How is polyurethane made

Polyurethane

Brief description

Polyurethane (Popular saying:PU, according to DIN: PURE) belongs to the group of foamed plastics. The starting materials are usually obtained from petroleum, but could also be made from vegetable raw materials, e.g. B. from potatoes, corn or sugar beet. The high insulation effect is achieved through the inclusion of dormant cell gases (or air when using CO2 as blowing agent) in the foamed cells.

Production process

The main components are approx. 40% each polyols and isocyanates, 10 - 15% propellants (e.g. pentane, CO2) plus flame retardants, plasticizers and fillers. Depending on the process, the starting materials are mixed homogeneously and foamed by adding the blowing agent. Immediately after mixing, a chemical reaction starts, during which the propellant escapes and the product foams up to 30 times its volume.

  • PUR rigid foam: The panels are produced using the double belt process, blocks are produced using the block foam process, shaped and cut to size.
  • PUR local foam: The starting materials are foamed on the construction site under air or liquid pressure.

Processing information

When properly processed, PUR is considered to be resistant, but not resistant to UV radiation and rodents. PUR local foam should only be processed by specialist companies, as incomplete curing can result in long-term odor-intensive emissions.

Areas of application

On construction in general: paints, adhesives, coatings, foams, sealants, etc.
As insulation material: steep and sloping roofs, surfaces subject to pressure (industrial floors, flat roofs, parking decks, under screeds) sandwich elements, rear-ventilated facade constructions, foaming of cavities (assembly foam, in-situ foam). The long-term application temperature should generally not exceed 90 ° C. Installation as insulation between the rafters is problematic, as the shrinkage or rotation of the rafters cannot be compensated and thermal bridges can arise as a result.

Building biological opinion

In the production of PUR and its chemical raw materials, hazardous substances with a considerable risk potential are involved. Therefore, greater caution is generally required when handling the starting material isocyanates. Components of the complex process chain are products that are harmful to health and the environment, e.g. B. benzene, sulfuric acid, nitric acid (together result in nitrobenzene), formaldehyde, chlorine, phosgene and others. The use of blowing agents can cause toxic isocyanates to escape, and toxic intermediate and end products can also arise. Allergy sufferers can react to very low concentrations. In the event of a fire, the isocyanates are partially regressed due to the thermal degradation of the PUR. In interaction with nitrogen from the PUR, hydrogen cyanide is produced, and further toxic fire gases with a high odor hazard potential due to the effects of carbon monoxide and flame retardants. In the event of disposal, both material and energy recovery are problematic. Landfilling of incineration residues containing halogen can pollute the soil.

Polyurethane production process and evaluation

In the manufacture of PUR and its chemical raw materials, hazardous substances with a considerable risk potential are involved. Therefore, greater caution is generally required when handling the starting material isocyanates. In the event of a fire, highly toxic hydrogen cyanide can be produced. (Source: ECOBIS 2000, Gisbau)

For more on this, see isocyanates

Tris (chloropropyl) phosphate (TCPP) is mainly used as a flame retardant (according to Wecobis). The “Ecological Building Materials Lexicon” writes: “There are indications of mutagenicity for TCPP. There is a suspicion of a carcinogenic effect ”.

The “Ökologische Baustofflexikon” writes about the intermediate product phosgene: “Phosgene is an extremely toxic chemical with a hay-like odor. It was also released in the chemical accident in Bophal, India in 1984, and was the cause of a large part of the poisoning (thousands dead + hundreds of thousands injured). In World War I phosgene was used as a war gas. In the lungs it releases hydrolytic hydrochloric acid, which corrodes the lung tissue. "

source

Herbert Danner, Building Biologist (IBN), Bauzentrum Munich, Ecological Thermal Insulation Materials in Comparison 2.0, June 2010, pp. 41, 67 (with additions by the editorial team)

See also