-like nature of the nanoparticles in the coating colour whereas the viscoelastic behaviour in the case of CMC is induced by differential flocculation amongst the pigment and latex binder. The flocculation mechanism is predicted to be necessary in order to provide the link between water retention and elastic structure recovery where anti-sagging is a prerequisite, such as in the coating of rough substrates, e.g. for board and packaging.

Superhydrophobic nanoparticle coating was created on the surface of board using liquid flame spray (LFS). The LFS coating was carried out continuously in ambient conditions without any additional hydrophobization steps. The contact angle of water (CAW) of ZrO 2 , Al 2 O 3 and TiO 2 coating was adjusted reversibly from >150° down to ~10−20° using different stimulation methods. From industrial point of view, the controlled surface wetting has been in focus for a long time because it defines the liquid-solid contact area, and furthermore can enhance the mechanical and chemical bonding on the interface between the liquid and the solid. The used stimulation methods included batch-type methods: artificial daylight illumination and heat treatment and roll-to-roll methods: corona, argon plasma, IR (infra red)- and UV (ultra violet)-treatments. On the contrary to batch-type methods, the adjustment and switching of wetting was done only in seconds or fraction of seconds using roll-to-roll stimulation methods. This is significant in the converting processes of board since they are usually continuous, high volume operations. In addition, the creation of microfluidic patterns on the surface of TiO 2 coated board using simple photomasking and surface stimulation was demonstrated. This provides new advantages and possibilities, especially in the field of intelligent printing. Limited durability and poor repellency against low surface tension liquids are presently the main limitations of LFS coatings.

Print mottle is observed as an unevenness of printed tone across an image area. There are many causes of mottle on typical print media, i.e. printing and writing papers, packaging and board, as well as foils and polymer surfaces amongst others, in both applications of traditional printing techniques, such as offset and flexography as well as digital methods, including inkjet and electrophotography. Causes range from inhomogeneous surface chemistry and absorption characteristics to instability factors on the printing press. Since the phenomenon is both physical and aesthetical, providing an evaluation for comparison purposes is challenging, frequently requiring panels of observers to provide a visual ranking. A new evaluation method is proposed using wavelet denoising and grey level gradient analysis of the print image. The index of print mottle is built on the bases of the average of grey level gradient and its distribution standard deviation. The method was tested for print mottle evaluation on paper in specific situations under different image basis functions and decomposition level. The results show that the method is in good agreement with visual assessment, and is also less time consuming both in the process and in statistical analysis, with correlation coefficient (r 2 ) of at least 0.79 and as high as 0.88 with every function basis (level 2 or 3).

By investigating how properties of a finished paper product are related to different process variables as well as pulp characteristics throughout the fiber line, the understanding of the process will increase. In this paper we investigate the correlation between some key paper quality parameters and five tunable process variables, along the entire fiber production line. A full two-level factorial experiment has been conducted, where five factors were varied. The factor settings were based on a laboratory replica of a specific kraft mill’s paper product. The mill replicate was then used as a center point in the factorial design and appropriate levels of the factors were set based on these center points. Several experimental runs could be simulated via a Monte Carlo approach making it possible to get a reliable estimate of the significance of each factor effect. Analysis of the results shows that there are interaction effects present between variables, and that these interaction effects can be utilized to achieve similar paper properties using different variable settings.

The directional emittance of dry and moist paper and board samples was measured in two wavelength ranges; the mid-wavelength infrared (MWIR) range and the long-wavelength infrared (LWIR) range. The influence of pulp type, pulp drying, pulp refining, fibre orientation, additives, coating, and observation angle on the emittance of dry paper was examined. The influence of sample moisture and observation angle on the emittance of moist samples was also investigated. The emittance in the LWIR range was higher than the MWIR emittance. The emittance varied with pulp type, especially for TMP, which had a significantly lower emittance compared to the samples made of chemical pulp. The impact of different properties, such as pulp type, refining or coating, was much smaller in the LWIR range than in the MWIR range. Observation angle was found to significantly impact the emittance at angles larger than 60° from the normal direction in the MWIR range, and angles larger than 70° in the LWIR range. The emittance increased with increasing moisture ratio. This increase was most pronounced at low absolute moisture ratios, where an addition of an already small amount of water could impart a large change in emittance. It was found that the emittance and sample moisture could be correlated well using a linear combination of the emittance of dry paper and pure water.

The objective was to evaluate the effects on paper properties when replacing a minor share of wood fibre by synthetic fibre. The aim was to increase tear strength and stretch while minimizing the loss of tensile strength in paper consisting of mechanical pulp. Tested synthetic fibres included PLA and viscose fibres mixed with mechanical or chemi-mechanical pulp. Even at relatively low proportions, the synthetic fibres contributed to a significant increase of tear strength in the wood fibre based papers. With the highest tested proportion (20%) the increase of tear index in PGW based stock was 243% with PLA and 177% with viscose fibre. However, a simultaneous decrease in tensile strength and tensile stiffness was observed. The stretch at break remained unchanged. Thickness reduction of the synthetic fibres resulted in an increase of tear strength. The effect is due to the high fibre length of synthetic fibres, producing mechanically well entangled networks, coupled with the high enough strength of the synthetic fibres.

