Vincent Monteil

In the environment, nanoplastics are covered with a conditioning film composed of various biomolecules present in the surrounding medium.

Ziegler-Natta catalysts, discovered in 1950s, are still nowadays central to the industrial production of polyethylene and polypropylene. Despite being the workhorse of the polymer industry and despite years of extensive research, the improvement of Ziegler-Natta catalysts has been mostly empirical. In particular, the coordination surrounding of Ti sites in pre-catalysts, key for the formation of active sites upon AlEt3 activation, has been highly debated. Notably, quantification of different Ti sites on the MgCl2 surface has not been possible so far, hindering the development of quantitative structure-activity relationships. In this work, we prepared a series of pre-catalysts with increasing concentration of BCl3 modifier during the catalyst synthesis, known to affect the amount of Cl- and alkoxo-ligands in the Ti local surrounding as well as the activity in ethylene polymerization. We develop a methodology, relying on a library of theoretical XAS spectra for DFT-optimized structural models, benchmarked on a series of well-defined molecular compounds. Quantitative analysis of XAS data allows us to evaluate the relative fractions of Ti sites in fully Cl-surrounding as well as containing alkoxide and O-donor ligands. The analysis shows that the number of Ti-O bonds (initially mostly present in their alkoxo-form) decreases upon treatment with BCl3 up to B/Ti ratio of 2, coherent with earlier proposals, and increases afterwards, due to O-donor ligands, likely related to B-alkoxo species coordinated to Ti. The catalytic activity of these pre-catalysts after activation with AlEt3 in ethylene polymerization passes through a maximum at B/Ti ratio of ~2, pointing to its relation to the detrimental effect of O-based ligands on the activity. This approach allows to address and quantify the metal speciation in the complex Ziegler-Natta pre-catalysts and relate this to their catalytic activity, a first step towards establishing quantitative structure-activity relationships.

Ziegler-Natta catalysts, discovered in 1950s, are still nowadays central to the industrial production of polyethylene and polypropylene. Despite being the workhorse of the polymer industry and despite years of extensive research, the improvement of Ziegler-Natta catalysts has been mostly empirical. In particular, the coordination surrounding of Ti sites in pre-catalysts, key for the formation of active sites upon AlEt3 activation, has been highly debated. Notably, quantification of different Ti sites on the MgCl2 surface has not been possible so far, hindering the development of quantitative structure-activity relationships. In this work, we prepared a series of pre-catalysts with increasing concentration of BCl3 modifier during the catalyst synthesis, known to affect the amount of Cl- and alkoxo-ligands in the Ti local surrounding as well as the activity in ethylene polymerization. We develop a methodology, relying on a library of theoretical XAS spectra for DFT-optimized structural models, benchmarked on a series of well-defined molecular compounds. Quantitative analysis of XAS data allows us to evaluate the relative fractions of Ti sites in fully Cl-surrounding as well as containing alkoxide and O-donor ligands. The analysis shows that the number of Ti-O bonds (initially mostly present in their alkoxo-form) decreases upon treatment with BCl3 up to B/Ti ratio of 2, coherent with earlier proposals, and increases afterwards, due to O-donor ligands, likely related to B-alkoxo species coordinated to Ti. The catalytic activity of these pre-catalysts after activation with AlEt3 in ethylene polymerization passes through a maximum at B/Ti ratio of ~2, pointing to its relation to the detrimental effect of O-based ligands on the activity. This approach allows to address and quantify the metal speciation in the complex Ziegler-Natta pre-catalysts and relate this to their catalytic activity, a first step towards establishing quantitative structure-activity relationships.

A robust analytical workflow enabling a full characterization of polyolefins solvent-based recycling applied to real-world plastic feedstocks

Surfactant-free aqueous emulsion polymerization enables polyethylene nanoparticles (50–200 nm) with tunable physicochemical properties, providing realistic models for nanoplastic behavior and toxicity.

Cross‐linked polyethylene (XLPE), widely utilized in electrical cables for example, remains a challenging material to recycle. While thermo‐mechanical devulcanization has been extensively studied for rubber recycling, its application in regenerating XLPE still requires an in‐depth investigation of the correlation between process parameters and ultimate material properties. Here, XLPE waste was regenerated by flash extrusion at high temperatures and shear. A thorough characterization of the so‐obtained polyolefins (rXLPEs), including gel content and chemical analyses such as NMR and SEC afforded a comprehensive picture of the mechanisms involved in the regeneration process—namely chain scission or chain branching—depending on the extrusion temperature. We address viscoelastic properties combining extensional and shear rheology finally establishing distinct relationships between polymer molecular structure and rheological behaviors. Moreover, when rXLPEs are reincorporated into virgin linear polyethylene (20% wt. of rXLPE), the resulting blends acquire unique and individual features. Depending on the regeneration temperature of rXLPEs, the blends exhibit different processability under high shear conditions comparable to industrial continuous processing as well as a wide range of elongational and shear viscosity. This exploration in rXLPE performances offers a novel insight into a regeneration process easily extendable at large scale, paving innovative ways for applications on cable waste.