Etienne Grau

Concerns raised by ubiquitate plastic contamination are urging to develop alternative materials. In the recent years, bio-sourced polymers also coined as “bioplastics” have been proposed to mitigate plastic pollution while meeting industrial and commercial expectations. Like petro-sourced plastics, they are expected to break-down in the environment into fragments down to sub-micron size. However, only scarce data are available on the impacts of such biosourced nanoplastics once released into the environment. This study examines the effects on aquatic species of model nanoplastics made from several bio-sourced polymers (Bio-NPs) that are either already on market (PHA, PLA, PA11) or still under development (NIPU, PCAR). We exposed three species of micro-algae (at 10, 100, and 1000 µg/L, for 24 and 48 hours, and one week) to test the effects of Bio-NPs on algal growth. We also exposed freshwater bivalves C. fluminea (at 1, 10 and 100 µg/L, for one week) to test the filtration activity and gene expressions in response to Bio-NPs exposure. All five Bio-NPs tested generated growth inhibitions in at least one of the three algae tested. PLA and PA11 were the most deleterious ones for algal growth among the five tested Bio-NPs. The highest growth inhibitions were observed on the fresh water species D. subspicatus. Each Bio-NP tested resulted in significant decreases of the filtration rates of C. fluminea. PHA impaired filtration at the lowest concentrations tested (1 µg/L), whereas PCAR, PA11 and NIPU led to significant effects only at higher concentrations (10 and 100 µg/L). The results from gene expressions in C. fluminea showed strong inductions of all gene functions tested for all the five bio-NPs tested. These Bio-NPs triggered endocytosis and detoxification mechanisms. They impaired the mitochondrial metabolism and triggered oxidative stress and immune responses. PA11, NIPU and PHA exposures resulted in the strongest gene regulations. The present study brings brand new findings about a kind of nanoplastics that may be released into the environment in a near future as the use of bioplastics is growing fast. It will help better understanding the impacts of such fragmented bioplastic NPs on aquatic species.

Polymérisation de l’éthylène : de l’homopolymérisation radicalaire à la copolymérisation hybride radicalaire / catalytique: Ce travail concerne l'étude de la polymérisation de l'éthylène allant de l'homopolymérisation purement radicalaire jusqu'à la copolymérisation utilisant un mécanisme hybride radicalaire/catalytique. Ce travail montre que le polyéthylène peut être synthétisé par voie radicalaire dans des conditions expérimentales beaucoup plus douces que celles utilisées industriellement (P>1000 bar et T>100°C). L'éthylène a été polymérisé à partir de 10°C et 5 bar de pression d'éthylène. Un important effet activateur du solvant a été mis en évidence. De plus la polymérisation en milieu dispersé aqueux de l'éthylène a aussi été étudiée. Des latex stables de PE avec des taux de solide de 40% ont pu être obtenus. Deux morphologies de nanoparticules, cylindre ou sphère, ont été observées. La copolymérisation radicalaire avec des monomères vinyliques polaires a été également étudiée en solution ou en émulsion. Des insertions d'éthylène jusqu'à 50% ont été obtenues. De plus l'influence du comonomère et du solvant organique utilisé sur la polymérisation radicalaire de l'éthylène a été quantifiée. Une nouvelle technique de polymérisation hybride radicalaire/catalytique a été développée pour pouvoir obtenir toute la gamme de compositions possibles de copolymères éthylène/monomère polaire à partir d'un complexe de nickel qui amorce la polymérisation radicalaire et catalyse également la polymérisation de l'éthylène. Ce complexe subit une rupture homolytique réversible de la liaison nickel carbone et permet la synthèse de copolymères multiblocs. Des insertions d'éthylène de 1% à 99% ont été obtenues en faisant varier la pression d'éthylène et la concentration en comonomères polaires

The detection of ammonia in aqueous solutions using solid‐phase microextraction (SPME)‐GC‐MS (gas chromatography‐mass spectrometry) is described. This technique enables the direct detection of ammonia without the need for derivatization or the use of colorimetric methods, which can be prone to interference from transition metal ions or organic cosolvents typically used in nitrogen reduction catalysis. The use of a fused‐silica SPME fiber coated with polydimethylsiloxane/divinylbenzene is found to allow fast and direct quantification of ammonia with a limit of detection = 0.17 ppm and a limit of quantification = 0.5 ppm in water. The method is straightforward to implement and can be readily automated using commercial instrumentation. It is also capable of detecting isotopically labeled ¹⁵NH₃ as well as simple alkylamines such as methylamine or ethylamine which may be produced or released during the course of a reaction.

