No description available.

Greaseproof paper has a dense structure and therefore provides a natural barrier against materials like fat and oils. The barrier is obtained by extensive refining of the pulp. This refining is however a costly operation, not only in terms of direct costs for the refining but also in terms of indirect costs because the energy consumption for the drying of the paper is affected by the refining. A full-scale trial was performed to investigate the role of the pulp with respect to the energy demand and the barrier properties of the final papers. Paper made of 100% sulphite pulp with a low degree of refining exhibited the lowest energy consumption at a given level of air permeance. In addition, the effect of refining on the air permeance was compared with that of calendering. The calendering affected the air permeance less than the refining. The papers produced in the full-scale trial were later used as substrates for coatings and for detailed studies of the paper structure. Coating with chitosan was examined on a bench-scale and on a pilot scale. The studies showed that greaseproof paper can be upgraded with an oxygen barrier, but also that suitable coating techniques are lacking for the application of the coating in a sufficient amount. The influence of the base paper on the barrier properties of chitosan-coated paper was investigated in another study, in which it was found that greaseproof paper possesses a unique coating hold-out which cannot be met by other types of paper with a more open structure. It was also found that the coated paper had a lower oxygen permeability than the chitosan coating itself, and this indicates that the dense surface layer of greaseproof paper contributed to the oxygen permeability of the coated paper. The pore volume fraction of the greaseproof paper was found to be approximately 40% and it is therefore surprising that its air permeance is so low. To bring understanding to this question, the structure of greaseproof paper was studied using several methods. It was found that the structure was dominated by very small pores with a median diameter of <0.3 µm. The fraction of closed pores was also substantial. A porosity gradient was also found, indicating that the papers used in the study had a closed surface. The hypothesis that the surface layer of the paper contributed to the oxygen barrier was tested in an experiment in which greaseproof paper was extrusion-coated with polyethylene. The oxygen permeability was measured at 0%, 50% and 90% relative humidity, and the permeability was found to increase with increasing moisture content. Because only the cellulose layer in the paper and not the polyethylene layer in the coating is affected by moisture, this result supports the hypothesis that the surface layer of the paper contributed to the oxygen barrier properties of the coated paper.

The objective of this thesis is to better understand the impact of paper and printer types on xerographic print quality. To achieve this objective, commercially printed samples comprising of ten different paper substrates printed using three different xerographic printers were examined. The print quality of these samples was assessed in terms of print microgloss and its nonuniformity, print density, print and gloss mottle, print roughness, and visual ranking. This study showed that print mottle conducted by Fast Fourier Transform produced the best correlation with visual ranking at the size range of 0.1 - 1mm, while print gloss mottle was found to affect print quality regardless of the mottle size. Brightness, opacity, basis weight, gloss 75, and roughness of these paper substrates were found to have the most significant effect on print quality. All of the optical properties of paper included in this analysis showed a strong correlation to print quality.

The objective of this thesis is to better understand the impact of paper and printer types on xerographic print quality. To achieve this objective, commercially printed samples comprising of ten different paper substrates printed using three different xerographic printers were examined. The print quality of these samples was assessed in terms of print microgloss and its nonuniformity, print density, print and gloss mottle, print roughness, and visual ranking. This study showed that print mottle conducted by Fast Fourier Transform produced the best correlation with visual ranking at the size range of 0.1 - 1mm, while print gloss mottle was found to affect print quality regardless of the mottle size. Brightness, opacity, basis weight, gloss 75, and roughness of these paper substrates were found to have the most significant effect on print quality. All of the optical properties of paper included in this analysis showed a strong correlation to print quality.

No description available.

