Written on 13.11.2012 - Technology
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Compact polyurethane system for FRP processing

Gap impregnation is a fairly new process for the production of high-performance parts of fibre-reinforced plastics (FRP) in only a few minutes. In this process, which is similar to RTM, a temporary flow gap is created. This temporary flow gap and the inclined position of the mould result in rapid, reproducible injection of the resin system with low resistance. The exceptionally fast impregnation of the preform in the space of only a few seconds allows the use of the highly reactive resin systems that are needed for part production on an industrial scale.

At the Institute of Plastics Processing (IKV) at RWTH Aachen University, an automated gap impregnation unit was developed back in 2009 and installed in the IKV pilot plant. Recent tests with the unit have been aimed at using not only epoxy resin systems but also alternative resin systems such as polyurethanes for the series production of fibre-reinforced plastics parts (FRP). In cooperation with IKV, BASF Polyurethanes GmbH, Lemförde, has developed, a new, highly reactive and compact crosslinking PU system for FRP.

Gap impregnation unit in the IKV pilot plant (photo: IKV)

In this project, attention is focused on the verification and optimisation of a long open processing time of the PU system during injection and impregnation of the FRP parts in combination with fast, latent crosslinkage with isothermal mould temperature control. Furthermore, the demoulding behaviour is analysed with the use of internal release agents.

For the tests, both flat parts and curved parts with varying thicknesses and a projected surface area of 500 x 500 mm² are used. The parts are made of glass- and carbon fibre-reinforced plastics. Irrespective of the reinforcing fibre, the fibre volume content of the continuous fibre-reinforced parts is between 45 % and 50 %. Process times of less than six minutes – from mould closure to removal of the crosslinked part – were achieved. Depending on the volume of the part, the injection, impregnation and consolidation account for a maximum of 23 s, while crosslinkage of the parts in the mould, heated isothermally to 80 °C, takes around four minutes. It was thus possible to successfully demonstrate a sufficiently long processing time of the latent reacting PU systems in the impregnation and consolidation process. Furthermore, a new modification of the PU systems with internal release agents allows reliable demoulding. The impregnation quality of the parts is very good and comparable with that of highly reactive epoxy resin systems. This means that the PU systems developed by BASF are an attractive alternative to epoxy resin systems.