David John Wedlock

Creaming and flocculation in emulsions containing polysaccharide

Abstract The influence of ionic polysaccharides on the stability of hydrocarbon oil-in-water emulsions made using sodium caseinate as emulsifier has been investigated at neutral pH. The four polymers studied were two microbial polysaccharides, xanthan gum and succinoglycan, and two carboxymethylcelluloses of high viscosity (CMC7HOF) and medium viscosity (CMC7MF). In each case, the presence of a small concentration of polymer produced a large increase in creaming, as indicated by the rate of serum separation observed visually. Increasing the polymer concentration led to improved creaming stability due to the rheological effects of the polymer in the continuous phase. The relative stabilizing abilities of the polysaccharides lie in the order: succinoglycan > xanthan gum ≫ CMC7HOF > CMC7MF. Complementary turbidity fluctuation measurements provide evidence for emulsion droplet flocculation in the presence of all four anionic polysaccharides. The effects of ionic strength on creaming and flocculation were investigated: the results confirm the general destabilizing effect of polysaccharides on food emulsibns at low concentrations. The extent to which the phenomenon may be generally ascribed to depletion flocculation, as opposed to some kind of bridging flocculation, is discussed in the light of other recent experimental observations.

Influence of polysaccharides on the creaming of casein-stabilized emulsions

Abstract The kinetics of creaming of concentrated oil-in-water emulsions made with sodium caseinate as emulsifier has been investigated at neutral pH as a function of the concentration of added polysaccharide using an ultrasound velocity scanning technique. Four different polysaccharides are studied: two microbial polysaccharides, xanthan and succinoglycan, and two carboxy-methylcellulose polymers of ‘medium’ and ‘high’ viscosity. A correlation is found between the relative stabilizing abilities of the polysaccharides and their rheological behaviour in solution at a polymer concentration of 0.25 wt%. A low concentration of each polymer leads to serum separation in emulsions of 10, 15 or 50 wt% oil. Stabilization of emulsions containing xanthan or succinoglycan at polymer concentrations of 0.25 wt% or above is associated with the formation of a gel-like emulsion structure with a significant yield stress. Surface viscosity measurement at a macroscopic oil-water interface provides evidence for weak interfacial interaction between casein and carboxymethylcellulose at the emulsion droplet surface. The implications of this for the mechanism of emulsion destabilization by polysaccharides are discussed.

Creaming and rheology of emulsions containing polysaccharide and non-ionic or anionic surfactants

The influence of the anionic polysaccharide rhamsan on the kinetics of creaming of concentrated oil-in-water emulsions (30 wt.% mineral oil, 1 wt.% surfactant, pH 7) has been monitored visually and by ultrasound velocity scanning, The rate and extent of serum separation was found to depend not only on the polysaccharide concentration but on whether the emulsifier was a non-ionic surfactant (polyoxyethylene (20) sorbitan monolaurate (Tween 20)) or an anionic surfactant (sodium dodecyl sulphate (SDS)). Creep rheological measurements have been made on the same emulsions over the shear stress range 10−2–10 Pa. There is a good correlation between the difference in the limiting low-stress apparent shear viscosity of Tween 20 and SDS emulsions containing 0.1 wt.% rhamsan and the difference in the creaming stability of the same emulsions. These results demonstrate the importance of surfactant—biopolymer interactions in controlling the stability of emulsions.

Simulation of simultaneous aggregation and sedimentation

Abstract Aggregation and sedimentation of fine particles are commonly encountered phenomena in mineral processing as well as in many other industrial processes. Previous computer models tend to concentrate on certain aspects of either aggregation or sedimentation but not on both at the same time, even though the two processes often take place simultaneously. This paper describes an integrated random walks based model in an attempt to ‘fill the gap’. The main features of the model include the ability to simulate aggregation, breakage and internal re-arrangement of aggregates; to allow aggregation and sedimentation to take place simultaneously; to allow conditions (e.g. particle concentration) to change either gradually or suddenly during the simulation; and to have multiple components where each component may behave differently from another. Simple comparison with some available experimental results is presented to demonstrate the versatility of the simulation program. Potential applications and future developments are also discussed.

