Proceeding Articles

Requirements for paper to be used as substrate for printed functionality were investigated. A recyclable, multilayer-coated paper substrate that combines adequate barrier and printability properties for printed electronics and sensor applications was developed. In this multilayer structure, a thin top-coating consisting of mineral pigments is coated on top of a dispersion-coated barrier layer. The top-coating provides well-controlled sorption properties through controlled thickness and porosity, thus enabling optimizing the printability of functional materials. The optimum barrier layer structure was investigated by studying the influence of latex type and amount in blends with different size and shape factor kaolin pigments. Highly aligned high shape factor kaolin improved barrier properties in general, but was found especially useful against organic solvents, which may degrade the latex. Dimensional stability and its influence on substrate surface properties as well as on functionality of conductive tracks were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of printed tracks. As proof of concept functional devices, hygroscopic insulator field effect transistors were printed on the multi- layer curtain coated paper using a custom-built roll-to-roll hybrid printer.

We explored the sensitivity and selectivity of gold nanoparticles (AuNPs) treated paper as a generic SERS diagnostic platform to identify and quantify low concentrations of a specific (bio)analyte in aqueous solutions. The effects of gold nanoparticles (AuNPs) concentration on their adsorption and aggregation states on paper were explored. The surface coverage of AuNPs on paper scaled linearly with their concentration profile in solutions. The SERS performances of the AuNPs-treated papers were evaluated with a model Raman molecule, 4-aminothiophenol (4-ATP), and their SERS intensities increased linearly with the density of AuNPs on paper. To increase the SERS sensitivity, the retention and aggregation state of nanoparticles on paper was controlled by pre-treating paper with a series of cationic polyacrylamide (CPAM) solutions. The CPAM pre-treated paper produced a more uniform distribution of AuNPs compared to untreated paper. Higher surface coverage and aggregation of AuNPs on paper were favoured by CPAM solutions of higher concentration, charge density and molecular weight. The optimized AuNPs-CPAM paper showed a higher sensitivity and Raman enhancement factor (EF), which was almost an order of magnitude higher than the untreated AuNPs paper. After the SERS sensitivity towards the detection of model Raman molecule (4-ATP) was proven, the SERS selectivity of AuNPs paper was demonstrated by functionalizing the AuNPs with a model biomolecule platform consisting of biotin/streptavidin assemblies for the detection of antibody-antigen binding. The modification of antibody local structure due to the interaction with antigen was detected. Evidence of antigen binding was elucidated from the SERS spectra, confirming the presence of antigen. Reproducible spectra features were observed for the functionalized AuNP papers which were exposed to different concentration of antigen; the spectra intensity increased as a function of antigen concentration. The sensitivity and selectivity of AuNPs paper substrates as a low-cost and generic SERS platform for bio-diagnostic application was demonstrated.

Many materials, including paper products, come in sheet form and exhibit orthotropic symmetry. Information about the elastic stiffnesses of such materials can often be obtained quickly and accurately using a measurement method based on the vibration modes and natural frequencies of rectangular panels. The method is outlined and illustrated, and some case studies discussed in which the method is applied to fibre-reinforced composite materials and to the selection of wood for musical instruments.

In this work we propose a novel separation technique based upon the control of the threshold for motion of different classes of particles in yield stress fluids. The principle is demonstrated by observing the motion of particles under the influence of a centrifugal force in a weak gel. Here we develop calibration curves of the force required to initiate motion in a gel under numerous configurations of the particles. Demonstration separations of bidisperse suspensions are reported. Here we achieve complete separation of dilute suspensions based upon length, diameter, or density.

The objectives of this article are:

– First, to theoretically propose a unified concept: the net normal force per crossing point,

– Second, to experimentally undertake refining trials on a pilot disc refiner in order to compare all concepts for the refining intensity and to validate the chosen one.

We will begin by re-visiting the old concepts of the refining intensity, in the low consistency regime. After a theoretical proof based upon the physics of the phenomena, applied to beaters and industrial refiners, a unified concept of the refining intensity is proposed and strengthened: the net normal force per crossing point.

Then, experimentations are undertaken on a pilot refiner (single disc) in hydracycle (or batch) conditions. More precisely, the effects of the grinding codes and of the average crossing angle of the bars are analyzed in a set of 6 refining trials. For these experimentations, different engineering concepts of the refining intensity are compared (specific edge load Bs, specific surface load SSL, modified edge load MEL, net tangential force per crossing point and net normal force per crossing point). These refining intensities should allow to analysing the cutting kinetics of fibres.

