Le caoutchouc naturel présente une très bonne résistance à la propagation de fissure. Cette particularité est généralement attribuée dans la littérature à sa capacité à cristalliser sous déformation. A ce jour, l'essentiel des travaux dans ce domaine porte sur des échantillons réticulés par une vulcanisation dite efficace, c’est-à-dire dont les noeuds de réticulation sont principalement composés de ponts monosulfures. Pour certaines applications, et parce qu’elle est réputée conduire à de meilleure propriétés en fatigue, il est intéressant d'utiliser une vulcanisation dite conventionnelle. Le matériau est alors composé majoritairement de ponts polysulfures. Le phénomène de cristallisation sous déformation, exacerbée en pointe de fissure en raison d'une amplification du champ de déformation, semble être l'un des mécanismes responsables de l'accroissement de la durée de vie en fatigue du matériau vulcanisé de manière efficace. Cependant, sur matériaux vulcanisés de manière conventionnelle et thermo-oxydés (77°C), cette corrélation doit être confirmée en raison d’une évolution importante de l'architecture du réseau élastomère pendant son vieillissement pouvant en effet avoir un impact important sur la capacité du matériau à cristalliser sous déformation. Cette étude se propose donc de caractériser l’évolution de réseaux élastomères vulcanisés de manières conventionnelles pendant leur vieillissement thermo-oxydant, puis d’évaluer leur résistance à la propagation de fissure à différents niveaux de déformation macroscopique. Des analyses in situ WAXS sous rayonnement synchrotron en fond de fissure permettent alors de relier ces résultats à l'évolution de l’aptitude de ces matériaux à cristalliser sous déformation. / Natural rubber (NR) is largely used in the tire industry due to its excellent mechanical properties, e.g. its very good resistance to fatigue crack growth at high strain. It is generally accepted that this outstanding behavior is related to its ability to crystallize under strain. Such phenomenon, so called SIC, strongly depends on parameters like temperature, strain rate as well as the architecture of the rubber network. The microstructure of this network is formed during the crosslinking process and depends on the vulcanization system, i.e. “Efficient” or “Conventional”. The former vulcanization recipe consists in the formation of short or monosulfide bridges in the elastomer network whereas the latter (necessary to ensure a good adhesion between metallic and rubber parts in a tire) will mainly create longer polysulfide bridges. During its life, the tire will be submitted to a slow aerobic ageing which will cause structural modifications of the initial network and therefore an evolution of the rubber ability to crystallize under strain and to resist against crack propagation. In general, the structural modifications are caused by complex chemical mechanisms, highly sensitive to temperature, leading to chain scission and chain crosslinking. They can also involve sulfur bridge reorganization when NR is conventionally vulcanized. Nevertheless, most of the literature on NR ageing has been performed on efficiently cross-linked NR, and in thermal conditions which are much too severe to be representative of the material ageing in tire applications. Within this frame, our objective is to study this material when it is aged at 77 °C in air. Such parameters have been identified as capable of reproducing more realistically and over a reasonable duration, the ageing of rubber in some use conditions. After characterization of the evolution of the aged materials microstructure, their crack propagation resistance will be studied at 0.01 Hz for different values of macroscopic deformations. Time resolved Wide Angle X-ray scattering (WAXS) measure-ments, carried out at room temperature, will then provide information on the crystallization process around the crack tip. Based on these results, the relation between the network evolution during ageing, the fatigue properties and the ability to strain crystal-lize in such conditions will be established in this work.

Ένας συναρπαστικός τομέας της σύγχρονης έρευνας είναι αυτός των νάνο-συνθέτων υλικών. Το πεδίο αυτό περιλαμβάνει τη μελέτη πολυφασικών υλικών, στα οποία μία ή περισσότερες από τις χωρικές διαστάσεις κάποιας φάσης βρίσκεται στην περιοχή των νανομέτρων (1 nm = 10-9 m = 10 ). Αυτό που ξεχωρίζει τα νανοσύνθετα από τα άλλα συμβατά σύνθετα υλικά είναι η ικανότητα τους να συνδυάζουν ιδιότητες, οι οποίες είναι απαγορευτικές για τα παραδοσιακά υλικά, αλλά και η μεγάλη λειτουργικότητα που παρουσιάζουν. Η εισαγωγή των νάνο-σύνθετων υλικών και οι πολλές επιστημονικές μελέτες που έγιναν τα τελευταία χρόνια στόχευαν και προσδοκούσαν σε μία δραματική βελτίωση των μηχανικών ιδιοτήτων, πράγμα που πολλές φορές δεν επαληθεύθηκε. Τα νάνο-σύνθετα πολυμερικής μήτρας των οποίων η θερμομηχανική συμπεριφορά μελετήθηκε περισσότερο είναι τα συστήματα που περιέχουν ως εγκλείσματα νάνο-σωλήνες άνθρακα (carbon nanotubes), νάνο-σωματίδια αλούμινας και στρωματικά άλατα πυριτίου (layered silicates). Στις μέρες μας υπάρχει ένα αυξανόμενο ενδιαφέρον για τη μελέτη της διηλεκτρικής