3D printing has recently gained much attention from media and the scientific community, touted as a replacement for traditional manufacturing and a potential to change the way we develop, produce, market, and distribute all sorts of products. With a short introduction to the general idea and initial development of rapid prototyping, we have a look at the prevalent technologies which are now summarized as 3D printing, each with its specific properties and reliance on the materials adapted to the automated application process. Polymers in various forms, reactive, liquid solutions, or as thermoplastic melts, play a key role in many applications and the further expansion toward manufacturing robust, real end use products.

We report on the mechanical properties of optically curable stereolithographic resins (SLRs) which were reinforced through the addition of small amounts of cellulose nanocrystals (CNCs). The resin/filler mixtures are readily accessible via simple mixing processes. A detailed rheological investigation of such mixtures and the successful processing of these materials on a commercial SLR machine show that at low filler concentrations (below 5%) the processability of the materials is barely impacted. The storage modulus, E', increased steadily with increasing CNC content in the regimes below and above the glass transition. A remarkable modulus enhancement was observed in the rubbery regime, where E' increased by 166, 233, and 587% for CNC/SLR nanocomposites with 0.5, 1.0, and 5.0% w/w CNC, respectively. The modulus increase was less pronounced in the glassy state, where E' increased by 21, 32 and 57%, for the same compositions. The increase in tensile strength was of similar magnitude. In comparison to previously reported CNC and carbon-nanofiller based nanocomposites, the presently investigated nanocomposites display a comparably large increase of stiffness and strength, which appear to originate from the high level of dispersion and the intimate contact of the CNCs with the SLR matrix. Through the fabrication of 3-dimensional parts, it was shown that the CNC-filled resins can be processed with standard equipment in a stereolithographic process that is widely used for rapid prototyping and rapid manufacturing.

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