(396d) Investigation of the Physiochemical Effects of Heat-Induced Aging on 3D Printed Photopolymers

In three-dimensional (3D) digital light processing (DLP), ultraviolet light (typically at 405 nm) is emitted from a digital projector and directed at a mobile build area in a layer-by-layer fashion to create solidified cross-linked networks that are composed of rectangular voxels via free radical polymerization of photopolymer resins. The photopolymers that are typically used in DLP (e.g., acrylate- or epoxy-based thermoset resins) can contain different properties after printing that are dependent on resin formulation, printing parameters, and post-processing conditions; hence, the need exists to appropriately engineer and characterize a resin formulation that is based on the specific requirements of the end-use application in both a time-efficient and cost-effective manner. By comparing results of post processing (e.g., UV cure, convection oven) to a set of green DLP prints, protocols for determining and predicting the dependence of mechanical performance on chemical and physical aging has been established. Surface profilometry shows the topological effects of different environments in 3D-DLP parts over time, which has proven to be the most time-efficient and reliable method in anticipating changes in mechanical performance of DLP specimens. Dynamic mechanical analysis (DMA) was found to be very useful in evaluating the mechanical performance, utilizing time-temperature superposition (TTS) to measure the modulus over more than eight (8) orders of magnitude in frequency. The activation energy that is associated with the glass transition and the magnitude of the constants that are associated with the shift factors for each test were further analyzed using the Arrhenius and William-Landel-Ferry (WLF) empirical equations as tools for predicting the effects of temperature-induced physical changes of the DLP specimens. The successful completion of the tasks that are described in this work provided the necessary experimental framework for predicting and evaluating prolonged mechanical functionality of DLP parts that otherwise may be unattainable.