Printing Materials with Spatially Resolved Properties Using a Single Resin Vat and Modified Digital Light Processing Technique
Authors:   , Kashcooli Yaser , Palmese Giuseppe 
Published: November 2023

Recently, additive manufacturing (3D printing) methods have been used as a tool to fabricate parts with spatially resolved properties. The most common approach when using vat photopolymerization methods is by changing resin vats during the printing process. Although, this approach is capable of making parts with spatially resolved properties, it has limited applications due to its drawbacks. The main drawbacks include systems complexity (due to adding resin switching system and washing steps between resin vats to avoid cross contamination) and high failure rates at material interfaces. This dissertation focuses on addressing these issues by altering the printed part properties by changing the printing process parameters starting with a single resin vat. To achieve this goal, first, we developed the photo-ATR-FTIR technique to probe reaction and diffusion phenomena in different systems. This method was subsequently used to characterize the diffusion and reaction phenomena in our resin systems in order to select DLP printing parameters that would result in printed materials with spatially resolved properties. Two photocurable resins, a single cure and a dual cure system, were explored. First, we considered a biorubber-toughened methacrylate-based resin system (DA4-20) as the single cure system and studied the effect of light intensity on the phase separation behavior by controlling reaction rate via changing the light intensity. We showed that it is possible to alter the morphology of printed parts by changing the light intensity. However, limitations regarding the degree to which the thermomechanical properties could be altered were observed. This was mainly due to the fast phase separation behavior of this system which did not allow for complete phase separation. Second, a dual cure system was developed to have better control of the chemical composition and the distribution of the formed phases. This study proposes a new approach to print parts with spatially resolved properties using a multicomponent resin system in one vat. The multicomponent resin system is based on an epoxy system with Tg well above room temperature and methacrylate systems with Tg well below room temperature. Photopolymerization process parameters were manipulated at the voxel scale to create composition differences between voxels resulting in corresponding spatially resolved material properties in the fully cured system. To determine the optimal conditions for maximizing the reaction-induced diffusion phenomenon, reaction and diffusion were investigated using a thin film geometry. Specifically, processing conditions for which the characteristic time scales for reaction and diffusion are of the same order were investigated. A commercially available DLP printer was used to print parts with spatially resolved properties. Samples were printed with alternating softer and harder 186 [mu]m layers aligned longitudinally and transversely relative to the direction of tensile testing. The results showed that the transverse and longitudinal properties of these materials differed significantly because of property differences between the layers. Voigt and Reuss models were used to analyze the results and calculate the modulus of the layers, which showed a more than twofold difference in modulus between the layers indicating that materials with spatially resolved mechanical properties can be produced using this method, overcoming some limitations of current 3D printing techniques.