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Predictive models for the transport of volatile organic compounds in paper need to consider the complex interplay of diffusion, adsorption, desorption, or chemical reactions. The relative importance of each of these processes is determined by the polarity of the volatile. Hence, it is challenging to pick a valid theoretical model that correctly predicts transport regardless of the polarity. Here, physics-informed neural networks (PINNs) assess which of five different models correctly describe transport of DMSO as polar and n-tetradecane as apolar model compound: (i) a pseudo first-order adsorption model for an irreversible sorption process, (ii) a first-order kinetics model allowing reversible sorption, (iii) a second-order model with a reversible process, and an effective diffusion model accounting for a constant (iv) and for a variable effective diffusivity (v). Each tested model is given as set of partial differential equations (PDE). Considering the model under testing and experimentally obtained spatially and temporally resolved concentration profiles through stacks of paper sheets, PINNs predict concentration of the volatiles and associated material constants such as sorption constants and effective diffusion coefficients by solving the inverse problem. Our PINNs revealed two models, pseudo first-order sorption and second-order reversible sorption, that correctly predict concentration profiles and polarity-driven differences in sorption times. While a PINN-based picking of valid transport models has important implications for the development of effective methods for controlling emission of volatiles from paper materials, PINNs represent a versatile mathematical tool to validate or refute the capability of PDE-based theoretical models to describe experimental data. • PINNs evaluate sorption kinetics in porous materials. • Focus: Transport of organic volatiles in cellulose. • Pseudo first-order model suits organic volatiles. • Predicting transport of volatiles through paper. [ABSTRACT FROM AUTHOR]

In this study, the spreading of a liquid droplet on the surface of a fibrous paper and its penetration into the paper is studied. The spreading of the droplet was visualized using confocal microscopy and the penetration depth was quantified using Automatic Scanning Absorptiometry (ASA) measurements. The three-dimensional structure of the paper was obtained through micro-tomography imaging with a resolution of 0.9 µm. The obtained images were used to reconstruct the pore space, which was in turn used in direct numerical simulations of penetration of a droplet into paper. Simulations were performed using open source code OpenFOAM, which solves equations of two-phase flow (in our case air and water) in pores based on the Volume of Fluid Method. Simulation results showed a good agreement with the experimental observations. In particular, the dimensions of spreading area of a droplet and the depth of penetration were simulated reasonably well. Then, we used the model to investigate effects of changes in various liquid properties on spreading and penetration of a droplet liquid. We made calculations for three different values of contact angle ( CA ): 0°, 60°, and 120°. We found the largest penetration depth for CA  = 0. For CA  = 60 and CA  = 120, we found that the liquid droplet moved sideways from the jetted location, which is not favorable in inkjet printing. We also made simulations with larger values for viscosity and density, based on properties of an ink-based liquid used in inkjet printing. The results have shown a slower spreading and penetration compared with water. The model can be used to study effects of changes in either ink physical properties or paper layer microstructure on final spreading/penetration extent. [ABSTRACT FROM AUTHOR]

In this study we investigated the underlying mechanisms of coffee stain formation on paper – a porous substrate. When a drop of aqueous liquid containing dispersed materials dries on paper, the faster water evaporation rate at the edge of the drop drives the redistribution of the dispersed materials to the edge of the drop-covered area on paper. Deegan׳s discovery has been accepted as the “coffee ring” phenomenon, which has wide implications. However, stains left by dried aqueous liquids on paper are not always ring-shaped. This is because, besides Deegan׳s coffee ring effect, the transport of dispersed materials in porous media is affected by chromatographic and filtration effects, which are highly dependent upon the properties of the substrates. In this work we clarify the influences of different mechanisms to the dispersed materials redistribution in paper. [ABSTRACT FROM AUTHOR]

