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FULL RESEARCH ARTICLE

Tailoring properties of photopolymers for additive manufacturing with mixture design Janez Slapnik1   · Irena Pulko1 Received: 24 July 2019 / Accepted: 12 August 2020 © Springer Nature Switzerland AG 2020

Abstract This study illustrates the application of the principles of the design of experiments for the development of photocurable resins for additive manufacturing with easily adjustable mechanical and thermal properties. Photocurable resins were prepared using a combination of various oligomers and monomers, cured in a UV-curing system, and characterized in terms of mechanical and thermal properties. Photocurable resins for stereolithography were prepared using varying concentrations of photoinitiator and pigment, 3D printed and characterized in terms of processability as well as mechanical and thermal properties. Multi objective optimization was performed to obtain the compositions with the highest desirability. The proposed approach enables convenient tailoring properties of photocurable resins by varying just four basic components. Keywords  Additive manufacturing · Stereolithography · Digital light processing · Design of experiments · Mixture design · Mechanical properties

1 Introduction Additive manufacturing (AM) enables the manufacturing of parts with complex geometries directly from the 3D model by depositing material on an X – Y direction layer by layer and thus creating the Z dimension. There are many different AM technologies available, such as inkjet 3D printing (3DP), fused deposition modelling (FDM), selective laser sintering (SLS), SLA, etc. [1, 2]. SLA is recently gaining attention due to the possibility of creating parts with very high accuracy. The main principle of the SLA is building the part by curing the photocurable resin with UV or visible light. There are two main types of SLA commercially available—classical SLA, which uses a laser and SLA that uses digital mask generators [e.g., digital mirror devices (DMD) or liquid crystal display (LCD)] [3]. Resins are usually based on acrylate chemistry (cured by radical mechanism), epoxide chemistry (cured by cationic mechanism), or a mixture thereof. These photocurable resins are typically based on four main components: a photoinitiator, which absorbs light at wavelengths overlapping with the SLA light * Janez Slapnik [email protected] 1



Faculty of Polymer Technology, Ozare 19, 2380 Slovenj Gradec, Slovenia

source emission spectra, a dye or a pigment that absorbs light at the same wavelengths as the photoinitiator and thus prevents unwanted scattering of light and controls the light penetration depth, functionalized oligomers that provide the desired mechanical properties and mono and/or multifunctional monomers that act as reactive diluents. For achieving good mechanical, thermal, and processing properties of the photocurable resins, the right balance of the concentrations of the components is needed [4–10]. First photocurable resins were very brittle, hence most efforts regarding the improvement of mechanical p