No description available.

Diimide generated from the hydrazine/hydrogen peroxide/catalyst system can be used to hydrogenate unsaturated polymers in latex form. As an economical and environmentally benign alternative to the commercial processes based on hydrogen/transition metal catalysts, this method is of special interest to industry. This thesis provides a detailed description of the diimide hydrogenation process. Reaction kinetics, catalysts and gel formation mechanism have been investigated. <br /> <br /> Four main reactions and a mass transfer process form three parallel processes in this system: diimide is generated at the interface of the latex particles; diimide diffuses into the organic phase to saturate carbon-carbon double bonds; diimide may be consumed at the interface by hydrogen peroxide, and may also be consumed by the disproportionation reaction in the organic phase. The two side reactions contribute to the low hydrogenation efficiency of hydrogen peroxide. Slowing down hydrogen peroxide addition and using stable interfacial catalysts may totally suppress the side reaction in the aqueous phase. The actual catalytic activity of metal ions in the latex depends on the hydrogen peroxide concentration and the addition procedure of reactants. Cupric ion provides better selectivity for hydrogenation than ferric ion and silver ion do. Boric acid as a promoter provides improved selectivity for hydrogenation and faster diimide generation rate. The side reaction in the rubber phase results in low efficiency and gel formation. The rate constants of the four reactions in this system are estimated. <br /> <br />It is shown that the hydrogenation of nitrile rubber latex with an average particle diameter of 72 nm is mainly a reaction-controlled process. Diimide diffusion presents limitation upon hydrogenation at high hydrogenation degree range. Antioxidants can not effectively inhibit gel formation during hydrogenation. Hydrogenation of a core-shell latex with NBR as the shell layer should be able to achieve a higher efficiency, a higher degree of hydrogenation and a lower level of crosslinking.

A pre-damage method was developed to determine whether rubber particle cavitation is responsible for craze initiation, or vice versa. Tensile tests were carried out on pre-strained high impact polystyrene (HIPS) specimens which had been annealed above 100 °C to heal any crazes formed in the PS matrix during pre-straining. Moderate prestraining followed by annealing was found to reduce the yield stress of the HIPS, but not the post-yield flow stress. These observations are related to cavitation for the rubber particles, which results in a fibrillar structure within the rubber membranes of a typical "Salami' particle. The reduction in yield stress provides evidence for primary chain scission in the rubber phase during yielding: on subsequent loading of the annealed tensile bar, the rubber particle exhibits a reduced resistance to cavitation because less energy is required to form a void. It was found in the follow-up pre-straining tests on HIPS blends and at different testing temperatures that the critical pre-strain is a function of rubber content and temperature. Comparable effects are seen in creep tests. Small levels of pre-straining have little effect if the specimen is not annealed before reloading. The TEM work also confirms rubber particle cavitation as a rate-determining step in the deformation of HIPS and supports the view that cavitation precedes crazing. A modified cavitation model is proposed to account for the deformation of a cavitated particle under tension. The predictions of this model agree with the experiments that the resistance of the particle is weakened by cavitation and crazes could initiate at the lower tension. The technique of pre-straining and annealing specimens, before submitting them to conventional tensile tests, provides valuable insight into the mechanisms and kinetics of toughening.

No description available.

Thin films of the fullerenes PC60BM and PC70BM and the non-fullerene N2200, three popular electron acceptor materials in organic photovoltaics, have been studied, using both the Kelvin probe method as well as ultraviolet photoelectron spectroscopy. With these methods the work function was measured, as well as the highest occupied molecular orbital (HOMO) onset. Additionally band bending effects were studied by illuminating the samples while measuring the work function with the Kelvin probe so called surface photovoltage. Sample of each material was exposed to either air and simulated sunlight or N2 and simulated sunlight, for different length of time, to observe how the materials work function evolves after exposure to the different conditions. It was observed that, as expected from previous studies, that PC60BM was less photo-stable than PC70BM. Additionally, the work function of PC60BM changed significantly by storage in N2. Each material after exposure for 24h to air and light, was annealed and measured with the Kelvin probe. A restoring effect was observed,  for the non-fullerene material N2200. All three materials developed an increasing surface photovoltage, which suggest increased band bending, when exposed to air and light, indicating that due phot-oxidization, charges are redistributed at the surface of the film. The fullerenes showed a larger surface photovoltage effect than the non-fullerene materials. A difference between the work function values obtained from the Kelvin probe method and the ultraviolet photoelectron spectroscopy could be seen, however the exact reason for this couldn't be isolated within this thesis, but was discussed.

