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Fiber reinforced thermosetting composites are essential materials for present and future technologies. However, their lack of reprocessability puts them far behind in achieving current sustainability targets. The recent development of covalent adaptable networks represents a promising approach to mitigate this. Here, mechanical recycling of short-cut aramid fiber reinforced epoxy composites was evaluated with a special focus on the impact of fiber surface functionality. The introduction of aramid fibers with four different surface chemistries to a covalent adaptable network was shown to influence the mechanical properties before and after reprocessing. Epoxy functionalized fibers enabled 52 % and 36 % retention of the original tensile stress and elongation at break after two recycling cycles. In comparison, the unmodified reference samples could only retain 19 % and 12 % of the original tensile stress and elongation at break. Fiber functionalization was thus proven to be a key piece in the development of more sustainable solutions for short-cut fiber reinforced polymer composites (SCFRPC)., QC 20240215

A combined experimental and theoretical investigation revealed mechanistic differences in the ring-opening polymerization (ROP) behavior of macrocyclic carbonates (MCs, 11-membered to 15-membered MCs). The study employs urea and potassium methoxide as the catalytic system for ROP. Besides the polymerization rate correlating with the ring size, where smaller rings have a faster polymerization rate, both the thermodynamic stability of the conformer and the stability of the transition state affect the polymerization rate. An experimental kinetic evaluation revealed a deviation between the polymerization rate of the 11-membered MC and the rest of the MCs. Computational investigation using density functional theory showed that the thermodynamic stability of the 11-membered MC differs from others, with a population distribution more toward the usually less energetically disfavored (E,Z)conformer, while the larger rings showed a preference for the Z,Z-conformation. In the transition state, the (E,Z)-conformer was found to be lower in energy compared to the (Z,Z)-conformation, which leads to a lower Gibbs free energy of activation for nucleophilic attack on the (E,Z)-conformation (Delta G(+/-) = 18.3 kcal center dot mol(-1)) compared to macrocycles with the more stable (Z,Z)-conformation (19.8 kcal center dot mol(-1)). The rate-determining step for the 11-membered MC with (E,Z)-conformation relates to the nucleophilic addition, while the rate-limiting step for the larger 15-membered MC corresponds to the ring-opening step. Linking the thermodynamic conformer stability of cyclic monomers to their inherent polymerization behavior is essential for the future design of selective catalysts for ROP., QC 20231101

The higher chemical sensitivity of aramid fibers, compared to carbon or glass fibers, adds to the challenge of designing recyclable aramid fiber reinforced polymer composites. Our study sheds some light on this endeavor through a surface functionalization approach. Twaron® aramid fibers were surface modified by self-polymerization of dopamine followed by the condensation of a silane coupling agent, bearing an epoxy group (PDA-Si). Thanks to the mild modification process, the fibers retained their thermal and mechanical properties. At the same time, the functionalization enhanced the adhesion strength between the meshes and a partially bio-based epoxy thermoset, which was demonstrated by a peeling adhesion test and lap-shear bonding test. Chemical recycling of the epoxy thermoset and epoxy composites reinforced with PDA-Si aramid meshes was achieved by mild solvolysis in ethylene glycol. The recycled thermoset was rich in hydroxyl groups, which promoted the adhesion with PDA-Si meshes. Furthermore, high-quality PDA-Si aramid meshes were recovered after the chemical recycling. The recovered meshes showed 82% removal of the thermoset matrix and the retention of the surface functionalization as suggested by thermogravimetric and spectroscopic analyses, respectively. This enabled 78% recovery of the initial interface strength between the recycled PDA-Si meshes and virgin thermoset matrix. This unveils the role of surface functionalization not only as a performance enhancer but also as a useful aid in the development of circular FRPCs., QC 20240702

