Double Resource Recovery from Plastic Waste: Development and Characterisation of an Eco-Friendly Carbon-Based Ink from Plastic Pyrolysis-Derived Carbon and Recycled Tea Leaf Extract for Sustainable Artistic Applications

The growing global plastic usage results in the enormous accumulation of non-biodegradable plastic garbage, causing serious environmental, ecological and socio-economic issues. Pyrolysis has become an efficient thermochemical technique to convert plastic waste to liquid fuels and combustible gases, but the carbonaceous solid byproduct created in the process is often underappreciated, despite its large material potential. Simultaneously, the production of conventional carbon black-based inks and watercolour pigments depends largely on the usage of petroleum-derived raw materials and energy-intensive industrial processes, resulting in the emission of greenhouse gases, depletion of fossil resources and contamination of the environment. At the same time, millions of tonnes of spent tea leaves produced globally are disposed of as organic waste, regardless of the fact that they contain naturally occurring tannins, polyphenols and colouring compounds that can be utilised as sustainable additives in pigment compositions. Our previous work successfully demonstrated the production and structural characterisation of plastic-derived pyrolytic carbon via an oxygen-limited pyrolysis process. It was established that the material obtained possesses a predominantly amorphous turbostratic carbon structure with potential applications in environmental remediation and functional carbon materials[1]. In this study, expanding on earlier work, a new value-added application of the recovered carbon is explored by generating an eco-friendly carbon-based ink using plastic pyrolysis-derived carbon and recycle dused tea leaves. The current work was focused on thermochemical conversion of plastic packaging waste in a lab-scale cylindrical metallic reactor under limited oxygen circumstances. The resulting pyrolytic carbon was collected, cleaned, dried and ground to a fine powder. Approximately 10 g of the generated pyrolytic carbon was combined with 10 g of recycled old tea leaves, which were processed to obtain a tannin-rich extract that was employed as a natural colour modifier and dispersing medium. The formulated formulation was characterised by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), pH and electrical conductivity. The ink as prepared had an acidic pH of 3.0, which was attributed to the presence of naturally existing acidic functional groups from the tea polyphenols and oxygen functionalities on the surface of the pyrolytic carbon. The measured conductivity of 10.42 µS/cm showed the existence of mobile ionic species in the dispersion that indicates the good electrochemical interaction between the dispersed carbon particles and the aqueous medium. XRD analysis showed that the carbon was mainly amorphous turbostratic with a low degree of graphitic order. FTIR analysis indicated the presence of hydroxyl, carbonyl, aromatic C=C and C–O functional groups responsible for the improved pigment dispersion and interaction with the natural tea extract. The integrated physicochemical characterisation indicates that the developed formulation has appropriate qualities for eco-friendly creative applications such as watercolour painting, brush painting, calligraphy, educational art materials and sustainable carbon-based pigments.
The presented technology handles two main waste streams, i.e., plastic garbage and used tea leaves, concurrently and transforms them into a usable carbon-based artistic material. The created approach contributes to the circular economy principles by valorising waste, decreasing the dependence on petroleum-derived pigments, and fostering sustainable material innovation for educational, artistic, and environmental purposes.

Plastic waste; Pyrolysis; Pyrolytic carbon; Sustainable ink; Carbon pigment; Tea leaf extract; Water colour; Circular economy; Waste valorisation

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