Paper materials are renewable and recyclable and are often used for packaging applications, e.g., as in corrugated fiberboard boxes. From an engineering perspective, paper materials can be used to construct packaging with low weight but with high relative strength. However, compared to other packaging materials, it can be a challenge to design paper-based packaging for distribution chains with demanding conditions. Boxes made from paper can be sensitive to exposure of moisture, duration of load, and dynamic forces. Along the distribution chain, boxes can be exposed to forces that could potentially cause failure before the boxes intended service life is fulfilled. Therefore, it is important to know how to predict the failure distribution for a specific combination of packaging and distribution chain so that materials with the right properties can be chosen for a given purpose and the risk of failures can be minimized. In this project, we have investigated a statistical material model developed by Bernard D. Coleman. It is based on three material parameters that describe the cumulative distribution function (CDF) of a fiber-breaking behavior for an arbitrary load history. The model has been shown to work for fiber network systems subjected to constant load and constant load rate (CLR). Our purpose was to investigate if it is applicable for fiber network systems of higher structural hierarchy and for more complex load histories. To investigate this, we have performed compression tests with CLR on four different types of corrugated fiberboard and determined the material parameters. Afterward, we performed compression tests for a more complex load history. A periodic, triangular-shaped, load curve was chosen for cyclic testing. Finally, we used the material parameters from the CLR tests to determine the CDF for the periodic load cases. We compared the result with an empirical CDF. The CDFs showed to be in relatively good agreement, but there were some differences. We found that our measurements turned out to produce load history data that deviated from the intended load history. The material parameters were also shown to be less accurate than expected. Due to these deviations, we could not expect a perfect agreement between the CDFs. Therefore, we can not with certainty state that Coleman’s theory is applicable for varying load histories. However, despite the difficulties to experimentally achieve the intended load history, the results showed good agreement in several cases, and the deviations from the theory could possibly be explained by the load history deviations. To be certain, more accurate measurements with higher accuracy need to be done.

Environmental issues are more and more present in our societies. Pollution engendered by plastic waste have drastically increased these past decades, causing several threats to the ecosystem. Therefore, the need of new biodegradable plastics to replace the actual petroleum-based ones is urgent. Cellulose could be a potential substitute since it is a biopolymer, abundant on Earth. However its properties have to be enhanced to be competitive towards actual plastics. The aim of the project is therefore to get a better understanding of cellulose-cellulose interactions. It focuses on the adhesion between cellulosic surfaces. Contact adhesion measurements have been performed on cellulose beads, with different treatments. All the beads had the same size and same concentration. Some of them were native whereas others were charged (600 µeq/g). Half of the native beads were surface modified with a starch coating or a Layer by Layer technique using cationic starch and an anionic polyelectrolyte (EXPN64 or FennoBond 85E). The project included preparation of the surface modified beads, pull-off tests, where load and position were recorded as a function of time, as well as measurements of the contact area. It was found that a higher energy was needed to separate charged and surface modified beads, especially the ones modified with EXPN 64, compared to native beads. The project have also shown that the types of beads influenced the contact area and the strength. However a trend was sometimes difficult to find. The data and results obtained in this project could be further re-used to enlarge the study field and investigate the influence of other parameters (size, concentration) on the adhesion of cellulose beads. / Miljöfrågor är mer och mer närvarande i våra samhällen. plastavfall har ökat drastiskt de senaste decennierna och orsakat flera hot mot ekosystemet. Därför är behovet av ny biologiskt nedbrytbar plast för att ersätta de petroleumbaserade brådskande. Cellulosa kan vara en potentiell ersättare eftersom det är en biopolymer. Emellertid måste dess egenskaper förbättras för att vara konkurrenskraftiga gentemot petroleumbaserad plast. Syftet med projektet är därför att bättre förstå cellulosa-cellulosa-interaktioner. Den fokuserar på vidhäftningen mellan cellulosaytor. Kontaktvidhäftningsmätningar har utförts på cellulosapärlor med olika behandlingar. Alla pärlor hade samma storlek och koncentration. Vissa av dem var naturliga medan andra laddades (600 µeq/g). Projektet inkluderade beredning av ytmodifierade pärlor, utdragningstester, där belastning och position registrerades som en funktion av tiden, samt mätningar av kontaktområdet. Det visade sig att högre energi behövdes för att separera laddade och ytmodifierade pärlor, särskilt de modifierade med EXPN 64, jämfört med tonativa pärlor. Projektet har också visat att typerna av pärlor påverkade kontaktområdet och styrkan. Men en trend var ibland svår att hitta. Uppgifterna och resultaten som erhållits i detta projekt kan vidare användas för att förstora studiefältet och undersöka påverkan av andra parametrar (storlek, koncentration) på vidhäftningen av cellulosapärlor.