Um problema importante na heveicultura é o seu longo período de imaturidade. A explotação precoce pode reduzi-lo, porém, o seu efeito a longo prazo não é bem conhecido. O objetivo do presente estudo foi de investigar a factibilidade da explotação precoce da seringueira e avaliar diferentes sistemas de explotação. Foram explotadas árvores com perímetro do tronco entre 36 e 41 cm e sua produção e crescimento comparados com daqueles em plantas sem explotação. Quando todas as plantas do experimento atingiram perímetro de tronco de aproximadamente 45 cm, foram explotadas pelo sistema convencional 1/2S d/3 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y. O delineamento experimental adotado foi inteiramente casualizado, com uma planta por parcela. O experimento 1 foi conduzido em Nhandeara-SP, com 25 repectições por tratamento, durante 17 meses de explotação precoce e três anos de explotação convencional. Os sistemas de explotação precoce foram: tratamento 1, 1/4S d/3 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, sangria matinal; tratamento 2, 1/2S d/7 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, sangria matinal; tratamento 3, 1/2S d/7 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, sangria vespertina; tratamento 4 6PI 70x1 d/2 6d/7 10m/y ET 5% Ga 1/1 10/y, sangria matinal. No experimento 2, conduzido em Rio Claro-SP, com 20 repetições, durante um ano de explotação precoce e um ano de convencional, repetiu-se o tratamento 1. As produções obtidas no experimento 1, na fase de explotação precoce, foram similares entre os tratamentos 1, 2 e 4, com aproximadamente 1,2 kg de borracha por árvore, porém significativamente menor no tratamento 3, com aproximadamente 0,9 kg por árvore. Durante o mesmo período as produções em g por árvore por sangria foram maiores no tratamento 2 (22,6 g) e 3 (18,82 g), do que no tratamento 1 (14,41 g) e 4 (8,97 g), diminuindo com o aumento da frequencia de sangria. A produção acumulada, nos 4,5 anos de explotação precoce e convencional, foi maior no tratamento 1 (7,92 kg) do que no controle (5,95 kg). Os outros tratamentos de explotação precoce tiveram um resultado intermediário. O incremento do perímetro do tronco durante a fase precoce foi significativamente menor nos tratamentos 3 e 4, em comparação com os outros tratamentos e o controle. Entretanto, durante a fase convencional, o incremento de perímetro de tronco de todos os tratamentos foi comparável ao do controle. O índice de colheita teve valores similares em todos os sistemas de explotação precoce, porém o tratamento 1 resultou em um valor para o \"fator de perda de biomassa\" (k) muito menor do que o dos outros tratamentos (entre 0,109 e 0,1794). No experimento 2, a produção obtida durante a explotação precoce foi de aproximadamente 0,85 kg por árvore. Durante o mesmo período, a produção por árvore por corte foi de 13,31 g e comparável com aquela do experimento 1. As produções obtidas durante o primeiro ano de explotação convencional no tratamento 1 (1,52 kg) e no controle (1,15 kg) foram bastante similares àquelas dos mesmos tratamentos no experimento 1, respectivamente, 1,53 kg e 1,08 kg. Durante as fases precoce e convencional, o incremento de perímetro de tronco foi igual no tratamento 1 e no controle. O coeficiente de colheita no tratamento 1 foi similar àquele observado no experimento 1, enquanto que o \"fator de perda de biomassa\" (k) foi maior. As principais conclusões foram: 1. O sistema de explotação precoce do tratamento 1 possibilita uma produção prévia de borracha, a níveis satisfatórios, mantendo um crescimento adequado das plantas. Pela sua capacidade, em ambientes diferentes, de produção precoce sem prejuízo permanente para as plantas, pode ser recomendado para uso em seringais comerciais. 2. Os sistemas de explotação precoce dos tratamentos 2, 3 e 4 possibilitam uma produção prévia de borracha, a níveis satisfatórios, porém reduzem o crescimento das plantas. / One major problem of rubber cultivation is the long immature period. Premature exploitation may reduce it, however, its long term effects are not fully understood. The aim of this study was to investigate the feasibility of premature exploitation of rubber, and evaluate different exploitation systems. Trees of about 36 to 41 cm of girth were tapped with premature exploitation systems, and their yield and growth were compared to untapped control trees. When all experimental trees reached approximately 45 cm of girth, they were converted to conventional tapping 1/2S d/3 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y. The experiments were arranged in a complete randomized design, with one tree per plot. Experiment 1 was carried out in Nhandeara-SP, with 25 replications for each treatment, during 17 months of premature and three years of conventional exploitation. The premature systems included: treatment 1, 1/4S d/3 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, morning tapping; treatment 2, 1/2S d/7 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, morning tapping; treatment 3, 1/2S d/7 6d/7 10m/y ET 2.5% La/Pa 1/1 5/y, afternoon tapping; treatment 4 6PI 70x1 d/2 6d/7 10m/y ET 5% Ga 1/1 10/y, morning tapping. In experiment 2, carried out in Rio Claro-SP, with 20 replications, during one year of premature and one year of conventional tapping, treatment 1 was repeated. In experiment 1, yield obtained during premature exploitation, was similar between treatment 1, 2 and 4, with about 1.2 kg of rubber per tree, but significantly lower in treatment 3 with approximately 0.9 kg per tree. During the same period, yield in terms of g per tree per tapping, was higher in treatment 2 (22.6 g) and 3 (18.82 g), than in treatment 1 (14.41 g) and 4 (8.97 g), declining with increased tapping frequency. Cumulative yield obtained over 4,5 years of premature and conventional exploitation was higher in treatment 1 (7.92 kg) than in the control (5.95 kg). The other treatments with premature exploitation had an intermediate result. The girth increment during premature phase was significantly lower in treatment 3 and 4, compared to other treatments and control. However, during the conventional phase, girth increment of all treatments was comparable to the control. Harvest index values were similar in all premature exploitation systems, but treatment 1 resulted in a much lower value (0.019) for the \'factor of biomass loss\' (k) than the other treatments (0.109 to 0.1794). In experiment 2, yield obtained during premature exploitation in treatment 1 was approximately 0.85 kg per tree. During the same period, yield per tree per tapping was 13.31 g thus comparable to that in experiment 1. Yields obtained during the first year of conventional exploitation in treatment 1 (1.52 kg) and in control (1.15 kg) were very similar to the yields in those treatments in experiment 1, respectively 1.53 kg and 1.08 kg. During premature and conventional phases girth increment was equal in treatment 1 and control. Harvest index in treatment 1 was similar to that in experiment 1, whereas the \'factor of biomass loss\' (k) was higher (0.098). The main conclusions were: 1. The premature exploitation system of treatment 1 gives a reasonable yield and maintains appropriate tree growth. Because its capacity, in different environments, to antecipate yield without permanent damage to the trees, this system may be recommended for use in commercial rubber plantations. 2. The premature exploitation systems of treatments 2, 3 and 4 give reasonable yield, but cause growth retardation.

