Chemeorheology: a new design for simultaneous rheological and Fourier transform near infrared analysis

In this paper we present a new laboratory-made system which allows the combination of rheometer dynamical analysis (RDA) and Fourier transform near infrared (FT-NIR) spectroscopy. Dynamic rheological data and NIR spectra were simultaneously collected. Previous studies of thermosetting systems and, more particularly, polyurethane studies, manufactured by the reaction injection moulding (RIM) process, emphasised the need for simultaneous rheological and kinetic measurements. The rheological measurements, performed using RDA, were obtained using oscillatory shear experiments at variable angular frequencies between two parallel plates. In-situ monitoring of the extent of reaction of the investigated polyurethane was carried out at room temperature using fibre optic FT-NIR spectroscopy. Multivariate analysis of transmittance spectra was performed to calculate the degree of conversion. The appliance for simultaneous measurement is described and their advantages and limitations are briefly discussed. The viscoelastic behaviour and the extent of reaction were studied during reactive blending of polyurethane formation, especially at the critical moment of gelation. A good agreement is observed, between separate and simultaneous rheological-FT-NIR measurements. Indeed, rheological experiments (up to 100 Hz) are not perturbed by the increase of the weight of the RDA plates. The RDA-FT-NIR technique may provide a powerful tool for studying curing reactions of polymers for both industrial and academic communities.