Chemical recycling to monomers (CRMs) of A-B-Ablockcopolymers is governed by the chemical structure and thereby the thermodynamicbehavior of different block constituents. Here, we show how a thermodynamictoolkit based on a cyclic monomer structure and solvent propertiescan be utilized in the design of recyclable A-B-A blockcopolymers with varying material properties. By combining four cyclicmonomers lactide, epsilon-decalactone, 2,2-diethyltrimethylene carbonate,and trimethylene carbonate, three different block copolymers werecreated, suitable for different CRM scenarios. The chemical structureof the soft midblock (epsilon-decalactone or trimethylene carbonate)appeared to have a critical impact both on the ring-closing depolymerizationbehavior and mechanical properties, where changing from a polyesterto a polycarbonate soft block increased Young's modulus from14 to 200 MPa. Hence, this work demonstrates the complexity as wellas the opportunities in the design of macromolecular structures fora circular economy., QC 20230706

The thermodynamic equilibrium between ring-opening polymerization and ring-closing depolymerization is influenced by monomer-solvent-polymer interactions, an effect that can be utilized to promote chemical recycling to monomer. Here, the influence of monomer structure on this solvent effect has been investigated, showing that the chemical structure of the monomer influences the power of the solvent to supress the ceiling temperature. The study also demonstrates how catalyst selectivity can be utilized to obtain selective ring-closing depolymerization of one component of a polymer blend, even when the thermodynamics dictate otherwise., QC 20230815

QC 20230509

Isocyanate-free chemistry and the introduction of dynamic bonds are a promising combination toward the development of more sustainable polyurethane (PU) networks. Here, we present the synthesis of reprocessable, isocyanate-free PU networks through atom-economical reactions for both monomers and polymers, valorizing CO2 as a building block. The monomers employed were five-membered cyclic carbonates prepared through an efficient (>99% conversion) reaction between CO2 and epoxides with high yield (up to 97% at a 100 gram scale), catalyzed by the moisture-tolerant and easily prepared DBU center dot I-2 complex. The structural diversity of the monomers and the utilization of cystamine bearing the dynamic S-S motif realized PU networks with a finely tuned profile of thermal (T-g from -9 to 44 degrees C), mechanical (E from 0.2 to 1700 MPa), and viscoelastic properties (E' from 0.03 to 5.5 MPa at 1 Hz). Facile recycling (100 degrees C, 20 min) of the networks was enabled thanks to the rapidly exchanging disulfide bonds and the modulated cross-link density. Moisture-induced plasticization of the networks was identified, and its effect on the properties of the networks was elucidated. The atom economy and energy-efficiency methodology, avoiding toxic reagents and preventing waste generation, make this approach an attractive and greener pathway to PU networks taking a step toward a circular plastic economy., QC 20220405

Designing polymeric materials for closed-loop material streams is the key to achieving a circular society. Here, a library of macrocyclic carbonates (MCs) was designed by a facile and direct one-pot, two-step synthesis approach without the use of a solvent at a 10 g scale. We demonstrate that anionic polymerization with tert-butoxide enables the ultrafast ring-opening polymerization (ROP) of MCs with high conversion (>97%) within seconds (3-10 s) at ambient temperature. The polymerization rate depends on the odd or even number of methylene groups between the carbonate linkages in the MCs, and not the overall ring size, yielding an "odd-even" effect. This polymerization rate is related to the difference in molecular conformation of the MCs, as determined by X-ray crystallography. The polymers (polypenta-, hexa-, heptamethylene carbonate) were subsequently regenerated back to their original MCs at a high selectivity (95-99 mol %) and good yields (70-85%), hence taking a step toward closing the loop on these long alkyl chain polycarbonates., QC 20220325

