Polyester resin

Polyester resins are condensation products of dihydric or polyhydric alcohols (e.g. glycols or glycerine ) and dicarboxylic acids . In contrast to the chemically related alkyd resins are used in the manufacture of no long-chain fatty acids used. Unsaturated polyester resins (UP resins) are used for the production of fiber-reinforced plastics , fillers and casting resins .

properties

Physical Properties

The cured plastic is typically clear, but can also appear cloudy to opaque. The hardness depends on the composition and is therefore variable over a wide range (from very soft to hard). Hard products are obtained with aromatic carboxylic acids and / or tri- or tetrahydric alcohols, aliphatic carboxylic acids and / or long-chain dihydric alcohols produce soft polyesters.

Chemical properties

Polyester resins are largely resistant to weak acids and bases as well as petrol and oil. However, they dissolve in strong acids and alkalis as well as in esters , ketones and chlorinated hydrocarbons . For their use as paint binders in particular, they are dissolved in organic solvents and serve as a carrier substance for the coloring pigments . Polyester resins form long, unbranched polymers which, however, can also be crosslinked. For this purpose, so-called functional groups are incorporated in the molecule, which z. B. crosslink with isocyanate components and cure. Unsaturated polyester resins contain double bonds which are cured with styrene or other reactive thinners with the aid of peroxides (e.g. dicumyl peroxide , dibenzoyl peroxide or methyl ethyl ketone peroxide ).

Burning test : Polyester resins burn with a bright yellow, sooty flame, causing them to char . They continue to burn outside the ignition source . When burned, unpleasant smelling decomposition products are produced (attention, harmful to health!).

processing

Pressing and injection molding
Laminate , e.g. B. with glass fibers (see also fiber-plastic composite , glass-fiber reinforced plastic and gelcoat )
In a mixing process with pigments and additives to make paints for boat building or household use.

application

As a plastic, they are used, among other things, to manufacture heat-resistant and electrically insulated handles for pots and irons . In addition, polyester resins are used to manufacture equipment housings and as insulation material , for paints and for plastination . Some manufacturers of rotor blades for wind turbines produce them from fiberglass-reinforced polyesters. Other applications: automotive parts, basement light wells, door panels (not common in Europe), drainage channels, kitchen worktops, sinks, auto repair putties, pipes, etc. v. m.

Manufacturing

Polyester resins are usually produced using azeotropic distillation at high temperatures. The esterification of alcohols with carboxylic acids produces water, which is removed from the mixture with the help of a so-called entrainer and a water separator . According to Le-Chatelier's law , this brings the balance to the product side. Below is a list of monomers for polyester synthesis .

Monomers with hydroxyl groups

Monomers with carboxyl groups

Web links

Chempage plastics: polyester resin

Individual evidence

↑ Entry on polyester resins. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.
↑ Ulrich Poth: Synthetic binders for coating systems. Vincentz Network, Hannover 2016, ISBN 978-3-86630-611-0 .
↑ Ulrich Poth: Polyester and alkyd resins: Basics and applications. Vincentz Network, Hannover 2014, ISBN 978-3-86630-663-9 .

[1] Entry on polyester resins. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.

[2] Ulrich Poth: Synthetic binders for coating systems. Vincentz Network, Hannover 2016, ISBN 978-3-86630-611-0 .

[3] Ulrich Poth: Polyester and alkyd resins: Basics and applications. Vincentz Network, Hannover 2014, ISBN 978-3-86630-663-9 .