Biodegradable polymers are emerging as a new solution to satisfy the increasing demand of greenenvironmentally friendly material. At the same time, the interest for lighter and stronger structures never stops growing. In this paper, we report the production steps to achieve cellulose nanofibrils (CNF) composite filaments via a new green synthesis route known as wet spinning. This new technique avoids the traditional harmful viscose process and produces biodegradable CNF filaments with interesting mechanical properties. This approach is then applied to produce never seen before composite CNF filaments using a three-layered head extruder. In order to obtain conductive filaments, PEDOT/PPS is successfully mixed with CNF to produce in-situ composite filaments. Scanning electron microscopy (SEM), atomic force measurements and tensile tests are employed to characterize the properties of the filaments. / Biologiskt nedbrytbara polymerer börjar framträda som en lösning för det ökade behovet avmiljövänliga material. Samtidigt så växer intresset för lättare och starkare strukturer. I denna rapport tar vi upp produktionsstegen för att uppnå nanofibril komposit cellulosa fibrer (CNF), med hjälp av en ny grön polymerisation mest känd som ”wet spinning”. Med denna nya teknik så behövs inte dem traditionella miljöfarliga viskosprocesserna och man producerar biologiskt nedbrytbara CNF filaments med intressanta mekaniska egenskaper. Denna metod appliceras sen för att producera en komposit som aldrig setts innan. CNF fibrer som består av tre lager ”head-extruder”. För att få fibrer med ledningsförmåga så mixas PEDOT/PPS med CNF för att producera ”in-situ komposit fibrer”. Svepelektronmikroskop (SEM), atomkraftsmikroskopi och töjningstester används för att karaktärisera egenskaperna av fibrerna.

This thesis deals with the wetting by oil mixtures of two different model cellulose surfaces. The surfaces studied were a regenerated cellulose (RG) surface prepared by spin-coating, and a film consisting of polyelectrolyte multilayers (PEM) of Poly(ethyleneimine) (PEI) and a carboxymethylated Microfibrillated Cellulose (MFC). After coating or covalently modifying the cellulose surfaces with various amounts of fluorosurfactants, the fluorinated cellulose films were used to follow the spreading mechanisms of the different oil mixtures. The viscosity and surface tension of the oil, as well as the dispersive surface energy of the cellulose surface, are essential parameters governing the spreading kinetics. X-ray Photoelectron Spectroscopy (XPS) and dispersive surface energy measurements were made on the cellulose films treated with fluorosurfactants. A strong correlation between the surface coverage of fluorine, the dispersive surface energy and the measured contact angle of the oil mixtures was found. For example, a dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (θe > 90º) by castor oil. Significant parts of this work were devoted to the development of cellulose surfaces for the wetting studies. The formation of a PEM consisting of PEI and MFC was studied and the total layer thickness and adsorbed amount were optimized by combining Dual Polarization Interferometry (DPI) with a Quartz Crystal Microbalance with Dissipation (QCM-D). The adsorption behaviour as well as the influence of the charge density, pH and electrolyte concentration of PEI, and electrolyte concentration of the MFC dispersion on the adsorbed amount of MFC were investigated. Results indicate that a combination of a high pH, a fairly high electrolyte concentration for PEI solution together with low or zero electrolyte concentration for the MFC resulted in the largest possible adsorbed amounts of the individual PEI and MFC layers. The structures of the two cellulose surfaces were characterised with atomic force microscopy measurements and a difference in terms of surface structure and roughness were observed. Both surfaces were however very smooth with calculated RMS roughness values in the range of a few nanometers. The adsorption behaviour of water-dispersible fluorosurfactants physically adsorbed at various concentrations onto the two model cellulose surfaces was investigated using DPI. The aggregate structure of an anionic fluorosurfactant, perfluorooctadecanoic acid, dispersed