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Materials 2016, 9(9), 760;

Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation

Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
Department of Applied Science and Technology, Politecnico di Torino, Torino 10129, Italy
Authors to whom correspondence should be addressed.
Academic Editor: Juergen Stampfl
Received: 29 July 2016 / Revised: 31 August 2016 / Accepted: 2 September 2016 / Published: 7 September 2016
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
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We investigate the impact of the non-uniform spatio-temporal conversion, intrinsic to photopolymerisation, in the context of light-driven 3D printing of polymers. The polymerisation kinetics of a series of model acrylate and thiol-ene systems, both neat and doped with a light-absorbing dye, is investigated experimentally and analysed according to a descriptive coarse-grained model for photopolymerisation. In particular, we focus on the relative kinetics of polymerisation with those of 3D printing, by comparing the evolution of the position of the conversion profile (zf) to the sequential displacement of the object stage (∆z). After quantifying the characteristic sigmoidal monomer-to-polymer conversion of the various systems, with a combination of patterning experiments, FT-IR mapping, and modelling, we compute representative regimes for which zf is smaller, commensurate with, or larger than ∆z. While non-monotonic conversion can be detrimental to 3D printing, for instance in causing differential shrinkage of inhomogeneity in material properties, we identify opportunities for facile fabrication of modulated materials in the z-direction (i.e., along the illuminated axis). Our simple framework and model, based on directly measured parameters, can thus be employed in photopolymerisation-based 3D printing, both in process optimisation and in the precise design of complex, internally stratified materials by coupling the z-stage displacement and frontal polymerisation kinetics. View Full-Text
Keywords: 3D printing; photopolymerisation; conversion profile; photopolymerisation model; UV curing 3D printing; photopolymerisation; conversion profile; photopolymerisation model; UV curing

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Vitale, A.; Cabral, J.T. Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation. Materials 2016, 9, 760.

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