συμπεριφοράς και αγωγιμότητας των νάνο-σύνθετων πολυμερικής μήτρας - ανόργανων νάνο-εγκλεισμάτων. Στην παρούσα εργασία εξετάσθηκε η διηλεκτρική απόκριση των συστημάτων: (α) πολυμερικής μήτρας (polyurethane rubber, PU) και νάνο-σωματιδίων αλούμινας (alumina- boehmite), (β) πολυμερικής μήτρας (PU ή Natural Rubber, NR ή PU/NR) με στρωματικά άλατα πυριτίου (layered silicates), με παραμέτρους την περιεκτικότητα σε νανοεγκλείσματα, τη θερμοκρασία και τη συχνότητα του εφαρμοζόμενου πεδίου. Η διηλεκτρική φασματοσκοπία (Broadband Dielectric Spectroscopy) έχει αποδειχθεί ως ένα ισχυρό εργαλείο για την έρευνα της μοριακής κινητικότητας, των αλλαγών φάσεων, τους μηχανισμούς αγωγιμότητας και τα διεπιφανειακά φαινόμενα στα πολυμερή και τα σύνθετα πολυμερικά συστήματα. Η διηλεκτρική απόκριση των νάνο-συνθέτων εξετάστηκε με τη βοήθεια της διηλεκτρικής φασματοσκοπίας (BDS) στο εύρος συχνοτήτων 10-1-10 6 Hz και στο εύρος θερμοκρασιών από -100οC έως +70οC. Από τα πειραματικά αποτελέσματα προκύπτει πως παρατηρούνται διηλεκτρικές χαλαρώσεις που οφείλονται τόσο στην πολυμερική μήτρα, όσο και στην ενισχυτική φάση. Τέσσερις διακριτοί τρόποι χαλάρωσης καταγράφηκαν στα φάσματα των συστημάτων που μελετήθηκαν και αποδίδονται στη διεπιφανειακή πόλωση (IP) μήτρας/εγκλεισμάτων, στην υαλώδη μετάβαση (α-mode) των πολυμερών NR και PU, στην κίνηση πλευρικών πολικών ομάδων (β-mode) των αλυσίδων του PU και σε τοπικές κινήσεις εύκαμπτων τμημάτων των αλυσίδων του PU (γ–mode). Στο σύστημα πολυουρεθάνης (PU)–νάνο-σωματιδίων αλούμινας ερευνήθηκε η επίδραση του μέσου μεγέθους των σωματιδίων στην ηλεκτρική απόκριση των υλικών. Από τα αποτελέσματα φαίνεται πως η μείωση του μέσου μεγέθους των νάνο-εγκλεισμάτων οδηγεί σε αύξηση της διεπιφάνειας και των αντίστοιχων φαινομένων που τη συνοδεύει. Τέλος, από τη θερμοκρασιακή εξάρτηση της θέσεως των κορυφών διηλεκτρικών απωλειών, κάθε διεργασίας, προσδιορίστηκαν οι αντίστοιχες ενέργειες ενεργοποίησης. / The impact of nano-materials and nano-structured materials is well known in our days. Nano-composites consists an exciting modern field of scientific research. Nano-composites are multiphase materials where at least one of the dimensions of the reinforcing phase is in nano-scale. The main difference of nano-composites with compatible composites is their ability to achieve superior performance at a very low concentration of the filler. The majority of the active or potential applications of nano-systems is based on their thermo-mechanical behaviour, flame resistance and electrical properties. Under this point of view nano-composites exhibit properties or functions, which seem to be prohibited for traditional materials. Recently, there is an increased interest in studying the dielectric behaviour of polymer matrix – inorganic nano-filler composites. Polymer matrix nano-composites are expected to be useful in replacing conventional insulating materials providing tailored performance, by simply controlling the type and the concentration of nano-inclusions. In the present study is investigated the dielectric behaviour of composites consisted of a polymer matrix and inorganic nano-filler. Natural rubber (NR) and polyurethane rubber (PU) as well as their blend are used as matrices. Nano-composites were prepared by adding synthetic layered silicates (LS) via the latex compounding route. Further, the dielectric response of polyurethane rubber – alumina particles nano-composites, varying the mean particle diameter, is also examined. The dielectric properties of all systems are studied with parameters the temperature and the frequency of the applied field. Broadband Dielectric Spectroscopy (BDS) has been proved to be a powerful tool for the investigation of molecular mobility, phase changes, conductivity mechanisms and interfacial effects in polymers and complex systems. The dielectric response of nano-composites was examined by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range10-1-106 Hz and temperature interval from -100 o C to +70 o C. Experimental results include relaxation phenomena arising from both the polymeric matrix and the filler. Four distinct relaxation modes were recorded in the spectra of all systems containing PU. They were attributed to interfacial polarization, glass transition (α-relaxation), motion of polar side groups and probably motions of the (CH2)n sequence of the PU chain (β and γ-relaxation). NR is a non polar polymer and thus only its glass/rubber transition is recorded in the low temperature range. Interfacial polarization is present in all composites systems. The dielectric response of polyurethane/boehmite alumina nano-composites was examined with an additional parameter, the size of the mean boehmite particle diameter. In order of ascending relaxation rate the following modes were recorded: interfacial polarization, glass/rubber transition (α-mode), motion of polar side groups (β-mode) and re-arrangements of small parts of the PU chain (γ-mode). The intensity and the position of these relaxations appear to vary with the size of the nano-filler. Finally, the activation energies of all the recorded processes were determined via the loss peak dependence on temperature.