Structural variations (oligolactide segments, functionalized end groups, and different plasticizer cores) were utilized to tailor the performances of biobased plasticizers for polylactide (PLA). Six plasticizers were developed starting from 1,4-butanediol and isosorbide as cores: two monomeric (1,4-butanediol levulinate and isosorbide levulinate) and four oligomeric plasticizers with hydroxyl or levulinate ester end groups (1,4-butanediol-based oligolactide, isosorbide-based oligolactide, 1,4-butanediol-based oligomeric levulinate, and isosorbide-based oligomeric levulinate). Structural variations in plasticizer design were reflected in the thermal stability, plasticizing efficiency, and migration resistance. The monomeric plasticizer 1,4-butanediol levulinate decreased the glass-transition temperature of PLA from 59 to 16 degrees C and increased the strain at break substantially from 6 to 227% with 20 wt % addition. 1,4-Butanediol-based oligomeric levulinate exhibited better thermal stability and migration resistance, though the plasticizing efficiency was slightly lower (glass-transition temperature = 28 degrees C; strain at break = 202%). Compared to PLA films plasticized by plasticizers with flexible butanediol cores, those plasticized by plasticizers with rigid isosorbide cores exhibited higher Young's modulus and thermal stability and lower plasticizing efficiency. Furthermore, plasticizers with levulinate ester end groups had improved thermal stability, plasticizing efficiency, and migration resistance compared to the corresponding plasticizers with hydroxyl end groups. Hence, a set of controlled structural variations in plasticizer design were successfully demonstrated as a potent route to tailor the plasticizer performances., QC 20230615

Parmi tous les matériaux, les plastiques sont parmi les produits les plus importants de notre vie quotidienne. Grâce à leur facilité de production et de transformation, leur faible coût et leurs propriétés personnalisables, les plastiques se retrouvent en effet dans pratiquement tous les secteurs d’applications, par exemple, dans l'emballage, l'automobile, l'industrie pharmaceutique ou pour les appareils électriques et électroniques. Cependant, ils sont principalement produits à partir de pétrole et contaminent l'environnement lorsqu'ils ne sont pas correctement recyclés, ce qui conduit à la catastrophe environnementale que nous connaissons tous. L'utilisation du dioxyde de carbone (CO2) comme substitut au pétrole devrait limiter notre dépendance à cette ressource fossile et éviter d'être affectés par les problèmes géopolitiques associés auxquels nous sommes actuellement confrontés. Le CO2 est en effet disponible en grandes quantités et à faible coût, et il pourrait contribuer à un secteur du plastique plus durable en permettant la production sur site de plastiques. Pour atteindre cet objectif ambitieux, des transformations efficaces opérant dans des conditions douces et produisant peu de déchets doivent être développées, et des scénarios de fin de vie des nouveaux polymères doivent être envisagés.L'objectif de cette thèse est de fusionner des transformations innovantes du CO2 avec des molécules biosourcées pour produire des polymères fonctionnels dans des conditions douces. Ce travail a été réalisé dans le cadre du projet Excellence of Science (EoS) "BIOFACT" qui traite de la transformation de la lignine en produits chimiques et polymères, en commençant par la dépolymérisation sélective de la lignine. Ma contribution à ce projet est de développer des voies innovantes pour copolymériser une variété de diols ou de diamines issue de lignine (ou de sucre) avec de nouveaux carbonates cycliques hautement réactifs produits à partir de CO2. Le but final est de donner accès, Among all materials, plastics have become one of the most important products of our daily life. Thanks to their ease of production and processing, low cost and customizable properties, plastics are indeed found in pretty much all sectors with applications, for example, in packaging, automotive, pharmaceutical industries or for electrical and electronical devices. However, they are mainly produced from petroleum and contaminate the environment when not properly recycled, which leads to the environmental disaster that we all know. The utilization of carbon dioxide (CO2) as a substitute to petroleum is expected to limit our dependency to this depleting fossil resource and to avoid to be dramatically affected by the associated geopolitical issues that we are currently facing. CO2 is indeed available at large quantities and low cost, and it might contribute to a more sustainable plastic sector by enabling the on-site production of plastics. To reach this ambitious goal, efficient transformations operating under mild conditions and producing limited waste have to be developed, and end-of-life scenarios of the new polymers have to be considered. In this perspective, the aim of this PhD thesis is to merge innovative CO2 transformations with bio-based molecules to produce functional polymers under mild conditions. This work was carried out in the framework of the Excellence of Science (EoS) “BIOFACT” project that deals with the transformation of lignin into high-value chemicals and polymers, starting with the very challenging selective depolymerization of lignin. My contribution to this project was to develop innovative routes to copolymerize a variety of lignin- (or sugar)-based diols or diamines with novel highly reactive CO2-based cyclic carbonates with the objective to produce non-phosgene-based polycarbonates (with diols) and non-isocyanate-based polyurethanes (with diamines) at room temperature. The influence of the structure of the amine/alcohol and reaction condition, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Conventional thermosets cannot be recycled once they reach their end-of-life creating unavoidable waste. Covalent adaptable networks (CANs) are a promising circular solution as they can be reprocessed by conventional techniques employed for processing thermoplastics. In this work, strong and chemically resistant, long-chain polyamide (PA) CANs were developed by introducing intrinsically reactive disulfides in PA networks. Following a solvent-free strategy and utilizing ethylene brassylate, a renewable cyclic diester, our approach brings together the high strength and chemical resistance of long-chain, crosslinked PAs with the reprocessability of dynamic networks in a sustainable fashion. The structure of the PA CANs was elucidated by X-ray diffraction analysis, and the effect of the disulfides on the thermal, mechanical, viscoelastic and dynamic properties was evaluated. The PA CANs had high gel content (86-98%) and they were reprocessable over three grinding-compression molding cycles, retaining their strength (15-20 MPa), crosslink density and gel content. They exhibited rapid stress relaxation with relaxation times as low as 1.06 s and were healable within 5 min. The long-chain PA CANs are easy to prepare and feature several elements of sustainable materials design, highly valued in plastics' circular economy., QC 20211103

