O texto discute a formação do Acre durante o ciclo da borracha entre 1904 e 1945, fazendo uma análise da economia, política e das representações. O objetivo principal desse trabalho é analisar a inserção do Acre no contexto do ciclo da borracha, procurando assim contribuir para um debate historiográfico mais amplo sobre esse tema. O foco do trabalho são as empresas seringalistas, elaborando uma narrativa que enfoca a maior de todas elas na região, a N & Maia e Companhia. A tese defende que com a falência do ciclo da borracha a partir de 1910, as empresas seringalistas no Acre que souberam se adaptar a esse cenário de crise foram se consolidando como senhoras dos domínios econômicos, políticos e sociais da região. A tese é desenvolvida dividindo-se em três partes, que contextualizam esse cenário da seguinte maneira: a) uma primeira onde se discute como se formou a mão de obra dos seringais e consequentemente aquela capaz de gerar renda aos seringalistas; b) uma segunda onde elabora-se uma investigação sobre a constituição da cadeia de aviamento da borracha e como as empresas seringalistas conseguiram superar essa rede, que entrou em colapso a partir de 1910; c) a última parte debate com as formas de representação do Acre no período do ciclo da borracha, sendo uma delas oriunda de uma visão senhorial ancorada na opulência e outra que se caracteriza pelos registros de uma região precária e marginal perante o restante da Amazônia. / The paper discusses the formation of Acre during the rubber boom between 1904 and 1945, making an analysis of the economy, politics and representations. The main objective of this work is to analyze the insertion of Acre in the context of the rubber, thus seeking to contribute to broader historiographical debate on this topic. The focus of the work will be rubber companies, developing a narrative that focuses on the greatest of them all in the region, the N & Maia and Company. The thesis defend is that with the collapse of the rubber boom from 1910, the Acre rubber companies that were able to adapt to this crisis scenario were consolidated as Ladies domains economic, political and social area . For this thesis is proven text was divided into three parts, which contextualize this scenario as follows: a) a first part where he discusses how it formed the manpower of the rubber and that consequently able to generate income to seringalistas b ) a second where we undertake a research on the formation of the chain of dispensing as rubber and rubber companies were able to overcome this network, which collapsed from 1910 c) the last part discussion with the forms of representation of Acre during the rubber boom, one of them coming from a vision anchored in stately opulence and other records which is characterized by a region of poor and marginal to the rest of the Amazon.

Dentre os materiais de fontes naturais e renováveis, a celulose se destaca pela sua abundância, podendo ser encontrada em diversos organismos vivos, como plantas, amebas, bactérias, fungos e alguns animais marinhos. Suas dimensões podem ser reduzidas por quebra das cadeias amorfas, com possibilidade de atingir escalas nanométricas, obtendo-se assim as chamadas nanopartículas de celulose ou nanocelulose. Devido à alta cristalinidade, a nanocelulose possui altos valores de módulo elástico, proporcionando alta capacidade de reforço em matrizes poliméricas, combinados com baixo peso, área superficial elevada e biodegradabilidade. A borracha natural é uma matéria-prima de fonte natural, sendo extraída das seringueiras na forma de látex - dispersão coloidal de partículas de borracha e substâncias não-borrachas em um meio aquoso, com aspecto leitoso. No presente trabalho foram estudados compósitos de borracha natural e nanocelulose. Inicialmente, foi realizada uma análise do látex de nacionalidade brasileira, centrifugado, contendo 60% em massa de sólidos. Os