Le but de cette thèse est d'améliorer la compréhension des liens entre microstructure et propriétés mécaniques de réseaux élastomères dégradés par irradiation en utilisant la dynamique moléculaire coarse-grained . Les chaînes polymères sont créées par un algorithme de polymérisation pseudo-radicalaire puis réticulées par un algorithme permettant d’obtenir une distribution spatiale maîtrisée, aléatoire ou non, des nœuds de réticulation. Un dernier processus permet de simuler des coupures de chaînes. L'équilibration des réseaux ainsi créés est ensuite réalisée avec des forces intergrains dont les paramètres sont issus des travaux de Kremer et Grest. Dans le cas de réseaux aléatoires, le lien entre densité de chaînes actives, de chaînes pendantes et longueur des sous-chaînes avec le nombre de nœuds de réticulation et la fraction soluble est bien décrit par les modèles statistiques adéquats. Des essais simulés de spectrométrie mécanique isochrones à différentes températures permettent de retrouver (i) lorsque les chaînes sont non réticulées, l'influence de la longueur des chaînes sur la longueur du plateau caoutchoutique et sur Tα , et (ii) lorsqu’elles sont réticulées, l’influence de la densité de réticulation sur la hauteur de ce plateau. Les essais simulés de traction uniaxiale permettent de confirmer la relation entre le module mécanique et la densité de nœuds chimiques et de nœuds d’enchevêtrements piégés. Différents processus interviennent avant rupture: dans le cas de réseaux aléatoires, survient d’abord la rupture de liens covalents de manière homogène, puis la cavitation, la striction et enfin la rupture de liens dans les filaments de la zone de striction ; l'allongement à rupture finale est toujours proche du double de celui à première rupture de lien (lui même relié au module du matériau). A même densité de réticulation, le comportement à petites déformations et à durcissement est peu influencé par une réticulation hétérogène par zones. On constate, à même densité de nœuds chimiques, une légère diminution du module d'Young pour des réseaux doubles interpénétrés explicable par les enchevêtrements ; par ailleurs ils rompent de manière homogène dans le sous-réseau le plus réticulé. Les réseaux hétérogènes contenant des zones sphériques plus réticulées présentent des ruptures à l'interface avec les zones moins réticulées qui entraînent une diminution de la contrainte maximale atteinte avant rupture totale ; cela s’explique par la diminution au passage de l'interface rigide->mou du nombre de chemins percolants pouvant supporter la sollicitation mécanique. Au final, on constate que les systèmes homogènes basés sur des chaînes longues présentent globalement un meilleur comportement en rupture (allongement à rupture finale et contrainte maximale) que les systèmes hétérogènes, y compris les réseaux doubles. En outre, parmi tous les réseaux simulés, ceux de loin les moins performants sont les réseaux homogènes coupés. / The aim of this thesis is to improve the understanding of the links between microstructure and mechanical properties of irradiated degradated elastomeric networks using molecular coarse-grained dynamics. The polymer chains are created by a pseudo-radical polymerization algorithm and then crosslinked by an algorithm which generate a controlled spatial distribution, random or not, of the crosslinking nodes. The process can include the simulation of bond breaks. The equilibration of the networks thus created is then carried out with intergroup forces whose parameters are derived from the work of Kremer and Grest. In the case of random networks, the link between the density of active chains, of pendant chains and the length of the chains portions with the number of crosslinking nodes and the soluble fraction is well described by the appropriate statistical models. Simulated tests of isochronous mechanical spectrometry at different temperatures make it possible to find (i) when the chains are not crosslinked, the influence of the length of the chains on the length of the rubber plateau and on Tα, and (ii) when they are crosslinked , The influence of the crosslinking density on the height of this plateau. The simulated uniaxial tensile tests confirm the relationship between the mechanical modulus and the density of chemical nodes and trapped entanglement nodes. Different processes intervene before failure: in the case of random networks, the break of covalent bonds occurs in a homogeneous manner, then cavitation, striction and finally the failure of bonds in the filaments of the zone of constriction; the elongation at final failure is always close to twice that at the first failure of the bond (itself connected to the modulus of the material). At the same crosslinking density, the behavior at small deformations and hardening is little influenced by a heterogeneous crosslinking by zones. At the same density of chemical nodes, a slight decrease in the Young's modulus is observed for interpenetrating double networks, which can be explained by entanglements; Moreover, they break homogeneously in the most reticulated sub-network. The heterogeneous networks containing more cross-linked spherical zones have ruptures at the interface with the less cross-linked zones which lead to a reduction in the maximum stress reached before total rupture; this is explained by the decrease in the number of percolating paths which can withstand mechanical stress when passing the rigid-> soft interface. In the end, homogeneous systems based on long chains generally show better failure behavior (ultimate elongation and maximum stress) than heterogeneous systems, including dual networks. Moreover, among all the simulated networks, those which are by far the least efficient are the homogeneous networks cut.

Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 % reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 % over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 % reduction of the driving electric field) as well as in the maximum actuation strain (250 %). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation. / Die Palette von elektro-mechanischen Aktuatoren, basierend auf dem Prinzip weicher dehnbarer Kondensatoren, scheint besonders für Anwendungen in der Medizin und für biomimetische Applikationen unbegrenzt. Diese Wandler zeichnen sich sowohl durch hohe Reversibilität bei großer mechanischer Deformation als auch durch ihre Flexibilität aus, wobei die mechanischen Deformationen durch elektrische Felder induziert werden. Die Notwendigkeit von hoher elektrischer Spannung zur Erzeugung dieser mechanischen Deformationen verzögert jedoch die technisch einfache und breite Markteinführung dieser Technologie. Diesem Problem kann durch eine gezielte Materialmodifikation begegnet werden. Eine Modifikation hat das Ziel, die relative Permittivität zu erhöhen, wobei die Flexibilität und die hohe elektrische Durchbruchsfeldstärke beibehalten werden sollten. Durch eine Materialmodifikation kann die Energiedichte des Materials bedeutend erhöht und somit die notwendige Betriebsspannung des Aktuators herabgesetzt werden. Eine Verbesserung der funktionalen Materialeigenschaften kann durch die Verwendung von Nanokompositen erzielt werden, welche die fundamentalen Eigenschaften der Nanopartikel, d.h. ein gutes Verhältnis von Oberfläche zu Volumen nutzen, um eine gezielte makroskopische Materialmodifikation zu bewirken. Diese Arbeit behandelt die Anwendung innovativer Strategien für die Erzeugung von Nanomaterialien mit hoher Permittivität. Die so erzeugten Materialien und deren relevante Aktuatorkenngrößen werden durch elektrische und mechanische Experimente vollständig erfasst. Mittels der klassischen Mischansätze zur Erzeugung von Kompositmaterialen mit hoher Permittivität konnte durch nichtleitendes Titaniumdioxid TiO2 (Rutile) in einem Thermoplastischen-Block-Co-Polymer SEBS (poly-styrene-co-ethylene-cobutylene-co-styrene) die Permittivität bereits um 370 % erhöht und die elektrische Energiedichte um 570 % gesteigert werden. Diese Veränderungen führten jedoch zu einem signifikanten Anstieg der Steifigkeit des Materials. Aufgrund der positiven Rückkopplung von elektrischen und mechanischen Eigenschaften des Kompositmaterials ermöglicht bereits dieser einfache Ansatz eine Verbesserung der Aktuation, bei einer 27 %-igen Reduktion der Aktuatorbetriebsspannung. Eine direkte Verwendung von leitfähigen Nanopartikeln kann ebenso zu einem Anstieg der relativen Permittivität beitragen, wobei jedoch die Leitfähigkeit dieser Nanopartikel bedeutende Wechselwirkungen verursacht, welche somit die Energiedichte des Materials negativ beeinflusst und die praktische Verwendung dieses Kompositsystems ausschließt. Als ein völlig neuer Ansatz zur Steigerung der relativen Permittivität und Energiedichte und abweichend vom klassischen Mischverfahren, wird die Herstellung eines "Molekularen Komposits", basierend auf einem chemischen Propfverfahren, präsentiert. In diesem Ansatz wird ein π-konjugiertes leitfähiges Polymer (PANI) an die Hauptkette des Elastomers der Polymermatrix gebunden. Die daraus resultierende Ladungsverteilung entlang der Elastomerhauptkette bewirkt eine 470 %-ige Steigerung der Permittivität des "Molekularen Komposits" im Vergleich zur Permittivität des unbehandelten Elastomermaterials. Aufgrund der Verkapselung der chemischen Bindungen der PANI-Kette entstehen kaum negative Rückwirkungen auf die elektrischen und mechanischen Eigenschaften des so erzeugten Komposits. Diese Materialeigenschaften resultieren in einem signifikanten Anstieg der Energiedichte des Materials. Das mittels dieses Verfahrens erzeugte Komposit zeigt sowohl eine Steigerung der Sensitivität der elektromechanischen Antwort (Reduktion des elektrischen Felds um 83 %) als auch eine bedeutende Steigerung der maximalen Aktuation (250 %). Die Ergebnisse und Ideen dieser Arbeit stellen einen wesentlichen Sprung im Verständnis zur Permittivitätssteigerung in Polymermaterialien dar und werden deshalb in der Erforschung und Entwicklung von Elastomeraktuatoren Beachtung finden.

Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.

In this thesis, a process is developed for designing elastomeric vibration isolators in order to provide vibration isolation for sensitive equipment being used in ROKETSAN A.S.&rsquo / s products. For this purpose, first of all, similar isolators are examined in the market. After that, appropriate elastomeric materials are selected and their temperature and frequency dependent dynamic properties are experimentally obtained. Parametric finite element model of the isolator is then constituted in ANSYS APDL using the properties of elastomeric materials and the conceptual design of the isolator. Then, according to design requirements, final design parameters of the vibration isolator are determined at the end of design iterations. In the next step, vibration isolator that was designed is manufactured using the elastomeric material chosen, by a local rubber company. Finally, design process is verified by comparing analysis and test results.

Studies concerning the formation of industrially useful polycarbonates are the focus of this dissertation. Of particular importance is the biodegradable polymer, poly(trimethylene carbonate) which has a wide range of medical applications. The production of polycarbonates can be achieved by the ring-opening polymerization of cyclic carbonate, or the copolymerization of carbon dioxide and oxiranes or oxetanes. For the production of polycarbonates from these monomers, Schiff base metal complexes have been designed, synthesized, and optimized as catalysts. Detailed kinetic and mechanistic studies have been performed for the ring-opening polymerization of cyclic carbonates, as well as the copolymerization of carbon dioxide and oxiranes or oxetane. In addition, the copolymerization of cyclic carbonates and cyclic esters to modify the mechanical and biodegradable properties of materials used for medical devices has been studied using biocompatible metal complexes. In the process for ring-opening polymerizations of trimethylene carbonate or lactides, Schiff base metal complexes (metal = Ca(II), Mg(II) and Zn(II)) have been shown to be very effective catalysts to produce high molecular weight polymers with narrow polydispersities. Kinetic studies demonstrated the polymerization reactions to proceed via a mechanism first order in [monomer], [catalyst], and [cocatalyst] if an external cocatalyst is applied, and to involve ring-opening by way of acyl-oxygen bond cleavage. The activation parameters (ΔH≠, ΔS≠ and ΔG≠) were determined for ringopening polymerization of trimethylene carbonate, ring-opening polymerization of lactides, and copolymerization of trimethylene carbonate and lactide. In the process for copolymerization of carbon dioxide and oxetane, metal salen derivatives of Cr(III) and Al(III) along with cocatalyst such as n-Bu4NX or PPNX (PPN = bis(triphenylphosphine)iminium, and X = Br, Cl and N3) have been shown to be effective catalysts to provide poly(trimethylene carbonate) with only trace amount of ether linkages. The formation of copolymer is proposed not to proceed via the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction. To support this conclusion, ring-opening polymerization of trimethylene carbonate has been performed and kinetic parameters have been compared with those from the copolymerization of carbon dioxide and oxetane.

