Some Aspects of Matrix Formation of Flexible Polyurethane Foams

Abstract

The reaction of liquid raw materials like isocyanates, polyols, and water, to build a structural polymer network is a very complex sequence of different chemical reactions. We can describe some of these essential processes by the use of a dynamic measurement of the viscosity during the course of the foaming reaction, on-line FTIR-spectrometry measurements and the determination of the curing behaviour. We employed a laboratory FT-IR system, that was interfaced to an optical fibre loop. The formation of the soluble and associated urea species, the decay of isocyanate groups and the development of urethane species during the polymerization reaction were studied by FT-IR. The onset of the formation of associated urea species is influenced by the chemical composition of the reacting mixture. For the viscosity measurements we used a rotational viscosimeter. The network development was shown by the determination of the viscosity profile. By extrapolation of the course of the indentation force over time, estimated after the demould of the flexible foam, we determined the green strength of the moulding and the vitrification of the foam at a frozen morphology. We also illustrated the dependence of the mechanical properties of flexible PU foams on the chemical structures formed during the reaction.