in water was studied by Cryo Transmission Electron Microscopy (Cryo-TEM). The fluorosurfactants had an adsorption and desorption behaviour in water which was dependent on the fluorinated chain length and the aggregation form of the fluorosurfactant. Perfluorooctanoic acid and a commercial cationic fluorosurfactant with a formal composition of CF3 (CF2)nSO2NH(CH2)3-4N(CH3)3+I- was found to desorb from the MFC and RG surfaces upon rinsing with water, whereas perfluorooctadecanoic acid was strongly adsorbed to the surfaces. It is essential for a fluorosurfacatant to be strongly adsorbed to the cellulose surface even after rinsing to yield hydrophobic and lipophobic (oleophobic) properties with a large contact angle for oils and water. / QC 20101103

The degradation of cellulose found in wood is one of the most important degradation processes for the carbon flux on earth. The degradation is performed by microorganisms that typically use enzymes. Since the cellulose in wood is crystalline and embedded in other polymers, making it inaccessible and durable, the enzymatic methods of cellulose degradation is also complex. In this thesis, the action of some of these enzymes, called cellulases, have been studied both fundamentally and for industrial purposes. By using model cellulose films and a quartz crystal microbalance it was found that endoglucanases not only depolymerize but also swell model cellulose films. Most probably, this contributes to the synergy seen between endoglucanases and exoglucanases. When an pulp fibers were pre--treated with endoglucanases and beaten subsequently, the fibers became more swollen than reference fibers. The effects of beating enzyme pre--treated fibers were investigated, indicating that endoglucanases improves the fiber/fiber interaction but also alters the behavior of the fibers in the beating process to become more susceptible to the beating. The second part of the thesis has been focused on the use of an albino fungi in order to decrease the amount of wood extractives in wood chips prior to thermo mechanical pulp production. The fungus decreased the most troublesome component, the triglycerides, by more than 90 percent in two weeks without any detrimental effects on pulp properties. On the contrary, pulp strength and optical properties were improved. / QC 20101117

This thesis reports on an investigation of the mechanisms of edge wicking in retortable paperboard. Retortable board is used for packaging preserved food, a process which requires that the package and its contents be sterilised by exposure to high temperature steam for up to three hours. The board used must thus have higher water repellence than traditional liquid packaging. Water vapour that condenses on the cut edges on the outside of the board causes particular concern. The paperboards studied were made from refined and unrefined bleached softwood kraft pulp and from refined unbleached softwood kraft pulp in one or two plies with different sizing levels and structures. Samples of each of the boards were immersed in a water bath at 95 °C. Other samples from the same boards were exposed to a combination of saturated steam at 130 °C and condensed steam in a special apparatus developed for this purpose. The board samples were placed on a cooling plate to simulate the temperature gradient when a container of cold food is sterilised with heated steam. Still other samples were exposed to heated steam in the absence of condensation by hanging them freely in the apparatus. The extent of edge wicking in the boards was determined by gravimetric measurements and also by near-infrared (NIR) spectroscopy, a technique that yields more information about the moisture content profiles and the mechanisms of liquid sorption. The moisture content profiles of boards exposed to saturated steam in the absence of condensation show more uniform water uptake. This phenomenon can be explained by rapid vapour phase transport throughout the pore structure, followed by slower water uptake in the fibres. By contrast, in samples exposed to both heated steam and condensed steam, there was both liquid sorption in the fibre network and rapid vapour phase transport of the steam. The moisture content in those samples was much higher close to the edge and lower