Ce travail consiste à contribuer à la valorisation de la lignine, un sous-produit important de l’industrie du papier. L’objectif est d’utiliser la lignine comme retardateur de flamme (FR) pour les matériaux polymères. Dans un premier temps, la lignine fut phosphorylée. Des analyses structurales ont permis d’établir que du phosphore est lié de manière covalente à la lignine. La conséquence est que la stabilité thermique ainsi que la quantité de résidu charbonné sont fortement améliorées. Les lignines de départ et phosphorylée ont été incorporées dans des polymères thermoplastiques afin d’évaluer l’influence du phosphore ainsi que les performances au feu. Des propriétés prometteuses ont particulièrement été obtenues dans l’acide polylactique (PLA) et l’acrylonitrile-butadiène-styrène (ABS). Des formulations combinant les lignines avec d’autres additifs furent développées, et leurs performances au feu discutées. Ainsi, un large screening considérant la lignine comme FR fut réalisé. Le système comprenant la lignine, de départ ou phosphorylée, dans l’ABS fut finalement étudié en détail afin d’en élucider leur mécanisme d’action. Un effort particulier fut porté sur la réaction au feu ainsi que la dégradation thermique de ce composite. Durant sa dégradation thermique, la lignine produit une couche carbonée qui limite les échanges de masse entre le polymère et la flamme, permettant d’améliorer la réaction au feu de l’ABS. Cette barrière est d’autant plus efficace en utilisant la lignine phosphorylée. Il a été observé que le phosphore est actif dans la phase condensée, provoquant une formation plus rapide de la barrière, qui est également plus stable thermiquement. / The aim of this PhD is to contribute to the valorization of lignin, an abundant byproduct of pulping industry by using it as flame retardant (FR) additive for polymeric materials. First, phosphorylation of lignin was undertaken. According to structural characterization, phosphorus was found to be covalently bonded to lignin. As a consequence, the thermal stability of lignin was enhanced as well as the char yield. Based on these results, both neat and phosphorylated lignin were incorporated in several polymers in order to assess their FR performance and the influence of phosphorus. Promising results were especially obtained in polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS). Then FR performance of formulations combining lignins and other additives was discussed. A large screening using lignin as FR additive in PLA and ABS was therefore achieved. The system considering phosphorylated lignin in ABS was finally investigated in detail. FR performance as well as thermal degradation were deeply studied. Lignin produces a char when exposed to a flame or a heat source which acts as a physical layer by mainly limiting mass transfers between the burning polymer and the flame. The char produced by phosphorylated lignin demonstrated a higher efficiency, thus leading to enhanced FR properties. Phosphorus was indeed active in the condensed phase, promoting the char formation and leading to structures which stabilize the char. The mode of action of lignin and phosphorylated lignin as flame retardant additive in ABS was elucidated.

En plein essor, le marché des vernis à ongles représente plusieurs milliards de flacons vendus chaque année à travers le monde. Malgré un durcissement de la réglementation au cours des vingt dernières années, la composition des vernis reste problématique d’un point de vue environnemental. L’agent filmogène secondaire, ou résine, qui permet d’apporter le supplément d’adhésion, de brillance et de stabilité faisant défaut à la nitrocellulose, est le principal obstacle à l’obtention d’un vernis 100 % biosourcé. Dans ce contexte, nous nous sommes attachés à comprendre la physicochimie de ces systèmes complexes, en vue d'orienter la conception de nouvelles résines biosourcées compatibles par l'établissement de relations structures-propriétés. En premier lieu, des caractérisations physicochimiques complètes (état de surface, composition, perméabilité) ont été menées sur l’ongle et deux modèles semi-synthétiques. Un test d’adhésion a été mis au point afin d’évaluer l’adhérence de formulations sur ces substrats. La corrélation des résultats a permis d’identifier le meilleur modèle de l’ongle natif et mis en évidence les mécanismes d’adhésion vernis-ongle. Parallèlement, les résines benchmarks ont été caractérisées afin de définir un cahier des charges précis. L’adaptation d’outils de prédiction aux polymères a permis de relier des modifications structurales à la solubilité et a été validée à l’aide d’oligoesters modèles synthétisés. L’impact de certains motifs structuraux sur la brillance ou la dureté des résines a été mis en évidence et les relations structures-propriétés identifiées ont été confirmées via l'évaluation des performances de nouvelles résines polyesters biosourcées. / Several billion nail polishes are sold every year throughout the world, and the market is still fast-growing. Despite a tightening of regulations over the past twenty years, the composition of varnishes remains problematic from an environmental point of view. The main obstacle to reach a 100% bio-based varnish is the secondary film-forming agent, or resin, which provides the additional adhesion, the gloss and the stability that nitrocellulose lacks. In this context, we have focused on understanding the physicochemistry of these complex systems in order to assist the design of new compatible biosourced resins through the establishment of structures-properties relationships. First, complete physicochemical characterizations (surface aspect and surface energy, composition, permeability) were carried out on native nails and two semi-synthetic models. An adhesion test was developed to evaluate the adhesion of formulations onto substrates. Correlated to physicochemical characterizations, these results allowed to identify the best model of the native nail and highlighted the adhesion mechanisms at the varnish-nail interface. In parallel, the "benchmarks" resins were characterized in order to define precise specifications according to their application performances. Thanks to the adaptation of prediction tools to polymers, we managed to link structural modifications to solubility and was validated using synthesized model oligoesters. The impact of some structural features on the gloss or the hardness of resins has been highlighted and the identified structures-properties relationships were confirmed through the evaluation of the performances of new bio-based polyester resins.

