Thin film mechanical characterization of UV-curing acrylate systems

Novel Dual-Curing Process for a Stereolithographically Printed Part Triggers a Remarkably Improved Interlayer Adhesion and Excellent Mechanical Properties

Stereolithography (SL) is widely used because of its numerous advantages over other three-dimensional printing (3DP) techniques. However, SL is a layer-by-layer process, where interlayer adhesion between adjacent layers becomes more brittle than the intralayer adhesion, common to all 3DP process. Here, we report a facile method to strengthen the interlayer adhesion for SL. By the addition of monomers with thermally curable functional groups (epoxy or hydroxyl groups), thermal post-curing induces chemical reactions between them in adjacent layers after the photoinitiated printing process. It leads to fully 3D cured objects with enhanced interlayer bonding and substantially improved mechanical properties, but not a significant change in the dimensional stability. This approach can expand the use of 3DP techniques in load-bearing applications that require mechanically robust printed objects with precise dimensions.

Characterization of Ultraviolet-Cured Methacrylate Networks: From Photopolymerization to Ultimate Mechanical Properties

In this study, the effect of different process conditions on the material properties of a single UV-cured layer of methacrylate resin, typically used in the stereolithography (SLA) process, is assessed. This simplified approach of the SLA process gives the opportunity to study the link between process conditions and mechanical properties without complicated interactions between different layers. Fourier-transform infrared analysis is performed to study the effect of light intensity, curing time, and initiator concentration on the monomer conversion. A model is developed based on the reaction kinetics of photopolymerization that describes and predicts the experimental data. The effect of curing time and light intensity on the glass-transition temperature is studied. A unique relation exists between conversion and glass-transition temperature, independent of the light intensity and curing time. Tensile tests on UV-cured resin show an increase in yield stress with increasing curing time and a linear relation between glass-transition temperature and yield stress. However, a lower light intensity leads to a different network structure characterized by a lower yield stress and glass-transition temperature. The correlations between process conditions and the mechanical properties of UV-cured methacrylate systems are established to better understand the role of the processing parameters involved in the SLA process.