Quantification of powder wetting by drop penetration time

29-01-2015 14:46, af Peter Dybdahl HedeSend to a colleague Send to a colleague

In a recent study by Oostween et al. the wetting step of rehydration of a food powder is investigated by studying drop penetration times (DPTs) in powder beds. A single droplet is placed on powder beds with various porosities and DPT is recorded by a digital microscope camera. DPTs for corn starch, potato starch and wheat starch are compared to the model proposed by Hapgood et al. (2002). Characterization of the internal structure of miniature powder beds is performed using a Phoenix microCT.

Loosely packed powder beds show expected macrovoids and recorded DPTs are within an order of magnitude of the theoretical predictions. However, DPTs for starches deviate from predicted values. Visual observations indicate that the drop penetration area within the bed exceeds the drawing area of the droplet itself. Adaptation of the model for the drop penetration area by constant factor increases DPTs, leading to better correspondence between experimental and theoretical DPTs. Most promising results are obtained by replacement of the effective pore radius predicted by the Carman–Kozeny equation with the experimentally observed pore radius seen in microCT imaging. Theoretical DPTs predicted by this semi-empirical model are in good agreement with experimental results. This is promising for the application of the current method to various food powders, to control quality, optimize properties or tackle problems during production.

Processing fine powders by roll press

29-01-2015 14:44, af Peter Dybdahl HedeSend to a colleague Send to a colleague

The gas trapped into fine powders causes specific problems like feeding disturbances during roll compaction process. In a recent study by Esnault et al., the gas flow and its effect on the rolling process are numerically investigated in the rolling direction, using Darcy’s law and assuming the permeability as a function of both material density and particle size through Carman–Kozeny relationship. The solid properties evolution is based on the Johanson model, whereas the solid speed is determined from the conservation of the material mass.

Computational results of solid properties and gas pressure distribution are presented by considering bentonite powder properties. According to material and process parameters, especially rolling speed and powder permeability, we discuss conditions for the escape of gas through the porous material during the process and stability conditions of the feeding at the rolls’ entry.

Beyond the simplicity of the model (1D), it allows for a better understanding of fine powders processing by roll press. It highlights the combined effect of the permeability of the powder and the rotating speed on the gas pressure, during roll compaction process.

Glass Transition Accelerates the Spreading of Polar Solvents on a Soluble Polymer

17-06-2014 10:10, af Anders HallströmSend to a colleague Send to a colleague

In a study that may have an impact on redispersibility of powders in water, the wetting of polymer layers by polar solvents has been studied. As known before, when a droplet of solvent spreads on a substrate, both the contact angle and the spreading velocity decrease with time as solvent is taken up by the substrate. In the study, it is shown that when the substrate is initially glassy, the contact angle may decrease steeply, and that this variation is related to glass transition due to the solvent uptake.

(Dupas, J., Verneuil, E., Van Landegheim, M., Bresson, B., Forny, L., Ramaioli, M., Lequeux, F., Talini, L., Phys. Rev. Lett. 112, 188302, published 6 May 2014)

Study on the progress of solidification, deformation and densification during semi-solid powder rolling

21-05-2014 13:40, af Peter Dybdahl HedeSend to a colleague Send to a colleague

Semi-solid powder rolling (SSPR) is a novel strip manufacturing process, which combines the features of semi-solid rolling and powder rolling. High-performance metallic strips can be successfully prepared by semi-solid powder rolling. Based on its features, solidification, deformation and densification occur simultaneously and collaboratively during rolling. Progresses of them during semi-solid powder rolling were investigated via temperature, rolling force and density. (more…)

The effect of the nucleation ability on solidified microstructures of gas-atomized Fe–6.5 wt.%Si alloy powder

21-05-2014 13:38, af Peter Dybdahl HedeSend to a colleague Send to a colleague

The Fe–6.5 wt.%Si alloy powders were prepared in a recent study by Son et al. (2014) by high-pressure gas atomization in which the nucleation ability of the melt varied with the different purities of the raw materials and experimental conditions. (more…)

Dust generation from powders: A characterization test based on stirred fluidization

28-03-2014 11:18, af Peter Dybdahl HedeSend to a colleague Send to a colleague

The aim of a recent paper by Saleh et al. (Powder Technology 256) was to develop an experimental test based on combination of fluidization and stirring in the perspective of its use for dustiness assessment. (more…)

Effects of atmosphere and milling time on the coarsening of copper powders during mechanical milling

28-03-2014 11:16, af Peter Dybdahl HedeSend to a colleague Send to a colleague

The coarsening behavior of copper nanopowders (50–150 nm in size) during mechanical milling was investigated in a recent paper by Madavali et al. (2014 – Powder Technology 256) as a function of milling atmosphere and milling time. Pure copper powders were milled under argon and air atmospheres for up to 80 h and the crystal structure, microstructure, and composition of the milled powders were investigated. (more…)

Microencapsulation of omega-3 fatty acids

31-01-2014 15:31, af Anders HallströmSend to a colleague Send to a colleague

A number of functional-food formulations were encapsulated by spray drying, and the protection from oxidation was studied. Microcapsules of gum arabic and of a ternary mixture of gum arabic, maltodextrin and whey protein isolate showed a high degree of protection and high microencapsulation efficiencies. These microcapsules also had smooth surfaces which kept unaltered during storage.

(Gallardo, G. et al., Microencapsulation of linseed oil by spray drying for functional food application, Food Research International 52 (2013) 473 – 482)

Surface Composition of Spray Dried Food Powders

28-12-2013 12:02, af Anders HallströmSend to a colleague Send to a colleague

The surface composition of model food products, consisting of varying amounts of sodium caseinate, maltodextrin and soya oil, was investigated after spray drying using Electron Spectroscopy for Chemical Ananlysis ESCA. (more…)

Particle Growth in Fluid-Bed Agglomeration of Milk Powder

28-12-2013 11:51, af Anders HallströmSend to a colleague Send to a colleague

Milk powder was agglomerated in a small batch fluidized bed using pure water sprayed from a two-fluid nozzle. The influence on particle growth of liquid flowrate, mass of powder in the bed, initial particle size and product type (skim milk and whole milk) was studied.