The main aim of this work was to study the effect of two comonomers, trimethylolpropane trimethacrylate (TRIS) and divinylbenzene (DVB) on the nature and efficiency of grafting of two different monomers, glycidyl methacrylate (GMA) and maleic anhydride (MA) on polypropylene (P) and on natural rubber (NR) using reactive processing methods. Four different peroxides, benzoyl peroxide (BPO), dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis-(tert-butyl peroxy) hexane (t-101), and 1,1-di(tert-butylperoxy)-3,3,5-trimethyl cyclohexene (T-29B90) were examined as free radical initiators. An appropriate methodology was established and chemical composition and reactive processing parameters were examined and optimised. It was found that in the absence of the coagents DVB and TRIS, the grafting degree of GMA and MA increased with increasing peroxide concentration, but the level of grafting was low and the homopolymerisaton of GMA and the crosslinking of NR or chain scission of PP were identified as the main side reactions that competed with the desired grafting reaction in the polymers. At high concentrations of the peroxide T-101 (>0.02 mr) cross linking of NR and chain scission of PP became dominant and unacceptable. An attempt to add a reactive coagent, e.g. TRIS during grafting of GMA on natural rubber resulted in excessive crosslinking because of the very high reactivity of this comonomer with the C=C of the rubber. Therefore, the use of any multifunctional and highly reactive coagent such as TRIS, could not be applied in the grafting of GAM onto natural rubber. In the case of PP, however, the use of TRIS and DVB was shown to greatly enhance the grafting degree and reduce the chain scission with very little extent of monomer homopolymerisation taking place. The results showed that the grafting degree was increased with increasing GMA and MA concentrations. It was also found that T-101 was a suitable peroxide to initiate the grafting reaction of these monomers on NR and PP and the optimum temperature for this peroxide was =160°C. A very preliminary work was also conducted on the use of the functionalised-PP (f-PP) in the absence and presence of the two comonomers (f-PP-DVB or f-PP-TRIS) for the purpose of compatibilising PP-PBT blends through reactive blending. Examination of the morphology of the blends suggested that an effective compatibilisation has been achieved when using f-PP-DVB and f-PP-TRIS, however more work is required in this area.

Hydroxyl terminated polybutadiene (HTPB) has been used as a rocket propellant binder which is required to be stored for at least twenty years. It is found that the excellent stress-strain characteristics of this propellant can be totally lost, during this long storage, due to the deterioration of the polybutadiene chains. As a result, the propellant can not stand the service loads, which may lead to a catastrophe. The study of the HTPB binder degradation, below 80°C, has been carried out by investigating the environmental factors and the changes which occur along the macromolecular chains. Results have shown that oxygen is the main factor which causes the crosslinking and chain scission reactions. The former is the predominant reaction and proceeds rapidly under oxygen sufficient environment. The unsaturation of polymer chain, which provides the desired physical properties to the binder, was lost with the increase in crosslink density. At the same time hydroperoxides were found to form and decompose along the polymer chains. Therefore, the deterioration of the binder results from the oxidation of polymer chains. Since the oxidation reaction occurred at higher rate than oxygen diffusion rate and oxygen diffusion rate is inversely proportional to the crosslink density, the binder, below the surface layer in a thick section container, could be naturally protected under an oxygen deficient condition for a long time. Investigation of the effectiveness of antioxidants in HTPB binder has shown that the efficiency of an antioxidant depends on its ability to scavenge radicals. Generally, aromatic amines are the most effective binder antioxidants. But when a peroxide decomposer is combined with an aromatic amine at the appropriate ratio, a synergistic effect is obtained, which gives the lowest binder gel increase rate.

