Development of nanostructured polyurethane nanocomposites

LEONEL MATIAS CHIACCHIARELLI; L. TORRE

Conferencia; SAMPE Europe Students Conference; 2012

The use of high-performance thermoset polyurethane composites has been limited to low volume applications. One of its main limitations is the inability to be processed by infusion methods. The main reason for this issue is that the formulations do not provide a long enough pot-life while also maintaining other essential mechanical and processing properties. The introduction of a new system has proved to break this paradigm by offering a long pot life (around one day at 25ºC), high Tg and comparable toughness. Nevertheless, limitations still remain regarding toughness improvement (maintaining high Tg) and the development of basic processing modeling. In this work, both the study of the cure kinetics, chemorheology and nanocomposites was performed. As far as the nanocomposites is concerned, a series of nanofillers were selected (following previous published results), that could provide improvement of mechanical properties while not substantially changing the cure kinetics. The selected candidates were Cloisite, Silica, Wollastonite and Sepiolite. A complete characterization of its mechanical/cure properties was performed. A criterion was established so as to select the best nanofiller for this system. From the results, it was possible to deduce that the best nanofiller was Silica, at 1%wt., which improved ductility up to 84% while not reducing substantially other properties. On the other side, cure kinetics was studied both with DSC, IR and adiabatic temperature rise. Due to the fact that the system was extremely reactive (snap-cure), a DSC procedure was established to obtain valid results. An autocatalytic phenomenological model proved to model the behavior of the system (neat and nanocomposite). The effect of both weight and inhibition time was analyzed and incorporated into the model. As far as the chemorheology is concerned, the viscosity build up during cure was measured using a dynamic technique at isothermal conditions. Both the Gel point and vitrification were identified, and by their proximity, it was assumed that both phenomena occurred almost simultaneously. So far, the modeling of the chemorheological behavior was hindered due to issues associated with the superposition of kinetic/rheological data. Finally, the last aspect of this work considered the development of a suitable process to mould the resin/nanocomposite system. A suitable process has been developed to obtain almost defect-free samples both with Polyurethane and Polyurethane-nanocomposite. In addition, the nanocomposites showed improved processability.