Aqueous (water-based) dispersions make paint or plasters water-repellent. They also enhance the properties of wood adhesives and concrete. In this case they are suitable either to accelerate or even decelerate the curing-time during processing. In flooring formulations they may enhance the ease of on-site applications.
Whether they’re used for paint, adhesives or concrete and mortar, dispersions all have something in common: they’re produced by emulsion polymerisation. Thanks to many years of experience with this process, Emerell can help customers produce these additives on any scale, from smaller to larger volumes.
What exactly are water-based dispersions and emulsion polymerisation?
Dispersions are physically stabilised mixtures of insoluble polymers in a liquid, in this case water. Emulsion polymerisation is the chemical process used to make them.
The following components are required:
● Water: liquid component and solvent
● Emulsifiers: stabilise the dispersion during manufacture, storage and use
● Monomers: the units that make up the polymers that determine the properties of the dispersion
● Initiators: chemically unstable molecules, causing after decomposition or initial reaction the monomers to react themselves to form a polymer chain or, depending on the monomer-structure and properties, a two- or three-dimensional network
Liquid monomers producing polymers
Emerell uses a whole range of different liquid monomers to produce the desired polymer. They are chemically unsaturated molecules containing one or more vinyl and/or carboxylic-groups, including styrene, VeoVa monomers, 2-Ethylhexyl acrylate, butyl acrylate, methyl methacrylate and methacrylic acid. There are many others available on a commercial scale and not limited to research and development.
Emulsifiers
Emulsifiers are mainly differentiated by their charge – anionic, cationic or even non-ionic. Polyvinylalcohols (PVA) are very commonly used for a variety of products (dispersions). As all of them stabilise the dispersion, it might be obvious that their (correct) choice does show a significant impact on product-properties in their specific applications.
The dispersion manufacturing process
First of all water and emulsifier(s) are blended, heated to the desired temperature in the reactor before the initiator and monomers are added. The latter process step usually takes several hours under well-defined conditions regarding temperature, monomer addition-rate(s) and stirring. After dosing, physical (evacuation) or chemical treatment (redox initiators) can be used to reduce residual monomers. Then the dispersion is allowed to cool before various additives are introduced to make the finished product, which is characterised by typical values such as active-content, pH-value and viscosity.
Oil-in-water-dispersions
You don’t necessarily need synthetic (i.e. crude-oil based) substances to make an emulsion. Nature has given us milk, and humans have come up with emulsions such as mayonnaise and whipped cream, where egg white or milk fat serve as natural – and of course also biodegradeable – emulsifiers. In the case of mayonnaise there is only one significant difference in technical terms spoken: in this case we have little water (egg) finely distributed in lots of (vegetable) oil – called a water-in-oil-dispersion. In all other examples, the opposite is the case: a little something unsoluble, such as polymers or even oil and fat, is finely distributed in lots of water – so called oil-in-water-dispersions.
Upscaling dispersions for commerciality
It’s possible to produce small amounts on a lab-scale of some millilitres or litres, or quantities up to a whole rail tanker delivery in one batch.
To be sure that small quantities can be made on a commercial basis, intermediate pilot equipment (i.e. 50 and 100kg) is used to test formulas, to run polymerisation smoothly and ensure the dispersions have the desired properties.
When going through this process of up-scaling, temperature control is the most important issue to take care of. A so-called and uncontrolled “runaway-reaction” can cause considerable damage to equipment, exposure to hazardous materials or even severe spillages, up to environmental pollution of the neighbourhood or nature.
Interestingly, you cannot easily switch from one reactor to another one, assuming they are not identical in design, i.e. dimensions, pumps or stirrers and process parameters such as temperature-control or feed-rates, etc. These variances are also one of the reasons why every single batch made goes through a quality-testing with at least a reading of the parameters mentioned earlier (solid content, pH and viscosity). In some cases, it may also be prudent to take other measures as well.
Emerell supports customers throughout the process, from a feasibility study through to regular production.
Eric Gay and Dr Michael Lang are with Emerell