resultados de caracterização do látex centrifugado comercial, a qual consistiu na análise de concentração de sólidos totais e na medida do pH, estavam de acordo com os dados apresentados pelo fornecedor. Além disso, a análise de distribuição de tamanho de partícula indicou que o material apresenta uma população, com tamanho médio de 1,0 ?m. A borracha coagulada com ácido acético apresentou, após mastigação em cilindro aberto, viscosidade Mooney e extrato acetônico igual a, respectivamente, 52,8 e 2,57%. As nanoceluloses foram obtidas por hidrólise com ácido ortofosfórico (NC P) e sulfúrico (NC S), sendo classificadas como nanocristal de celulose (NC). NC P apresentaram comprimento médio, razão de aspecto e cristalinidade igual a, respectivamente, 270 ± 89 nm, 50 ± 24 e 78%; e as NC S apresentaram 209 ± 51 nm, 29 ± 10 e 75%.. Os compósitos de borracha natural com nanocristais de celulose apresentaram, nos ensaios de tração, aumentos nos valores de todas as propriedades analisadas, quando comparados à borracha natural pura. Ao adicionar-se 10 phr de nanocelulose preparada com ácido fosfórico na borracha natural, os valores de resistência à tração na ruptura, alongamento na ruptura e módulo a 300% aumentaram, respectivamente, em 90%, 16% e 52%. Já com a adição de 10 phr de NC S, essas propriedades aumentaram, respectivamente, em 68%, 5% e 109%. O mesmo foi observado para a dureza Shore A. Com a adição de 10 phr de nanocelulose obtida por ácido fosfórico à composição da borracha natural, a dureza Shore A aumentou em cerca de 22%; já com a adição de 10 phr de NCs S, a dureza da borracha natural aumentou em 36%. / Among the natural and renewable sources\' materials, cellulose stands out for its abundance, it can be found in many living organisms, such as plants, amoebas, bacteria, fungi and some marine animals. Its dimensions can be reduced by breaking the amorphous chains, with the possibility of reaching nanometric scales, obtaining the nanocellulose or cellulose nanoparticles. Due to the high crystallinity, the nanocellulose has high elastic modulus value, providing high reinforcement capacity combined with low weight, high surface area and biodegradability. Natural rubber is a raw material from a natural source, extracted from the latex - colloidal dispersion of rubber particles and non-rubbers in a milkylooking aqueous solution. At this work, composites of natural rubber and nanocellulose were studied. Initially, a Brazilian centrifuged latex with 60% of its weight in solids was characterized, by analyzing if the total solids concentration and the pH measurement is in agreement with the data presented by the supplier. In addition, particle size distribution analysis demonstrated that the material had an average size of 1.0 ?m. Then, the mastication in the open cylinder and the Mooney viscosity and acetone extract was measured and them were equal to, respectively, 52.8 and 2.57%. The nanocelluloses obtained by hydrolysis with phosphoric and sulfuric acids are classified as cellulose nanocrystal. NC P present average length, aspect ratio and crystallinity equal to 270 ± 89 nm, 50 ± 24 and 78%; and the NC S had 209 ± 51 nm, 29 ± 10 and 75%. In the tensile test, it was observed that there was an increase in all the mechanical properties analyzed for natural rubber when adding the nanocellulose in its composition. By adding 10 phr of prepared nanocellulose with phosphoric acid in the natural rubber the values of tensile strength at rupture, strain at rupture and modulus at 300% increased, respectively, by 90%, 16% and 52%. When added 10 phr of NC S, these properties increased, respectively, by 68%, 5% and 109%. The same was observed for Shore A hardness. When adding 10 phr of nanocellulose obtained by phosphoric acid in its composition, the Shore A hardness increased by about 22%; When adding 10 phr of NCs S, the hardness increased by 36%.