Bond strength is classically characterized into two separate factors; area of the bond and specific bond strength. This separation is especially important in pulps that lack strength properties, and are specifically used for their optical properties, such as mechanical pulps. In this research the applicability of the Ingmansson and Thode method for distinguishing between specific bonded area and specific bond strength in mechanical pulps is studied. It is shown that the rigid, non-collapsable, nature of the mechanical pulp can be overcome by press drying the sheets until they approach their 50% relative humidity moisture content. Mechanical pulps have been assumed to operate in a domain where fiber failure can be considered insignificant, and the bonded area to tensile strength relationship is linear. In this study it was shown that most commercial pulps operate in a significant fiber failure domain. However, it is shown that pure fines and fines rich mechanical pulp better follow a linear bonded area to tensile strength relationship rather than a non-linear (significant fiber failure) model, suggesting that only the fiber fraction undergoes fiber failure and the finer fractions predominantly bond failure. The Ingmansson and Thode method relies on the use of scattering coefficient as a measure of specific surface area. It is shown that scattering coefficient is an accurate estimate of mechanical pulp specific surface area at a constant wavelength of light, provided that the wavelength used to measure scattering coefficient is above the significant absorption limit.

Formation plays an important role in the end-use properties of paper products, but before formation can be optimized to achieve superior properties, an understanding about the causes of formation must be developed. Formation is caused by variations in the basis weight of paper that are results of fiber floc formation before and during the forming of the sheet. This project is a first step in a larger research program aimed at studying formation. By observing the effects that mechanical energy dissipation (in the form of turbulence) and retention chemical dosage have on floc formation, we may develop a better understanding of how to control formation. In this study, a rectangular cross-section flow channel was constructed to aid in the acquisition of digital images of a flowing fiber suspension. The furnish consisted of a 55:45 spruce:pine bleached market pulp mix from a Western Canadian mill. Turbulence was varied by changing the flow rate; Reynolds numbers achieved range from 20,000 to 40,000. The retention aid used was a cationic polyacrylamide with a medium charge density. Dosage of the retention aid was varied from 0 to 2 pounds per ton OD fiber. Digital images of the flowing fiber suspension were acquired with a professional digital SLR camera with a forensics-quality lens. Three separate image analysis techniques were used to measure the flocculation state of the fiber suspension: morphological image operations, formation number analysis, and fast Fourier transform analysis. Morphological image analysis was capable of measuring floc size increases seen in the acquired floc images. It was shown how floc diameter could increase simultaneously with decreasing total floc area and total floc number. A regression model relating retention aid dosage and energy dissipation was constructed in an effort to predict flocculation. The regression model was used to predict F2 (formation number squared) results from the study. The interaction effect RE was shown to have a differing effect across the retention aid dosage levels. As a result, this model and technique may prove to be a beneficial tool in optimizing retention aid applications.

The understanding of what properties the fibre should have in order to give the right end-product paper properties, along with the type of processing, is a subject for a lot of research and development. Today the ability to measure fibre properties on-line is widely used for pulps. It is often necessary to measure many properties and variables in a process. The data collected is therefore almost always multivariate. It is very hard to analyse process data due to a lot of noises. Correlations between fibre and paper properties are hard to find, but this does not mean that correlations do not exist. Fibre properties, measured by the pulp analyser PulpEye, were investigated and correlations to paper properties were studied. The work was divided into three different studies. Study 1 was an investigation of historical process data, in study 2 pulp samples from the production was analysed and study 3 was a refiner setting trial, were different refiner segments, flows through refiners and intensities were studied. Both the group-plots and MVDA’s based on the historical process data in study 1, showed that the Scott Bond was increased with increased amount of kinks and curl for the unbleached pine pulp (softwood pulp). Coarseness measurements, made in the study of historical data, indicated that the coarseness was varying in such a large extent that it was believable that it had effects in the papermaking process. Another interesting fibre property, investigated in the refiner setting trial, was crill. The amount of crill is said to have strong correlation to paper strength. The analysis showed that the incoming pulp had different amount of crill and that the amount of crill after the refiners also was varying for the different samples. The development of crill at different kappa numbers and for pulps refined with different segments and refiner strategies should be further investigated. In this work it has been difficult to find correlations between fibre properties and paper properties in the refiner setting trial. This could have been due to small variations of the different parameters. This work showed that the normal production can be handled very well and variations are rather small. It can be seen though, that problems do appear when parameters are deviating from the normal case. An efficient way to work is to do measurements when the incoming pulp parameters are deviating. It should also be more investigated how the most common deviating pulp parameters should be handled in the refining process and at the board machine. The communication between the pulp production and the board machines is recommended to be further developed, especially when the pulp production have disturbances that can be affecting the refining and further the board production.