QC 20210527

QC 20210820

Despite technological feasibility and industrial scalability in toughening polylactide (PLA) by direct blending, avoiding the sacrifice of mechanical strength or full renewability remains a challenge. Here, low-molecular-weight poly(ethylene 2,5-furandicarboxylate)-block-polylactide (PEF-b-PLA) was synthesized to yield a fully biobased copolymer with expected partial miscibility with PLA. The ability of PEF-b-PLA to toughen PLA at 10 wt % (PLA10) and 20 wt % (PLA20) loadings was then evaluated. To understand the achieved properties, the formation of a nanostructured dispersion phase due to favorable interfacial adhesion arising from the miscibility of the PLA block with the PLA matrix was investigated. The morphological features, together with comparable strength inherited from the PEF blocks, afforded an unusual combination of toughness and strength for the PLA blends. Compared to the poor tensile toughness of a pure PLA film (1.77 MJ/m(3)), a striking increase of 839 and 912% was achieved for PLA10 and PLA20, respectively. More importantly, both pure PLA and the blends were characterized by comparable yield strength (similar to 30 MPa). This was accompanied by excellent UV-shielding imparted by the functional groups on the PEF blocks, which would improve the prospects of realizing PLA-based functional packing materials. The proposed design of copolymers, with good industrial feasibility, should be useful to guide the toughening approaches for PLA and probably other degradable polyester blends by profound morphology control., QC 20220525

Polyhydroxyurethanes (PHUs) are strong candidates for replacing conventional isocyanate-based polyurethanes (PUs), yet analogous structural diversity and subsequent properties have so far not been reached for PHUs. Here, we demonstrate that by rational design of the PHU microstructure and utilization of solubility as an enabling tool, complex architectures can be realized with benign reagents and atom-economical reactions, without harsh reaction conditions and solvents. Polyhydroxyurethane-graft-poly(epsilon-caprolactone), PHU-graft-PCL, copolymers were synthesized through graft ring-opening polymerization of epsilon-caprolactone (CL) from the pendent -OH groups of a PHU. The structure of the PHU was carefully designed to allow its dissolution in CL and enable bulk polymerization conditions. Solubility tests of different PHUs in various lactones corroborated that the PHU-lactone structure pair was critical to achieve dissolution. The optimum reaction conditions were kinetically determined, the copolymers' structure was confirmed by H-1, DOSY and P-31 NMR spectroscopy and their thermal properties were evaluated by DSC and TGA analysis. Our work demonstrated the effectiveness of utilizing solubility to achieve complex architectures, expanding the synthetic intricacy for PHUs and could expand their future applications and opportunities., QC 20220520