O estudo do comportamento quanto ao desgaste de compostos de borracha utilizados na banda de rodagem de pneus automotivos é um fator determinante para o desenvolvimento de produtos mais duráveis, que se adaptem às condições de severidade de diferentes mercados. Para tanto os formuladores precisam desenvolver compostos em um processo interativo, no qual são alterados os componentes da receita e seus níveis na formulação em função da resposta do produto. A tarefa de avaliar o desgaste do pneu é desafiadora, pois este comportamento pode ser influenciado por muitos fatores, tais quais o pavimento, o veículo, o motorista e condições climáticas. Os testes de pneus com veículos em campo proporcionam uma avaliação do desgaste, mas necessitam por volta de 6 meses para apresentar resultados, além de serem custosas. Equipamentos de laboratório foram desenvolvidos para agilizar a obtenção de dados, mas freqüentemente apresentam severidade muito maior que aquela encontrada em campo. Através de parceria científica e tecnológica entre a Escola Politécnica da USP e a Pirelli Pneus, foi desenvolvido equipamento de laboratório que utiliza como contra-corpo amostras de asfalto retiradas das rodovias, trabalhando sob condições controladas. A primeira parte deste trabalho apresenta que esta máquina de testes é capaz de reproduzir o mecanismo de desgaste encontrado em pneus (ondas de Schallamach), simulando as condições de campo e classificando os diferentes compostos em laboratório de modo semelhante ao obtido nos testes em campo. A parte final deste trabalho apresenta a análise do desgaste de composto de borracha em função de diferentes tipos de pavimentos encontrados em rodovias brasileiras. Em um pavimento em boas condições de conservação (ausência de buracos e irregularidades) a sua microtextura terá influência significativa no desempenho dos compostos de borracha utilizados na banda de rodagem dos pneus automotivos. / The wear behavior of tire tread rubber compounds is a fundamental factor in order to develop durable products, which can deal with the severity conditions of a multitude of markets. The rubber compounders must develop products in an interactive process, in which the ingredients and its levels are changed as a function of the market response The tire wear assessment is challenging because this behavior can be influenced by a multitude of factors, as the pavement, the vehicle, the driver and the weather conditions. Outdoor tests in vehicles provide a wear assessment but are expensive and need around 6 months to present results. Laboratory devices were developed to accelerate the data acquisition but frequently present a severity much higher than outdoor tests. A scientific and technological partnership between Escola Politécnica da USP and Pirelli Tires developed laboratory equipment that uses asphaltic counterfaces extracted from Brazilian roads, working under controlled conditions. The first part of this work presents that this testing machine can reproduce the tire wear mechanism (Schallamach waves), simulating the outdoor conditions and sorting the different rubber compounds in a way similar to the outdoor tests. The last part of this work presents a wear analysis of a rubber compound as a function of different pavements found in Brazilian roads. For a pavement with good integrity (absence of holes and irregularities) its microtexture will significantly influence the performance of vehicle tire tread rubber compounds.

Dentre os materiais de fontes naturais e renováveis, a celulose se destaca pela sua abundância, podendo ser encontrada em diversos organismos vivos, como plantas, amebas, bactérias, fungos e alguns animais marinhos. Suas dimensões podem ser reduzidas por quebra das cadeias amorfas, com possibilidade de atingir escalas nanométricas, obtendo-se assim as chamadas nanopartículas de celulose ou nanocelulose. Devido à alta cristalinidade, a nanocelulose possui altos valores de módulo elástico, proporcionando alta capacidade de reforço em matrizes poliméricas, combinados com baixo peso, área superficial elevada e biodegradabilidade. A borracha natural é uma matéria-prima de fonte natural, sendo extraída das seringueiras na forma de látex - dispersão coloidal de partículas de borracha e substâncias não-borrachas em um meio aquoso, com aspecto leitoso. No presente trabalho foram estudados compósitos de borracha natural e nanocelulose. Inicialmente, foi realizada uma análise do látex de nacionalidade brasileira, centrifugado, contendo 60% em massa de sólidos. Os resultados de caracterização do látex centrifugado comercial, a qual consistiu na análise de concentração de sólidos totais e na medida do pH, estavam de acordo com os dados apresentados pelo fornecedor. Além disso, a análise de distribuição de tamanho de partícula indicou que o material apresenta uma população, com tamanho médio de 1,0 ?m. A borracha coagulada com ácido acético apresentou, após mastigação em cilindro aberto, viscosidade Mooney e extrato acetônico igual a, respectivamente, 52,8 e 2,57%. As nanoceluloses foram obtidas por hidrólise com ácido ortofosfórico (NC P) e sulfúrico (NC S), sendo classificadas como nanocristal de celulose (NC). NC P apresentaram comprimento médio, razão de aspecto e cristalinidade igual a, respectivamente, 270 ± 89 nm, 50 ± 24 e 78%; e as NC S apresentaram 209 ± 51 nm, 29 ± 10 e 75%.. Os compósitos de borracha natural com nanocristais de celulose apresentaram, nos ensaios de tração, aumentos nos valores de todas as propriedades analisadas, quando comparados à borracha natural pura. Ao adicionar-se 10 phr de nanocelulose preparada com ácido fosfórico na borracha natural, os valores de resistência à tração na ruptura, alongamento na ruptura e módulo a 300% aumentaram, respectivamente, em 90%, 16% e 52%. Já com a adição de 10 phr de NC S, essas propriedades aumentaram, respectivamente, em 68%, 5% e 109%. O mesmo foi observado para a dureza Shore A. Com a adição de 10 phr de nanocelulose obtida por ácido fosfórico à composição da borracha natural, a dureza Shore A aumentou em cerca de 22%; já com a adição de 10 phr de NCs S, a dureza da borracha natural aumentou em 36%. / Among the natural and renewable sources\' materials, cellulose stands out for its abundance, it can be found in many living organisms, such as plants, amoebas, bacteria, fungi and some marine animals. Its dimensions can be reduced by breaking the amorphous chains, with the possibility of reaching nanometric scales, obtaining the nanocellulose or cellulose nanoparticles. Due to the high crystallinity, the nanocellulose has high elastic modulus value, providing high reinforcement capacity combined with low weight, high surface area and biodegradability. Natural rubber is a raw material from a natural source, extracted from the latex - colloidal dispersion of rubber particles and non-rubbers in a milkylooking aqueous solution. At this work, composites of natural rubber and nanocellulose were studied. Initially, a Brazilian centrifuged latex with 60% of its weight in solids was characterized, by analyzing if the total solids concentration and the pH measurement is in agreement with the data presented by the supplier. In addition, particle size distribution analysis demonstrated that the material had an average size of 1.0 ?m. Then, the mastication in the open cylinder and the Mooney viscosity and acetone extract was measured and them were equal to, respectively, 52.8 and 2.57%. The nanocelluloses obtained by hydrolysis with phosphoric and sulfuric acids are classified as cellulose nanocrystal. NC P present average length, aspect ratio and crystallinity equal to 270 ± 89 nm, 50 ± 24 and 78%; and the NC S had 209 ± 51 nm, 29 ± 10 and 75%. In the tensile test, it was observed that there was an increase in all the mechanical properties analyzed for natural rubber when adding the nanocellulose in its composition. By adding 10 phr of prepared nanocellulose with phosphoric acid in the natural rubber the values of tensile strength at rupture, strain at rupture and modulus at 300% increased, respectively, by 90%, 16% and 52%. When added 10 phr of NC S, these properties increased, respectively, by 68%, 5% and 109%. The same was observed for Shore A hardness. When adding 10 phr of nanocellulose obtained by phosphoric acid in its composition, the Shore A hardness increased by about 22%; When adding 10 phr of NCs S, the hardness increased by 36%.