behind the liquid frontier. The edge wicking of high temperature water was greatest in board that was not fully sized, in low density board, and in board made from unrefined pulp. The greater edge wicking in board made from unbleached pulp can be accounted for in terms of its greater swelling potential. In the low density board and the board made from unrefined pulp, the lumens at the unsized edge and the weaker bonding strength are suggested to affect the results. Capillary sorption takes place in lumens and delaminated bonds at the edge and then any further propagation takes place entirely by fibre diffusion. Capillary sorption may also be important in damaged areas where broken fibre-fibre bonds are exposed to liquid. The weaker bonded area in low density board therefore also contributes to water sorption. Edge wicking in the boards placed on the cooling plate and exposed to a combination of saturated and condensed steam was of a different nature. For these samples, density was not an important factor. The difference is due to the different mechanism at work in this case, where the relative area of the edge exposed to condensed steam was larger in the high density boards than in the low density boards. In the high density boards, condensed steam was sorbed in the structure by diffusion in the fibre structure, whereas in low density boards, the dominant effect was vapour phase transport in the void spaces followed by water uptake in the fibres. / QC 20101125

The presteaming of wood chips is an important step in the chemical pulping industry. It removes the air from within wood chips, allowing the cooking liquor to better impregnate wood chips, which leads to a more uniform cooking process, and lowers the amount of rejects. When steaming at atmospheric pressure, it is important that the temperature of the wood chips reach 100ᴼ C, as otherwise there will be an equilibrium leaving some air left inside. Having poorly steamed chips in a process could cause severe problems when it comes to reaching the targeted kappa number, or having the adequate retention time in the digester. There are a few different ways in which the wood chips are presteamed within the industry, however, there is little experimental data regarding the heating time of wood chips that can be used when designing these systems. Most studies have mainly focused on the air removal, or improvement of the impregnation step, and the few studies that have included the heating of the wood chips were limited to only one type of wood chip, or failed to specify the experimental details. Therefore, handmade wood chips pine and birch, two tree species commonly found in Sweden, were steamed in an ATEX designed digester with a steam jacket. The wood chips had thermocouples inside them and the temperature and time was recorded, and the effect of different parameters on the heating could thus be studied.The results revealed that there could be more than a minute in average time difference between wood chips of different thicknesses, both for birch and pine, although the difference in heating time was more linearly correlated to thickness for the birch chips. Pine chips of different thickness were also studied when the pressure inside the digester was allowed to build up, which showed that it is mainly thicker chips that have reduced heating time under such circumstances, as the thinner chips stop heating for a while when the steam condensates on colder surroundings. When comparing heartwood and sapwood chips, it was noted that the difference in heating time could be around 1 minute at most for pine, but only a few seconds for birch. This was most likely due to the pine heartwood and sapwood having distinct moisture contents, 25 % and 58 % respectively, while it was 41% and 42 % in birch heartwood and sapwood. Birch and pine chips wee also steamed together, however, the difference in heating time was only a few seconds on average. When comparing these experimental results with simulation data of the steaming of wood chips, it fit rather well when it came to the general heating time. However, the effect of increased moisture content had a much larger impact in the simulations, which predicted that more moist wood chips would need several minutes more steaming time, while