Polycarboxylate ethers

Basic structure of a first generation polycarboxylate ether, consisting of methacrylate units (green) and PEG methacrylate units (blue) in a ratio of 6: 1 to 1: 1.

Schematic representation of a PCE chain with negative charge on the main chain and splayed side chains.

The polycarboxylate ethers ( PCE ) are organic polymers that are common superplasticizers or concrete plasticizers . The effect of PCE on the strength of concrete can be explained on a chemical level. The main chain of the PCE has negative charges for attachment to the cement particles, while the side chains protrude into the cement paste solution.

Manufacture and properties

Concrete plasticizers and superplasticizers are essential additives when processing concrete . These additives are among the polymers that have a negative charge density on the main chain of the polymer. The polymers are chemically produced from monomers via various polymerization reactions . For example, the polymers based on melamine are produced via a so-called polycondensation . The basis of this polymerization is the chain structure with the elimination of water molecules. In contrast, the polycarboxylate ethers, which are becoming more and more important, are obtained via radical polymerization. The polycarboxylate ethers have different chemical bases, with the properties of the polymers being shaped depending on the type of monomer used to build the polymer. Further parameters for the production of modified polymer types are the length of the main chain, as well as the length of the side chain in comparison to the main chain and the number of negative charges or charge density in the main chain.

The effect of superplasticizers is based on the accumulation or adsorption of the main chain of the polymer with its negative charge density on the surface of the concrete. By the adsorption of the polymer to the concrete surface it comes to the dispersion of the agglomerated particles concrete. In addition, the trapped water is released, which is available to lower the plastic viscosity of the concrete. This process also optimizes the deformability of the concrete.

Mechanism of action

The molecular mechanism of action is based on the fact that the superplasticizer has a dispersing effect, as its negative charge density attaches itself to the positively charged positions of the concrete particles and thus counteracts agglomeration .

The dispersion can take place via the following mechanisms: electrostatic, electrosteric or steric dispersion. The polymer polycarboxylether exerts all mechanisms during the dispersion. With the electrostatic mechanism, the polymer adsorbs with its negative charge on the cement particles and thus negatively charges the surface, which leads to an increased repulsion of the particles from one another. With steric dispersion, the adsorption of uncharged polymers on the cement particles leads to a decrease in entropy. The reason for this is that the particles are hindered when approaching by steric hindrance of their chains. Ultimately, it comes with electrosteric dispersion, which has been described as a merger of the processes listed above.

swell

• Effect of superplasticizers in cement-bound building materials
• Christian Manfred Hirsch: Investigations on the interaction between polymer superplasticizers and cements or mineral phases of early cement hydration , dissertation 2005, TU Munich.

Individual evidence

1. ↑ ^{a b} Alexander Göthlich, Sebastian Koltzenburg, Gunnar Schornik: Functional polymers in everyday life . In: Chemie in our time 39 (2005) pp. 262–273, doi : 10.1002 / ciuz.200400346 .