From what raw materials are alkyd resins made?
Alkyd resins are made of dicarboxylic acids (generally phthalic acid is used), multivalent alcohols (usually a trivalent alcohol – glycerin) and fatty acids (e.g. from linseed oil).
What are modified alkyd resins?
In modified alkyd resins, in addition to the traditional three basic substances – dicarboxylic acid, polyvalent alcohol and fatty acid – a fourth component is chemically incorporated into the molecule. The modification is aimed at improving certain properties of alkyd resins. Unfortunately, there is associated deterioration in some other properties. Phenolic resins are used as the modifying component, styrene, vinyl toluene, acrylic, epoxies, isocyanate, silicones and amines.
Please provide a breakdown of alkyd resins depending on the oil content and the use of the individual resin groups
1. Chude żywice alkidowe zawierają poniżej 40% oil and are used in combination with urea and phenolic resins in acid-hardening varnishes or in combination with melamine resins in industry, in stoving varnishes.
2. Średnio tłuste żywice alkidowe zawierają 40-60% oil and are used in air-drying varnishes for interior and exterior applications, as well as in car paints.
3. Tłuste żywice alkidowe zawierają powyżej 60% oil and are used in air-drying wood and steel paints outdoors.
How is the curing process of air-drying alkyd varnishes and paints?
During the chemical curing of air-drying alkyd lacquers and paints, solvents and thinners first evaporate. In this way, access for oxygen to the double bonds of unsaturated fatty acids in the resins is opened. By breaking the double bonds, the oxygen becomes chemically bound. This way the molecules get enlarged, and alkyd resins harden due to oxidation. Because, oxygen can be added, the double bonds must break, also in this case we can talk about polymerization.
What component of alkyd resins causes them to turn yellow, e.g. in the absence of light?
The yellowing of alkyd resins is caused by the linolenic acid they contain. This fatty acid is a component of linseed oil, whose share is 51%. Because linseed oil is especially willingly used in the production of alkyd resins, many of these resins are more or less prone to yellowing. It is true that linolenic acid could be removed from linseed oil, but it would make it more expensive. Otherwise, linolenic acid having three double bonds in one molecule promotes oxidative hardening. This is the reason, for which it is difficult to give up this fatty acid.
What component of alkyd resins determines their flexibility and resistance to atmospheric agents?
The flexibility and weather resistance of alkyd resins depends on the amount and type of fatty acids. In the case of alkyd varnishes and paints, flexibility and weather resistance also depend on pigmentation.