Circular Economy Electrochemistry: Creating Additive Manufacturing Feedstocks for Caffeine Detection from Post-Industrial Coffee Pod Waste

Abstract

The recycling of post-industrial waste poly(lactic acid) (PI-PLA) from coffee machine pods into electroanalytical sensors for the detection of caffeine in real tea and coffee samples is reported herein. The PI-PLA is transformed into both nonconductive and conductive filaments to produce full electroanalytical cells, including additively manufactured electrodes (AMEs). The electroanalytical cell was designed utilizing separate prints for the cell body and electrodes to increase the recyclability of the system. The cell body made from nonconductive filament was able to be recycled three times before the feedstock-induced print failure. Three bespoke formulations of conductive filament were produced, with the PI-PLA (61.62 wt %), carbon black (CB, 29.60 wt %), and poly(ethylene succinate) (PES, 8.78 wt %) chosen as the most suitable for use due to its equivalent electrochemical performance, lower material cost, and improved thermal stability compared to the filaments with higher PES loading and ability to be printable. It was shown that this system could detect caffeine with a sensitivity of 0.055 ± 0.001 μA μM–1, a limit of detection of 0.23 μM, a limit of quantification of 0.76 μM, and a relative standard deviation of 3.14% after activation. Interestingly, the nonactivated 8.78% PES electrodes produced significantly better results in this regard than the activated commercial filament toward the detection of caffeine. The activated 8.78% PES electrode was shown to be able to detect the caffeine content in real and spiked Earl Grey tea and Arabica coffee samples with excellent recoveries (96.7–102%). This work reports a paradigm shift in the way AM, electrochemical research, and sustainability can synergize and feed into part of a circular economy, akin to a circular economy electrochemistry.

Utilising bio-based plasticiser castor oil and recycled PLA for the production of conductive additive manufacturing feedstock and detection of bisphenol A

“…In rPLA, there are equal amounts of the three carbon environments, leading to an XPS C 1s fitting of three peaks with similar intensities. 8 In castor oil, there is significantly more C–C/C–H bonding than C–OH and O–CO bonding, leading to a peak of much higher intensity, significantly more than that seen in Fig. 2A.…”

“…5 This perfect circular economy remains hypothetical for the time being, but research around the concept is gaining traction, with more work transitioning from a reliance on virgin materials, particularly non-renewable sources. 6,7 Recently, the idea of circular economy in electrochemistry was introduced, 8 focussing on using additive manufacturing within electrochemistry to produce electroanalytical sensing platforms. The use of additive manufacturing within electrochemistry has seen a sharp increase in the last decade due to its many benefits, such as low cost of equipment and consumables, rapid prototyping capabilities, the ability to explore complex electrode geometries without high manufacturing costs, 9,10 and low waste production, amongst other benefits.…”

“…However, most electrodes produced through additive manufacturing remain a single-use item due to the ingress of solution 11 and the lack of simple electrode cleaning processes. To introduce improved sustainability practices into the field, Sigley et al 8 produced bespoke filament from recycled poly(lactic acid) (rPLA), previously utilised as coffee machine pods. Using the rPLA they created a recycled filament for the electroanalytical cell production.…”

Circular Economy Electrochemistry: Recycling Old Mixed Material Additively Manufactured Sensors into New Electroanalytical Sensing Platforms

“…Additionally, the rAME shows an increased electrochemical surface area of 0.081 ± 0.001 cm 2 compared to 0.075 ± 0.001 and 0.074 ± 0.002 cm 2 . This increase in electrochemical area is in agreement with the XPS and SEM data obtained earlier, whereby an increased amount of graphitic carbon was seen on the surface of non-activated rAMEs compared to standard commercial ones, as seen in other studies. , This data shows that the recycled conductive filament gives excellent electrochemical performance compared to the commercial equivalent.…”

Recycling 3D Printed Residues for the Development of Disposable Paper-Based Electrochemical Sensors

“…Outstanding papers in the literature revealed that the polymeric materials can be reusable by numerous ways, (i) recycling carbon fibers and using them as additive option in the fused filament fabrication (FFF) process of PLA, (ii) reusing glass fiber obtained from turbine blades to reinforce the mechanical properties of PLA material, (iii) recycling PET and polypropylene aim for manufacturing additive filaments with similar mechanical proprieties to the commercial filament and, (iv) combining waste of PLA recovered from coffee pods with native poly­(ethylene glycol) and carbon black particles aim for manufacturing a suitable option of conductive additive filament that can be dedicate to constructed electrodes. , However, to the best of our knowledge, the aforementioned studies do not explore residues of thermoplastic as binder structures for manufacturing disposable electrochemical sensors, which are of high potential in the modern analytical chemistry field, including forensic, , pharmaceutical, environmental, , food and biological ones. − …”