Pregregs are high quality semi-finished products out of a textile reinforcement structure impregnated with a resin matrix. For ecological and economic reasons, the production of the prepregs is increasingly done in the solvent-free Hot-Melt-Process. The Hot-Melt-Process is more demanding regarding the process control than the rivalling solvent-process. To achieve a stable operating process and thus a high-grade product an efficient inline monitoring is necessary.
As a reactive resin system is concerned, the prepreg is typically kept cold until its finishing process. The storage life of cooled prepregs adds up to 6-24 months. Expired prepregs are usually disposed of.
A technology presumably suitable for inline monitoring as well as for quality control of prepregs during storage and processing is vibrational spectroscopy, especially Near-Infrared-Spectroscopy (NIR) and Raman-Spectroscopy. Using light, characteristic molecular vibrations are created. The molecular vibrations result in characteristic spectra that can be used to determine certain parameters, such as the degree of curing or resin content.
So-called NIR-Micro-Spectrometers differ from classical process spectrometers through low weight and volume as well as a significantly lower price. Equivalently there are some cut backs e.g. in resolution. Nonetheless they seem suitable alternatives to the conventional spectrometers for certain areas of application. They could be the basis for a hand-held tool, with which prepregs can be tested during their storage and processing. A fast, easy and non-destructive check of the prepreg quality could initiate the renunciation of the time-based disposal of prepregs in favor of a quality-based disposal.
In the FFG-Project SAPP (“Spektroskopische Analyse von Prepregs“) the potential of NIR- and Raman-Spectroscopy as an inline monitoring technique for the pregpreg production and for quality control during storage and processing is examined. Focus of the Processing of Composites Group is to evaluate the performance of NIR-Mirco-Spectrometers and demonstrating potential fields of application.