Adhesion and cure kinetics of photopolymers
First, the dynamic adhesion phenomenon between a photopolymer matrix composite and solid surfaces was studied. Theoretical analysis of the energy balance and experiments of insertion/extraction cycles both indicated that an oscillation at the solid/liquid interface induced by solid probes with non-axisymmetric geometries can efficiently prevent the composite material from adhering to the probe. This discovery was applied to a problem in restorative dentistry and made it possible to manipulate highly adhesive polymeric material without troublesome adhesion of the material to the deforming bit. Further experiments were performed to investigate the effects of the various process parameters on final packing density of the restorative materials. Second, a simple unified kinetics model for the curing reaction of photopolymers was developed by analogy to the classical Avrami approach. Differential Scanning Calorimetry (DSC) was applied to obtain the isothermal reaction kinetics data. The proposed model was verified by good agreement between its prediction and the experimental data from our own work and from the literature. The effects of sample dimension, cure temperature, and irradiation intensity on cure kinetics are also discussed. Finally, a semi-empirical chemorheological model based on the cure model was proposed in order to describe the viscosity profile in terms of time during the isothermal cure of thermosetting polymers. Three sets of experimental data were compared with the model prediction and good agreement was achieved.
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