Jean-Eudes Maigret

Glass transition of anhydrous starch by fast scanning calorimetry

By means of fast scanning calorimetry, the glass transition of anhydrous amorphous starch has been measured. With a scanning rate of 2000Ks-1, thermal degradation of starch prior to the glass transition has been inhibited. To certify the glass transition measurement, structural relaxation of the glassy state has been investigated through physical aging as well as the concept of limiting fictive temperature. In both cases, characteristic enthalpy recovery peaks related to the structural relaxation of the glass have been observed. Thermal lag corrections based on the comparison of glass transition temperatures measured by means of differential and fast scanning calorimetry have been proposed. The complementary investigations give an anhydrous amorphous starch glass transition temperature of 312±7°C. This estimation correlates with previous extrapolation performed on hydrated starches.

Effects of MAPP Compatibilization and Acetylation Treatment Followed by Hydrothermal Aging on Polypropylene Alfa Fiber Composites

This work investigates the effect of hydrothermal aging on the properties of polypropylene/alfa fiber composites. Hydrothermal aging was induced in an environmental testing chamber at 65°C and 75% relative humidity (RH) over a 1000 h period. At the beginning ( h), the results showed that Young’s moduli of the untreated alfa fibers and the acetylation-treated fibers increased by 21% and 36%, respectively, compared with the virgin polypropylene (PP). Additionally, Young’s moduli decreased by 7% for the compatibilized composites composed of maleic anhydride grafted polypropylene (MAPP). After 1000 h of aging, Young’s moduli decreased by 36% for untreated alfa fibers and 29% for the acetylation-treated alfa fibers and the compatibilized composites. Significant degradation was observed in the untreated alfa fiber samples. The Fourier transformed infrared (FTIR) allows us to distinguish the characteristic absorption bands of the main chemical functions present in the composite material before and after aging. The thermal properties showed that the thermal stability and the degree of crystallinity of the composites decreased after hydrothermal aging; this result was corroborated by the dynamical mechanical analysis (DMA) results.

Macromolecular structure and film properties of enzymatically-engineered high molar mass dextrans

New α(1→2) or α(1→3) branched dextrans with high molar masses and controlled architecture were synthesized using a dextransucrase and branching sucrases. Their molecular structure, solubility, conformation, film-forming ability, as well as their thermal and mechanical properties were determined. These new dextrans present structures with low densities from 9,500 to 14,000gm-3 in H2O/DMSO medium, their molar mass, size and dispersity increase with increasing branching degree (weight-average molar mass up to 109gmol-1 and radius of gyration around 500nm). Dextrans exhibit a glass transition between 40.5 and 63.2°C for water content varying from 12.2 to 14.1%. The effect of branching is mainly observed on the ability of dextran to crystallize. They have a good film-forming ability with a storage modulus which varies from 2 to 4GPa within a relative humidity range of 10-50%.

All-natural bio-plastics using starch-betaglucan composites

Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides. In this study, we used a maize starch (ST) and an oat β-glucan (BG) composite system to produce bio-plastic prototype films. To optimize performing conditions, we investigated the full range of ST:BG ratios for the casting (100:0, 75:25, 50:50, 25:75 and 0:100 BG). The plasticizer used was glycerol. Electron Paramagnetic Resonance (EPR), using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a spin probe, showed that the composite films with high BG content had a flexible chemical environment. They showed decreased brittleness and improved cohesiveness with high stress and strain values at the break. Wide-angle X-ray diffraction displayed a decrease in crystallinity at high BG content. Our data show that the blending of starch with other natural polysaccharides is a noteworthy path to improve the functionality of all-natural polysaccharide bio-plastics systems.

Damage mechanisms in defected natural fibers

A novel experimental setup is presented to reveal damage mechanisms in bast fibers. 3D imaging at submicronic scale based on X-ray micro-tomography is combined with in-situ tensile experiments of both elementary fibers and bundles. The results reveal that the relevant scale that drives failure of hemp lignocellulosic fibers is submicronic. In-situ tensile experiments assisted by X-ray micro-tomography shows complex damage mechanisms involving the constitutive sub-layer structure, fiber extraction defects like kink bands, and the tubular porosity of the natural fiber.

Cellulose-xyloglucan composite film processing using ionic liquids as co-solvents

The aim of the present work is to develop a high-performance composite using biomimetic approaches that will exploit the interactions between two biopolymers, cellulose and xyloglucan, and these interactions play an important role but still not fully understood in the biomechanical properties of primary plant cell walls [1]. In this study, the co-solubility of cellulose and xyloglucan in an ionic liquid (1-ethyl-3-methylimidazolium acetate (EMIMAC)) is used to prepare regenerated films by subsequent precipitation with a non-solvent. Films of pure cellulose, pure xyloglucan and various cellulose/xylogucan blends were obtained and characterized by Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD) and hygro-mechanical analysis. The biopolymer blends show an increase of the storage modulus comparatively to the regenerated pure biopolymers.