Abstract: The reaction kinetics of alkaline phosphatase (ALP) adsorbed on paper was quantified by image analysis using a colorimetric technique under conditions of excess enzyme. A classical reaction kinetics approach integrated with image processing technique was used to analyse the coloured product formation from the enzyme substrate reaction against time. The order of reaction and rate constant of enzyme activities on paper surface were calculated. ALP was either physisorbed directly on paper or adsorbed on paper treated with a monolayer of a high molecular weight cationic polyacrylamide (CPAM), an anionic polyacrylic acid (PAA) or a high molecular weight polyethylene oxide (PEO). The reaction rate of enzymatic paper follows a first order reaction with respect to the concentration of enzyme–substrate complex. ALP immobilized on paper has a reaction rate 2 to 3 orders of magnitude lower than the free ALP enzyme in buffer solution. This might be due to a critical loss of enzyme flexibility upon adsorption. No increase in reaction rate was achieved by immobilizing ALP on paper treated with a high molecular weight cationic polyacrylamide (CPAM) or a highly charged anionic polyacrylic acid oligomer (PAA), which suggests the enzyme orientation was not significantly affected. However, the reaction rate for ALP on PEO treated paper was lower than that on CPAM or PAA treated papers. That is probably due to some PEO-enzyme interaction affecting the tertiary structure of the ALP enzyme. [Copyright &y& Elsevier]

Abstract: Platinum/aluminum oxide (Pt/Al2O3) catalyst powders were successfully fabricated to give paper-like composites using ceramic fibers by a papermaking technique. As-prepared composites, called paper-structured catalysts, possessed a fiber-network microstructure on which the Pt/Al2O3 powders were scattered. The paper-structured catalysts were subjected to a catalytic reduction process of nitrogen oxides (), and demonstrated a higher performance than the original Pt/Al2O3 powders and a commercial honeycomb catalyst. A simple mixture of catalyst powders and inorganic fibers was not effective, suggesting that the characteristic porous microstructure (average pore size: ca. porosity: ca. 70%) in the paper-structured catalyst possibly contributed to the efficient reduction. Besides, the paper-structured catalyst exhibited a quick response in the catalytic reduction at a rapidly increasing reaction temperature as compared to the honeycomb catalyst. The paper composite is flexible, lightweight and easy to handle; thus the paper-structured catalyst is expected to be a promising catalytic material for exhaust gas purification. [Copyright &y& Elsevier]

Abstract: Paper drying is an exergy costly operation, so also a few percent saving may be of importance. The entropy production for the paper drying process was therefore optimised for a conventional multi-cylinder drying machine, the PM2 newsprint machine at Norske Skog ASA in Skogn, Norway. The machine has 51 cylinders grouped in three drying groups; the cylinders are either heated from the inside by steam, unheated or operated under vacuum conditions. The same inlet drying air is supplied in all upper air-pockets of the machine. Our drying model for the paper temperature profile was first compared with measured data from the machine. The total entropy production of the drying process was next calculated, and then minimised subject to a fixed outlet paper moisture content. Inlet humidity and cylinder group conditions were varied. Optimum conditions were obtained for a range of inlet air humidities, and for different cylinder groupings. We found that it was very favourable to increase the inlet air humidity. Other changes had a negligible effect on the total entropy production. The results further pointed to the need for a revision of the current paper drying model, as the second-law of thermodynamics was violated at high air humidities with this model. [Copyright &y& Elsevier]

Abstract: Agitated pulp chests act as low-pass filters attenuating high-frequency variability and thus complimenting the action of control loops which attenuate slow disturbances. Dynamic tests made on industrial and scale-model chests show that non-ideal flows, including short-circuiting, recirculation, and dead zones, are common and significantly reduce the ability of the chest to attenuate fluctuations. In this paper, we explore the effect of suspension yield stress on the extent of non-ideal flow and upset attenuation by conducting dynamic tests using two different pulp suspensions: a long-fibred softwood pulp and a shorter-fibred hardwood pulp. Dynamic tests were also made as a function of the fibre mass concentration, with the yield stress used to characterize the dynamic behaviour observed in mixing. It was found that while the yield stress plays a significant role determining the mixing of pulp suspensions, the dynamic behaviour of pulp mixing could not be fully described by yield stress alone. Tests show that when the surface of the cavern created by the impeller approaches the pulp outlet, which was located on the impeller wall, the percentage of short-circuiting approached zero. [Copyright &y& Elsevier]