La vulcanització per microones és un procés madur i no hi ha dubte sobre la seva eficiència per produir articles de cautxú d'alta qualitat. Les microones són conegudes no només per la seva capacitat d'accelerar els processos i augmentar la eficiència de la transferència energètica, sinó que també són capaces en certs casos de canviar els camins de reacció. Hi ha evidències, basades en canvis en propietats físiques al comparar productes vulcanitzats amb el mètode convencional i amb microones, que indiquen que alguns canvis poden succeir al treballar amb diferents fonts d'escalfament. No obstant això, hi ha una falta d'informació sobre els efectes que les microones tenen en la química de la vulcanització. Per tant, el principal objectiu d'aquesta tesi es basa en estudiar la vulcanització assistida amb microones des d'una nova perspectiva, centrant-se en els efectes d'aquesta radiació en els ingredients principals de les formulacions de cautxú, en el mecanisme de vulcanització, en la reticulació de la xarxa polimèrica i també en el procés de devulcanització.La primera part de la feina va consistir en desenvolupar i optimitzar tots els mètodes analítics necessàris per explorar totes les etapes del procés de vulcanització i identificar tots els intermedis formats. Estudis de Model Compound Vulcanization (MCV) utilitzant esqualè com a molècula model s'han realitzat per entendre millor la influència d'aquesta radiació en el mecanisme de la reacció, encara que alguns experiments també s'han realitzat amb mostres de cautxú natural. Tècniques com HPLC-MS, MALDI-TOF o GPC s'han utilitzat per caracteritzar les mostres de MCV, mentre que mesures d'inflament, de tensió-elongació, compressió i duresa s'han realitzat per caracteritzar les mostres de cautxú natural.Dos dels sistemes de vulcanització més comuns han estat estudiats (sulfenamides i tiurams). A més, s'ha donat un especial èmfasi a l'estudi de la influència de les microones en el sistema activador, intentant reduir el contingut de ZnO i cercar, a través de diverses estratègies, substituts més amigables amb el medi ambient. Finalment, tot el coneixement adquirit en aquests estudis s'ha utilitzat per optimitzar el comportament devulcanitzant del disulfur de difenil (DPDS) amb l'ajut de les microones, demostrant que les microones poden ajudar a avançar en la recerca d'una solució al problema del reciclatge dels residus de cautxú. / La vulcanización por microondas es un proceso maduro y no cabe duda sobre su eficiencia para producir artículos de caucho de alta calidad. Las microondas son conocidas no sólo por su capacidad de acelerar los procesos y aumentar la eficiencia de la transferencia energética, sino que también son capaces en ciertos casos de cambiar los caminos de reacción. Hay evidencias, basadas en cambios en propiedades físicas al comparar productos vulcanizados con el método convencional y con microondas, que indican que algunos cambios pueden suceder al trabajar con diferentes fuentes de calentamiento. Sin embargo, hay una falta de información sobre los efectos que las microondas tienen en la química de la vulcanización. Por lo tanto, el principal objetivo de esta tesis se basa en estudiar la vulcanización asistida por microondas desde una nueva perspectiva, centrándose en los efectos de esta radiación en los ingredientes principales de las formulaciones de caucho, en el mecanismo de vulcanización, en la reticulación de la red polimérica y también en el proceso de devulcanización.La primera parte del trabajo consistió en desarrollar y optimizar todos los métodos analíticos necesarios para explorar todas las etapas del proceso de vulcanización y identificar todos los intermedios formados. Estudios de Model Compound Vulcanization (MCV) utilizando escualeno como molécula modelo se han realizado para entender mejor la influencia de esta radiación en el mecanismo de la reacción, aunque algunos experimentos también se han realizado con muestras de caucho natural. Técnicas como HPLC-MS, MALDI-TOF o GPC se han utilizado para caracterizar las muestras de MCV, mientras que medidas de inflamiento, de tensión-elongación, compresión y dureza se han realizado para caracterizar las muestres de caucho natural.Dos de los sistemas de vulcanización más comunes han sido estudiados (sulfenamidas y tiuramos). Además, se ha dado un especial énfasis al estudio de la influencia de las microondas en el sistema activador, intentando reducir el contenido en ZnO y buscar, a través de diversas estrategias, substitutos más amigables con el medio ambiente. Finalmente, todo el conocimiento adquirido en estos estudios se ha utilizado para optimizar el comportamiento devulcanitzante del disulfuro de difenilo (DPDS) con ayuda de las microondas, demostrando que las microondas pueden ayudar a avanzar en la búsqueda de una solución al problema del reciclaje de los residuos de caucho. / Microwaves vulcanization is a mature process and there is no doubt about its efficiency on producing high quality goods. Microwaves are found not only to speed up the processing and increase the energy transfer efficiency, but also to be in some cases able to change reaction pathways. There are some evidences, based on changes in physical properties when comparing conventional and microwaves vulcanization, that suggest that some changes occur when working with different heating sources. However, there is a lack of information of the effects of MW in vulcanization chemistry. Therefore, the principal aim of this thesis consists of studying microwave-assisted vulcanization from a new perspective, focusing on the effects of this radiation in the main ingredients of a rubber compound, in the vulcanization mechanism, in the final crosslinked network and also in the devulcanization process.The first part of the work consisted in developing and optimizing all the analytical methods necessary to explore all the steps of vulcanization process and identifying all the intermediates formed. Model Compound Vulcanization (MCV) studies, using squalene as a model molecule, have been used to understand better the influence of this radiation in the reaction mechanism, even though some tests have been also performed in natural rubber samples. Techniques as HPLC-MS, MALDI-TOF or GPC have been used to characterize the MCV samples, whereas swelling measurements, stress-strain measurements, compression set or hardness have been used to characterized natural rubber samples. Two of the most common vulcanizing systems have been studied (using sulfenamide and/or thiuram accelerator types). In addition, a special emphasis has been given to the study of the microwaves influence on the activator system, trying to reduce ZnO contents and finding more environmental friendly substitutes through different strategies. Finally, all the knowledge acquired in all these studies has been used to optimize the devulcanizing behavior of diphenyl disulfide (DPDS) with the help of microwaves, proving that microwaves can help to advance in the search of a solution to the problem of waste rubber recycling.

