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Summary Composites made of a thermoplastic matrix reinforced by bamboo fibers were obtained by extrusion and injection methods. It was found that the lignin of the bamboo fibers protects them from thermal exposure and prevents their degradation. As a consequence, in spite of the relatively high processing temperatures required for polymer melting, it is possible to obtain composite materials with acceptable properties for specific low-tech applications.

A review of the history of the evolution of material science and material technology shows us that one tendency for the future could be the use of agriculture resources. In this work, we review the performances of one of these resources, that is, wheat flour. We show that it is possible to get thermoplastic films with properties quasiequivalent to what is obtained for expensive pure starch. By adding natural fibres, composites are also obtained. These composites exhibit performances which allow their use only for short duration.

A 100% green thermoplastic obtained by extrusion of a mixture of wheat flour and plasticizers has been realized. The existence of two vitreous phases in this 100% green thermoplastic film has been pointed out by means of calorimetric measurements ( T g =−56 °C and T g =10 °C) and confirmed by electron microscopy. The molecular dynamics have been investigated by means of DMA measurements for temperature domains in the vicinity of the glass transition of each phase. We show that each phase exhibits a molecular dynamic characteristic of a fragile glass liquid former. The size of the cooperative domain engaged in the relaxation processes have also been estimated and we show that this new green thermoplastic exhibits relaxation mechanisms as expected for a conventional thermoplastic, as for instance a PMMA.

New composites materials, 100% ecofriendly, having waste cotton fibre as reinforcement in wheat flour based thermoplastic matrix were prepared by extrusion method. The fibre content in the composite varied from 0 to 15% w/w. Using X-ray diffraction and scanning electron microscopy, the structure and morphology of the composites have been analysed. This investigation is focused on the effects of the fibre content on the mechanical and thermal properties of the composites. Addition of the waste cotton fibre to the matrix increased the tensile properties. For the composite with 10% w/w of fibre the values of the tensile stress are found maximum. We also show that thermal conductivity and resistivity are not affected by the fibre content. By thermogravimetry we show that the addition of fibres to the matrix has no significant influence on the thermal stability of the composites. Finally, to analyse the efficiency of the present system, a comparative study of the mechanical properties obtained with flax and cotton fibres is performed.

International audience

Molecular mobility and physical ageing of amorphous plasticized polylactide (PLA) with two different contents of mesolactide are studied with the help of thermal analysis. Used plasticizers are acetyl tributyl citrate (ATBC) and triacetin (TA), two molecules with established miscibility and plasticizing efficiency. Lower plasticizer permanence of TA compared with ATBC is found. The plasticizer molecules decreased the size of the cooperativity domains at the glass transition temperature Tg and likely in the glassy state by decreasing intermacromolecular interactions and notwithstanding the mesolactide content of PLA and the chemical identity of the plasticizer. The recovery function is given and shows a significant effect of the plasticizer on the physical ageing. The supplementary free volume brought by the plasticizer enhances molecular mobility in the glassy state and increases structural relaxation at one order of magnitude. The comparison between different plasticizers reveals that the structural relaxation is however independent from the type of plasticizer and the percentage of mesolactide in PLA. POLYM. ENG. SCI., 2014.

International audience; Investigations into the formation of nanosized structures, particularly nanotubes, by a diamide ester compound are reported. Two aspects are concurrently examined: the role of the solvent and the role of the alkyl chain. The former is addressed by using a benzene derivative (o-xylene) and a totally saturated double ring (trans-decahydronaphthalene) whereas the latter is achieved by replacing the hydrogenous alkyl chain with its fluorinated counterpart while keeping the overall architecture the same. The thermodynamic behavior by differential scanning calorimetry, the morphology by transmission electron microscopy, and the structure by X-ray scattering and small-angle neutron scattering are studied. Despite the identical architecture, the fluorinated molecule does not produce any nanotubes, unlike its totally hydrogenous counterpart. Also, o-xylene prevents the hydrogenous molecule from forming nanotubes, while nanotapes are produced instead. Conversely, the fluorinated molecule produces regularly twisted protostructures in either solvent. Neutron scattering experiments show that the fluorinated alky chain is located within the core of this structure. This suggests that the prerequisite for forming nanotubes relies on the necessity of the alkyl group to point outward.

Summary 100% natural composites comprising low protein content wheat flour and bamboo fibers were elaborated by means of an extrusion process using glycerol, water and sorbitol as plasticizers. The morphology, the mechanical properties and the acoustic response of the materials were analysed by means of scanning electron microscopy (SEM), tensile testing and acoustic measurements respectively. The extruded samples showed randomly dispersed bamboo fibers in the wheat flour matrix whereby a clear reinforcement in mechanical properties was observed with increase of the fiber percentage up to 15% w/w. The vibro-acoustic measurements performed by analysing the surface wave propagation of the sound signal show the effects of the fiber dispersion and of the frequency on the damping properties of these new composites. At low frequency, the presence of the fibers is well observed and they play the role of secondary wave sources.

Summary: A new biodegradable thermoplastic material based on a wheat flour by-product has been developed. The influence of various additives (glycerol, silica) and fibers (flax, cotton, hemp) on the mechanical properties of the material has been investigated. The development of expanded materials is also presented.