Authors:G. Van Assche, A. Van Hemelrijck, and B. Van Mele
The influence of temperature modulation and signal treatment (deconvolution procedure) of modulated temperature differential
scanning calorimetry is discussed with respect to the investigation of cure kinetics of thermosetting systems. The use of
a ‘dynamic’ heat capacity calibration is not important for this purpose due to normalization of the heat capacity signal in
all cure experiments. The heat flow phase during isothermal and non-isothermal cure is always small, giving rise to negligible
corrections on the heat capacity and reversing heat flow signals in-phase with the modulated heating rate. The evolution of
the heat flow phase contains information on relaxation phenomena in the course of the chemical reactions.
Authors:G. Van Assche, E. Verdonck, and B. Van Mele
The free radical cross-linking copolymerization of an unsaturated polyester resin with styrene is studied in isothermal conditions using temperature modulated differential scanning calorimetry (TMDSC) and dynamic rheometry. The dynamic rheometry measurements show that gelation occurs at a conversion below 5%, while TMDSC measurements show that an important autoacceleration starts near 60% conversion, giving rise to a maximum cure rate closely before the (partial) vitrification of the system near 80%. This indicates that the autoacceleration is not due to the sharp increase in bulk viscosity at gelation, but rather to a change in molecular mobilities at higher conversion.
Authors:N. Gotzen, G. Van Assche, A. Ghanem, Y. Van Ingelgem, A. Hubin, and B. Van Mele
In this paper we compare Wollaston and silicon probes for localized thermal analysis measurements (LTA) on biaxially oriented
polypropylene (BOPP) films. Up till now, no real comparison was reported in literature between the different transition temperatures
measured using Wollaston and silicon probes. Using different types of probes for studying the same material proves to be very
interesting. Using the Wollaston probe, the thermal properties and thickness of a 1 μm thick skin layer can be determined
by through-thickness local thermal analysis measurements. The improved resolution of the silicon probes, enables the measurement
of thermal properties of individual layers in a cross-sectioned film, even for layers of only 1 μm thickness. Based on the
results, the silicon probes seem to be more sensitive toward the start of the melting process, since the silicon probe already
penetrates at lower temperature, as compared to the Wollaston probes. This sensitivity can be exploited for studying the effect
of variations in thermal history between or within samples.
Authors:G. Scheltjens, J. Brancart, I. De Graeve, B. Van Mele, H. Terryn, and G. Van Assche
A self-healing material for coating applications was synthesized using the Diels–Alder (DA) reaction as cross-linking reaction. The built-in reversibility allows local mobility and rearrangements in the polymeric network, which is composed of a furan functionalized epoxy-amine and a bismaleimide. The self-healing material was characterized by physical–chemical means using Fourier Transform Infrared spectroscopy, thermogravimetric analysis (TG) and rapid heat-cool differential scanning calorimetry. It has been shown that the reversibility, as a result of a change in DA/retro-DA equilibrium, occurs in a temperature window ranging from ca. 80 to 150 °C. The repeatability of the non-autonomous healing was checked by TG, showing no evaporation or degradation of the components involved in the temperature window of interest.