Orientadora: Profa. Dra. Mariselma Ferreira / Tese (doutorado) - Universidade Federal do ABC. Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2014

Orientador: Prof. Dr. Carlos Henrique Scuracchio / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016. / O objetivo desse trabalho foi preparar e caracterizar compostos elastoméricos de borracha natural com a incorporação de óleo vegetal derivado da soja e com material derivado da cana de açúcar, em substituição aos materiais tradicionalmente utilizados na indústria da borracha. Iniciou-se o estudo com a caracterização física, química e térmica dos dois aditivos de origem vegetal e de fonte renovável. A caracterização do óleo de soja foi realizada por análise termogravimétrica (TGA) e por espectroscopia de infravermelho com transformada de Fourier (FTIR). A caracterização do derivado da cana de açúcar foi realizada por análise granulométrica, análise termogravimétrica (TGA) e espectroscopia de infravermelho com transformada de Fourier (FTIR). No primeiro capítulo do trabalho, composições foram feitas com substituição do óleo naftênico por óleo de soja em um misturador do tipo Banbury. A caracterização das composições foi realizada através de reometria, densidade de ligações cruzadas, análise dinâmico-mecânica (DMA) e por microscopia de força atômica. Os resultados de vulcanização mostraram que todas as amostras desenvolvidas com o óleo de soja apresentaram variação significativa na cinética de cura em comparação com aquelas preparadas com óleo naftênico. No segundo capítulo, composições foram feitas com substituição do ácido esteárico e do óxido de zinco por derivado da cana de aúcar, em um misturador do tipo Banbury. A caracterização das composições foi realizada através de reometria, densidade de ligações cruzadas, efeito Payne, análise dinâmico-mecânica (DMA) e por microscopia eletrônica de varredura (MEV). Para os resultados da caracterização das composições atraves do efeito Payne, foi possível identificar que a amostra 3 phr de derivado da cana de açúcar, apresentou um rompimento de maior número de interações carga-carga. No terceiro capítulo, foi realizada a modificação química por silanização do derivado da cana e posterior incorporação em matriz de borracha natural. O derivado da cana modificado (DCM) foi analisado através de FTIR e as composições por reometria, densidade de ligações cruzadas, DMA e MEV. Notou-se que o efeito da silanização atuou positivamente sobre as propriedades de vulcanização e dispersão. Na vulcanização a propriedade mais influenciada foi à diminuição da reversão da borracha natural. Pelos resultados de DMA comprovou-se a melhora na dispersão da carga na matriz. / The aim of this work was to prepare and characterize elastomeric compounds of natural rubber with the addition of vegetable oil derived from soy and material derived from sugar cane to replace the materials traditionally used in the rubber industry. It began the study of the physical, chemical and thermal of the two additives of plant origin and renewable source. The characterization of soybean oil was carried out by thermogravimetric analysis (TGA) infrared spectroscopy and Fourier transform (FTIR). The characterization of sugar cane derivative was performed by sieve analysis, thermogravimetric analysis (TGA) infrared spectroscopy and Fourier transform (FTIR). In the first chapter of the work, compositions were made by replacement of the naphthenic oil with soybean oil in a Banbury type mixer. The characterization of the compositions was performed by rheometry, crosslink density, dynamic mechanical analysis (DMA) and atomic force microscopy. The vulcanization results showed that all the samples developed with soybean oil showed significant variation in cure kinetics compared to those prepared with naphthenic oil. The second chapter compositions were made by replacing stearic acid and zinc oxide derived from a sugar cane, in a Banbury type mixer. The characterization of the compositions was performed by rheometry, crosslink density, Payne effect, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). For the characterization results of the compositions through the Payne effect, it was possible to identify that sample 3 phr derived from sugar cane, showed a breaking load greater number of-charge interactions. In the third chapter, with the chemical modification by silanization derivative of sugar cane and subsequent incorporation into the natural rubber matrix. The modified sugar derivative (DCM) was analyzed by FTIR and compositions rheometry, crosslink density, DMA, and SEM. It was noted that the effect of silanization positively acted upon vulcanization properties and dispersion. In the vulcanization property was influenced more by the reduction of reversal of the natural rubber. The results of DMA proved the improvement in load dispersion in the matrix.