Ein Dielektrischer Elastomer Aktuator (DEA) ist ein dehnbarer Kondensator, der aus einem Elastomerfilm besteht, der sich zwischen zwei flexiblen Elektroden befindet. Bei Anlegen einer elektrischen Spannung, ziehen sich die Elektroden aufgrund elektrostatischer Wechselwirkungen an, wodurch das Elastomer in z-Richtung zusammengepresst wird und sich dementsprechend in der x-,y-Ebene ausdehnt. Hierdurch werden Aktuationsbewegungen erreicht, welche sehr präzise über die Spannung gesteuert werden können. Zusätzlich sind DEAs kostengünstig, leicht und aktuieren geräuschlos. DEAs können beispielsweise für Produkte im medizinischen Bereich oder für optischer Komponenten genutzt werden. Ebenso kann aus diesen Bauteilen Strom erzeugt werden. Das größte Hindernis für eine weite Implementierung dieser Materialien liegt in den erforderlichen hohen Spannungen zum Erzeugen der Aktuationsbewegung, welche sich tendenziell im Kilovolt-Bereich befinden. Dies macht die Elektronik teuer und die Bauteile unsicher für Anwender. Um geringere Betriebsspannungen für die DEAs zu erreichen, sind signifikante Materialverbesserungen - insbesondere des verwendeten Elastomers - erforderlich. Um dies zu erreichen, können die dielektrischen Eigenschaften (Permittivität) der Elastomere gesteigert und/oder deren Steifigkeit (Young-Modul) gesenkt werden. In der vorliegenden Arbeit konnte die Aktuationsleistung von Silikonfilmen durch die Addition organischer Dipole erheblich verbessert werden. Hierfür wurde ein Verfahren etabliert, um funktionalisierte Dipole kovalent an das Polymernetzwerk zu binden. Dieser als "One-Step-Verfahren" bezeichnete Ansatz ist einfach durchzuführen und es werden homogene Filme erhalten. Die Dipoladdition wurde anhand verschiedener Silikone erprobt, die sich hinsichtlich ihrer mechanischen Eigenschaften unterschieden. Bei maximalem Dipolgehalt verdoppelte sich die Permittivität aller untersuchten Silikone und die Filme wurden deutlich weicher. Hierbei war festzustellen, dass die Netzwerkstruktur der verwendeten Silikone einen erheblichen Einfluss auf die erreichte Aktuationsdehnung hat. Abhängig vom Netzwerk erfolgte eine enorme Steigerung der Aktuationsleistung im Bereich von 100 % bis zu 4000 %. Dadurch können die Betriebsspannungen in DEAs deutlich abgesenkt werden, so dass sie tendenziell bei Spannungen unterhalb von einem Kilovolt betrieben werden können. / Dielectric elastomer actuators (DEAs) are compliant capacitors consisting of an elastomer film between two flexible electrodes. When a voltage is applied the electrostatic attraction of the electrodes leads to a contraction of the polymer in the z-direction and to a corresponding expansion in the x,y-plane. DEAs show high actuation strains, which are very accurate and adjustable by the applied voltage. In addition these devices are low-cost, low-weight and the actuation is noise-free. DEAs can be used for medical applications, optical components or for energy harvesting. The main obstacle for a broad implementation of this technology is the high driving voltage, which tends to be several thousand volts. For this reason the devices are unsafe for users and the needed electronic components are expensive. A significant improvement of the materials - especially of the used elastomer - is necessary to lower the actuation voltages. This can be achieved by improving the dielectric properties (permittivity) of the elastomer and/or by lowering it's stiffness (Young's modulus). In this work the actuation performance of silicone lms was improved significantly by the addition of organic dipoles. A simple procedure was developed, in which functionalized dipoles were bound to the polymer matrix, leading to homogenous and transparent films. This so-called "one-step-film-formation" was tested on various silicones with different mechanical properties. For the highest dipole content the permittivity of all tested silicones was doubled and the modified films showed a substantially lower stiffness. It was proven that the structure of the macromolecular network has a clear impact on the achievable actuation properties. For the highest dipole contents the actuation performance increased remarkably by 100 % up to 4000 % in respect to the investigated network. The addition of organic dipoles to the elastomer enables a signicant reduction of the needed driving voltage for DEAs below one kilovolt.

