Paint products: Accelerated stability and quality testing

On line article at SpecialChem4coatings.com

Paint products: Accelerated stability and quality testing
Part I: Direct measurement of separation and segregation by multisample analytical centrifugation

Scope

To assure continued consumer satisfaction the following stability issues of paint products have to be minimized or avoided:

• syneresis - separation of the liquid dispersion media
• Pigment segregation - change of colour composition inside a container
• Particle segregation - change of particle size distribution inside a container

These stability issues have to be addressed not only during development of new paint products but also for quality assurance during production on a regular basis. This application note demonstrates that multisample analytical centrifugation can be used as an efficient tool for the accelerated evaluation of separation stability of paint products.
In addition this technique provides for high resolution data of particle size distributions of pigments or emulsions.

In part II the application of multi-sample analytical centrifugation for optimization of deagglomeration of pigment particles will be addressed.

Formula V - Formulation Science and Technology 2007

Formula V 19 - 22 November Potsdam, Germany

' Formulating opens the way for tailoring products for specific applications and combining components with often contradicting properties. Formulation science and technology is a core discipline for industries and applications like home care, cosmetics, plant protection and coatings but also of emerging importance in fields like electronics, composite materials and biomedical technology.'

Poster contributions

Accelerated screening of formulations towards freeze-thaw stability

T. Sobisch, D. Lerche, L.U.M. GmbH, www.lum-gmbh.com

Rudower Chaussee 29, 12489 Berlin, Germany

The formulation of dispersion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as a material property. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.
A new multisample approach is presented using analytical centrifugation (STEP-Technology), which allows for an accelerated characterization of destabilization processes (creaming, sedimentation, coalescence, phase separation). The kinetics of these destabilizing processes can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 60 °C.
Analytical centrifugation measures in a rapid way the inherent stability of the samples. Therefore, alterations due to accelerated aging by freeze/thaw cycling can be traced far more earlier than by naked eye.

The wide application potential of this approach is demonstrated by examples of measurements on paints, cosmetics and food products.

Thickener performance traced by multisample analytical centrifugation

T. Sobisch, D. Lerche, L.U.M. GmbH, www.lum-gmbh.com

Rudower Chaussee 29, 12489 Berlin, Germany

Polymeric thickeners are important ingredients to adjust flow properties and stability of formulations. The effect of polymeric additives on dispersion properties is rather complex (viscosity of the continuous phase, adsorption and depletion effects, interaction with other ingredients). Therefore optimum formulation requires extensive experimental investigations.

A new multisample approach is presented using analytical centrifugation (STEP-Technology), which allows for an accelerated characterization of separation stability. Even more, comparing measurements at different centrifugal acceleration information on flow properties is also available (Newtonian, shear thinning or thickening behaviour, yield point, compressive yield stress). The kinetics of separation can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 60 °C.
The potential of multisample analytical centrifugation for formulation design was demonstrated investigating the effect of particle (calcium carbonate, silica) and polymer (polyacryl amide) concentration on dispersion properties of different stabilized suspensions.

making palm oil production less polluting - the wastewater issue

besides the issue of rain forest destruction conventional palm oil production generates up-to 4 tonnes highly contaminated wastewater and more then 40 cubic meter methane per tonne of palm oil produced.

To reduce environmental impact German researchers have developed a treatment process using wastewater and plant residues of oil production for co composting.

Concerns Over Bisphenol A

Human exposures are usually as high as those causing profound effects in rodents

"THE SUSPECTED LINK between low levels of human exposure to bisphenol A (BPA), a monomer widely used to make polycarbonate plastic and epoxy resins, and adverse health affects was bolstered last week with the publication of four toxicology studies that investigated the link.

The most significant paper is a consensus statement from 38 scientists released online in Reproductive Toxicology (DOI: 10.1016/j.reprotox.2007.07.005). It concludes that human exposure to BPA, primarily from food containers, is within the range shown to be biologically active in animal studies. In rodents, low BPA exposures in the womb cause increases in the rates of prostate and breast cancer, reproductive abnormalities, lowered sperm counts, early onset of puberty in females, and obesity and insulin-resistant diabetes."