Quando a cidade de Corumbá foi fundada no século XVIII demorou muito tempo para encontrar sua vocação econômica. Assim, dentro das referências revisadas para a elaboração deste trabalho desta tese, não houve constatação de uma vocação econômica específica que tenha relevância pelo menos até os 50 primeiros anos do século XIX, só a partir daí, é que a economia corumbaense teve um rumo, quando prevalece o comércio para a extração de excedente e na qual existe uma articulação devido à navegação e a comunicação com os portos principais da Bacia do Prata. Fato diferente ao acontecido com a cidade logo após o conflito bélico. A delimitação temporal estabelecida para este projeto de pesquisa obedece a alguns critérios adotados para sua definição. A delimitação inicial do período, 1870, se justifica em razão do fim da guerra da Tríplice Aliança, evento este que teve uma relevância marcante para esta região do Brasil, porque foi ocupada pelas tropas paraguaias deixando um rastro de destruição e desolação por toda Corumbá, isso ocorreu justamente no momento em que a cidade estava definindo a sua vocação econômica. Já a escolha do ano de 1914 se deve a alguns fatos como a chegada ao Pantanal a estrada de ferro Noroeste do Brasil, que à época se estendia até as margens do Rio Paraguai, a 70 quilômetros de Corumbá. O clima pantaneiro favorece uma adaptação à atividade pecuária, assim a introdução do gado no início do século XVIII, a atividade pecuária encontrou no sul de Mato Grosso as condições climáticas e ecológicas propícias à sua reprodução e proporcionou a fixação da população em torno das grandes fazendas de criação. Desta maneira, a grande parte riqueza desta parte do Mato Grosso foi o gado, base de sua economia no início do povoamento e também foi o fator de articulação da economia incipiente no Pantanal em Corumbá, quando a atividade agrícola ainda era restrita à zona litoral do país. Esta articulação consiste na ligação com outros setores econômicos. Desta forma, o setor primário consiste na própria exploração da atividade pecuária. No setor secundário estavam as charqueadas que, apesar de não apresentarem uma transformação completa da matéria-prima em outro produto, propiciam agregação de valor à carne. E no setor terciário, a distribuição dos produtos que se daria, num primeiro momento, pela via fluvial e mais adiante, pela ferroviária nos principais centros consumidores. Outros produtos passaram pelo porto corumbaense, mas o mais importante foi borracha, ambos comercializados tanto visando o mercado externo, assim como a importação de produtos para toda a região do Mato Grosso. / When the city of Corumba was founded in the 18th century, it took a long time for finding its economic vocation. Thus, among the references herein revised, we found no evidence of a specific and relevant vocation at least until the first 50 years of the 19th century. From that moment on, the corumbaense economy took a direction towards the commerce of the extractions, articulated by the navigation growth and the communication among the main harbors of the Prata river basin, what differs from what happened to the city right after the war. The temporal limits herein established followed some criteria and the starting point of 1870 was chosen for marking the end of the War of Triple Alliance, whose event was strongly relevant for this Brazilian region because the troops occupation of the territories brought together a trail of destruction and desolation all over Corumba city, what happened when the economic vocation was being chosen. The year of 1914 closed the period of research. It coincided with the arrival of the railroad Noroeste do Brasil [Northeast of Brazil], which, at that time, reached the margins of Paraguay river, 70 km away from Corumba. The pantanalian climate favored the adaptation of livestock activity, which dated the beginning of the 18th century, especially in south of the Mato Grosso state, whose climate and ecologic conditions were propitious to reproduction, proportioning the formation of a new villages around the big livestock farms. Thus, the great wealth of this part of the state was based on livestock, which was the basis of the economy during the population settlement and were the main economic factor of the in both Pantanal and Corumba regions in a period which the agriculture was still restricted to the coastal areas of Brazil,whose articulation was bonded to other economic sectors. Thus, the primary sector consisted on the livestock itself. The secondary sector was formed by the charqueadas [area destined to jerk beef maturation] which, although showed no modification on the raw materials, added financial value to the meat. The tertiary sector was the distribution of the products to consume centers, firstly done by waterways and later by railways. Other products were commercialized on corumbaense harbor the most important one was the rubber and their destination were both the foreign market and the importation around Mato Grosso state.