Die inhärenten elastomeren Eigenschaften von Gummiwerkstoffen sind im Vergleich zu Thermoplasten in vielen Spezialanwendungen vorteilhaft. Jedoch sind ihre schlechten Reibungs- und Verschleißeigenschaften ein wesentlicher Nachteil besonders bei tribologischen Anwendungen. In der vorliegenden Arbeit wurden Reibung, Verschleiß und mechanische Eigenschaften von Gummiwerkstoffen, die Polytetrafluorethylen(PFTE)-Pulver enthalten, untersucht. Hauptziel war dabei die Verbesserung der Reibungs- und Verschleißeigenschaften bei weiterer Erhöhung der mechanischen Eigenschaften der Elastomere. Es ist bekannt, dass sich Reibungs- und Verschleißeigenschaften gummiähnlicher Materialien in vielfältiger Weise von den Reibungseigenschaften der meisten anderen Festkörper unterscheiden. Die Gründe dafür sind das viskoelastische Verhalten und der sehr geringe elastische Modul von Gummi. Die Verwendung von mit Elektronen modifizierten PTFE-Pulvern in Ethylen-Propylen-Dien-Monomer (EPDM) Kautschuken führt zu einer signifikanten Reduzierung der Reibung, Erhöhung der Verschleißfestigkeit und gleichzeitig zu verbesserten mechanischen Eigenschaften in Folge einer speziellen chemischen Kopplung zwischen dem modifiziertem PTFE-Pulver und dem EPDM. Gummirezeptur, Vernetzungsmethode und die viskoelastischen Materialeigenschaften beeinflussen wesentlich die tribologischen und mechanischen Eigenschaften. Morphologie, Dispersion und die chemische Kopplung des PTFE-Pulvers haben einen signifikanten Einfluss auf die Reibungs- und Verschleißverhalten. Die viskoelastischen Materialeigenschaften, d.h. Härte, E-Modul und tan delta (Verlustfaktor) der Gummimischungen sind kritische Parameter und erfordern deshalb eine Optimierung. In dieser Arbeit wurden zwei Modellsysteme untersucht, die auf zwei unterschiedlichen Kautschuktypen basieren: a) Ethylen-Propylene-Diene-Monomer (EPDM) Kautschuk und b) Polychloropren Kautschuk (CR). / The inherent elastomeric properties of rubber compounds in comparison to thermoplastics are advantageous in many special purpose applications. However, their characteristic poor friction and wear properties are of prime concern especially in tribological applications. In the present work, friction, wear and mechanical properties of rubber compounds based on PTFE powder have been investigated. The main aim was to improve the friction and wear properties while further enhancing the mechanical properties of rubber compounds. As known, friction and wear behaviour of rubber-like materials differ in many ways from the frictional properties of most other solids. The reason for this is the high viscoelasticity and very low elastic modulus of rubber. The use of electron-modified PTFE powder in EPDM results in significant improvement in reducing friction, enhancing wear resistance and simultaneously improving mechanical properties due to specific chemical coupling between modified PTFE powder and EPDM. The rubber formulation, crosslinking mode and bulk viscoelastic properties strongly influences friction, wear and mechanical properties. The morphology, dispersion, and specific chemical coupling of PTFE powder play a significant role on friction and wear behaviour. The bulk viscoelastic properties, i.e. hardness, modulus and tan delta (loss factor) of the compounds are critical parameters and therefore, requires optimization. In this work two model systems based on two different rubber matrixes i.e. Ethylene-Propylene-Diene-Monomer (EPDM) and Chloroprene (CR) rubber have been investigated.