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Alkyd emulsions
YKI – Ytkemiska institutet.
1996 (English)In: Polymeric Materials Encyclopedia / [ed] Salamone, J.C., CRC Press, 1996, p. 154-160Chapter in book (Refereed)
Abstract [en]

Introduction: The use of waterborne alkyds as binders in coatings is not new, their history going some 30 years back in time. Mostly, this has been in the form of water soluble alkyds, with high acid numbers that provide the water solubility of the resins after neutralization with amines. Such alkyds are mostly used in industrial coatings. Emulsified water insoluble alkyds have so far found most use in the field of decorative and protective coatings, although their use is still limited. A major factor limiting the use of alkyd emulsions is their low rate of oxidative drying, together with some remaining problems concerning colloidal stability of the emulsions. Several factors are believed to contribute to the reduced drying properties of alkyd emulsions as for example interaction between the drier and other paint components and solubility properties of the drier. A water borne paint is a complex system that besides the alkyd droplets in water also contains pigments, dispersants (to stabilize the pigments), surfactants (stabilizing the alkyd droplets), thickeners and several other additives, see Figure 1. The impaired film properties may at least partly be caused by the surfactant which will remain in the paint film and act as a plasticizer. For the segment decorative and protective coatings in Western Europe the market volumes are as follows (solid binder): Solventbased, low solids: 400 ktonne/annum Waterbased, polymer dispersion: 375 ktonne/annllrn Solventbased, high solids: 20 ktonne/annum Alkyd emulsion based: 15 ktonne/annum In most cases the alkyd emulsion is used as co-binder, especially in (hiding) stains and primers for exterior use. In these segments alkyds in white spirit are however still the binder of choice. In the case of alkyd resins for the decorative field, the environmentally friendly possibilities are either as high solids systems or as waterborne emulsions. With the present state of technology, it is very unlikely that alkyd emulsions can match the performance of the present solvent based siliconized alkyds and other extreme outdoor durable systems. Because of their more conventional permeability behaviour and the higher applied layer thickness, high solids seem more suitable for this purpose. Going to the lower end of the market, high solids systems can be applied in almost every segment, the only limitation being their price. For the lowest segments (primers and stains) their application will be limited.It is in these segments that acrylic dispersions have acquired a good reputation both their performance and price have been accepted. In the middle section, ranging from normal outdoor durable alkyds to the better performance stains, alkyd emulsions can be positioned. Their versatility and excellent environmental score (no volatile organic components are necessary) make them exceptionally suitable for this. In many outdoor applications alkyd emulsions will be compared with acrylate dispersions. Typical advantages of acrylate dispersions are their low particle size, quick drying, and good outdoor durability. The last two of these advantages can also be regarded as a disadvantage, since the drying often is considered to be too quick when only small amounts (under 5 %) of coalescing agent are used. The nomenclature then changes from "quick drying" to "short open times". The advantage of good outdoor durability is a.o. based on a good hydrolysis resistance, meaning that although it may take long, once a coating based on acrylic dispersion has deteriorated, the remainders cannot be removed by the usual alkaline paint stripper or heat gun (the dispersions are thermoplastic). Instead flakes of coating will come loose and remain in the environment. The main disadvantage of acrylate dispersions however, the seriousness of which is once again depending upon the application area, is that there always has to be some compromise between film formation (low MFI ) and good blocking properties (high Tg). Since in alkyd emulsions not all chemistry is "finished" when the film is applied, these emulsions can be expected to outperform the thermoplastic dispersions when it comes to properties that are related with film formation from a low Tg material, such as penetration (one of the factors controlling adhesion) and gloss, combined with good dirt pick-up resistance. Whereas the contents of a particle in a polymer dispersion is a true polymer (MW = 100.000 to 1.000.000), in an alkyd emulsion particle we find an oligomer, with a molecular weight ranging from 2000 to 8000. To make a real polymer out of it, the help of cobalt and atmospheric oxygen is required , just as is the case with a conventional alkyd. The fact that molecular buildup still has to take place also means that "derailments" of the crosslinking process will also take place. This means that a film cast from an alkyd emulsion will still exhibit the usual alkyd yellowing and slightly pungent smell. These are caused by decadienal-like structures and hexaldehyde, respectively, resulting from decomposition of the initial hydroperoxide and subsequent beta scission. Always compare an alkyd emulsion with an alkyd and not with a polvmer dispersion in this respect. The aspects where alkyd emulsions differ mostly form solvent-borne alkyd systems are: a) that they are formulated together with water, inducing a risk of hydrolysis upon storage, b) the disperse state of the alkyd, necessitating a high degree of colloidal stability and c) the peculiarities shown in the drying properties of alkyd emulsions. These aspects will be dealt with in the following paragraphs.

Place, publisher, year, edition, pages
CRC Press, 1996. p. 154-160
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-13581OAI: oai:DiVA.org:ri-13581DiVA, id: diva2:981287
Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved

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