Στην παρούσα διατριβή θα παρουσιαστούν αποτελέσµατα πειραµατικών µετρήσεων που πραγµατοποιήθηκαν στο Εργαστήριο Τεχνολογίας Πλάσµατος του Πανεπιστηµίου Πατρών, ενώ συµπεριλαµβάνονται και αποτελέσµατα από την εξάµηνη παραµονή στο Istituto di Metodologie Inorganiche e Plasmi (IMIP) του Πανεπιστηµίου του Bari. Στο πρώτο κεφάλαιο (Ι) παρουσιάζονται κάποιες βασικές έννοιες του πλάσµατος και η θεωρητική ερµηνεία της συµπεριφοράς του απέναντι σε µια επιφάνεια τοποθετηµένη µέσα σε αυτό. Στην συνέχεια, στο κεφάλαιο ΙΙ θα παρουσιαστούν οι πειραµατικές διατάξεις και οι τεχνικές που χρησιµοποιήθηκαν για την πειραµατική µελέτη της αλληλεπίδρασης πλάσµατος-επιφάνειας αλλά και για τον χαρακτηρισµό του επεξεργασµένου πολυµερούς. Το επόµενο κεφάλαιο (ΙΙΙ) αναφέρεται στην σύγκριση των χαρακτηριστικών των εκκενώσεων αίγλης ηλίου µε ή χωρίς την τοποθέτηση πολυµερικού υλικού στον χώρο της εκκένωσης. Στο κεφάλαιο ΙV θα εξετασθεί ο ρόλος της συνολικής πίεσης, δηλαδή πως αλλάζουν οι οπτικές ιδιότητες της εκκένωσης σε συνθήκες διαφορετικής πίεσης, ενώ ακόµα θα παρουσιαστούν πειραµατικά αποτελέσµατα που αφορούν σε περιπτώσεις που το ηλεκτρόδιο στήριξης πολώνεται εξωτερικά ή βρίσκεται σε δυναµικό επίπλευσης. Στο πέµπτο κεφάλαιο (V) παρουσιάζεται η µελέτη του πλάσµατος µίγµατος ηλίου – οξυγόνου και αργού-οξυγόνου. Η µελέτη των ιδιοτήτων του υλικού υπό αυτές τις συνθήκες και επίσης οι επαγόµενες µεταβολές στο πλάσµα είναι ένα βήµα πιο µπροστά από την επεξεργασία µε καθαρό ήλιο, που αναπτύχθηκε στα προηγούµενα κεφάλαια καθώς συντελείται χηµική αλληλεπίδραση της αέριας φάσης µε το δείγµα. Θα αποδειχτεί ότι ο ρυθµός εγχάραξης του Πολυτερεφθαλικού Αιθυλενεστέρα είναι µεγαλύτερος σε αυτό το µίγµα και τα δείγµατα παρουσιάζουν ενισχυµένη διαβρεξιµότητα. Στο κεφάλαιο VI θα παρατεθούν συµπεράσµατα από την µελέτη των πολυµερικών επιφανειών Πολυαιθυλενίου και Πολυτερεφθαλικού Αιθυλενεστέρα µετά την επεξεργασία σε εκκενώσεις αίγλης ραδιοσυχνότητας αδρανών αερίων (Ηe, Ar) αλλά και δραστικών αερίων (ΝΗ3, Ο2). Επιχειρείται η επιβράδυνση του φαινοµένου γήρανσης των πολυµερών και η βελτίωση του υδρόφιλου χαρακτήρα τους µε την επιλογή των κατάλληλων παραµέτρων της διεργασίας. Τέλος στο Κεφάλαιο VII θα παρουσιαστούν τα συµπεράσµατα όλης της µελέτης καθώς και προτάσεις για µελλοντική έρευνα. / -

