Unexpectedly, it was found that when a waterborne polyacrylate adhesive was placed on carbon steel it was not tacky; this was not the case for the same adhesive placed on stainless steel. It was determined that the surface energy, as measured with liquid contact angles, of the adhesive films is significantly different between the two films, with the non-tacky film having a higher surface energy. Atomic force microscopy (AFM) showed that the non-tacky surface has a higher roughness which minimizes the contacting area between the film and a contacting surface. Analysis of the heating of the carbon steel coupon with infrared thermography shows a non-uniform temperature profile at the surface. This experimental data is corroborated using a 2-D heat transfer model that incorporates the heat transfer characteristics of the various components of carbon steel. Surface driven flow, or Marangoni convection, can develop from temperature gradients and are known to cause increased roughness in polymer films. IR thermography measurements of the adhesive film during drying shows larger temperature differences for the films on carbon steel than on stainless steel. These larger temperature differences induce greater Marangoni convection, which result in the rougher surfaces on carbon steel that were measured with AFM. The effect of lowering the tack of a polyacrylate film has significant impact in the dryer section of a paper machine. This effect was quantified using the Web Adhesion Drying Simulator, which is a laboratory-scale apparatus that measures the energy required to pull the sheet from a metal surface. By substituting the adhesive-on-stainless steel with the less-sticky adhesive-on-carbon steel surface, the energy required to pull the sheet from the metal surface was reduced significantly and the picking associated with the test was nearly eliminated.

Pulp from recycled paper products contains various waxes, glues, adhesives, filler, and inorganics that are collectively referred to as contaminants. Contaminants that are not drained out during the forming process are trapped in the sheet and carried down the paper machine. These contaminant particles and contaminants in solution can become deposited on the dryer cylinders. The contaminants which deposit on the dryer cylinders lead to reduced quality and production of paper on the machine. The process by which contaminants are deposited on a dryer cylinder has not been explored at a fundamental level. Rather, quick industrial fixes have been tested to try and eliminate the contaminant deposition and only reductions in deposition have been achieved. The literature reviewed does not relate the flow of particle suspensions through porous media to the heat transfer and fluid dynamics processes associated with drying paper. The experiments in the literature showed the general trends of particle and dye distributions across the thicknesses of different porous media during forming or filtration processes. Filler and fines distribution were not able to be changed by flows induced by pressing a sheet. The mechanisms for how particles move through porous media found in the literature were a basis for what kind of phenomena would be expected in the particle flow experiments. A means of completely eliminating sticky deposits could be found by examining the parameters which contribute to the deposition process. The hypothesis proposed in this thesis is that contaminant particles and liquid containing contaminants are transported to the dryer can surface by liquid flows induced by the drying process. By performing particle flow experiments during drying, bounds for the particle size, initial drying surface temperature, drying time, and initial solids content will be determined for which the hypothesis is true. The particle and dye transport studies performed showed an array of processes at work simultaneously. The results from the particle and dye transport studies show that a particle diameter of ~1.0 and #956;m or less, handsheet solids content of less than 30%, open sheet structure and a high surface drying temperature (200C) were needed to create a significant change in filler and dye distribution across the thickness of a handsheet.

There is a significant problem for the paper recycling industry known as “stickies”. “Stickies” are tacky species, present in recycled paper and coated broke, derived from coating formulations, adhesives, etc. They impact negatively on paper quality and cause web runnability problems by deposit build-up. To sustain recycling, stickies are controlled by adsorbing them onto minerals added to the recycled stock. So the aim of the project was to characterise non-porous and porous minerals suitable for paper-making, and then use the knowledge gained to improve the adsorption of stickies. The pore level properties of the minerals used to control stickies are highly relevant in regulating adsorption of the stickies. Levels of pore architecture were investigated by characterising filter media with porosimetry, porometry, electron microscopy and modelling the combined results. Seven samples were studied, with pore size distributions ranging from simple unimodal to complicated bimodal. Porometry, porosimetry and SEM, individually can only determine primary pore architecture. A combination of experimental and modelling techniques allows a full characterisation of pore architecture from primary to quaternary levels. Calcium carbonates can be modified to change the pore architecture, which affects properties such as wetting. Their pore architecture was investigated to understand why some modified calcium carbonates do not show two distinct wetting rates. The investigation implied a significant surface area could be attributed to nano rugosity. The nano rugosity was responsible for the enhanced wetting of a sample. A zero length column was used to study diffusion and desorption of benzene with calcium carbonate. Desorption and diffusion coefficients for calcium carbonate systems were calculated from the corrected concentration versus time measurements. They showed how the pore architecture affects diffusion and desorption. By comparing the experimental results with a pore network simulation, it was possible to deduce the relative effect of surface diffusion. The adsorption of stickies onto different mineral grades was investigated using a novel proxy method to determine equilibrium constants and adsorption isotherms. The results were then used to understand the influence of particle size on the adsorption behaviour, with three mechanisms proposed. The equilibrium constant and adsorption isotherm data also allowed comparisons between hydrophilic and hydrophobic adsorption onto grades of talc. Recommendations are made for the optimum use of minerals for the removal of stickies, and for in-situ methods for monitoring and optimising removal.

No description available.