Orientador: Adriano Wagner Ballarin / Coorientador: Magali Leonel / Banca: Hernando Alfonso Lara Palma / Banca: José Nivaldo Garcia / Banca: Thais Paes Rodrigues dos Santos / Banca: Ana Paula Cerino Coutinho / Resumo: O amido é o principal carboidrato de reserva das plantas, composto por dois tipos de α-glucanas, amilose e amilopectina, e tem um importante papel no metabolismo das árvores, incluindo sua importância para estudos de resposta das plantas à diferentes situações durante seu ciclo fenológico e como uma ferramenta complementar para predição do desempenho de sistemas de sangria nas seringueiras, assim como a associação de seu acúmulo com o crescimento e com a rebrota. Este constituinte é encontrado em grande quantidade na madeira de H. brasiliensis. Contudo, a quantificação de amido em madeira ainda é considerada problemática por diversas razões que vão desde a escolha até a implementação de um método adequado, apesar da grande quantidade de estudos encontrados na literatura. Considerando a importância deste carboidrato nas plantas e a problemática envolvida na escolha de um método de quantificação adequado para madeira, quantificou-se o teor de amido em amostras provenientes da direção radial (sentido medula ‒ casca) em discos de H. brasiliensis por dois protocolos diferentes, buscando, entre as técnicas convencionais de hidrólise (ácida e enzimática), qual é a mais apropriada para esta espécie e sugerir um protocolo de quantificação de amido viável à empresas produtoras de seringueira, caso queiram utilizar a quantificação de amido num processo de controle de qualidade da espécie, e à laboratórios de pesquisa com madeiras. Também analisou-se a distribuição radial de amido em amo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Starch is the principal carbohydrate reserve in plants, represented by two types of α-glucans, amylose and amylopectin and has a significant role in tree metabolism including its importance for studies of plant response to different situations during its phenological cycle and as a complementary tool to predict the performance of tapping systems in rubberwood, as well as the association of its accumulation to rebudding and growth. This constituent is found in great content in the wood of H. brasiliensis. However, the starch analysis is still problematic despite of the large amount of studies found in the literature. Considering these key factors, the starch content was quantified in samples from the radial direction (pith - bark) of H. brasiliensis disks by two different protocols, seeking, among the existing conventional hydrolysis techniques (acid and enzymatic), which is the most appropriate for that species and to suggest a protocol for starch quantification that can be viable to the rubberwood producing companies in a quality control process of the species and to research laboratories that works with wood characterization. It was also analyzed the radial distribution of starch content of H. brasiliensis samples collected in two different seasons of the year and two different growth site and additionally, it was estimated the sapwood longevity of this species by microscopic analyzes. For the methodological study, we analyzed five radial samples from disks of fifteen trees by two different protocols. The protocol 1 used acid to hydrolyze the starch and anthone method for glucose assay and protocol 2 used enzymes to hydrolyze the starch and peroxidase-glucose oxidade (PGO) and o-dianisidine for glucose assay. To analyze the radial distribution of starch content in different seasons and different growth sites it was used the protocol 2 (enzymatic hydrolysis) in five radial samples from disks ... / Doutor

