(64c) A Thermal Kinetic Model for the Study of Stereolithography Process

A numerical and experimental study of thermosetting resins used in infrared stereolithography is presented. In usual practice, stereolithography makes use of photosensitive resins where HeCd (0.352?Ým) laser ultraviolet light initiates the curing process. In this work it is considered the process of local curing through the application of infrared radiation, which has proved to be useful in a new technique for the making of prototypes by means of selective heating with a CO2 laser (10.6?Ým). The sample consists on a thermosetting resin (epoxy) with the curing agent (diethylenetriamine) and filler (silica). The ideal composition of the thermosetting resins has proved to be 10 parts epoxy, 1.4 part diethylenetriamine (the curing agent) and 0.7 part silica powder. A physical theoretical model is applied to control the parameters which influence the confinement of the curing in the irradiated bulk. A phenomenological model was developed through the solution of the time dependent heat conduction equation in finite elements, which enables the determination of the behavior of curing in terms of irradiation conditions and concentration of reagents. A kinetic model for the study the reaction polymerization processes was developed and describe the main features of the polymerization process, namely diffusion-controlled effects after vitrification and incomplete conversion, presenting a good agreement between experimental and predicted values. An experimental analysis, using Differential Scanning Calorimeter (DSC), was uses to determine the fractional conversion, reaction rate, heat of reaction, and activation energy at which the curing process starts.