The thermal activation of oxamic acids, using a hypervalent iodine, leads to the in situ generation of isocyanates and CO₂, precursors of self-blown polyurethane foams.

Polyhydroxyurethane (PHU) thermosets are the most promising isocyanate-free substitutes to polyurethane ones when targeting the main applications of the PU business (coatings, adhesives, foams). However, the curing of their solvent-free formulations at near room temperatures is often very slow and requires the utilization of organocatalysts, limiting the large-scale deployment of the technology. Herein, we study the impact of water, introduced as an additive (2 to 10 wt.%), on the crosslinking rate of common solvent-free thermosetting PHU formulations composed of a polycyclic carbonate and a diamine. Rheology measurements, using a multi-frequency approach, indicate that even very small amounts of water (<5 wt.%) impressively shorten gel times, by up to 5 folds at 40 °C. The multi-frequency methodology highlights for the first time the strong interactions of water with the growing PHU network during the crosslinking reaction. It suggests that water breaks down the multiple intra-/inter-molecular H-bond interactions within the PHU clusters, consequently enhancing the molecular mobility and delaying the vitrification (hydroplasticization), both phenomena contributing to accelerate the crosslinking rate. On top of that, through a combination of model reactions and computational calculations, we demonstrate that water is an actual catalyst of the cyclic carbonate aminolysis. Eventually, thanks to its multifaceted role, water can efficiently substitute the organocatalysts (e.g. TBD, DBU) usually required to cure PHU formulations at near ambient temperature. This work demonstrates that the use of additive amounts of water in solvent-free formulations is a cost-effective, non-toxic, and robust solution to accelerate the production of PHU materials, free of any organocatalyst. It offers promising prospects for the deployment of PHU-based materials requiring mild processing conditions.

Polyurethane (PU) foams are key players within the large foam market, with applications such as thermal insulating materials, cushioning, protective equipment, etc. With the current regulatory constraints on the use of toxic isocyanates and the ambitious goals to increase the renewable content of plastics while valorizing waste, isocyanate-free liquid formulations containing biofillers that are able to easily self-foam are needed for more sustainable PU foams in the future. Herein, we incorporate various abundant waste stream-sourced biofillers (proteins, lignin derivatives, and polysaccharides) into isocyanate-free PU formulations composed of CO₂-based poly(cyclic carbonate)s, diamines and a catalyst. The formulations containing up to 30 wt% of biofillers are foamed at 100 °C without adding any external foaming agent. Moisture naturally present in the biofillers partially hydrolyses the cyclic carbonates, which generates the blowing agent (CO₂). The biofiller, even at a low content (1 wt%), stabilizes the growing cells, providing homogeneous foams. Although the nature of the biofiller does not significantly affect the foams’ density and morphology, their mechanical properties are strongly affected, for example from a rigid foam with 10 wt% keratin (compression modulus (E) = 21.9 MPa) to a flexible one with chitosan (E = 0.2 MPa). Preliminary studies indicate that the biofiller does not prevent the foam recycling into polymer films by hot pressing. Virtually any kind of moisture-containing biowaste can be used as a water reservoir to foam the formulations while increasing the bio-based content of the material, which reaches 97% when selecting bio-based monomers. This process valorizes abundant waste stream-sourced biofillers for producing more sustainable PU foams.

Polyurethane (PU) thermoplastics and thermosets were prepared through the step-growth polymerization of in situ generated polyisocyanates through the decarboxylation of polyoxamic acids, in the presence of phenyliodine diacetate (PIDA), and polyols. The CO2 produced during the reaction allowed the access to self-blown polyurethane foams through an endogenous chemical blowing. The acetic acid released from ligand exchange at the iodine center was also shown to accelerate the polymerization reaction, avoiding the recourse to an additional catalyst. Changing simple parameters during the production process allowed us to access flexible PU foams with a wide range of properties.