Les matériaux polymères sont utilisés dans de nombreux domaines tels que l'automobile, la construction,...etc. Comme tout polymère organiques, ils sont inflammables et doivent donc être modifiés afin d'éviter ou de retarder le départ d’un incendie. L’incorporation d’une large quantité de retardateurs de flammes dans le « cœur » du polymère est la principale voie pour ignifuger un polymère. Cette voie présente des inconvénients tels que le coût élevé, la dégradation des propriétés mécaniques. Dans ce travail de thèse, de nouveaux revêtements anti-feu ont été élaborés par l’utilisation de deux approches innovantes et originales: la méthode dite « couche par couche » (LbL) et la technologie plasma. Dans un premier temps, de nombreux revêtements anti-feu ont été développés par LbL afin d'améliorer la réaction au feu de divers substrats : tissus de polyester et de polyamide 6.6, film de polyamide 6. Déposé sur un film de polyamide 6, le revêtement anti-feu à base de poly(allylamine) et montmorillonite (PAH-MMT) présente d’excellentes propriétés au feu. Il permet de réduire la quantité de chaleur (-74%) libérée lors du test au cône calorimètre. Le mécanisme d’action de ces revêtements, en termes de résistance au feu, a été étudié. Dans la deuxième partie, un revêtement anti-feu à base de phosphore et de silicium a été développé par plasma. Ces revêtements ont été caractérisés et testés sur des films de polyamide 6 (PA6) et de polycarbonate (PC). Ce revêtement permet d’augmenter considérablement le temps d'ignition du PA6 et du PC. Finalement, nous avons scrupuleusement étudié le mécanisme d’action, en termes de résistance au feu, de ces revêtements appliqués sur polycarbonate. / Polymeric materials are used in many fields such as automotive, building and textile. As all organic materials, they are inherently flammable and therefore need to be modified to prevent or delay fire departure. Incorporation of significant amount of flame retardant additives is currently the main solution to fire-retard polymers. Nevertheless, this approach exhibits some limitations such as high cost, low processability and degradation of the mechanical properties. In this PhD thesis, new flame retardant coatings were developed by using two innovative and original surface treatment approaches: Layer-by-Layer (LbL) and atmospheric plasma technologies. On one hand, several hybrid LbL-flame retardant coatings were developed in order to improve the fire properties of various substrates such as polyester, polyamide 6.6 fabrics and thin polyamide 6 films. A poly(allylamine) and montmorillonite (PAH-MMT) based coating deposited onto polyamide 6 film particularly exhibits fire results as it significantly reduces the amount of fuels (-74%) released during the cone calorimeter test. The mechanism of action of this coating in term of fire retardancy was thus investigated. In the other hand, an organophosphorus silane based coating was designed by means of atmospheric plasma technology, fully characterized and tested to fire when applied on thin polymer films. This coating significantly delays the time to ignition of polyamide 6 and polycarbonate films. Finally, we carefully investigated the mechanism of action, in term of fire retardancy, of this coating applied on polycarbonate.

Polyarene dendrimers with rigid aromatic regions are of interest due to their shape persistent nature. A novel series of G1 dendrimers containing a substituted 1,3-phenyl core are reported and were found to exhibit atropisomerism. This was investigated in the solid state (X ray), in solution (NMR), and via computational studies. The synthesis of fluorinated G1 dendrimers allowed for the analysis of interconversion between conformations via 19F-19F EXSY NMR (exchange spectroscopy). These were shown to exist as two distinct sets of three interconverting atropisomers. Each atropisomer was identified as well as their respective interconversion pathway. By increasing the size of the core of the G1 dendrimers resulted in physical separation of atropisomers by preparative HPLC. Results suggest certain conformers are energetically unfavourable reducing the total number of atropisomers observed.

