Hemp-Derived Cannabinoids and Cannabinoid-Based Biopolymers for Synthesis and Formulation of Conductive Copper Ink Composites

As concerns about electronic waste increase, the field of printed electronics is exploring more sustainable materials. New platforms for conductive traces considering cost, manufacturability, sustainability, and performance must be developed. Low-cost alternatives to conventional printed circuit conductors such as gold and silver are hampered by the susceptibility to corrosion of alternatives with comparable conductivity, namely copper. Copper inks have seen success when sintered or cured in reducing environments, but further effort is required to achieve low-temperature, sustainable and ambiently processable conductors.
We have introduced a new biopolymer platform that utilizes cannabinoids from hemp oil as feedstock for novel hydrophobic, inherently antioxidant, high glass transition temperatures polymers. Here, we show that poly(cannabinoid)s, in unison with cannabinoid ligands, show promise in preventing oxidation of copper in inks for printed electronics.
An aqueous pH-controlled chemical reduction synthesis of copper particles (CBD-CuP) from metal salt with hemp-derived cannabidiol (CBD) as a surfactant and capping agent. The polymer phase is synthesized from CBD and linking monomers, adipoyl chloride or phosgene, through solution polymerization to form poly(cannabidiol)-adipate or poly(cannabidiol)-carbonate respectively. Conductive copper inks are formulated by dispersing synthesized particles into polymers. Conductivity is compared to similar formulations with conventional petroleum derived polymers and biopolymers. Poly(cannabidiol)-adipate copper composites are dissolved to isolate copper and polymer. Copper is assessed iteratively for degradation through reclamation cycles. Poly(cannabidiol)-adipate is degraded through base-assisted hydrolysis with common bases such as ammonium hydroxide.
Scanning electron microscopy indicates that CBD-CuP synthesized at pH 6 with a 1:1 mass ratio of metal salt precursor to reducing agent are spherical, polycrystalline, and have an average particle size of 2 micrometers. XRD and EDX shows that surface composition has minimal oxides with >99% weight percent copper. Comparing CBD-CuP to ligand exchanged particles indicates that CBD particles exhibit the strongest resistance to corrosion in compressed air up to 220 C, whereupon CBD degradation results in accelerated oxidation. XRD data collected over long-term indicates the stability of synthesized particles over time in ambient conditions. CBD-CuP in ink formulations show shear thinning properties indicating improved compatibility of CBD with CBD-based biopolymers with micron-scale particle dispersions. Composites cured at 80 C demonstrated conductivities up to 2.5% of bulk copper and 6% at 200 C. Conductive composites were subsequently dissolved in solvents to reclaim copper that could be redispersed in the polymer phase and exhibit conductivity. The polymer was demonstrated to degrade hydrolytically within a day of submersion in basic environment.
Cannabinoids and cannabinoid-derived biopolymers illustrate a comprehensive capability to inhibit corrosion through inherent antioxidant properties of these materials, while maintaining inter-particle conductivity of copper particles both in and outside of ink formulations. Inks formulated can be used to make high conductivity traces at low temperatures compatible with many flexible substrates. Reclamation and degradation of feedstock materials opens pathways to circularity of a new bio-derived materials platform.