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-07-06T11:02:00Z No. of bitstreams: 1 GERALDO SÁVIO ALMEIDA HOLANDA - TESE (PPGCEMat) 2016.pdf: 9735527 bytes, checksum: 9e91f1e9c99fbe2f4b51aad716c26581 (MD5) / Made available in DSpace on 2018-07-06T11:02:00Z (GMT). No. of bitstreams: 1 GERALDO SÁVIO ALMEIDA HOLANDA - TESE (PPGCEMat) 2016.pdf: 9735527 bytes, checksum: 9e91f1e9c99fbe2f4b51aad716c26581 (MD5) Previous issue date: 2016-12-15 / O Silastic® MDX4-4210 é um dos materiais mais utilizados no mundo na confecção de próteses faciais devido às suas propriedades, contudo, ele apresenta algumas limitações, notadamente a que reduz o tempo de vida útil destas. O objetivo deste estudo foi avaliar a influência de pigmentos nas propriedades de um silicone para prótese facial submetido ao envelhecimento acelerado. Foram confeccionados 288 corpos de provas e divididos em três grupos: o Grupo Controle (GC) constituído por amostras do silicone Silastic® MDX4-4210 sem acréscimos de pigmento e os grupos experimentais G1 e G2. O Grupo 1 (G1), formado por amostras do silicone Silastic® MDX4-4210, pigmento com pó de maquiagem e, o Grupo 2 (G2), constituído por amostras de silicone com a incorporação da solução do pigmento de Urucum-Bixina (Bixa orellana L). Cada grupo foi constituído de 24 corpos de prova, sendo 09 unidades destinadas às caracterizações e 15 unidades aos ensaios mecânicos. Setenta e dois corpos de prova foram selecionados para serem avaliados antes do envelhecimento acelerado. Os 216 corpos de prova restantes, foram submetidos ao envelhecimento acelerado por exposição a ciclos de Ultravioleta, Temperatura e Umidade (UV/T/U) nos tempos de 120, 240 e 1000 horas. As amostras foram caracterizadas por meio de análise por Microscopia Ótica, Microscopia Eletrônica de Varredura, Espectroscopia na região do infravermelho com transformada de Fourier, Termogravimetria e os ensaios de Citotoxicidade, Sorção e Biodegradação Enzimática. Foram realizados os ensaios mecânicos (dureza Shore A, resistência ao rasgamento e à tração, módulo de elasticidade e alongamento a ruptura). Os dados obtidos foram analisados e obtidas as medidas estatísticas: média; mediana; desvio padrão. Os dados mostraram que não foram observadas mudanças significativas na cor ou textura em diferentes períodos de envelhecimento acelerado. Em geral, o material tornou-se mais resistente, mais duro, mais rígido e menos dúctil, conforme foi envelhecido, mas manteve uma deformação percentual superior a 100-120%. Apesar das alterações causadas pelo envelhecimento em suas propriedades mecânicas, o material envelhecido permaneceu suficientemente flexível e adequado para a aplicação proposta. Não houve diferença significativa entre as propriedades dos materiais pigmentados com maquiagem ou bixina. / Silastic® MDX4-4210 is one of materials most widely used in the world for facial prosthesis due to its properties, however, it has some limitations, that reduce its lifespan. The aim of this study is to evaluate the influence of pigments in the properties of a silicone for facial prosthesis subjected to accelerated aging. 288 samples were manufactured and divided in three groups: the control group (CG) consisting of Silastic® MDX4-4210 silicon samples without pigment and experimental groups G1 and G2. Group 1 (G1), consisted of Silastic® MDX4-4210 silicone samples, with makeup pigment powder and Group 2 (G2) consisting of silicone samples with the addition of a solution of Bixin (Bixa orellana L). Each group consisted of 24 specimens: 09 units for the characterizations and 15 units for mechanical tests. Seventy-two specimens were selected for further evaluation prior to accelerated aging. The 216 remaining specimens were subjected to accelerated aging by exposure to UV,temperature and humidity cycles (UV/T/U) for 120, 240 and 1000 hours. The samples were characterized by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Cytotoxicity assays, Sorption and Enzyme Biodegradation. Mechanical tests were also performed (Shore A hardness, tear resistance