So far, chemical pulp fibres have been utilized as conventional stock materials for nanocellulose production. The main aim of this work is to use stock materials from mechanical or chemi-thermomechanical pulping process to produce lignin containing nanofibres, which are referred to as nano-ligno-cellulose (NLC) in this study. The present study shows the influence on handsheets of chemi-thermomechanical pulp (CTMP) fibres blended with NLC. For comparison reasons, nanocellulose (NC) from bleached kraft pulp (BKP) was produced in a similar approach as NLC. Both the NLC and the NC were blended with their respective pulp fibres and their corresponding handsheets properties were evaluated with respect to sheet density. It was found that the handsheets of pulp fibres blended with NLC/NC improved the mechanical properties of handsheets with only a slight effect in relation to the sheet density. Improvements in strength properties of handsheets such as z-strength, tensile index, tear index, burst index, Emodulus, strain at break, tensile stiffness, air resistance were observed.

Extensibility is an important property for papers undergoing large deformations in converting or end use application (e.g. industrial bags). Industrially, high extensibility is created by compacting the moist paper web in machine direction (MD) using an extensible unit such as the Clupak or Expanda methods. In this study, a method was developed to produce extensible paper on the laboratory scale. The Clupak unit was simulated using a purpose-built MD compaction apparatus. A paper sheet is placed between two stretched rubbers which are recoiled under perpendicular pressure to create sufficient friction between paper and rubber. The laboratory method for producing extensible paper sufficiently corresponds to the industrial process, i.e. strain increased while tensile stiffness index and tensile index decreased. Increased solids content during rubber recoiling enhanced the sigmoidal shape of the specific stress versus strain curves whereas tensile index remained unchanged. The reproducibility of the method is at a good level and thus the developed method offers a feasible way to study the production of extensible paper on the laboratory scale.

This is the first in a series of papers presenting the development of a comprehensive multiscale model with focus on fiber energy efficiency in thermo mechanical pulp processes. The fiber energy efficiency is related to the defibration and fibrillation work obtained when fibers and fiber bundles interact with the refining bars. The fiber energy efficiency differs from the total refining energy efficiency which includes the thermodynamical work as well. Extracting defibration and fibrillation work along the radius in the refining zone gives information valuable for fiber development studies.Models for this process must handle physical variables as well as machine specific parameters at different scales. To span the material and energy balances, spatial measurements from the refining zone must be available. In this paper, measurements of temperature profile and plate gaps from a full-scale CD-refiner are considered as model inputs together with a number of process variables. This enables the distributed consistency in the refining zone as well as the split of the total work between the flat zone and the CD-zone to be derived. As the temperature profile and the plate gap are available in the flat zone and the CD-zone at different process conditions it is also shown that the distributed pulp dynamic viscosity can be obtained. This is normally unknown in refining processes but certainly useful for all fluid dynamic models describing the bar-to-fiber interactions. Finally, it is shown that the inclusion of the machine parameters will be vital to get good estimates of the refining conditions and especially the split between the thermodynamical work and the defibration/fibrillation work.

In this paper it is shown that the defibration and fibrillation work in thermo mechanical pulp refiners can differ significantly dependent on the process conditions. This has a direct impact on the distributed force in the refining zones obtained when the bars hit the fibers or fiber bundles. The distributed force, which is defined as a vector along the surface of the refining segments, is estimated using a model where the total work can be split into reversible and irreversible work. Besides traditional refiner variables such as motor load, dilution water added and inlet- and casing pressures, measurements of temperature profiles in the refining zone and plate gaps from a fullscale CD-refiner are available as inputs. Three data sets are analyzed and it is shown that the shape of the temperature profile and the force distribution vary significantly. This means that the fiber distribution in the refining zone varies as well which affects the final development of the pulp properties. The refining segment pattern and taper play an important role when estimating the force distribution and it is stated that the force distribution close to the contraction part of the flat zone as well as the outer part of the conical section are larger than in other positions. Therefore, specific energy which can be seen as the integral of the total energy distribution along the refining segments cannot be used when describing the variations in the distributed forces.

To evaluate the causes behind the formation of colour in mill systems, the effect of different process waters on the optical properties of hydrogenperoxide bleached Norway spruce mechanical pulp during storage was studied. The influence of process water type, temperature, time, pulp consistency and pH was evaluated over the visible range of wavelengths. The darkening was more pronounced when pulp was stored in process waters compared to in distilled water. Increased temperature and prolonged storage times increased the darkening as expected, whereas a higher storage consistency gave less darkening than a lower storage consistency (15% compared to 5%). The pH value that gave the lowest brightness reduction and a minimum in Δk 460 was found to be 5.5-6.0. Storage of pulp in white water from the paper machine resulted in a broad shoulder in the k spectra indicating colour formation related to the particles in this water. Part of this shoulder in absorption spectra was related to added dyes, but the increase in absorption with time is likely to be caused by some other colour formation. The colour measured as a*, b* showed that the storage changed the colour of the pulp towards red and yellow, and initially more towards red.

The discolouration of hydrogen-peroxide bleached Norway spruce mechanical pulp during storage in mill systems was studied and the contributions of process water, iron and dyes were evaluated over the visible spectrum. Washing of the pulp made it less sensitive to storage, possibly due to the removal of extractives, lignin-like substances, iron and pulp fines. Storage in white water gave extensive discolouration with a shoulder in the absorption spectrum at around 550- 650 nm. Most of the colour was associated with pulp fines or filler but some colour was also found in smaller fractions and in the water phase. The addition of ferric ions increased the light absorption coefficient during storage, initially at short wavelengths and then over the whole spectrum, but could not explain the increased absorption at 550-650 nm and could not be the only cause of the darkening in the mill system. A cationic basic violet dye gave a shoulder in the absorption spectrum similar to that in the mill system, but the absorption in this area did not increase during storage. Model calculations indicate that ferric ions together with violet and red dyes could explain a major part, but not all, of the colour observed in the mill system after storage. The darkening not accounted for at longer wavelengths and around 550-650 nm is suggested to be related to fines and fillers including dissolved and colloidal substances associated with these particles.