This thesis concerns crack growth phenomena in rubber. It is widely known that a relationship exists between the magnitude of the stored energy release rate available to drive a crack, called the tearing energy (7'), and the resultant crack growth rate. For rubbers this basic relationship is said to be a characteristic of the material. The magnitude of T is related to both the visco-elastic losses and the crack tip diameter (d) However the actual size of d and its relationship with the viscoelastic losses is not clear. This thesis examines the crack growth behaviour in relation to d and the visco-elastic losses for a wide range of rubbers, whose visco-elastic properties are altered either by swelling in a liquid, altering the test temperature or the cross-link density and by the incorporation of fillers. Static, constant T, crack growth tests were carried out. These revealed that two different crack growth processes exist. For the fast crack growth process, T is determined by variations in the visco-elastic losses alone. For the slow crack growth process, T is determined by variations in both the visco-elastic losses and d. It is proposed here that the factors, which alter d, are associated with cavitation ahead of the crack tip for unfilled materials and with strength anisotropy for carbon black filled materials. In cyclic crack growth tests, the crack growth per cycle, dc/dn, can be considered to result from the sum of time and cyclic dependent crack growth components. For the first time, the detailed magnitudes of the contribution of each of these components to dc/dn have been determined, for a wide range of materials and mechanisms responsible for this behaviour are postulated. Also crack growth tests, both static and cyclic, were extended to very large extensions. Lastly this investigation revealed that the tensile strength for both ciystallising and noncrystallising rubber can be predicted using the tearing energy concept for a variety of loading regimes.

Tyres are used in everyday life for a variety of practical and recreational tasks. Frictional behaviour of tyres on any surface is important for vehicle safety and control; this behaviour becomes more important when that surface is snow. The interaction of rubber and a snow surface is complex and a deeper understanding of both is needed in order to help develop better tyres. Outdoor full scale tyre test results were compared to results from indoor laboratory tests using a linear tribometer and a surface of compacted artificial snow; these were in excellent correlation allowing a systematic and comprehensive study of rubber friction on snow to be conducted in the laboratory. Rubber samples of varied rubber compositions and geometries were used to gain an understanding of friction on snow. Samples with varying glass transition temperature (Tg), dynamic rigidity (G*) and Payne effect (dependence of the dynamic moduli on the amplitude of the applied strain) were investigated along with samples with and without sipes. The rubber friction coefficient (μ) was measured as a function of velocity and temperature. The siped samples exhibited a higher μ than those without sipes. FE simulations, rubber friction tests for varying contact pressures and steel blade force tests were performed to evaluate contributions from ‘surface’ friction and ploughing separately. The increased μ was attributed to the ploughing force from the front edges of the ‘subblocks’ created by the sipes. Although it is well known in the industry that siped tyres grip well, this is the first time it has been explained how sipes grip effectively through a combination of ploughing and rubber snow interaction. A comprehensive study of varying rubber properties (Tg, G* and Payne effect) was conducted to better understand their impact on snow friction. The findings were evaluated using the WLF shift factor to account for the running frequency of the rubber from the snow surface roughness. G* was found to be the dominant parameter for rubber μ when considering running frequency. Increased μ values were exhibited by rubbers with a lower G*. The decreased G* makes the rubber more compliant, thus increasing the contact area between the rubber and the snow, in turn increasing μ. A better knowledge of the surface roughness of snow will aid the understanding of the interaction between rubber and snow for tyres. A method was developed to characterise the artificial snow surface utilising sectioning and imaging of chemically stabilised snow samples. From images of the snow surface before friction testing the average indentor size can be found, this is used to analyse the running frequency of the rubber. Qualitatively comparing the surfaces before and after rubber friction testing shows a decrease in surface profile aggressivity after a test; this is attributed to melting of the snow from frictional heating and snow grain fracture. Friction tests were conducted to directly compare rubber friction on snow and ice using round edged samples. Again it was found that the rubber with the decreased G* exhibited higher friction; this was seen on both snow and ice confirming G* as the dominant rubber property for both surfaces, regardless of the surface roughness change. It was found that at low temperatures ice had a higher μ than snow, while at high temperatures snow exhibited a higher μ than ice. It is hypothesised that this intriguing switch is due to the surface roughness change leading to differing contact areas both with and without melt water. This switch is not seen when a simple heat transfer model is used, confirming the effect as a surface roughness change. The use of a modified Hertz model shows that indentation is the dominant mechanism at low velocities on snow. It is hypothesised that at high velocities melt water dominates on both snow and ice while adhesion may have a more significant role on ice at low velocities. These findings provide knowledge that can be used in the design of tyres for snow and ice in the future.