Abstract High Yield Pulp (HYP), i.e. TMP, SGW or CTMP, is normally used in printing papers (News, SC and LWC) or in a middle layer on cardboard i.e. in products that either have high demands on printability and runnability in fast printing presses or contribute to high bulk in cardboards in order to minimize pulp consumption at a certain sheet stiffness. Tensile strength as a function of density is significantly higher for HYP compared to chemical pulps such as sulphate and sulphite pulps. However, chemical pulp is mainly used in packaging materials that require very high tensile strength, while at the same time allowing the density of the paper to be high. By utilizing the softening properties of high-yielding lignin-rich fibres by hot-pressing technology, it is possible to significantly increase sheet density and thereby strength closer to the level of chemical pulps. Furthermore, due to the presence of high levels of lignin, it was shown that considerably higher wet strength can be achieved compared to chemical pulp without the addition of strengthening agents. The study focuses on the softening of stiff and lignin-rich fibres in papers based on HYP with sufficiently high moisture contents, when hot-pressing at temperature levels significantly above the softening temperature (Tg) of lignin Hot-pressing increases the density of the sheet which increases the contact surface between the fibres in the paper structure. The high pressing temperature can be said to induce a viscous flow of lignin, which also increases the potential for fibre-fibre bonding. It is conceivable that covalent bonds are obtained via condensation reactions and partly that interdiffusion between the lignin in the fibre walls can be obtained as they come close enough to each other during the hot-pressing. The research also shows that hot-pressing greatly improves properties in the form of dry and wet strength as well as hydrophobicity for HYP and for lignin-rich kraft paper. The first part of the study shows the effect of hot-pressing on strength properties of paper sheets based on CTMP, HT-CTMP, TMP, NSSC, SCPal and NBSK. The second part includes a study on how and to what extent different amounts of residual lignin in the pulp contribute to the dry and wet strength of the sheets of paper during hot-pressing as a function of increasing temperature. To demonstrate this, pilot scale cooking of unbleached pulp to various lignin levels was carried out. In all experiments in parts one and two, laboratory sheets with a surface weight of 150 g/m2 and a dry content of 50% were made with a Rapid Köthen (RK) sheet former, after which the sheets were hot-pressed in a cylinder press at temperatures up to 200°C, constant high pressure of about 7 MPa, nip pressure dwell time of 1.5 sec and production speed 1 m/min. The third part includes a study on the optimization of variables in a new design of a dynamic cylinder press for hot-pressing technology. This design is based on previous research at Mid Sweden University combined with key knowledge of steel band technology within IPCO AB. The new pilot machine is based on heating of a steel belt with infrared heat (IR) up to 300°C, a maximum line load of 15 kN/m in two press nips and a dwell time of 23-240 ms in the nip depending on the production speed which is up to 5 m/min. The experiments in part three were based on RK paper sheets with 100 g/m2 and approximately 63% dry content made by HT-CTMP. The results confirm that hot-pressed HYP-based paper sheets enable permanent densification by softening lignin, which provides a very high dry tensile strength and a remarkable improvement in wet tensile strength compared to bleached kraft pulp without the need for wet strength agents. A tensile index of 75 kNm/kg, compression strength index (SCT) of 45 kNm/kg and wet tensile strength index of 16 kNm/kg were obtained, which can be compared with the corresponding values for bleached kraft pulp based paper