Submitted by GIOVANNI BARRERA TORRES null (gbarrerat01@gmail.com) on 2017-08-04T04:24:40Z No. of bitstreams: 1 TESE VERSÃO FINAL Giovanni Barrera Torres.pdf: 6197644 bytes, checksum: d321626a0e947c39627bbfe43b7aaf87 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-08-04T19:37:47Z (GMT) No. of bitstreams: 1 torres_gb_dr_prud.pdf: 6197644 bytes, checksum: d321626a0e947c39627bbfe43b7aaf87 (MD5) / Made available in DSpace on 2017-08-04T19:37:47Z (GMT). No. of bitstreams: 1 torres_gb_dr_prud.pdf: 6197644 bytes, checksum: d321626a0e947c39627bbfe43b7aaf87 (MD5) Previous issue date: 2017-06-21 / Asociación Universitaria Iberoamericana de Postgrado (AIUP) / A presente pesquisa foi projetada para promover o desenvolvimento de compósitos poliméricos a partir da mistura de polietileno de baixa densidade (PEBD) com borracha natural (BN) reforçada com a cinza, resíduo da queima do bagaço, a cinza da cana de açúcar (CBC). Uma das propostas desta pesquisa foi direcionar uma aplicação ao resíduo, que é um material abundante e descartado, gerado no processo usual das usinas. A borracha natural empregada foi obtida a partir do látex de seringueira de Hevea Brasiliensis, Clone RRIM 600 muito cultivado no Brasil. A fim de se estudar separadamente a interação entre a CBC junto a BN e os agentes de vulcanização. Foi estudada numa primeira etapa: a mistura de borracha natural com a cinza de bagaço da cana até desenvolver uma mistura chamada de master, com boas propriedades de tensão e deformação. Foram produzidos compósitos elastoméricos aplicando agente silano como sistema de acoplamento. Numa segunda etapa o master compatibilizado foi misturado ao PEBD sem o uso de agentes de vulcanização; a finalidade destes compósitos foi de estudar a interação dos constituintes visando obter um compósito com o mínimo de agentes químicos e funcional para a indústria. Numa última etapa foram desenvolvidas blendas e compósitos termoplásticos vulcanizáveis (TPV); nesta etapa foram aplicados os agentes de vulcanização empregados na primeira etapa da pesquisa. As amostras foram estudadas por meio das técnicas de análises estruturais (FT-IR); físico-mecânicas (tensão e deformação; dinâmicas e mecânicas, DMA); térmicas (DSC e TG); dureza (Shore A). Foram obtidos resultados sobressalientes em comparação com as amostras sem agentes de vulcanização nas amostras com 50 % de master e 50 % de PEBD na resposta de elongação e tensão; a dureza acima do Shore A 85 obtida, foi produto da porcentagem da fase de PEBD presente nas amostras; nas análises térmicas foi possível observar degradação acima dos 160 oC resultando uma boa característica para aplicações industriais. Com os resultados obtidos tornou-se possível direcionar tanto a CBC como os compósitos para aplicações tecnológicas a fim de serem utilizados na fabricação de cabos de ferramentas, amortecedores, produtos para o lar, entre outros. / The present research was aimed to promote the development of polymeric composites from the mixture of low density polyethylene (LDPE) with natural rubber reinforced with ash, residue of the burning of sugarcane bagasse (SCB). One of the proposals of this research was to direct an application to the residue, which is an abundant and discarded material, generated in the usual process of the plants. The natural rubber used was obtained from rubber latex clone of Hevea Brasiliensis, Clone RRIM 600 widely cultivated in Brazil. In order to study separately the interaction between SCB with NR and vulcanization agents. It was developed in the first stage: the mixing of natural rubber with the sugarcane bagasse ash to develop a mixture called master, with good tensile and deformation properties. Elastomeric composites were produced by applying silane as a coupling agent. In a second stage the compatibilized master was mixed to the LDPE without the use of vulcanization agents; the purpose of these composites was to study the interaction of the constituents in order to obtain a composite with the minimum of chemical and functional agents for the industry. In the latter stage vulcanizable thermoplastic blends and thermoplastic composites were developed; In this stage the vulcanization agents used in the first stage of the research were applied. The samples were studied using structural analysis techniques (FT-IR); Physical-mechanical (tension and deformation, dynamic and mechanical, DMA); (DSC and TG); Hardness (Shore A). Sparing results were obtained in comparison with the samples without vulcanization agents in samples with 50 % of master and 50 % of LDPE in the strain and stress response; the hardness above Shore A 85, obtained was the product of the percentage of the LDPE phase present in the samples; In the thermal analyzes it was possible to observe degradation above 160 oC resulting in a good characteristic for industrial applications. With the results obtained, it became possible to target both SCB and composites for technological applications in order to be used in the manufacture of tool cables, shock absorbers, household products, among others. / AIUP: A0 185864