Effect of formaldehyde pre-treatment on the intrinsic viscosity of alginate from various brown seaweeds

Abstract Sodium alginate samples were extracted from brown seaweeds by various methods and the effect of the extraction procedure on the intrinsic viscosity and, by implication, the molecular weight were studied. Pre-treating the weeds with formaldehyde and ethanol prior to extraction with sodium carbonate or extracting the weeds under neutral conditions with selected calcium ion sequestrants resulted in alginates with enhanced intrinsic viscosities. The intrinsic viscosity of alginate samples during extraction decreases significantly with increasing pH due to the presence of phenolic compounds. By isolating the phenolic compounds with formaldehyde or extracting them with ethanol, degradation processes can be inhibited.

Future fuels and lubricant base oils from Shell Gas to Liquids (GTL) technology

Shell was the first oil marketer to bring to commercial scale, Gas to Liquids (GTL) technology for fuels and base oils production. This started with the commissioning of the multi-purpose GTL facility at Bintulu, Malaysia in 1993. The plant produces both automotive gas oil (GTL Fuel) as well as a number of speciality products including detergent feedstocks, a range of Fisher-Tropsch commercial wax grades, and a feedstock for base oils production. The base oil feedstock has been shipped to Shell facilities in Japan and France since 1994 where it is solvent de-waxed to produce the first commercially available GTL base oils. The GTL Fuel is currently being used in premium diesels in Germany, Greece and Thailand. Shell has announced in 2003 its intention to build two world scale GTL trains in Qatar and this will include substantial fuels and base oils facilities. The diesel cut is characterised by very good cetane quality, low density, plus negligible sulphur and aromatics contents; such properties make it potentially valuable as a fuel with lower emissions than conventional automotive gas oil, either as a standalone fuel or in blends. The base oils will cover a wide grade range with the majority of volume being API Group III grades of 4 cSt and above. These base oil grades will show the superior additive responses expected from 100% saturates catalytically de-waxed base oils.

Factors influencing the molecular weight of sodium alginate preparations

Abstract The sodium alginate derived from some brown seaweeds is shown to have a molecular weight in excess of ~ 1 × 10 6 . In order to isolate such samples care must be taken in the choice of calcium ion sequestrant used and the type of treatment that the sample is subjected to post-extraction. The tendency of the sodium alginate to depolymerise during freeze-drying has been unequivocally demonstrated. The degradation is manifest not only as a reduction in the mol. wt of the samples but also a reduction in the persistence length or chain stiffness of the samples, inferring that not only does glycosidic bond cleavage occur but also some further modification of some of the uronic acid residues, resulting in a more flexible chain.

Automation of ultrasound velocity scanning for concentrated dispersions

Abstract There have been a number of reports of the scanning of concentrated emulsion and suspension systems to obtain ultrasound velocity profiles which are subsequently converted to concentration profiles. These have contributed significantly to the understanding of sedimentation and creaming behaviour. The systems described have generally required manual intervention to measure the ultrasound velocity at each vertical level. For scans which can possess upwards of 100 individual measurements, each taking a significant time (minimum 30 s), the approach is tedious and limiting for dynamic systems. This paper describes an approach to an automated system which utilises an inherently highly accurate ultrasound velocity measuring technique, the sing-around technique. The method is modified to deal with problems of variable ultrasound attenuation and interference, which potentially present some limitations to the application of even the sing-around technique. The result is a “black box” which provides the basis of an automated ultrasound velocity scanner system without the need for relatively expensive signal generation equipment. The results obtained in terms of concentration profiles compare well in terms of volume fraction values with the established manual technique, with each scan point being obtained at least an order of magnitude faster than by the manual technique. Measurement of times of flight to within 1 ns in 30 μs is possible using the modified sing-around approach, compared with 5 ns in 30 μs for the manual pulse comparison technique.