the experiments only showed at difference of, at most, around 1 minute. When comparing with old experimental data, that has been the basis for the design of older steaming processes, it gave very distinct results, where the effect of thickness did not have as big of an impact as in the old data. No further comparison could be made, however, as the experimental conditions for the old experimental data were not known. Based on these results, it was noted that a steaming time of at least 5 minutes would be needed to ensure that even the largest and more moist chips could reach 100ᴼ C in this system. Finally, the condensate from the handmade birch and pine chips was analyzed. It revealed the presence of low molecular weight compounds like methanol, formic acid and acetic acid. Common metal ions were also present,although the amount of sodium ions clearly surpassed the rest. The pH of the pine condensate was measured and it was very high, which implies that the condensate was contaminated. / Basning av flis är ett viktigt steg inom kemisk massaindustri. Det avlägsnar luft från flisens insida vilket gör att impregneringen av luten blir bättre, vilket i sin tur leder till en jämnare kokning och färre rejekt. När basningen sker vid atmosfärstryck är det viktigt att flisen når en temperatur på 100ᴼ C, annars kommer det finna ett jämviktstillstånd där lite luft blir kvar på insidan. Att ha otillräckligt basad flis i en process skulle kunna orsaka stora problem när det gäller att nå önskade kappatal, eller att ha en önskad retentionstid i kokaren.Basningen görs på ett par olika sätt inom industrin, men det finns väldigt lite experimentell data tillgänglig angående flisens upvärmning, som skulle kunna användas när dessa system designas. De flesta vetenskapliga studier har fokuserat på luftborttagningen eller på förbättringar av impregneringssteget, medan de få studier som inkluderat mätningar av temperaturen ofta varit begränsade till ett slags trä, eller så har de inte inkluderat detaljer kring experimentet. Därför basades handgjorda flisbitar av björk och tall från Sverige i en ATEX-designad kokare med en ångjacka. Flisen hade termoelement inuti och temperaturen samt tiden kunde avläsas, vilket gjorde det möjligt att studera effekten av olika parametrar. Resultaten visade att det kunde skilja mer än en minut i uppvärmningstid mellan flisbitar av olika tjocklekar, både för tall och björk, även fast skillnaden i uppvärmningstid var mer linjärt relaterad till tjockleken för björkflisen. Tallflisen studerades också när trycket inuti kokar tilläts stiga vilket visade att det de tjockare flisbitarnas uppvärmningstid som kortas ned mest, eftersom de tunnare flisbitarna slutar värmas upp när ångan börjar kondensera på kallare ytor runt omkring. När flis av splintved och kärnved jämfördes visade det sig att skillnaden i uppvärmningstid kunde vara omkring 1 minut för tall, men endast ett par sekunder för björk. Detta beror troligtvis på att kärnveden och splintveden i tall hade stora skillnader i fukthalt, 25 % respektive 58 %, medan det för björk var 41 % och 42%. Björkflis och tallflis basades även tillsammans men det skillde bara ett fåtal sekunder i genomsnitt i uppvärmningstid. När den experimentella datan jämfördes med data från simuleringar visade det sig att de stämmer väl överens när det gäller uppvärmningstiden i allmänhet. Å andra sidan förutspådde simuleringsdatan att en ökad fukthalt skulle leda till flera minuters skillnad i uppvärmningstid, medan endast 1 minuts skillnad uppmättes. När jämförelser gjordes med gammal experimentell data som använts som grund för tidigare processers design, var resultaten ganska olika eftersom den gamla datan visade en större effekt av ökad tjocklek än den som uppmättes.Tyvärr kunde inte fler jämförelser göras eftersom detaljerna kring experimentet bakom den gamla datan inte var kända. Slutligen analyserades även kondensatet från de handgjorda flisbitarna av tall och björk. Det visade att det fanns små mängder av små polära organiska ämnen, såsom metanol, myrsyra och ättiksyra. Vanliga metalljoner detekterades också, där mängden natrium var klart större än övriga metalljoner. Tallkondensatets pH mättes och det visade sig vara väldigt högt, något som tyder på att det troligtvis var förorenat.

