Consumption of plastics has increased exponentially, in line with the world's population. Not surprisingly this is reflected in enormous growth of the plastic industry especially during the last five decades. Commensurate with this, waste produced from plastics consumption has created a major environmental problem. Many types of waste disposal methods have been used all over the world so far, but all of them have disadvantages. Furthermore, some methods are responsible for the generation of green house gases and further contribution to global warming. Recently, reduction of green house gas emission has become a target of most industries. Plastic recycling and reuse breaks the cycle of endless production of virgin polymer and thus contributes to a net reduction of green house gas emission. Recycling of plastics should produce materials with improved properties to replace virgin plastics for a variety of applications. Improvement in the properties of recycled plastics can be achieved by blending with other plastics, by filler addition and by modification using free radical initiators. Introduction of the free radical initiator (organic peroxide) during reprocessing of the recycled plastics has been found to offer significant property improvements to the recycled materials. Extremely small amounts of a free radical initiator (typically ranging between 0.01 wt% to 0.2 wt%) is capable of enhancing the properties of the recycled plastics to a great extent. This project investigates the use of free radical initiators in the recycling of post consumer recycled high density polyethylene using reactive extrusion. Both molecular and rheological characterisation of recycled and reprocessed materials was carried out and this was followed by tensile testing of the modified materials to satisfy end use applications such as packaging and drainage piping. Post consumer recycled high density polyethylene (R-HDPE) resin and virgin high density polyethylene (V-HDPE) were reactively extruded with low concentrations of dicumyl peroxide (DCP) and 1, 3 1, 4 Bis (tert- butylperoxyisopropyl) Benzene (OP2) respectively in a twin screw extruder in order to produce modified materials with varying composition (0.0 wt%, 0.02 wt%, 0.05 wt%, 0.07 wt%, 0.10 wt% and 0.15 wt%) of both organic peroxides. Morphological characterisation using modulated differential scanning calorimetry (MDSC) demonstrated that there is a decrease in the crystallinity level for all the modified samples. Shear rheological tests were carried out to study the structure of the modified materials within the linear viscoelastic region. Viscoelastic parameters, such as storage modulus (G'), loss modulus (G

Yes / Highly-oriented poly (lactic acid) (PLA) with bionic micro-grooves was fabricated through solid hot drawing technology for further improving the mechanical properties and blood biocompatibility of PLA. In order to enhance the melt strength and thus obtain high orientation degree, long chain branched PLA (LCB-PLA) was prepared at first through a two-step ring-opening reaction during processing. Linear viscoelasticity combined with branch-on-branch (BOB) model was used to predict probable compositions and chain topologies of the products, and it was found that the molecular weight of PLA increased and topological structures with star like chain with three arms and tree-like chain with two generations formed during reactive processing, and consequently draw ratio as high as1200% can be achieved during the subsequent hot stretching. With the increase of draw ratio, the tensile strength and orientation degree of PLA increased dramatically. Long chain branching and orientation could significantly enhance the blood compatibility of PLA by prolonging clotting time and decreasing platelet activation. Micro-grooves can be observed on the surface of the oriented PLA which were similar to the intimal layer of blood vessel, and such bionic structure resulted from the formation of the oriented shish kebab-like crystals along the draw direction.

SOLUTION AND MELT BEHAVIOUR OF HIGH-DENSITY POLYETHYLENE - Successive Solution Fractionation mechanism - Influence of the molecular structure on the flow In the field of polyethylene characterization, one of the most challenging research topic is certainly an accurate molecular structure determination of industrial products, in terms of molar mass distribution (MMD), corresponding average-molar masses and molecular architecture (branching nature, content and heterogeneity). Solution to this long-term problem necessarily calls for a multi-disciplinary approach. Therefore, respective advantages of molecular structure characterization in solution and in the melt are exploited. In solution, chromatographic and spectroscopic methods allow determination of MMD, average branching content and intermolecular heterogeneity within their detection limits. Rheological testing in the melt could be a very powerful molecular structure investigation tool, due to its extreme sensitivity to high molar mass (MM) tailing or long chain branching (LCB) traces. But when the rheological tests results are in hand, we often still wonder what kind of molecular structure gives rise to such results. Indeed, melt signal depends on MM, MMD and LCB presence. MMD determination and LCB quantification by melt approach is impossible as long as respective effects of these molecular parameters are not clearly quantified. The general purpose of the present work is to contribute to a better molecular structure characterization of high-density polyethylene by developing, in a first time, a preparative fractionation method able to provide narrow-disperse linear and long chain branched samples, essential to separate concomitant effects of MM, MMD and LCB on rheological behaviour. Once such model fractions isolated, influence of MM and LCB on both shear and elongational flow behaviours in the melt is studied. /Dans le domaine du polyéthylène, un des sujets de recherche les plus investigués à l'heure actuelle est la détermination précise de la structure moléculaire de résines industrielles, en termes de distribution des masses molaires (MMD), de masses molaires moyennes correspondantes et d'architecture moléculaire (nature, teneur et hétérogénéité). La résolution de cette problématique nécessite une approche multi-disciplinaire, afin d' exploiter simultanément les avantages d'une caractérisation en solution et à l'état fondu. En solution, certaines méthodes chromatographiques et spectroscopiques permettent de déterminer une MMD, une teneur moyenne en branchement et leur distribution, dans leurs limites de détection. La mesure du comportement rhéologique à l'état fondu pourrait s'avérer un formidable outil de caractérisation de la structure moléculaire en raison de son extrême sensibilité à certains détails moléculaires, tels que la présence de traces de LCB ou de très hautes masses molaires (MM). Malheureusement, le signal rhéologique dépend de manière conjointe de la MM, MMD et de la présence ou non de LCB, de telle sorte que la détermination d'une MMD ou d'une teneur en LCB par cette voie est impossible aussi longtemps que les effets respectifs de ces paramètres moléculaires sur le comportement rhéologique n'ont pas été clairement et distinctement établis. L'objectif global de cette thèse est de contribuer à une meilleure caractérisation de la structure moléculaire du polyéthylène haute densité en développant, dans un premier temps, une méthode préparative de fractionnement capable de produire des échantillons, linéaires ou branchés, à MMD la plus étroite possible, indispensables en vue de séparer les effets concomitants de la MM, MMD et LCB sur le comportement rhéologique à l'état fondu. Une fois de tels objets modèles isolés, l'influence de la MM et du LCB sur le comportement rhéologique, en cisaillement et en élongation, sera étudié.

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