Rubber abrasion is one of the most important properties for rubber products, such as tyres. However, due to its complexity rubber abrasion is still a very challenging topic in rubber research. Rubber abrasion is not governed by a single mechanism. Different mechanisms can dominate the abrasion behaviour depending on the rubber compound, base polymer type, loading severity, contact conditions, testing temperature and chemical environment. This study investigates the different mechanisms for rubber abrasion and the transition between these mechanisms using two types of abrasion apparatus, a blade abrader and a surface abrader, respectively. Blade abrasion was used to generate the abrasion pattern. Once the abrasion pattern was formed on the rubber surface under unidirectional sliding, the underlying mechanism was primarily one of fatigue crack growth, which is referred as "fatigue wear" in the literature. An independent pure shear fatigue test with various loading profiles was conducted to predict the crack growth rate using a fracture mechanics approach during these abrasion tests. The tearing energy during blade abrasion was calculated using a fracture mechanics approach. A Finite Element Analysis (FEA) technique using the Virtual Crack Closure Technique (VCCT) was adopted. The VCCT approach was a simpler, faster and more reliable approach to derive the tearing energy under these complicated large strain contact conditions. The prediction of the abrasion rate using this independent measurement of the crack growth resistance of materials worked best for unfilled SBR material. A bespoke surface contact abrasion machine was used to investigate rubber abrasion on silicon carbide sandpaper under both dry and wet conditions. Depending on the materials, contact conditions and sliding velocity, two different mechanisms were observed. The first being a mechanochemical degradation, during which a sticky layer was generated on the rubber surface. This behaviour is also called "smearing wear". The second failure mode resulted from a purely mechanical fracture named "abrasive wear". It seemed that the carbon black filled rubber was more susceptible to smearing wear than the silica filled one. Higher sliding velocities promoted smearing wear, possibly due to higher temperatures being generated at the interface. Alternatively, water lubrication was seen to promote abrasive wear. Therefore, the abrasion mechanism changed to more rapid abrasive wear under wet conditions, which resulted in a significant increase in the rate of weight loss. Finally, the sticky debris generated during the smearing wear was characterised using various different techniques. This revealed that the sticky debris had more oxygen and lower carbon and sulphur content. It contained a greater amount volatiles and generated more char formation during its degradation in the air. The molecular weight of the sticky debris was much lower when compared to the original uncured rubber. It seemed that in the sticky debris the filler network can slowly recover and the degraded polymer chains can re-absorb back onto filler surface forming "bound rubber", which leads to faster rates of weight loss.

