Ermittlung der Gelzeit mittels Nahinfrarotspektroskopie in der lösungsmittelfreien Prepreg Herstellung

Translated title of the contribution: Determination of gel time using near-infrared spectroscopy in solvent-free prepreg manufacturing

Sebastian Schmid

Research output: ThesisMaster's Thesis

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The determination of the gel time of fiber-reinforced plastics (FRP) with a thermosetting resin matrix can be carried out in various ways. In industrial practice, the determination of the gel time is usually done according to ISO standard 15040:1999. In this process, resin is pressed from specimens with defined geometry using a heated press, and the time until the resin drop gels is measured. However, there are very few studies that deal with a fast and especially non-contact measurement of the gel time directly in the production process. One promising method for this is near-infrared spectroscopy (NIRS), which is already used in inline monitoring for the determination of various material parameters. For this reason, various measurement positions were set up along a prepreg production line based on the hot-melt process, where spectra were taken from the impregnated glass fabric at different stages of the prepreg manufacturing process. The measured spectra correspond to different stages in the prepreg production process. The influence of different heating field temperatures, as well as the influence of different release film colours and surface structures on the spectra, is then examined. Based on the measured spectra, models were developed using the Partial Least Squares (PLS) method to determine the gel times of the prepregs. The gel times are determined according to the industry standard ISO 15040 serve as reference values for model creation. Causes of deviations were identified and form the basis for further investigations. In addition to favorable measurement positions, trends were also found, indicating that release films have a less pronounced influence on the spectra, allowing for better model quality. Ultimately, it was demonstrated that determining the gel time using NIRS is possible, and the PLS models provide sufficiently good quality for determining the gel time.
Translated title of the contributionDetermination of gel time using near-infrared spectroscopy in solvent-free prepreg manufacturing
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Fauster, Ewald, Supervisor (internal)
Award date22 Mar 2024
Publication statusPublished - 2024

Bibliographical note

no embargo


  • near-infrared spectroscopy
  • geltime
  • NIRS
  • prepreg
  • hot-melt
  • fiber-reinforced polymers
  • FRP
  • partial least squares
  • pls
  • gel time determination
  • inline-monitoring non-contact measurement
  • composites
  • CFK
  • GFK

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