Cette thèse comporte une étude expérimentale sur la dynamique de croissance par fatigue d’une fissure dans un caoutchouc naturel renforcé avec des nanoparticules (silice, noir de carbone). Elle s’inscrit dans un cadre industriel visant à mieux comprendre si l’amélioration des performances apportée par la silice dans les caoutchoucs synthétiques est transposable au caoutchouc naturel qui cristallise sous contrainte. L’objectif est de comprendre comment la rupture en fatigue dépend de la nature du matériau et des paramètres de contrôle de l’expérience. La dynamique de croissance de la fissure est suivie à l’aide d’une caméra optique et une caméra infrarouge permet d’évaluer l’auto-échauffement. La morphologie des faciès de rupture est caractérisée par observation post mortem (MEB, profilométrie optique). L’influence de la température, de la fréquence, de la nature et du taux de charge a été étudiée. Dans tous les cas, la croissance de la fissure devient instable à partir d’un certain niveau de déformation. Cela se traduit sur les courbes de l’énergie de déchirure en fonction de la vitesse de la fissure par l’existence de deux branches distinctes : une branche à vitesse basse où une morphologie de rupture très rugueuse, pouvant présenter des signes de cavitation, est observée ; une branche à haute vitesse où la surface de rupture présente des stries dont la taille croît avec la vitesse. En contraste avec les données de la littérature, nous démontrons qu’il faut au minimum deux cycles de fatigue pour former une strie. Le seuil d’apparition des instabilités et le seuil de rupture catastrophique dépendent de la nature des renforts et des conditions expérimentales / In this thesis, we present an experimental study on fatigue crack growth dynamics in a natural rubber filled with silica or carbon black nanoparticles. This work has been developed in an industrial context aiming to transpose the qualities of silica filler on synthetic rubber to natural rubber, which has a strain induced crystallization behavior. The main research objective is to understand the influence of material and test parameters on fatigue fracture of rubber. Crack growth dynamics is followed by video tracking using optical and thermo-graphic cameras. The later allows us to measure the heating build-up of specimens due to cyclic loading. The morphology of rupture surfaces is characterized by post mortem observation (SEM, optical profilometry). The influence of temperature, frequency, kind of filler and filler rate has been studied. Whatever the compound or test conditions, crack growth becomes unstable starting at a certain strain level. This behavior is clearly visible on the curves of tear energy vs. crack growth rate, where two branches of crack velocity appear. In the low velocity branch, the roughness of rupture surfaces is very important because of cavities formation. In the high velocity branch, the morphology of rupture surfaces is characterized by sawtooth striations; their size increase with velocity. We demonstrate that, in contrast with literature data, at least two fatigue cycles are needed to form one striation. The instability occurrence and catastrophic rupture thresholds depend on filler type and test conditions

Cette thèse a pour objectif de développer une nouvelle approche bio-inspirée des processus de polymérisation conduisant à la formation de polyterpènes et ultérieurement du caoutchouc naturel, un polyisoprène de structure purement 1,4-cis de forte masse molaire dont les propriétés sont encore inégalées par ses homologues synthétiques. Pour cette raison la production mondiale de caoutchouc naturel demeure stratégique et est toujours proche de 10 millions de tonnes, soit environ 45% de la demande mondiale annuelle en élastomères. Alors que les voies de synthèse développées jusqu’à présent pour accéder à des homologues du caoutchouc naturel sont basées sur la polymérisation par voie anionique ou par coordination de l’isoprène,l’approche suivie par la nature pour synthétiser les polyterpènes est basée sur la polymérisation à caractère cationique d’un autre monomère, le pyrophosphate d’isopentényle (IPP) qui est la brique de construction universelle de la famille des terpènes. Le projet a pour objet de tenter de reproduire au plus près le procédé naturel et d’utiliser, d’une part, la voie cationique pour polymériser des modèles de l’IPP et l’isoprène en utilisant des homologues du pyrophosphate dediméthylallyle (DMAPP, amorceur employé par la nature) comme amorceurs et des acides de Lewis pour mimer les cations divalents (Zn2+, Mg2+ or Mn2+) qui assistent les enzymes au cours des étapes d’ionisation et d’activation mises en jeu au cours de la biosynthèse, afin d’accéder à des polyterpènes approchant la structure des produits naturels. Contrairement à la nature, nous avons obtenus des oligomères de structure 1,4-trans avec de plus, de nombreuses structures cyclisées. D’autre part, nous avons également cherché à améliorer les propriétés d’un polyisoprène 1,4-cis obtenu par polymérisation anionique afin d’approcher celles du caoutchouc naturel. Nous avons développé une fonctionnalisation des chaines de polyisoprène 1,4-cis permettant d’ancrer des groupements urées susceptibles d’établir un réseau physique de liaisons hydrogènes. Nous avons montré que les polyisoprènes modifiés possèdent des propriétés viscoélastiques comparables à celles du caoutchouc naturel non vulcanisé obtenu par coagulation du latex. / Although synthetic rubbers, including high cis-content polyisoprene (PIP), are used in a broad range ofapplications, they are far from achieving the performances of natural rubber (NR), a 100% 1,4-cis polyisoprenewith very high molar mass. Therefore, NR produced exclusively by hevea (whereas more than 2,500 plant species are known to produce polyterpene-based polymers) is still dominant in many engineering applications since its exceptional properties grants this polymer a strategic resource material which holds a significant marketshare (about 45%).. The only alternative plant species under cultivation, Parthenium argentatum, also calledguayule, produces a latex yielding rubber with properties close to those of hevea rubber, and marketed as “non allergenic natural rubber” but with a higher cost complex extraction processes The NR biosynthesis process isdescribed as a polymerization process involving a series of enzymatic reactions using isopentenyl