Tyres are highly engineered complex rubber composite products. They are constructed from a wide range of different materials in addition to the rubber. In different parts of the tyre's construction, the rubber elements are expected to perform different functions and as a consequence many different types of rubber are used, each of which will have its own specific detailed compound formulation. These different regions of a tyre's construction are joined together by different types of molecular bonding. This variety of materials introduces potential sources of failure both in the homogenous regions within the tyre's construction but also at the interfaces between them. This thesis investigates the crack growth resistance of the rubber materials used in different regions of a tyre's construction as well as the interfaces that are found between the different parts of the tyre. A fracture mechanics framework was used to investigate the fatigue behaviour of bulk rubber and some of the interfaces. The loading of a tyre is periodic in nature as a consequence of the wheel's rotation therefore the materials were characterised over a range of loading conditions. The effect of cyclical loading frequency on the fatigue behavior of the bulk rubber was also investigated. This work discovered that the amount of crack growth per cycle was comprised from two different crack growth contributions. The first is related to the steady tear which is related to the length of time the load is applied. The second resulted from additional damage caused by the repeated loading and unloading of the material. Potential reasons for this additional crack growth contribution are discussed. The interfacial fatigue properties between adjoining and potentially dissimilar rubber compounds were examined using a fatigue peeling experiment. A novel test piece geometry was developed to evaluate the fatigue properties of interfaces in tyres and it was also used to investigate how different processing parameters such as the pressure at the interface during vulcanisation alter the interfacial strength. A significant effect was observed and this was related to the different phenomena occurring when two rubbery polymers are brought into contact. Finally, a fracture mechanics approach was also used to derive the value of the tearing energy, the variable governing crack growth propagation in the rubber materials found in tyres, using submodelling technique in finite element analysis. The tearing energy values at different locations within a tyre were calculated and are shown not to exceed the minimum energy criteria for crack propagation under normal service conditions.

O estudo do comportamento quanto ao desgaste de compostos de borracha utilizados na banda de rodagem de pneus automotivos é um fator determinante para o desenvolvimento de produtos mais duráveis, que se adaptem às condições de severidade de diferentes mercados. Para tanto os formuladores precisam desenvolver compostos em um processo interativo, no qual são alterados os componentes da receita e seus níveis na formulação em função da resposta do produto. A tarefa de avaliar o desgaste do pneu é desafiadora, pois este comportamento pode ser influenciado por muitos fatores, tais quais o pavimento, o veículo, o motorista e condições climáticas. Os testes de pneus com veículos em campo proporcionam uma avaliação do desgaste, mas necessitam por volta de 6 meses para apresentar resultados, além de serem custosas. Equipamentos de laboratório foram desenvolvidos para agilizar a obtenção de dados, mas freqüentemente apresentam severidade muito maior que aquela encontrada em campo. Através de parceria científica e tecnológica entre a Escola Politécnica da USP e a Pirelli Pneus, foi desenvolvido equipamento de laboratório que utiliza como contra-corpo amostras de asfalto retiradas das rodovias, trabalhando sob condições controladas. A primeira parte deste trabalho apresenta que esta máquina de testes é capaz de reproduzir o mecanismo de desgaste encontrado em pneus (ondas de Schallamach), simulando as condições de campo e classificando os diferentes compostos em laboratório de modo semelhante ao obtido nos testes em campo. A parte final deste trabalho apresenta a análise do desgaste de composto de borracha em função de diferentes tipos de pavimentos encontrados em rodovias brasileiras. Em um pavimento em boas condições de conservação (ausência de buracos e irregularidades) a sua microtextura terá influência significativa no desempenho dos compostos de borracha utilizados na banda de rodagem dos pneus automotivos. / The wear behavior of tire tread rubber compounds is a fundamental factor in order to develop durable products, which can deal with the severity conditions of a multitude of markets. The rubber compounders must develop products in an interactive process, in which the ingredients and its levels are changed as a function of the market response The tire wear assessment is challenging because this behavior can be influenced by a multitude of factors, as the pavement, the vehicle, the driver and the weather conditions. Outdoor tests in vehicles provide a wear assessment but are expensive and need around 6 months to present results. Laboratory devices were developed to accelerate the data acquisition but frequently present a severity much higher than outdoor tests. A scientific and technological partnership between Escola Politécnica da USP and Pirelli Tires developed laboratory equipment that uses asphaltic counterfaces extracted from Brazilian roads, working under controlled conditions. The first part of this work presents that this testing machine can reproduce the tire wear mechanism (Schallamach waves), simulating the outdoor conditions and sorting the different rubber compounds in a way similar to the outdoor tests. The last part of this work presents a wear analysis of a rubber compound as a function of different pavements found in Brazilian roads. For a pavement with good integrity (absence of holes and irregularities) its microtexture will significantly influence the performance of vehicle tire tread rubber compounds.