sheets of 85 kNm/kg, 35 kNm/kg and 5 kNm/kg respectively, all with the same density after hot-pressing at 200°C. The NSSC reached the highest tensile strength index of 92 kNm/kg. The study with the unbleached kraft pulps showed that the lignin content had a significant effect on both the dry and wet tensile strength indices. The pulps showed a linear relationship between wet strength and lignin content. The increase in lignin content from 0% to 12% improved the dry tensile index by 20% and SCT by 35% and gave a very significant increase in the wet strength index from 3 to 23 kNm/kg after hot-pressing. All lignin-rich paper samples exhibit good wet stability for at least 24 hours and an improved surface hydrophobicity by increasing the pressing temperature and lignin content. Optimization of the new steel belt based press machine showed that high nip pressure and two press nips had a great effect on density and strength. Whereas high temperature, well above Tg of lignin, and long pressing time were more important to achieve high wet strength. The highest wet strength index value, 27 kNm/kg, was reached when the pressing temperature was 290°C, the nip pressure about 8 MPa, the pressing time in the press nip 40 ms and the dwell time in contact with the steel belt 23.5 sec. It was also noted that no delamination occurred in these tests. In order to obtain both high dry and wet strength, it is important to have high lignin content, high temperature, high nip pressure and sufficiently long pressing time / Sammanfattning Högutbytesmassa (HYP), d.v.s. SGW, TMP eller CTMP, används normalt i tryckpapper (News, SC och LWC) eller i mittskikt i kartong dvs i produkter som har höga krav på tryckbarhet och körbarhet i snabba tryckpressar eller för att bidra till hög bulk i kartong så att man därmed kan minimera förbrukningen av massa för att nå en viss arkstyvhet. Dragstyrka som funktion av densitet är väsentligt högre för HYP jämfört med kemiska massor som sulfat- och sulfitmassor. Däremot används främst kemiska massor i förpackningsmaterial som kräver mycket hög dragstryka, där man samtidigt tillåter att papperets densitet får vara hög. Genom att utnyttja mjukningsegenskaperna hos högutbytesmassors ligninrika fibrer genom varmpressningsteknik kan man väsentligt öka arkdensitet och därigenom styrka till i nivå med kemiska massors. Vidare visas att man tack vara närvaro av höga halter lignin kan nå väsentligt högre våtstyrka jämfört med kemisk massa utan tillsats av styrkehöjande kemikalier. Studien fokuserar på mjukgörning av styva och ligninrika fibrer vid varmpressning vid temperaturnivåer väsentligt över mjukningstemperaturen (Tg) för lignin av HYP-baserat papper med tillräckligt hög fukthalt. Varmpressning ökar arkens densitet, vilket ökar kontaktytan mellan fibrerna i pappersstrukturen. Den höga pressnings-temperaturen kan sägas inducera ett visköst flöde av lignin, vilket då ökar möjligheten att få starkare för fiber-fiber-bindning. Man kan dels tänka sig att kovalenta bindningar erhålls via kondensationsreaktioner och dels att man kan erhålla interdiffusion mellan ligninet i fiberväggarna då de kommer tillräckligt nära varandra vid varmpressningen. Forskningen visar också att varmpressning högst väsentligt förbättrar egenskaper i form av torr- och våtstyrka samt hydrofobicitet för både HYP-baserat och ligninrikt kraftpapper. Den första delen av studien visar effekten av varmpressning på styrke-egenskaper hos pappersark baserade på CTMP, HT-CTMP, TMP, NSSC, SCPal och NBSK. Den andra delen inkluderar en studie om hur och i vilken utsträckning olika mängder av kvarvarande lignin i massa bidrar till pappersarkens torrstyrka och våtstyrka vid varmpressning som funktion av ökande temperatur. För att demonstrera detta tillverkades oblekt kraftmassa till olika ligninhalter i pilotskala. I alla experiment i del ett och två i avhandlingen tillverkades laboratorieark med ytvikten 150 g/m2 och torrhalten 50% i en Rapid