No description available.

Les matières plastiques ont désormais envahi notre quotidien. Elles sont le symbole de la société de consommation, car elles sont considérées comme un matériau non noble : les consommateurs l'assimilent à un produit jetable après usage. N'étant pas dégradables, les plastiques représentent donc un réel danger pour l'environnement, la faune et la flore.L’objectif de ce travail de thèse a été de développer en collaboration avec l’Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux (Université de Pau) de nouvelles formulations avec des additifs naturels pour obtenir des plastiques résistants et recyclables. Deux types de résines ont été utilisées : le polypropylène isotactique (i-PP) et le polyéthylène à basse densité (LDPE). Des antioxydants naturels tels que l’acide ascorbique, l’alpha-tocophérol et l’huile de lin ont été testés et leur encapsulation a permis d’améliorer leur résistance à la dégradation. Les caractérisations thermique et rhéologique des résines ont montré des qualités supérieures aux résines commerciales actuelles. Nous avons pu démontrer que les plastiques obtenus pouvaient être recyclés 9 fois sans perte de leurs caractéristiques. Des essais avec des barquettes fabriquées avec les produits élaborés sont en cours pour valider les modèles développés. / Plastics have now invaded our daily lives. They are the symbol of the consumer society, because they are considered a non-noble material: consumers equate it with a disposable product after use. Since plastics are not degradable, they represent a real danger to the environment, fauna and flora.The objective of this thesis work was to develop in collaboration with the Institute of Analytical Sciences and Physico-Chemistry for Environment and Materials (Pau University) new formulations with natural additives to produce resistant and recyclable plastics. Two types of resins were used: isotactic polypropylene (i-PP) and low density polyethylene (LDPE). Natural antioxidants such as ascorbic acid, alpha-tocopherol and flaxseed oil were tested and encapsulated to improve their resistance to degradation. Thermal and rheological characterizations of resins have shown superior qualities to current commercial resins. We were able to demonstrate that the plastics obtained could be recycled 9 times without losing their characteristics. Tests with trays made with the developed products are underway to validate the developed models.

No / The in-line development of crystalline morphology and orientation during melt extrusion of low density polyethylene (LDPE) tape at nil and low haul-off speeds has been investigated using Small-Angle X-Ray Scattering (SAXS). The processing parameters, namely haul-off speed and distance down the tape-line have been varied and the resulting crystalline morphology is described from detailed analysis of the SAXS data. Increasing haul-off speed increased orientation in the polymer tape and the resulting morphology could be described in terms of regular lamellar stacking perpendicular to the elongation direction. In contrast, under nil haul-off conditions the tape still showed some orientation down the tape-line, but a shish-kebab structure prevails. The final lamellae thickness (similar to 50 angstrom) and bulk crystallinity (similar to 20%), were low at, for all processing conditions investigated, which is attributed to the significant short-chain branching in the polymer acting as point defects limiting lamellae crystal growth. (C) 2013 Elsevier Ltd. All rights reserved.

No / The advances of the polymer melt flow-induced crystallization behaviour and its influence on mechanical properties of high density polyethylene (HDPE) in micron injection (MI) were studied in the present paper. Analysis of mechanical performance, including yield stress and elongation at break, for samples adopted from different regions in a molded plaque showed that a higher injection speed, a higher mold temperature and a longer cooling time could effectively enhance the yield stress but negatively promoted the ductility. Then, the mechanisms of such variation of mechanical performance and the factors affecting it were investigated by means of differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarized light microscopy (PLM). The super high shear rate during cavity feeding in MI molding not only induced a typical three-layered structure but also developed a highly oriented fibrously morphological structure in the skin layer. However, such fully oriented morphology was much negative in the interlayer and even could not be observed in the core layer. The results from SEM and PLM observations indicated that the orientation morphology varied significantly through the plaque's cross-section and thickness of the each layer changed with the process parameters and geometric position, and finally led to variation of the mechanical performance.