In-plane properties of paperboard have always been of interest to paper mechanical researchers. The reason for this is that they play a large role for the usability of the paperboard throughout its lifespan.  Tensile properties are crucial when the board is fed through printing and converting machines at high speeds in the beginning of its life. While compressive properties are essential in the later use of e.g. packages. In this thesis some methods for evaluating in-plane properties are reinvestigated. In Paper A the tensile test was investigated with focus on sample size and strain distributions. Three different multiply paperboards were examined with varying sample sizes using speckle photography. Different strain behaviour was found for different sample sizes. This difference was dependent on the length to width ratio of the sample and was caused by the activation of strain zones in the sample. These zones were of a constant size and therefore occupied different amounts of the total sample area. Paper B investigates the mechanism that causes failure in the short span compression test (SCT). Three different multiply paperboards were examined, this time chosen to have distinctly different through-thickness profiles. The boards were characterized and the data was used to simulate a SCT test with the three different boards. The simulation was conducted with a finite element model consisting of layers of continuum elements with cohesive interfaces in-between. From the model it was concluded that the main mechanism for failure in SCT is delamination that was caused by shear damage. / <p>QC 20130603</p>

In this work, the formation of polyelectrolyte complexes (PECs) has been studied using a jet mixing method not previously used for mixing polyelectrolytes. The PECs were formed from two weak polyelectrolytes, i.e., polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH), with different mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method.   The adsorption behaviour of the formed PECs on silicon oxide substrates and pulp fibres was analysed, and the results were compared with those for polyelectrolyte multilayers (PEMs) prepared from the same two polyelectrolytes.   The results indicated that by using the jet mixer, the size of the formed PECs could be controlled, which was not the case with the polyelectrolyte titration method. The PECs produced by jet mixing were also found to be smaller than those produced by polyelectrolyte titration. From these results, a two-step mechanism for the formation of PECs was suggested: initial precomplex formation, which is a fast and diffusion-controlled process, followed by a reconformation process, during which the vigorous mixing in the jet mixer can partially limit secondary aggregation.   When the complexes were adsorbed to silicon oxide or pulp fibre surfaces, adsorption studies indicated that it was impossible to reach the same adsorption levels for PECs as for PEMs. This was explained in terms of free energy, entropical, reasons rather than to any geometric limitation of the surface. Despite the smaller amount of polyelectrolyte adsorbed from the PEC treatment than from the PEM treatment of pulp fibres, the PEC treatment had the greatest effect on paper strength per adsorbed amount of polymer. This was thought to be because the three-dimensional structure of the PECs, versus the smoother structure of PEMs, allows for the formation of multiple contact points between the macroscopically rough fibres and increased molecular contact area.   In the adsorption experiments, it was also found that net cationic complexes can adsorb to both anionic and cationic substrates. This phenomenon was explained by the occurrence of anionic patches on the surface of the net cationic PECs and the ability of the PECs, formed from weak polyelectrolytes, to partially change charge upon exposure to a surface of the same charge as the complex itself, due to a change of the degree of dissociation of the polyelectrolytes constituting the complex. / QC 20101102

The interdependency between filler retention and paper formation is well-known, where a high retention is accompanied by impaired formation. A challenge for today’s papermakers is to increase the competitiveness for uncoated and coated fine paper, by improving the formation at the same level of retention. Over the years, the use and the demands of retention aids have increased as a consequence of a higher system closure, increased machine speeds and increased filler content. The knowledge of whether some retention aid systems are more or less detrimental to paper formation than other systems, is very limited. The insuffiency of knowledge is, however, also true for other chemical, mechanical and interacting factors, which influence the retention/formation relationship in a complex manner. In order to investigate the retention/formation relationship (features, retention aids, dosage points, etc.), a pilot-scale fourdrinier former (R/F-machine) has been developed. The R/F-machine provides a short circulation of the white water and controlled experimental conditions and is appropriate for cost-effective investigations. Moreover, the R/F-machine has been designed to have a short residence time to chemical equilibrium and the machine has also shown high reproducibility in the results. This licentiate thesis presents the R/F-machine and examines, during constant experimental conditions, the retention/formation relationships for some different retention aid systems. Three single-component cationic polyacrylamides with varying molecular weights and two polyacrylamide-based microparticulate systems with varying microparticles were examined. The retention aid systems were investigated on the R/F-machine, for a fine paper stock (90 % bleached hardwood and 10 % bleached softwood) with addition of 25 % filler (based on total solids content). The results showed that the retention/formation relationship was not dependent on the retention aid system used. All systems showed the same relationship between retention and formation. On the other hand, the various retention aid systems provided different effects considering their retention performance. / QC 20101118