Shear induced structuration of liquid crystalline epoxy thermosets

International audienceLow-molecular weight liquid crystals (LC) have wide technological applications due to their self-assembly in the mesophase. An azomethine nematic monomer based on diglycidyl functionalized mesogenic core and without spacers has been cured with a diamine. The great affinity of LC epoxy to the formation of ordered structures introduces a spatial driving force into the process of curing. Thermal and LC behaviors were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The nature of the LC phases was confirmed by X-ray diffraction. Rheological experiments were conducted during crosslinking at different shear stresses. The viscosity of the mixture is strongly decreasing by three orders of magnitude when the solid epoxy is melting into a LC phase, and is increasing again due to the curing. Unexpected results were found. Applying a stress during curing had a profound influence on the ordering of the structure. The material becomes isotropic if a small shear stress is applied. Then, the higher the stress is, more ordered the final material is. For the highest stresses, the final material is in a highly ordered, quasi-crystalline, smectic structure

Developing future visions for bio-plastics substituting PET – a backcasting approach

The demand for plastics far exceeds that for any other bulk material and is expected to grow further due to global economic and population growth. Packaging is by far the largest end-user segment for plastics. Interest in bioplastics is increasing as public awareness of plastic waste accumulation in natural environ- ments increases. 2,5-Furandicarboxylic acid (FDCA) is the key monomer in the production of polyethylene 2,5-furandicarboxylate (PEF), a polymer that offers a sustainable solution to replace the commonly used polymer polyethylene terephthalate (PET). A backcasting workshop with 42 experts was held to identify current barriers and challenges that block the commercialization of FDCA-based products and to outline potential pathways toward future market diffusion. Several barriers which are strongly related to techno- logical and market-related aspects are preventing the full potential of FDCA from being unlocked. FDCA products cited in the literature are versatile and cover a wide array of niche applications. In the back- casting workshop, participants described their specific – yet highly divergent – future visions for PEF. Participants with a background in FDCA production referred mostly to developments that would need to take place in the field of FDCA applications to turn their vision into reality, while participants with a background in FDCA product development tended to refer to open issues related to FDCA synthesis. The findings of this study indicate that there is a great need for intensified cross-disciplinary communication and collaboration.publishe

A Perspective on PEF Synthesis, Properties, and End-Life

This critical review considers the extensive research and development dedicated, in the last years, to a single polymer, the poly(ethylene 2,5-furandicarboxylate), usually simply referred to as PEF. PEF importance stems from the fact that it is based on renewable resources, typically prepared from C6 sugars present in biomass feedstocks, for its resemblance to the high-performance poly(ethylene terephthalate) (PET) and in terms of barrier properties even outperforming PET. For the first time synthesis, properties, and end-life targeting-a more sustainable PEF-are critically reviewed. The emphasis is placed on how synthetic roots to PEF evolved toward the development of greener processes based on ring open polymerization, enzymatic synthesis, or the use of ionic liquids; together with a broader perspective on PEF end-life, highlighting recycling and (bio)degradation solutions

Furanic biobased materials from the biorefineries

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Hydrophobization of cellulose microfibrils with benzylamines by periodic oxidation and subsequent reductive amination

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Crystallization behaviour of PTFE over very large cooling rate domains

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Structural Variations in Biobased Polyfurfuryl Alcohol Induced by Polymerization in Water

Poly(furfuryl alcohol) is a thermostable biobased thermoset. The polymerization of furfuryl alcohol (FA) is sensitive to a number of side reactions, mainly the opening of the furan ring into carbonyl species. Such carbonyls can be used to introduce new properties into the PFA materials through derivatization. Hence, better understanding of the furan ring opening is required to develop new applications for PFA. This article studies the structural discrepancies between a PFA prepared in neat conditions versus a PFA prepared in aqueous conditions, i.e., with more carbonyls, through NMR and MALDI ToF. Overall, the PFA prepared in water exhibited a structure more heterogeneous than the PFA prepared in neat conditions. The presence of ketonic derivatives such as enols and ketals were highlighted in the case of the aqueous PFA. In this line, the addition of water at the beginning of the polymerization stimulated the production of aldehydes by a factor two. Finally, the PFA prepared in neat conditions showed terminal lactones instead of aldehydes