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Precious metals such as palladium (Pd) have many applications, ranging from automotive catalysts to fine chemistry. Platinum group metals are, thus, in massive demand for industrial applications, even though they are relatively rare and belong to the list of critical materials for many countries. The result is an explosion of their price. The recovery of Pd from spent catalysts and, more generally, the development of a circular economy process around Pd, becomes essential for both economic and environmental reasons. To this aim, we propose a sustainable process based on the use of supercritical CO2 (i.e., a green solvent) operated in mild conditions of pressure and temperature (p = 25 MPa, T = 313 K). Note that the range of CO2 pressures commonly used for extraction is going from 15 to 100 MPa, while temperatures typically vary from 308 to 423 K. A pressure of 25 MPa and a temperature of 313 K can, therefore, be viewed as mild conditions. CO2-soluble copolymers bearing complexing groups, such as pyridine, triphenylphosphine, or acetylacetate, were added to the supercritical fluid to extract the Pd from the catalyst. Two supported catalysts were tested: a pristine aluminosilicate-supported catalyst (Cat D) and a spent alumina supported-catalyst (Cat A). An extraction conversion of up to more than 70% was achieved in the presence of the pyridine-containing copolymer. The recovery of the Pd from the polymer was possible after extraction, and the technological and economical assessment of the process was considered. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a platform of novel functional fluorinated gradient copolymers soluble in liquid and supercritical CO2 is reported. These functional copolymers are bearing different types of complexing units (pyridine, triphenylphosphine, acetylacetate, thioacetate, and thiol) which are well-known ligands for various metals. They have been prepared by reversible addition–fragmentation chain-transfer (RAFT) polymerization in order to obtain well-defined gradient copolymers. The copolymers have been characterized by proton nuclear magnetic resonance (1H-NMR) spectroscopy, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, thermal gravimetric analysis (TGA), dynamical scanning calorimetry (DSC) and cloud point measurements in dense CO2. All the investigated metal-complexing copolymers are soluble in dense CO2 under mild conditions (pressure lower than 30 MPa up to 65 °C), confirming their potential applications in processes such as metal-catalyzed reactions in dense CO2, metal impregnation, (e.g., preparation of supported catalysts) or metal extraction from various substrates (solid or liquid effluents). Particularly, it opens the door to greener and less energy-demanding processes for the recovery of metals from spent catalysts compared to more conventional pyro- and hydro-metallurgical methods. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNC) possess desirable mechanical and optical properties that make them a candidate in the development of the next generation of polymer‐based composites. However, CNC also have a critical issue associated with their use: their hydrophilicity and incompatibility with hydrophobic polymers. CNC surface properties must be modified for them to be successfully implemented by the industrial sector. Grafting (co)polymers chains on the CNC surface can provide compatibility to CNC with hydrophobic matrices and expand their potential range of applications. In this communication preliminary results of a simple method to functionalize CNC surface are reported using block copolymers, where a cationic block anchors via complexation to the anionically charged CNC surface and the other block acts as a stabilizing block, providing dispersibility in various solvents. This is a much simpler and less expensive method than current routes based on covalent modification. The block copolymers poly(polyethylene glycol methacrylate)‐b‐poly(N‐butyl‐N′‐vinyl imidazolium bromide) (PPEGMA‐b‐PBuVIm) and poly(styrene)‐b‐PBuVIm (PS‐b‐PBuVIm) are first synthesized via nitroxide‐mediated polymerization and then non‐covalently adsorbed on the CNC surface. The functionalization has been confirmed via FT‐IR and TGA. The dispersion of polymer‐modified CNC materials in organic solvents is evaluated via dynamic light scattering. Modified CNC yielded stable dispersions in organic solvents. [ABSTRACT FROM AUTHOR]

A biobased latex was obtained by copolymerization in emulsion of ethoxy dihydroeugenyl methacrylate (EDMA) and coumarin methacrylate (CMA). Thin films of poly(EDMA-co-CMA) were irradiated with UV light at 365 nm, to promote the [2+2] photocycloaddition reaction of the coumarin moieties. The advancement of the reaction was followed by monitoring the intensity of the UV-Vis absorbance at 320 nm, characteristic of coumarin, after different irradiation times. Complete dimerization of the coumarin moieties could be achieved. A microfibrillated cellulose (MFC) reinforcement was added to the poly(EDMA-co-CMA) latexes to prepare composite materials. The permeability of the composite films to oxygen, before and after crosslinking, was assessed. For the noncrosslinked films, increasing the cellulose content from 5 wt% to 30 wt% decreased the oxygen transmission rate (OTR) by approximately 70%. When 1 wt% CMA moieties were present in the polymer backbone the OTR was approximately 50 % lower with respect to poly(EDMA) composites. A further slight decrease of permeability was observed upon crosslinking of the composite poly(EDMA-co-CMA)/MFC films. [ABSTRACT FROM AUTHOR]