Abstract Stickies refer to tacky contaminants in recovered paper, excluding wood extractives. Stickies originate from adhesives, ink binders and coating binders. Stickies able to pass a sieve of 100 or 150 μm (depending on standard) are called micro stickies, whereas the particles retained on the screen are called macro stickies. Dissolved and colloidal stickies are called secondary stickies. There are standard methods for macro stickies, but a standard method measuring the total amount of stickies is lacking. Furthermore, the size distribution, and nature of stickies in the sense if they are free particles or agglomerated with some other substances, has not been previously known. The information on the removal of stickies in different unit operations was also not known very well except for macro stickies. The aim of this thesis was thus to develop an analysis method for the total amount of stickies, determine the size distribution and nature of stickies, and find ways to better remove stickies in the deinking process. Extraction with tetrahydrofuran (THF) and High Pressure Liquid Chromatography (HPLC) with Size Exclusion Column (SEC) was used here to separate hydrophobic polymers (stickies) from the pulp suspension. An Evaporating solvent Light Scattering (ELS) detector was utilized to quantify the polymers after SEC. This analysis procedure was used in this thesis to measure stickies. Fractionation of pulp before the analysis was carried out if information of different-sized stickies was desired. The majority of stickies are micro stickies. A significant, although lower, portion of stickies are macrostickies, especially in the beginning of the deinking process. The dissolved and colloidal phase was found to contain wood extractives, and only trace amounts of stickies. Flotation is very effective in stickies removal. Ink and micro stickies were removed nearly equally in flotation, because they both are hydrophobic and are both in an optimal size range for removal in flotation. Ink measurements may be used for estimating the trends of stickies removal in flotation. The stickies removal in flotation may be enhanced by optimizing the pulper chemistry.

Abstract Fouling in papermaking causes major economic drawbacks due to downtime of process and paper quality defects. The surface fouling is a complex phenomenon in a paper making process, which is affected by several interconnected factors such as process environment changes from wet to dry with increasing temperature along with the variety of sticky materials present in paper raw materials. These impurities, such as waxes, coating binders, hot melts and pressure-sensitive adhesives have a tendency to attach to the surfaces of machinery during paper production and cause surface fouling. The focus of this thesis was on the mechanisms of sticking and surface fouling on a paper machine surfaces caused by problematic sticky organic materials. The sticking potential of six styrene–butadiene latices varying in carboxylation degree, crosslinking density and viscoelasticity and one polyacrylate pressure sensitive adhesive were studied using a cylindrical probe tack method under dry and aqueous conditions. Sticking potential was measured using low and high energy surfaces as an adherent. Also a new practical method for the on-site evaluation of nonstick properties of cylinder coating materials was developed. This method enables monitoring the condition of the coating during its life cycle and also provides the opportunity to compare the performance of different drying cylinder coating materials. The research performed clearly showed that low viscoelastic modulus of latex increases sticking tendency. The results also showed that presence of water can either increase or decrease adhesion depending on the moisture content ant the physic-chemical properties of sticky materials. A low surface energy coating strongly decreases sticking compared to a high energy surface and have a lower susceptibility to fouling in the dry environment. In aqueous conditions, the use of high-energy surfaces decreases adhesion of latices due to their strong interaction with water. Also, the results indicated that carboxylation decreases sticking potential of latex in both dry and aqueous environments. / Tiivistelmä Paperikoneiden likaantuminen aiheuttaa suuria tuotannollisia menetyksiä johtuen tuotantoprosessin katkoksista ja paperin laadun ongelmista. Paperikoneen pintojen likaantuminen on monimutkainen prosessi, johon vaikuttavat monet toisistaan riippuvat tekijät ja siten likaantumisilmiötä on vaikea hallita. Paperin raaka-aineet voivat sisältää epäpuhtauksia, kuten vahoja, kuumasulate- ja tarraliimoja, jotka tarttuvat paperikoneen pintoihin aiheuttaen niiden likaantumista. Lisäksi paperin prosessiympäristö muuttuu märästä kuivaan valmistusprosessin edetessä ja lämpötilan kasvaa samanaikaisesti. Tässä väitöskirjassa on kuvattu paperikoneen pintojen likaantumisen mekanismeja ja erityisesti orgaanisten lika-aineiden tarttumista. Tutkimuksessa selvitettiin probe tack -menetelmää käyttäen kuuden erilaisen styreeni-butadieenilateksin ja polyakrylaattitarraliiman tarttuvuutta matalan ja korkean pintaenergian pinnoilla sekä kuivissa että märissä olosuhteissa. Työhön oli valittu latekseja, joiden karboksylointiaste, ristisilloitustiheys ja viskoelastiset ominaisuuden olivat erilaisia. Lisäksi väitöskirjatyössä kehitettiin paikan päällä suoritettava mittausmenetelmä paperikoneen kuivaussylinterien pinnoitteen puhtaana pysyvyyden määrittämiseksi. Tällä menetelmällä voidaan mitata pinnoitteiden kuntoa niiden elinkaaren aikana ja myös vertailla erilaisia pinnoitteita keskenään. Tutkimuksen tulokset osoittivat, että styreeni-butadieenilateksien matala kimmokerroin lisää niiden tarttumista paperikoneen pinnoille. Veden läsnäolo voi joko lisätä tai vähentää tarttumista riippuen veden määrästä ja lika-aineiden fysiokemiallisista ominaisuuksista. Myös paperikoneen pinnoitteen pintaenergia vaikuttaa tarttuvuuteen. Paperikoneen pinnoitteiden pieni pinta-energia vähentää tarttumista kuivissa olosuhteissa, kun taas korkean pintaenergian pinnoitteet vähentävät lateksien tarttuvuutta vesiolosuhteissa. Lisäksi lateksien karboksylointi vähentää niiden tarttumista sekä kuivissa että märissä olosuhteissa.