and tensile strength, elastic modulus and elongation to break). Data were analyzed and average, mean, median and standard deviation values were obtained. The data showed that no significant changes were observed in the color or texture in different periods of accelerated aging. In general, the material became tougher, stiffer, more rigid and less ductile, with aging but maintained a percentage deformation exceeding 100-120%. Despite the changes caused by aging changes the mechanical properties of the aged material remained suitable for the proposed application.There were no significant differences in the proprerties of the materials pigmented with either makeup or bixin.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho foram preparados nanocompósitos de elastômeros termoplásticos à base de PP/EPDM/argila organofílica. Foram utilizados como agentes interfaciais polipropileno e terpolímero de etileno-propileno-dieno ambos modificados com grupos anidrido maleico, PP-MA e EPDM-MA, respectivamente. Dois tipos de argila organofílica, que se diferenciam pela estrutura química do surfactante e conseqüentemente pela estabilidade térmica, foram empregados como carga inorgânica. Os nanocompósitos foram preparados pela técnica de intercalação por fusão em câmara interna de mistura e a incorporação da argila foi feita pela adição de masterbatches previamente preparados. Foram investigadas as propriedades de tração, reométricas e ainda a morfologia (cristalinidade e estrutura obtida) dos nanocompósitos a fim de estabelecer a influência do tipo e quantidade de argila organofílica e agente interfacial. Os resultados mostraram que a adição de agente interfacial melhorou a dispersão da argila organofílica na matriz de PP/EPDM, particularmente o PP-MA. Foram obtidos nanocompósitos com estruturas mistas intercaladas e esfoliadas, que resultaram em maiores valores de módulo de elasticidade e manutenção dos valores de deformação. As propriedades reométricas confirmaram o maior grau de dispersão da argila organofílica em nanocompósitos contendo PP-MA. Teores crescentes de argila reduziram a cristalinidade dos nanocompósitos, os quais quando reprocessados, mantiveram as características inerentes ao TPE de origem. Por fim, a estrutura do surfactante presente / In this work it was prepared nanocomposites based in PP/EPDM thermoplastic elastomer and organoclay. Maleinized polypropylene and ethylene-propylene-diene rubber, PP-MA and EPDM-MA, respectively, were employed as interfacial agents. Also two kinds of organoclays, differing about surfactant chemical structure and as consequence thermal stability, were investigated as inorganic filler. Nanocomposites were prepared by melt intercalation in an internal chamber mix and organoclay was incorporated by masterbatches addition, which ones were previously made. It was investigated the influence of amount and kind of organoclay and interfacial agent on tensile properties, rheology and morphology (crystallinity and structure type) of nanocomposites obtained. The results showed that interfacial agents addition promoted a better dispersion degree of organoclay platelets in PP/EPDM matrix, mainly PP-MA. Nanocomposites with both intercalated and exfoliated structures were obtained. These exhibited higher Young modulus and kept their elongation values. The better dispersion degree of clay platelets in nanocomposites containing PP-MA was confirmed by rheology measurements. Increasing amounts of organoclay lowered the crystallinity degree of nanocomposites but the reprocessability was maintained similar to that of pure TPE. Finally, the chemical structure of surfactants did not change the intercalation/exfoliation process due to the similarity of organoclay basal spacing and moderated TPE processing temperature.