.................
"Despite growing evidence of toxic effects in lab animals, manufacturers of BPA insist that their product is safe. Steven Hentges, executive director of the polycarbonate/BPA group at the American Chemistry Council, an industry group, disputes the new research in Reproductive Toxicology. He says it is not credible, pointing to a European Food Safety Authority report that indicated no adverse effects of BPA"

Risk due to endocrine effect of compounds used in personal care products

COMMENTARY: Do Personal-Care Products Need a Makeover? (By Gary Ginsberg)

E/The Environmental Magazine - Norwalk,CT,USA
'The typical surfactants, emulsifiers, oils and fragrances are
generally safe. However, as with many things, the devil is in the details
and it's the small ...'

problems associated with phtalates, parabens, benzophenons, bisphenol A, triclosan

What´s Toxic, What´s not

Powered by ScribeFire.

Gefährdungen durch Chemikalien in Bekleidungstextilien - Übersicht

BfR- Bundesinstitut für Risikobewertung gibt einführende Übersicht über Gefährdungen durch Chemikalien in Bekleidungstextilien

depleted uranium amunition leads to groundwater contamination - Uranmunition im Boden führt zu radioaktiver Grundwasserkontamination

Langzeitstudie zur Auflösung von Uranmunition im Boden

"In einer bisher einmaligen Langzeitstudie haben Wissenschaftler vom GSF Forschungszentrum für Umwelt und Gesundheit in Kooperation mit dem Forschungszentrum Dresden-Rossendorf (FZD) untersucht, was mit panzerbrechender Uranmunition passiert, die lange im Boden lagert und damit Verwitterungs- und Auswaschungsprozessen ausgesetzt ist. Die Ergebnisse zeigen, dass die Munition schnell zersetzt wird und Uranverbindungen in das Grundwasser gelangen können."

Exposure to depleted uranium (DU) particles strongly increases risk of lung cancer

The Alchemist Newsletter: May 8, 2007

'Exposure to depleted uranium (DU) particles is a source of growing concern internationally as it increases the risk of lung cancer, according to John Pierce Wise Sr of the University of Southern Maine. Writing in the journal Chemical Research in Toxicology the researchers explain that DU has a density twice that of lead and so is used in military armor and munitions. However, DU dust produced in combat can lead to frequent and widespread exposure of military personnel and civilians during an after combat. Few studies have been undertaken, bit Wise and his colleagues have now tested the effects of DU on cultures of human lung cells. "This is the first report on the cytotoxicity and clastogenicity [chromosome damaging potential] of particulate and soluble DU in human bronchial cells," the researchers say.'

Fast evaluation of dispersion properties for particle size analysis / Charakterisierung der Dispersionseigenschaften für die Partikelgrößenanalyse

LUMiFuge / LUMiSizer - Application

Evaluation of dispersion properties for particle size analysis

Scope

To obtain reasonable information about the size of particles in powders and suspensions full dispersion of the particles is required prior to particle size measurement. Therefore the question arises how to select dispersion conditions and dispersion media properly. Often not the size distribution of aggregates/agglomerates is of interest but the distribution of the size of primary particles. In this case intense processing and suitable dispersants have to be applied. Multisample analytical centrifugation can be used as an efficient screening tool to assist in sample preparation. Even more it allows for high resolution determination of particle size distributions.

LUMiFuge / LUMiSizer - Anwendungsschrift

Charakterisierung der Dispersionseigenschaften für die Partikelgrößenanalyse

Problemstellung

Sinnvolle Ergebnisse zur Partikelgrößenverteilung von Pulvern und Suspensionen sind nur erhältlich, wenn die Partikel bei der Messung hinreichend gut dispergiert vorliegen. Es ergibt sich die grundsätzliche Frage, wie die experimentellen Dispergierungsbedingungen und das Dispersionsmedium zu wählen sind. In vielen Fällen interessiert nicht die Verteilung der Aggregate sondern die der Primärpartikel. In diesen Fällen müssen die Agglomerate intensiv mechanisch beansprucht und Dispergiermittel eingesetzt werden. Die Analytische Zentrifugation mit Multiprobenrotor läßt sich als effizientes Werkzeug beim Screening der geeigneten Probenvorbereitung einsetzen. Darüber hinaus ermöglicht die Analytische Zentrifugation die Bestimmung der Partikelgrößenverteilungen mit hoher Auflösung.