All the chosen engineering concepts reach this goal more or less however the net normal force per crossing point is the best tool. Indeed, through the range of the data concerned, it revealed a clear monotonous evolution with the cutting kinetics on fibres. The more is the net normal force per crossing point, the more is the cutting effect on fibres.

Transport coefficients and correlations recently used to describe surfactant contribution to particle and water transport in a laboratory flotation column were used to simulate the impact of surfactant contamination on the flotation selectivity of industrial two-stage deinking lines. Simulation results showed that surfactants are slightly removed in the first flotation stage and are concentrated in the second one, where they induce a drop in ink flotation and in fibre entrainment. Subsequently, flotation units in the second stage displayed lower ink removal than in the first stage. In the presence of a constant water reject flow, the increase in surfactant contamination in the pulp stock gave a general decrease in the removal of suspended solids. Surfactant removal increased from 5 to 50%, however, this increase was not sufficient to prevent surfactant accumulation in the deinking line. Simulation results were compared with data collected in an industrial deinking line running in similar conditions and pulp composition, ink and surfactant removal obtained with low surfactant contamination were in line with experimental data.

Biochemical additives encompass materials added to the papermaking operation that are derived from biological origins. Other than starch, the majority of the biochemical additives currently used in the paper industry are enzymatic. Enzymes are protein structures that speed a particular chemical reaction. The enzymes are not consumed during the reaction and can be used repeatedly. The enzymes used in the paper industry typically target one of the four major components of wood: cellulose, hemicellulose, lignin or extractives. Enzymes have been used industrially to aid in bleaching, reduce pitch, enhance strength, alter pulp freeness, and aid in paper machine cleaning. This review focuses on the use of enzymes in the papermaking operation, but also addresses the use of enzymes in other areas of the pulp and paper mill. There has also been considerable work in the use of fungus for improving both mechanical and chemical pulping operations. This is considered a separate topic and is only briefly addressed in this review. The future of biochemical additives may extend well beyond the current use of enzymes and a few notes on potential application are given.

We consider here the behaviour of wood fibre suspension with fibre concentration above that of sedimentation in a pressure driven flow in a straight pipe with smooth walls. The flow behaviour can be roughly divided in two main regimes: the plug flow regime that occurs at low flow rates and the drag reduction regime that occurs at high flow rates. We utilized new experimental methods in order to gain more detailed understanding on the flow behaviour of wood fibre suspensions, and especially on the relevant physical phenomena inducing such behaviour. In addition to carrying out conventional loss experiment, the velocity profiles across the pipe were measured using pulsed ultrasound velocimetry (PUDV) techniques, and the thickness of the lubrication layer in fully developed flow was measured using a laser optical device. Based on our direct measurements, we were able to identify five different flow regimes in suspension flows. In addition, we refined the qualitative picture of these flows in relation to the forming of fibre plug and to the physical phenomena taking place in transition from one flow regime to another one.

A model is presented to describe the orientation and concentration state of semi-dilute, rigid fiber suspensions in a rectangular channel flow. A probability distribution function is used to describe the local orientation and concentration state of the suspension and evolves according to a Fokker-Plank type equation. Long range hydrodynamic fiber-fiber interactions are modeled using the approach outlined by Folgar and Tucker (J. Reinforced Plast. Comp. 3 98–119 1984). Near the channel walls, we apply the no-flux boundary conditions proposed by Schiek and Shaqfeh (J. Fluid Mech. 296, 271–324, 1995). Geometric constraints are used to couple the fibers’ rotary motion with its translational motion. This eliminates physically unrealistic orientation states in the near-wall region. A two-way coupling between the fiber orientation state and the momentum equations of the suspending fluid is considered. Experiments are performed to validate the numerical model by visualizing the motion of tracer fibers in an index-of-refraction matched suspension. The orientation distribution function is determined experimentally as a function of channel height. The results indicate that at distances less than one half fiber length from the channel walls, the model accurately predicts the available fiber orientation states and the distribution of fibers amongst these states. The model further predicts a sharp concentration gradient in this region.

A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects of the dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects on the through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.