pyrophosphate(IPP) as elementary building brick. Besides, synthetic PIPs with high cis-content were already produced fromisoprene monomer by Ziegler-Natta, lanthanide-based or anionic-type polymerizations. Currently, no syntheticPIPs mimics the performance of NR, maybe because 100% 1,4-cis PIP could so far not been produced synthetically. A close inspection of the NR biosynthesis process led us to postulate that this latter is consistent with a transferless, stereospecific carbocationic-type polymerization mechanism. We then propose to develop this new bio-inspired cationic-like polymerization approach with the aim to produce polyterpenes and then NR homologues of tailored molar mass and microstructure that could exhibit properties close to natural polyterpenes by using IPP homologues and isoprene as monomers, DMAPP homologues asinitiators and Lewis acids to mimick the divalent cations (Zn2+, Mg2+ or Mn2+) that assist the enzymes during the initiation end activation steps. For the cationic polymerization of isoprene, oligomers with 1,4-trans and cyclized structures were obtained. We also develop new routes to modify polyisoprenes obtained by anionic polymerization in order to establish hydrogen interaction. To this end, different urea groups were grafted and the modified polyisoprene exhibite delastomeric properties close to the one of a non-vulcanized NR obtained by latex coagulation

Le but de la présente étude était de vérifier l'influence de deux compartiments du latex d'Hevea brasiliensis, les lutoïdes et le sérum C, sur le durcissement au stockage et sur la mésostructure du caoutchouc naturel (NR). L'implication des composants minéraux du latex a fait l'objet d'un focus spécial. La mésostructure du NR a été étudié par fractionnement par couplage flux-force à flux asymétrique couplé à un détecteur à diffusion de lumière multiangulaire (AF4-MALS) et par chromatographie d'exclusion de tailles équipée d'un détecteur de diffusion de lumière multiangulaire (SEC- MALS). La spectrométrie de masse couplée à une torche à plasma (ICP- MS) a été utilisée pour déterminer la composition en éléments minéraux du NR.L'AF4 - MALS et l'ICP-MS n'ayant jamais été utilisées pour l'analyse du NR, les méthodes ont été développées. Pour l'AF4 - MALS, la meilleure séparation entre les deux populations principales, chaînes de polyisoprène isolées (pelote statistique) et les microagrégats (Gel<1μ), a été obtenue avec une diminution linéaire, plutôt qu'exponentielle, du flux croisé. Pour l'ICP-MS, les optimisations réalisées concernent la quantité de NR à échantillonner, la méthodologie de solubilisation des cendres, la concentration des solutions de cendres et la gestion des interférences m/z . Tous les éléments, excepté le soufre, ont été analysés en utilisant un mélange H2/He comme gaz de collision-réaction (mode CCT H2/He). La teneur en soufre a été déterminée par le rapport m/z égal à 48 (32S16O+) en mode CCT O2.Les différents compartiments du latex des champs (crème, skim, sérum C et lutoïdes) ont été séparés par centrifugation à grande vitesse. L'évolution de la mésostructure des films obtenus à partir de ces trois latex; latex des champ (FL), le latex de crème (CL) et de latex de skim (SK), par un procédé de structuration lente (échantillons stockés à température ambiante dans le laboratoire pendant 3 mois) a été suivie par SEC- MALS. Le skim n'étant pas sensible au processus de structuration lente, le nombre des étapes de centrifugation a été réduit. La stabilité des lutoïdes a été étudiée par un paramètre qualitatif (état visuel des lutoïdes après centrifugation) et un paramètre quantitatif (indice d'éclatement ou BI). Bien que les deux méthodes n'aient pas donné de résultats strictement corrélées, le BI peut être un bon indicateur de la stabilité des lutoïdes. Pour les échantillons de FL, une bonne corrélation entre la stabilité des lutoïdes et le durcissement au stockage (P) a été observée. Pour déterminer si des composés du C-sérum étaient également impliqués dans le durcissement au stockage, des expériences supplémentaires ont été effectuées en ajoutant des quantités variables de sérum C ou de lutoïdes à des particules de caoutchouc purifiées. L'augmentation à la fois de les quantités de sérum C et des lutoïdes a entrainé une augmentation du durcissement au stockage (P).La mésostructure des films et des feuilles séchées de l'air (ADS) préparés à partir des FL et CL a été analysée par SEC-MALS et AF4-MALS. Pour les échantillons d'ADS, quelle que soit la technique utilisée, les échantillons de FL présentaient des Mw, Mn et Gel>1μ supérieurs aux échantillons de CL. Cette différence entre échantillons de FL et de CL n'a pas été observée pour les échantillons de films. / The aim of the present work was to study the influence of two Hevea brasiliensis latex compartments, namely lutoids and C-serum, on the storage hardening and on mesostructure of natural rubber (NR). A special focus was done on the involvement of mineral components of latex. The NR mesostructure was studied by asymmetrical flow field-flow fractionation coupled to a multiangular light scattering detector (AF4-MALS) and by size exclusion chromatography equipped with a multiangular light scattering detector (SEC-MALS). Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the mineral element composition of NR.As AF4-MALS and ICP-MS were never used for NR analysis, the methodologies were developed. For AF4-MALS, the best separation between the two main populations, namely isolated polyisoprene chains (random coil) and microaggregates (Gel<1µ) was given by a linear decrease, rather than exponential, of the cross-flow. For ICP-MS, the optimizations were in terms of amount of NR to be sampled, ash solubilisation methodology, ash solutions concentrations and m/z interference management. All elements, except sulfur, were determined using a mixture H2/He as collision-reaction gas (CCT H2/He mode). Sulfur content was determined through the m/z equal to 48 (32S16O+) in the CCT O2 mode.The different compartments of the whole field latex (cream, skim, C-serum and lutoids) were separated by high speed centrifugation. The mesostructure evolution of films obtained from these 3 lattices; whole field latex (FL), cream latex (CL), and skim latex (SK), by a slow structuring process (samples stored at room temperature in the laboratory for 3 months) was followed by SEC-MALS. As it was observed that the skim was not sensitive to the slow structuring, the centrifugation steps were reduced.Lutoid stability was studied by a qualitative parameter (visual lutoid status after centrifugation) and a quantitative parameter (bursting index or BI). Although the two methods could not provide strictly correlated results, BI can be a good indicator of lutoid stability. For the FL samples, a good correlation between the lutoid stability and storage hardening (ΔP) was observed. To determine if some compounds of C-serum are also involved in the storage hardening, additional experiments were done adding variable quantities of C-serum or lutoids to purified rubber particles. The storage hardening (ΔP) increased by the increase of both C-serum and lutoid quantities.The mesostructure of films and air dried sheet (ADS) made from FL and CL lattices (obtained from reduced centrifugation process) were analyzed by SEC-MALS and AF4-MALS. Concerning the ADS samples, whatever the technique used, FL samples exhibited a higher Mw, Mn, and Gel>1µ than CL samples. This difference between FL and CL samples was not observed for film samples. The microaggregates (Gel<1µ) were presented in all samples but the FL samples had more compact microaggregates, with a much higher Mw than the CL samples. Moreover, AF4 showed that the structure of microaggregates was very different between ADS and film samples. The Mw of microaggregates of ADS was 2 to 4 times higher than that of films. The mineral elements were determined only on samples from ADS (FL and CL). The main elements in NR were K, P, Mg, and S, in decreasing order. The purification of rubber particles affected the decrease in the element contents. During the storage of the latex at room temperature, only calcium content decreased, for both FL and CL samples.

Cette étude vise à mieux comprendre les mécanismes physiques à l'origine des propriétés mécaniques et des propriétés ultimes des caoutchoucs renforcés. Des échantillons de caoutchouc naturel dans lequel sont dispersés des agrégats de Silice précipitée ou de Noir de Carbone et vulcanisés au Soufre ont étés mis en oeuvre. Les principaux paramètres étudiés sont la densité de réticulation et l'interface charge-caoutchouc modifiée au moyen de différents traitements de surface de silice. L'impact des charges et du type d'interface sur les propriétés mécaniques dans le domaine des faibles déformations (effet Payne) et des grandes déformations est présenté. Le phénomène de cristallisation sous étirement dans le caoutchouc naturel est étudié par diffraction des rayons X in-situ au cours d'essais de traction quasi-statiques ou d'essais dynamiques couplés à un système d'acquisition stroboscopique. Nous montrons une corrélation des mesures du module, du degré de gonflement à l'équilibre, de l'orientation des chaînes mesurée par diffusion de rayons X et de la densité de réticulation mesurée par RMN dans le caoutchouc naturel non chargé. Dans le caoutchouc naturel renforcé, les corrélations établies à l'aide de ces mêmes mesures permettent de préciser les mécanismes de renforcement aux faibles et aux grandes déformations. Enfin, la résistance à la déchirure est évaluée en géométrie cisaillement pur sur les matériaux non-renforcés et renforcés. Les effets du type d'interface, de la densité de réticulation et de la vitesse d'essai sur la résistance à la déchirure sont présentés. Nous discutons également les profils de déformation locale obtenus par corrélation d'image / This study aims at better understanding the physical mechanisms responsible for the mechanical and ultimate properties in reinforced rubber materials. Sulfur vulcanized samples made of a Natural Rubber matrix in which aggregates of precipitated Silica or Carbon Black are dispersed have been manufactured. The main control parameters are the crosslink density and the filler/rubber interactions through different silica surface treatments. The effect of fillers and interface type on the mechanical properties in the small strain regime (Payne effect) and large strain regime is presented. X-ray diffraction experiments have been performed to study the phenomenon of strain-induced crystallization (SIC) both during quasi-static tensile tests and dynamical tests coupled to a stroboscopic acquisition device. Mechanical measurements have proved to correlate fairly well to the crosslink density measured by NMR, to equilibrium swelling degree and to the average chain segment orientation measured by X-ray scattering in unfilled natural rubber in agreement with the rubber elasticity theory. In reinforced materials, the correlation of those different measurements of local chain stretching give new insights on the reinforcement mechanisms at small and large strain. Tear experiments have been performed on Pure Shear pre-notched unfilled and filled samples. The influence of interface type, crosslink density and test drawing speed on tear resistance are presented. Local strain profiles obtained from digital image correlation and the crystallized fraction profiles from in-situ X-ray diffraction are also discussed