Poster presented at the 4th World Congress on Emulsions Lyon 2006

Evaluation of long term stability of model emulsions by multisample analytical centrifugation

T. Sobisch, D. Lerche,

L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany,

www.lum-gmbh.com, info@lum-gmbh.de

F. Aguilar, G.G. Badolato, H.P. Schuchmann,

Institute of Engineering in Life Sciences, Department of Food Process Engineering, University of Karlsruhe, Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany

Abstract

Destabilisation processes in emulsions are very complex. Aging and breaking of emulsions are the result of several processes – creaming or sedimentation, flocculation, coalescence, Ostwald ripening, phase inversion – which can occur separately or simultaneously. This is the main reason why the development of reasonable procedures for shelf life prediction is very difficult and always depends on the product which is subject to evaluation.

Multisample analytical centrifugation with photometric detection (STEP-technology) is a tool for an accelerated characterisation of any demixing processes (creaming, sedimentation, phase separation) as well as for the quantification of time dependent structural alterations (e.g. flocculation, coalescence, Ostwald ripening).
Model emulsions were designed exhibiting creaming, coalescence, flocculation or Ostwald ripening as the dominating mechanism for instability. To answer the question whether multisample analytical centrifugation can be used to predict the long term stability of emulsions results obtained are compared with rheological measurements, particle size analysis by light scattering and common accelerated stability tests like freeze/thaw cycling and storing at 45 °C.

In all cases the creaming (or sedimentation) velocity measured by analytical centrifugation markedly increased during storage induced by increasing salt concentration (flocculation), increasing droplet size (using emulsifier with lower HLB value) or increasing the fraction of clove oil (Ostwald ripening). During a relatively short period of observation only a small part of these alterations could be detected using conventional methods of emulsion characterization.

Method of multisample analytical centrifugation

The multisample analytical centrifuge (LUMiFuge, LUM GmbH, Berlin Germany) used in this study employs the STEP technology, which allows to measure the intensity of the transmitted light as function of time and position over the entire sample length simultaneously (measurement scheme see Figure).

Measurement scheme of the multisample analytical centrifuge with photometric detection. Parallel NIR-light is passed through the sample cells and the distribution of local transmission is recorded at preset time intervals over the entire sample length.

The data are displayed as function of the position within the sample, representing the distance from the centre of rotation. The transmission profiles obtained are representative for the variation of droplet (particle) concentration inside the sample (low transmission means high, high transmission means low droplet concentration).

The progression of the transmission profiles provides information on the kinetics of the separation process and allows particle characterization.

At the same time up to 8 different samples can be analysed simultaneously at constant or variable centrifugal speed up to 2300 g. The separation behaviour of the individual samples can be compared and analysed in detail by tracing the variation in transmission at any part of the sample or by tracing the movement of any phase boundary.

As for a given type of sample cells the position corresponds to a defined sample volume the relationship between the position and the volume can be established by calibration. This allows to directly determine separated phase volumes and to calculate packing densities.

For further details of the application of the method for characterization of emulsions see [1,2,3].

Silicon oil-in-water emulsions with and without induced flocculation

Oil-in-water emulsions φ= 30 %

Sample preparation:

1. 40 % oil / 1% sodium dodecyl sulfate

Process:Microfluidizer® 500 bar

2. Diluted with deionized water or concentrated salt solution to result in 30 % oil and 0, 150 and 300 mM NaCl

Creaming without centrifugation (high salt concentration)

Centrifugation – creaming at 1100 g (low salt concentration)

• During the storage time no significant changes in droplet size and viscosity at 0 and 150 mM NaCl

• Creaming and water separation clearly visible after the addition of salt (c > 500 mM NaCl)

• For small concentration of salt the height of separated water (in a cylinder) not detected or remains constant

