Photocurable 3D printed anisotropic electrically conductive materials based on bio-renewable composites

The manufacturing industry is moving towards an environmentally friendlier and more sustainable economy by substituting fossil fuel-based materials for plant-based and related renewable resources obtained materials, such as soybean oil. The combination of these materials with electrically conductive fillers allows the fabrication of conductive tracks and sensors essential for the implementation of the internet of things (IoT) and Industry 4.0 concepts. Here, we've fine-tuned the combination of acrylated epoxidized soybean oil (AESO) and isobornyl methacrylate (IBOMA), considering factors like viscosity, photoreactivity, and physico-chemical properties, with the further addition of multiwalled carbon nanotubes (MWCNT) in varying amounts for selected formulations. The resulted materials obtained in films present gel times between 1 and 30 s, FTIR conversion between 75 and 50%, Tg in the range of 57-123 °C and crosslinking densities between 1.90 and 0.015 mmol/cm3. In addition, good MWCNT dispersion is achieved with conductivities as high as 1.4 × 10-4 S/m. The optimal formulation in terms of 3D printability was obtained for 0.6 wt.% MWCNT content and AESO:IBOMA polymer matrix in a 50:50 ratio, showing a good fabrication precision for bulk and hollow structures (average dimensional differences between the model and printed objects of ± 100 mm). The 3D printed samples demonstrate anisotropic electrical conductivity ascribed to a MWCNT orientation that occurs during 3D printing process. The electrical conductivity values can vary in nearly 6 orders of magnitude depending on the orientation with respect to the printed pattern, -6.6·10-3 S/m for parallel and 5.2·10-9 S/m for perpendicular - demonstrating the suitability for 3D printed electronic applications.