Récemment, une nouvelle technique pour renforcer les élastomères acryliques non chargés a été développée. L'élastomère a été préparé par séquences de gonflement par du monomère acrylique et polymérisation radicalaire en faisant des réseaux interpénétrés. Le prétirement des chaines du premier réseau créent des liaisons sacrificielles qui améliorent de manière significative les propriétés mécaniques de l’élastomère sans modifier sa Tg. Il est donc intéressant d’étendre cette méthode à d’autres familles d’élastomères. Ainsi, dans cette étude, la stratégie des réseaux interpénétrés a été appliquée à deux matériaux intéressants. Premièrement, un élastomère silicone a été synthétisé en utilisant une polymérisation par polycondensation par réaction d'hydrosilylation qui est significativement différente de la polymérisation utilisée pour les réseaux acryliques. Les réseaux multiples ont été ensuite synthétisés en gonflant ce réseau avec des précurseurs de petite masse et un faible pourcentage de réticulant D4H. Ces réseaux multiples en silicone ont les propriétés d’un élastomère classique, avec une énergie de rupture améliorée d’environ 100%. Deuxièmement, des particules coeur-ecorce formés de copolymères dibloc amphiphiles de poly(acide acrylique)-b-poly(acrylate de n-butyle) ou PAA-b-PBA ont été synthétisés par auto-assemblage simultané par polymérisation RAFT et préparés sous la forme de films. Ensuite, les films ont été utilisés comme des charges polymères en poly (acrylate de butyle) en utilisant une technique de réseau interpénétrés multiples. Nous avons réussi pour la première fois à renforcer l'élastomère par des particules de latex. Grâce à cette stratégie d'interpénétration qui distribue des particules de latex de manière très homogène dans l’élastomère, les films interpénétrés montrent de bonnes caractéristiques mécaniques, une résistance à la fracture et une ténacité extrêmement élevées en utilisant moins de 1% de PAA vitreux et pas de réticulant ajouté dans la particule renforçante. / Recently, a new technique to reinforce unfilled acrylic elastomers has been established. The elastomer was prepared by sequential free radical polymerization and swelling of acrylic monomers making interpenetrated networks. By introducing sacrificial bonds, the elastomer had significantly enhanced mechanical properties without changing the Tg of the material. We extended this method to two different elastomeric system to probe its generality. First, a silicone elastomer was synthesized by using polycondensation polymerization via a hydrosilylation reaction which is significantly different from the free radical polymerization used for acrylic networks. The multiple networks were synthesized by sequential swelling and polymerization steps with low molecular weight preducrosrs and a small amount of D4H crosslinker. The resulting silicone multiple networks were fully elastic elastomer with a mechanical toughness improved by about 100%. Second, core-shell latexes made of amphiphilic diblock copolymers Poly(acrylic acid)-block-poly(butyl acrylate) or PAA-b-PBA were synthesized by RAFT polymerization induced self-assembly and prepared into thin films. Different types of core-shell latexes and crosslinked latexes were synthesized and characterized both in the aqueous state and in the dry film state. The films were then used as a polymeric filler to a poly(butyl acrylate) by using the interpenetrated network technique. We succeeded for the first time to reinforce elastomers by latex particles. Thanks to interpenetrated networks strategy which distributed homogenously latex particles though the entire material, the interpenetrated films show extremely enhanced mechanical characteristics, fracture energy and toughness by using less than 1 % of glassy PAA content and no crosslinker in the reinforcing particles.