• The creaming velocity measured by the analytical centrifuge increases during storage, increasing the salt concentration and increasing the temperature

• All emulsions were very vulnerable to freeze/thaw cycling

Coalescencing vegetable oil-in-water emulsions –

stabilised with emulsifiers having different polarity

Oil-in-water emulsions j = 30 %

Process:Microfluidizer® 500 bar

Non ionic emulsifier Emulsions

η mPa/s x_3,2 µm

Tween 20, HLB 16.7 3.73 0.66

Tween 80, HLB 15 3.11 0.62

Tween 65, HLB 10.5 3.12 1.35

Centrifugation – creaming at 1100 g

Movement of the position of the interface emulsion –water (distance to the centre of rotation) during centrifugation measured just after preparation of the emulsions.

Already at this stage distinct differences in stability traced due to bigger droplets (Tween 65) or higher viscosity (Tween 20)

• During storage no significant changes in droplet size and viscosity

• Creaming velocity increase due to bigger droplet sizes with decreasing emulsifier HLB value (more coalescence during production) or lower viscosity

• Increased destabilization at higher temperature
• Only unstable emulsion vulnerable to freeze-thaw cycling
  

Ostwald ripening in water-in-oil emulsions

Water-in-oil emulsions j = 30 %

Process:Microfluidizer® 500 bar

Continuous phase mixture clove/vegetable oil viscosity η

Sample 1 50/50 76 mPa/s

Sample 2 75/25 47 mPa/s

Sample 3 25/75 102 mPa/s

Sample 4 0/100 141 mPa/s

Emulsifier: polyglycerol polyricinoleat PGPR 90 – HLB 1

• Marked Ostwald Ripening only at mass fraction clove oil > 0.5

• Emulsions droplet size and sedimentation velocity increase during storage, however the viscosity remains unchanged

• Instability increases increasing the storage temperature

• Results of droplet size measurements and sedimentation velocity are in good agreement

Conclusion

The investigations revealed that analytical centrifugation is well suited for accelerated stability testing of emulsions of varying composition and for various types of slow destabilizing mechanisms. Whereas measurements of droplet size distributions and viscosity measurements were not able to always detect the beginning of destabilization, centrifugal analysis enabled to detect instabilities faster and more accurately. The multisample technique therefore is ideally suited for screening purposes in emulsion product development.

Acknowledgement

This study was supported by a grant from the Bundesministerium für Wirtschaft und Technologie (grant number KA 0047301AWZ3).

References

[1] T. Sobisch, D. Lerche, Rapid characterization of emulsions for emulsifier selection, quality control and evaluation of stability using multisample analytical centrifugation

SCI/RSC/SCS conference Cosmetics and Colloids, London 15 February 2005

http://www.soci.org/SCI/groups/col/2005/reports/pdf/gs3257_sob.pdf

[2] T. Sobisch, D. Lerche,

Rapid selection of dispersants and evaluation of emulsion stability by analytical centrifugation

La Rivista Italiana delle Sostanze Grasse 6/2005 308 – 316

[3] T. Sobisch, D. Lerche, 2007

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

http://docs.google.com/Doc?id=dcvcr5vw_1fqx3hp

PERFLUORIERTE VERBINDUNGEN - Hintergrundpapier Umweltbundesamt

Zitat:

Perfluorierte Verbindungen sind verstärkt in die öffentliche Diskussion geraten: „Perfluorierte Verbindungen in aller Munde“, „Gift in Pommes“: Unter diesen und ähnlichen Titeln berichten die Medien über Funde in Trinkwasser und Nahrungsmitteln.

.....

Das ist leider nicht alles: Für Umweltschützer ist es ein Problem, dass Perfluorcarbonsäuren und -sulfonsäuren überall verbreitet sind: Sie lassen sich in Flüssen, in den Weltmeeren, in Robben, Nerzen, Füchsen, Eisvögeln und Fischen aus der kanadischen Arktis und selbst in der Leber von Eisbären auf Grönland nachweisen. Besonders bedenklich sind jedoch die weltweiten Nachweise im menschlichen Blut.

Hintergrundpapier Perfluorierte Verbindungen