Abstract
The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to changes in the viscoelastic characteristics of the curing resin, since the velocity is related to the resin storage modulus and density, while the attenuation is related to the energy dissipation and scattering in the curing resin. The paper reviews the results obtained by the authors’ research group in the last decade by means of in-house made ultrasonic set-ups for both contact and air-coupled ultrasonic experiments. The basics of the ultrasonic wave propagation in polymers and examples of measurements of the time-evolution of ultrasonic longitudinal modulus and chemical conversion of different thermosetting resins are presented. The effect of temperature on the cure kinetics, the comparison with rheological, low frequency dynamic mechanical and calorimetric results, and the correlation between ultrasonic modulus and crosslinking density will be also discussed. The paper highlights the reliability of ultrasonic wave propagation for monitoring the physical changes taking place during curing and the potential for online monitoring during polymer and polymer matrix composite processing.
Highlights
Thermosetting resins are gaining increasing use in many structural composite applications in different fields and in the developments of polymer nanocomposites [1,2,3]
Obtained by Contact Ultrasonic Cure Monitoring
The experimental work, carried out with the contact ultrasonic set-up realized in our laboratory, has been focused on evaluating the reliability of ultrasonic dynamic mechanical analysis (UDMA) in monitoring the phase transformations that occur during the cure of thermosetting resins, called gelation and vitrification
Summary
Thermosetting resins are gaining increasing use in many structural composite applications in different fields and in the developments of polymer nanocomposites [1,2,3]. Different techniques have been applied to cure monitoring of thermosetting resins, including differential scanning calorimetry (DSC) [5,6], dynamic mechanical thermal analysis (DMTA) [7,8], dielectric analysis (DEA) [8,9,10], Fourier Transform FT-IR spectroscopy [11], near infrared spectroscopy (NIR) [12,13], and Raman spectroscopy [14] Many of these cure monitoring methods are laboratory based and not suitable for industrial application, require expensive equipment, are destructive, and typically are suited to working with small samples of restricted dimensions [15]. The details concerning the in-house build experimental set-up for contact and air-coupled ultrasonic cure monitoring will be presented together with the major results obtained by the authors over the past decade on unsaturated polyester and epoxy resins
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