Universal Approach to Integrating Reduced Graphene Oxide into Polymer Electronics.

Flexible electronics have sparked significant interest in the development of electrically conductive polymer-based composite materials. While efforts are being made to fabricate these composites through laser integration techniques, a versatile methodology applicable to a broad range of thermoplastic polymers remains elusive. Moreover, the underlying mechanisms driving the formation of such composites are not thoroughly understood. Addressing this knowledge gap, our research focuses on the core processes determining the integration of reduced graphene oxide (rGO) with polymers to engineer coatings that are not only flexible and robust but also exhibit electrical conductivity. Notably, we have identified a particular range of laser power densities (between 0.8 and 1.83 kW/cm2), which enables obtaining graphene polymer composite coatings for a large set of thermoplastic polymers. These laser parameters are primarily defined by the thermal properties of the polymers as confirmed by thermal analysis as well as numerical simulations. Scanning electron microscopy with elemental analysis and X-ray photoelectron spectroscopy showed that conductivity can be achieved by two mechanisms-rGO integration and polymer carbonization. Additionally, high-speed videos allowed us to capture the graphene oxide (GO) modification and melt pool formation during laser processing. The cross-sectional analysis of the laser-processed samples showed that the convective flows are present in the polymer substrate explaining the observed behavior. Moreover, the practical application of our research is exemplified through the successful assembly of a conductive wristband for wearable devices. Our study not only fills a critical knowledge gap but also offers a tangible illustration of the potential impact of laser-induced rGO-polymer integration in materials science and engineering applications.

"Functional upcycling" of polymer waste towards the design of new materials.

Diversification of polymer waste recycling is one of the solutions to improve the current environmental scenario. Upcycling is a promising strategy for converting polymer waste into molecular intermediates and high-value products. Although the catalytic transformations into small molecules have been actively discussed, the methods and characteristics of upcycling into new materials have not yet been addressed. Recently, the functionalisation of polymer wastes (polyethylene terephthalate bottles, polypropylene surgical masks, rubber tires, etc.) and their conversion into new materials with enhanced functionality have been proposed as an appealing alternative for dealing with polymer waste recycling/treatment. In this review, the term 'functional upcycling' is introduced to designate any method of post-polymerisation modification or surface functionalisation without considerable polymer chain destruction to produce a new upcycled material with added value. This review explores the functional upcycling strategy with detailed consideration of the most common polymers, i.e., polystyrene, poly(methyl methacrylate), polyethylene, polypropylene, polyurethane, polyethylene terephthalate, polyvinyl chloride, polycarbonate, and rubber. We discuss the composition of plastic waste, reactivity, available physical/chemical agents for modification, and the interconnection between their properties and application. To date, upcycled materials have been successfully applied as adsorbents (including CO2), catalysts, electrode materials for energy storage and sensing, demonstrating a high added value. Importantly, the reviewed reports indicated that the specific performance of upcycled materials is generally comparable or higher than that of similar materials prepared from virgin polymer feedstock. All these advantages promote functional upcycling as a promising diversification approach against the common postprocessing methods employed for polymer waste. Finally, to identify the limitations and suggest future scope of research for each polymer, we comparatively analysed the aspects of functional upcycling with those of chemical and mechanical recycling, considering the energy and resource costs, toxicity of the used chemicals, environmental footprint, and the value added to the product.