Isotactic polypropylene (iPP), as one of the most versatile commodity thermoplastic polymers, is a polymorphic material having several crystal modifications, among which the β-form exhibits higher performance including excellent impact strength and improved elongation at break.Up to now, the effective and convenient way to prepare the iPP with high content of β-phase has been successfully achieved by addition of certain β-nucleating agent. Since the coexistence of β-nucleating agent and flow (shear flow, extensional flow or mixed), which usually exists in common industrial processing, makes the crystallization process more complex, their combined effect on the structure evolution of polymers, especially in the early stage of crystallization is still not well understood. The mechanical properties of iPP depend strongly on its crystallinity, crystal orientation and morphology determined by the conditions during preparation. On the other hand, the mechanical properties of polymers can also be modulated by deformation processing, which is directly related to the deformation-induced structure transition. However, the transition mechanism of different crystal forms and structure-property correlation still remain unclear. In this thesis, time-resolved synchrotron X-ray scattering was firstly used for the in-situ study of the structural and morphological developments of β-nucleated iPP during shear-induced crystallization. It was found that the crystallization process was strongly influenced by the concentration of β-nucleating agent, shear rate and shear temperature. Then extension-induced crystallization was investigated by a novel melt draw experiment, where a different crystallization mechanism compared to the shear-induced crystallization was found. Subsequently, β-nucleated iPP samples with different thermomechanical histories were scanned by synchrotron X-ray microbeam to construct their overall morphological distributions, including distributions of crystallinity, lamellar thickness, orientation, etc. Finally, these morphology-identified samples were investigated by in-situ synchrotron X-ray measurements coupled with mechanical testing to follow the structure evolution during deformation at elevated temperature. It was found that the deformation behaviour of β-nucleated iPP was closely associated with its initial morphology, its subsequent variation during stretching as well as the stretching conditions including the stretching rate and stretching temperature. The current study would not only contribute to the development of crystallization and deformation theory but also be beneficial for the material design.

Isotactic polypropylene (iPP), as one of the most versatile commodity thermoplastic polymers, is a polymorphic material having several crystal modifications, among which the β-form exhibits higher performance including excellent impact strength and improved elongation at break.Up to now, the effective and convenient way to prepare the iPP with high content of β-phase has been successfully achieved by addition of certain β-nucleating agent. Since the coexistence of β-nucleating agent and flow (shear flow, extensional flow or mixed), which usually exists in common industrial processing, makes the crystallization process more complex, their combined effect on the structure evolution of polymers, especially in the early stage of crystallization is still not well understood. The mechanical properties of iPP depend strongly on its crystallinity, crystal orientation and morphology determined by the conditions during preparation. On the other hand, the mechanical properties of polymers can also be modulated by deformation processing, which is directly related to the deformation-induced structure transition. However, the transition mechanism of different crystal forms and structure-property correlation still remain unclear. In this thesis, time-resolved synchrotron X-ray scattering was firstly used for the in-situ study of the structural and morphological developments of β-nucleated iPP during shear-induced crystallization. It was found that the crystallization process was strongly influenced by the concentration of β-nucleating agent, shear rate and shear temperature. Then extension-induced crystallization was investigated by a novel melt draw experiment, where a different crystallization mechanism compared to the shear-induced crystallization was found. Subsequently, β-nucleated iPP samples with different thermomechanical histories were scanned by synchrotron X-ray microbeam to construct their overall morphological distributions, including distributions of crystallinity, lamellar thickness, orientation, etc. Finally, these morphology-identified samples were investigated by in-situ synchrotron X-ray measurements coupled with mechanical testing to follow the structure evolution during deformation at elevated temperature. It was found that the deformation behaviour of β-nucleated iPP was closely associated with its initial morphology, its subsequent variation during stretching as well as the stretching conditions including the stretching rate and stretching temperature. The current study would not only contribute to the development of crystallization and deformation theory but also be beneficial for the material design.