This thesis details the synthesis and characterisation of novel nanocomposite materials. The unifying theme of all the projects investigated, is the aim to combine metal or metal oxide nanoparticles with polymer systems. In order to investigate the structure of the materials produced, the extensive use of advanced electron microscopy techniques is essential throughout. Chapter 1: This introductory chapter outlines key themes that are relevant to all the areas of research in this thesis. Theory, background and applications are provided for the fields of nanoparticles, polymers, and supercritical fluids. Chapters 2, 3 and 4 each report a separate area of research. In each chapter additional theory and background is provided where appropriate, and previous literature is discussed. The aims, results and discussion of each research area are contained within the relevant chapter, as well as conclusions and future work. Chapter 2: Supercritical CO2 is used to impregnate optical polymer substrates with silver complexes, which are then decomposed to form nanoparticles. Chapter 3: Metal oxide nanoparticles are used to stabilise dispersion and suspension polymerisations, providing a method of recovering nanoparticles from aqueous solutions and embedding them on the surface of polymer powders. Chapter 4: Two alternative routes, for creating polymer microspheres surface decorated with silver nanoparticles, are compared. Chapter 5: A detailed description of the synthetic methods, equipment, and analysis techniques used in this research is provided. Chapter 6: A brief but overall conclusion to the research is given.

Vacuum infusion technology, even though first reported more than 50 years ago, was not popular for mainstream fibre reinforced polymer composites manufacturing until recently. Its present-day popularity is due to the increasing emphasis on the manufacturing cost as well as environmental and health concerns. As a result, novel processes such as Vacuum Infusion (VI) and Seemans' Composite Resin Injection Moulding Process (SCRIMPTM), employing the same basic technology, have been developed. As latecomers, these processes have not been investigated in detail and there exists a lack of understanding that can undermine the potential improvements in composites manufacturing offered by them. The present work is focused on (i) enhancing the fundamental understanding, and (ii) advancing the processing technology to fully exploit their potential. Limitations of the existing analytical models for fluid flow in VI are explored. Then, improvising upon and extending these models, analytical formulations for the pressure profile and fill-times in rectilinear and radial flow VI processes are developed. An important result from this study is that with increasing reinforcement compliance, the analytical VI pressure profile diverges from the RTM pressure profile. It is found that for rectilinear as well as radial flow processes, the fill-time ratio between equivalent RTM and VI remains constant. Experimental validation for these formulations show that the pressure profile varies with flow progression in both rectilinear and radial flow VI. This leads to a dynamically changing fill-times ratio between RTM and VI. This dynamic behaviour, which is contrary to analytical predictions, is explained by hypothesising that the compliance characterisation experiments do not replicate the actual events in VI. The issue of process control is also investigated for the VI process. A novel approach, using non-intrusive sensors and real-time flow simulations, is designed and implemented. The study gives important insights about the controllability of this process. It is found that in VI, due to low driving pressure, an optimum window of opportunity exists for process control. Reinforcements with high permeability give higher flow velocity, while low permeability reinforcements lead to lower flow velocity. Both of these cases lead to a marginal window of opportunity and poor process controllability. For reinforcements that offer good controllability, the control system is able to identify flow deviations and correct them, increasing the process efficiency.

The overall objective of this study was to develop and validate a predictive modelling methodology for simulating the static and dynamic impact failure response of thermoplastic composite sandwich structures. The work has primarily focused on sandwich constructions with commingled woven fabric glass/polypropylene composite skins and a crushable polypropylene foam core. The static and high strain rate mechanical properties of the thermoplastic composite skin material have been experimentally characterised. This investigation showed that the tensile and compressive modulus and strength increased with strain rate while the shear modulus and strength decreased as strain rate increased. A modelling methodology was developed for predicting damage in the thermoplastic composite using the advanced MAT 162 material model that is implemented in the LS-DYNA explicit finite element code. An inverse modelling technique for calibrating and validating the MAT 162 damage parameters was developed. The material model was validated for predictive simulation of the static and crash response of a large scale complex shaped demonstrator thermoplastic composite automotive component. The static and dynamic mechanical properties of the thermoplastic foam core have been experimentally investigated and presented. This was followed by an experimental investigation and finite element modelling of the failure modes of the thermoplastic composite sandwich under static and dynamic localised indentation and bending loads. A fracture criteria was implemented in the model to simulate core shear fracture. The main contributions to knowledge from this doctoral study are: the static and dynamic characterisation of the mechanical properties and failure modes of the thermoplastic composite and the crushable thermoplastic foam material; development of a validated modelling methodology for predicting damage in thermoplastic composites; and development of a finite element modelling procedure for simulating the static and dynamic impact failure behaviour of thermoplastic composite sandwich structures.