Köthen (RK) arkformare varefter arken varmpressades i en cylinderpress vid temperaturer upp till 200°C och konstant högt tryck på cirka 7 MPa i ett pressnyp med uppehållstiden 1,5 s i pressnypet  vid maskinhastigheten 1 m/min. Den tredje delen i avhandlingen inkluderar en studie om optimering av variabler i en ny design av en dynamisk cylinderpress för varmpressteknik. Den nya designen baseras på tidigare forskning vid Mittuniversitetet kombinerat med nyckelkunskap om stålbandstekniker inom IPCO AB. Den nya pilotmaskinen är baserad på att ett stålbälte uppvärms med infraröd värme (IR) upp till 300°C, en linjelast upp till 15 kN/m i två pressnyp vardera, med variabel presstid 23-240 ms i pressnypet beroende av maskinhastigheter upp till 5 m/min. Experimenten i del tre i avhandlingen baserades på RK-pappersark tillverkade av HT-CTMP med ytvikten 100 g/m2 och torrhalten ca 63%. Resultaten bekräftar att varmpressande HYP-baserade pappersark möjliggör permanent densifiering genom mjukning av lignin, vilket ger en mycket hög torr dragstyrka och en anmärkningsvärd förbättring av våt dragstyrka jämfört med blekt kraftmassa utan att våtstyrkemedel behöver användas. Ett dragindex på 75 kNm/kg, kompressionsstyrkeindex (SCT) på 45 kNm/kg och våtstyrkeindex på 16 kNm/kg erhölls vilket kan jämföras med motsvarande värden för pappersarken från blekt kraftmassa på 85 kNm/kg, 35 kNm/kg respektive 5 kNm/kg, alla med samma densitet efter varmpressning vid 200°C. Lövvedsbaserad NSSC nådde det högsta dragstyrkeindexet på hela 92 kNm/kg. Studien med de oblekta kraftmassorna visade att lignininnehållet hade en signifikant effekt på både torr- och våtstyrkeindex. Kraftmassorna uppvisade ett linjärt samband mellan våtstyrka och lignininnehåll. Ökningen i ligninhalten från 0% till 12% förbättrade dragindexet med 20% och SCT med 35% och gav en mycket signifikant ökning i våtstyrkeindex från 3 till 23 kNm/kg efter varmpressningen. Alla ligninrika pappersprover uppvisar god våtstyrkestabilitet under minst 24 timmar och en förbättrad ythydrofobicitet genom ökning av presstrycktemperaturen och lignininnehållet. Optimering av den nya stålbandsbaserade cylinderpressen visade att högt pressnyptryck och två pressnyp hade stor effekt på densitet och styrka. Emedan hög temperatur, långt över Tg för lignin, och lång presstid var viktigare för att nå hög våtstyrka. Det högsta värdet på våtstyrkeindex, 27 kNm/kg, uppnåddes när presstemperaturen var 290°C, pressnyptrycket cirka 8 MPa, presstiden i pressnypet 40 ms och tiden i kontakt med stålbältet 23,5 sek. Det noterades också att ingen delaminering inträffade i dessa tester. För att erhålla både hög torr- och våtstyrka är det viktigt med högt lignininnehåll, hög temperatur, högt nyptryck och tillräckligt lång presstid. / <p>Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 1 (accepterat), delarbete 2 (inskickat), delarbete 3 (manuskript).</p><p>At the time of the defence the following papers were unpublished: paper 1 (accepted), paper 2 (submitted), paper 3 (manuscript).</p>

One of the primary objectives of this thesis was to design fiber/filler/polymer structures for newsprint and in the process develop a greater understanding of fiber/filler/ polymer structures. Five different designed structures were created for study. The designed structures were composed of virgin, hydrosulfite bleached, TMP southern pine, Georgian kaolin clay and various polymers. Five filler levels from 0% to 20% were employed with each of these different structures. Numerous physical tests were used to gather data which would help to develop an understanding for the macroscopic properties of the structures. Paper structures were created and data from bulk physical tests and particle based SEM image analyses were compared. Comparisons were made using a statistical method called Principal Component Analysis (PCA) where the data is grouped and reduced to find data correlations not readily apparent in the raw data.