In a new study published in Scientific Reports, a team of researchers from Italy detailed the development and function of a paper-based sensor that uses biodegradable polylactic acid (PLA) emulsion ink. This research focuses on the fabrication of sustainable electronic devices using eco-friendly components like carbon nanotubes (CNTs) and silver (Ag) flakes.
Schematic representation of the fabrication process of the pressure sensor. Image Credit: https://www.nature.com/articles/s41598-024-60315-z
This innovative approach aims to mitigate electronic waste concerns and foster a circular economy within the electronics sector. By utilizing PLA and conductive fillers, the study seeks to showcase the potential of green electronics and their application in sensor technology, aligning with the growing emphasis on eco-conscious practices in various industries.
Background
Piezoresistive sensors are commonly crafted from materials that exhibit alterations in electrical resistance in response to mechanical stress or strain. Traditional sensor components often consist of non-biodegradable substances, contributing to environmental degradation and the accumulation of electronic waste.
To address these sustainability challenges, researchers are exploring alternative materials like PLA and sustainable conductive fillers such as CNTs and Ag flakes. Developing a paper-based sensor by incorporating these eco-friendly elements is imperative to demonstrate the feasibility of creating biodegradable electronic devices with enhanced sustainability and performance characteristics, thereby contributing to the advancement of green technologies.
The Current Study
The experimental procedure was initiated by dissolving PLA 6060D in 20 mL of ethyl acetate. Subsequently, the PLA dispersion underwent emulsification by dispersing oil in water with the addition of non-ionic surfactants. To maintain an equivalent weight of PLA and polyurethane dispersions (PUDs) post-drying, water-borne polyurethane was introduced to a polymeric emulsion containing 1 % wt. PLA.
Conductive inks, incorporating multi-walled carbon nanotubes (MWCNTs), Ag flakes, graphene nanoparticles (GNPs), or a hybrid of Ag flakes with GNPs or MWCNTs, were integrated into the PLA/PUDs emulsion at a 30 % wt. concentration relative to the polymer. The resulting mixture was probe-sonicated for 3 minutes to ensure uniform dispersion of the fillers.
Adjustment in the PLA concentration was made for applications necessitating higher-viscosity materials like screen printing or 3D printing. The binder-to-filler ratio was varied to achieve the desired conductivity levels. The duration of tip sonication was optimized to facilitate an even distribution of fillers within the emulsion.
Various coating techniques were evaluated for the deposition of the conductive ink onto substrates. Spray coating, chosen for its scalability and low polymer consumption, was employed to uniformly apply the conductive ink onto substrates. This method ensured consistent coating thickness and coverage, essential for the fabrication and evaluation of sensors.
The fabricated sensor and coatings were characterized using techniques such as scanning electron microscopy (SEM), energy-dispersive X-Ray spectroscopy (EDS), X-Ray diffraction (XRD), and Raman spectroscopy to analyze the properties of the materials and coatings.
Results and Discussion
The study successfully formulated an emulsion ink based on PLA incorporating sustainable fillers, exhibiting favorable adhesion and conductivity properties. SEM imaging provided insights into the morphology of the coatings, while EDS analysis confirmed the presence of the desired elements within the materials. XRD patterns elucidated the crystalline structure of the components, and Raman spectroscopy offered valuable information regarding the chemical composition.
Dynamic light scattering was utilized to determine the average droplet size of the emulsion, while infrared spectra provided insights into the chemical characteristics of the materials. Thermo-gravimetric analysis (TGA) and surface mapping further enhanced the understanding of the ink formulations. The coating techniques, particularly spray coating, proved effective in uniformly depositing the conductive ink on substrates.
The incorporation of CNTs, Ag flakes, and graphene nanoparticles significantly enhanced the conductivity of the PLA-based emulsion ink, rendering it suitable for sensor applications. By adjusting the binder-to-filler ratio, the researchers could tailor the ink's conductivity to meet specific application requirements. The utilization of sustainable materials and the development of efficient coating techniques underscore the potential of eco-friendly ink formulations in additive manufacturing and sensor technology, paving the way for enhanced sustainability in electronic device production.
Conclusion
In conclusion, the study presents a pioneering approach to developing paper-based sensors using biodegradable PLA emulsion ink enriched with sustainable conductive fillers. The successful integration of eco-friendly materials like CNTs and Ag flakes underscores the feasibility of creating green electronic devices with enhanced functionality and reduced environmental impact.
The study enhances additive manufacturing technologies by optimizing ink formulations and coating methodologies, aiming for more sustainable and efficient solutions. The results highlight the viability of eco-friendly electronics and sensor applications, underscoring sustainability's essential role in the future of the electronics industry. This promotes a shift towards greener and more environmentally conscious manufacturing practices in electronic device production.
Journal Reference
Najafi, M., Forestier, E., Safarpour, M. et al. (2024). Biodegradable polylactic acid emulsion ink based on carbon nanotubes and silver for printed pressure sensors. Scientific Reports 14, 10988. https://doi.org/10.1038/s41598-024-60315-z, https://www.nature.com/articles/s41598-024-60315-z