Several aspects of the stress-strain behaviour of rubber, important for evaluating its properties for finite element analysis and engineering applications, are investigated. Measurements of the deformation behaviour of an elastomer containing a compressible filler are used to assess theoretical equations for the compression modulus of rubber pads bonded to rigid endplates. The volume fraction of filler is estimated from a simple model. The first cycle stress-strain behaviour of filled and unfilled rubbers is characterised from uniaxial tests and by measuring both non-zero principal stresses with a novel pure shear technique. Various theoretical forms for the strain energy density function are assessed. The results support the assumption that the strain energy of filled natural rubber is a function only of the first strain invariant. Finite element modelling of the behaviour of a hyperelastic material in simple shear reveals that the proximity of the free edges in conventional simple shear testpieces strongly influences the stresses and deflections in the thickness direction. These finding are qualitatively supported by experiment. The effect of free edges on the shear modulus is also assessed. Deviations from hyperelastic behaviour are investigated through experimental studies of stress relaxation, cyclic stress softening and the superposition of a torsion on a uniaxial extension. Anisotropic deformations can result in corresponding differences in the amounts of stress relaxation or stress softening in different directions. Isotropic models cannot model these features but may be adequate for most practical applications. The relationship between the modulus and crystallinity of partially crystalline rubber is determined experimentally. The reinforcing effect of the crystals is found to be approximately independent of their morphology and of the modulus of the amorphous rubber. Studies of yielding of partially crystalline rubber show that the yield stress increases with increasing amounts of crystallization whereas the yield strain remains roughly constant.

The frictional behaviour of rubber is a topic of great interest and importance due to the invaluable uses of rubber in industry. The very particular behaviour of rubber also makes rubber friction a fascinating subject matter. Despite this it is still a topic not well understood. Previous studies have attempted to link the fracture mechanics of rubber crack propagation to the adhesive friction of rubber. The feasibility of such an approach to the adhesive friction of a rough rubber against a smooth surface, a configuration which can occur in various situations such as rubber seals or windscreen wipers, has been investigated. Rolling friction, described well by a fracture-like peeling process, is used to evaluate the viscoelastic dependence of sliding friction for various combinations of surfaces. A novel use of rubber is proposed as a material for particles to be used for jamming based soft robotics applications. This area of soft robotics is comparatively new and the materials that are being used at present are neither well established nor have been examined in great detail. Rubber would offer a material easily manufactured to desired shapes and dimensions with a wide range of moduli allowing modification to suit specific applications. The effect of jammed rubber particles on the response of a jammed packing to an externally applied load is examined. The evolution of inter-particle forces is studied using a rheometer configuration. Finite element techniques and modelling are employed to study the rubber in more detail.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Jaime Kanarek Kornfeld. / M.S.