Study of Recyclable and Repairable Dynamic Covalent Polymers for Sustainable 3D Printing Development
Abstract
3D printing technology with valuable features, including cost-saving, easy access, and unlimited structure design, has attracted significant attention and been employed for production use. This technology has also been considered as a sustainable manufacturing method and quickly developed in recent years. However, the development of sustainable 3D printing is still facing challenges, especially in waste management. Thanks to the flexibility of 3D printing and diversified printing mechanisms, the big step forward can be approachable by the transformation from materials. This dissertation presents a variety of strategies designed for sustainable 3D printing development based on the combination of dynamic covalent chemistry and 3D printing technique. Dynamic covalent bonds provide polymers, including thermosets, with responsive covalent adaptable networks, allowing the materials to be reversible, leading to a recyclable material technology. Through synthesizing epoxy and polyurethane based dynamic covalent polymers as 3D printing materials, together with developing a corresponding 3D printing technique, the strength of green 3D printing is explored.
In this study, OH functionalized multi-walled carbon nanotubes (MWCNTs-OH) are incorporated in the printing material to improve the mechanical property and tailor the photothermal conversion capability of the developed materials. Due to the super high strength and minuscule size of MWCNTs, they are widely used to reinforce polymer as fillers. With MWCNTs-OH incorporating, the ultimate tensile strength and Young's modulus of samples both increased. In particular, young's modulus of 2 wt% DTDA-PU was about 8.6 times higher than the pure sample. Furthermore, MWCNTs are functioning as an excellent photothermal converter to allow the heat triggering to be replaced with a laser light. Therefore, near-infrared (NIR) laser source is utilized as the heat source for targeting the damaged spot of printing parts precisely for in-situ repair application. After the sample is cut in half and repaired, the mechanical properties recover to 86.3% after three times NIR laser-triggered in-site repair. In addition, a creative approach of contactless supporting structure removalis explored to promote post-processing automation and reduce printing parts defective rate. Our sustainable 3D printing strategy has developed an environmentally friendly and energy-efficient technology, which paves the way toward a circular economy.