No description available.

The allylic bromide functionality within brominated poly(isobutylene-co-isoprene), or BIIR, is amenable to substitution by a wide range of nucleophiles. The objective of this work was to gain insight into the dynamics of these substitution reactions, and to develop methods for accelerating these processes. Of particular interest was the reactivity of exomethylene (Exo-Br) and bromomethyl (BrMe) isomers found within BIIR toward various nucleophiles, and catalytic techniques for affecting the proportion of these isomers. BIIR isomerization can be catalyzed through ionic chemistry involving soluble Lewis acids such as zinc stearate and through a nucleophilic SN2’ rearrangement with soluble bromide salts such as tetrabuylammonium bromide (TBAB). The compatibility of TBAB with other nucleophiles makes it a preferable choice, but further rate enhancements can be realized using the corresponding iodide salt (TBAI). TBAI serves not only as nucleophilic isomerization catalyst, but also accelerates halide displacement from BIIR by an in-situ formation of an allylic iodide intermediate. Studies of BIIR isomerization and substitution reactions involved solvent-borne reactions of tetrabutylammonium acetate (TBAAc) and solvent-free reactions with PPh3 and 2-[2-(dimethylaminoethoxy)ethanol]. In all cases, the BrMe isomers were more reactive to nucleophilic substitution than Exo-Br. Since the esterification of BIIR with TBAAc generates TBAB as a reaction by-product, displaced bromide catalyzes the isomerization of Exo-Br to the more reactive BrMe isomers. As a result, these esterifications exhibit auto-accelerating dynamics. Similar behaviour is observed for solvent-fee alkylations of PPh3 and tertiary amines, since the resulting onium bromide salts are effective isomerization catalysts. All reactions show some increase in rate with the addition of TBAI, supporting the concept of nucleophilic catalysis. / Thesis (Master, Chemical Engineering) -- Queen's University, 2009-09-28 09:50:26.649

The allylic bromide functionality in brominated poly(isoprene-co-isobutylene) rubber (BIIR) reacted readily to nucleophilic substitution by imidazole-derivatives. When reacted with the rubber, alkylimidazoles formed a stable non-thermoset ionomeric elastomer that has dynamic mechanical properties similar to those of vulcanizates; however, the strength is in its ion-pair aggregation. Structural characterization of the polymeric products was accomplished by spectroscopy with comparisons to the model compound prepared from brominated 2,2,4,8,8-pentamethyl-4-nonene (BPMN). Physical properties tests on the elastomers of varying ionic content (0-1 mol%) were done using solution viscosity and rheology, and demonstrated that small amounts of ionic functionality noticeably improved properties with a plateau of properties being attained as full conversion to ionic content was reached. The reaction of imidazole with BIIR created a thermoset elastomer that formed an ionomer and thermoset after its second alkylation. These materials provided excellent scorch protection and delayed curing at high temperatures, while still reaching good storage modulus. Formation of an elastomer with a pendant imidazole group was also achieved; however, it did not perform as well as the free imidazole. / Thesis (Master, Chemical Engineering) -- Queen's University, 2010-10-27 11:52:54.442

No description available.

Despite real applications having complex triaxial loading, current physical test methods to predict component behaviour are mainly uniaxial. But previous work has indicated that there may be substantial differences between the rubber's uniaxial and biaxial behaviour and hence through incompressibility, its triaxial properties. In order to quantify these differences equipment was developed to assess the biaxial performance of selected rubber compounds using inflated circular diaphragms. Although allowing higher extensions than stretching a sheet in its own plane, such tests do not allow stress and strain to be measured directly, requiring careful marking of the sample, or calculation through simulation. On the grounds of perceived accuracy, the latter was chosen, requiring accurate, general, elastic constants to high extensions. In this thesis the development of this apparatus, along with the associated techniques is described, along with the development of a new elastic theory. The tests on this new apparatus indicated significant differences between the uniaxial and biaxial strength and fatigue of rubber. In a unimdal test natural rubber (NR) is much stronger than styrene butadiene rubber (SBR) below 35pphr of carbon black. In a biaxial test though the converse is true, although there is some evidence of crystallinity in NR during the biaxial test. Distinct differences were also found in fatigue between the two load cases. When plotted against extension ratio the biaxial life of SBR was found to increase, while the converse is true for NR. However if life is plotted against a function of strain energy, the biaxial life of both polymers increases for a given energy.

Styrene-butadiene rubber (SBR) copolymer nanosized latex particles were synthesized via differential microemulsion polymerization (DMP) in a 300ml bench-scale semi-batch reactor, equipped with a thermocouple and a magnetic four-blade stirrer. This approach employed a continuous and slow addition of styrene and butadiene monomers drop-wise into a continuous aqueous phase comprising DI water, an initiator, a surfactant and a chain transfer agent. It was found that this approach offered an efficient heterogeneous phase path to synthesize styrene-butadiene copolymer latices with a high-butadiene-level of the resulting latex particles. The latex nanoparticles were formed as the SBR copolymer monomers undergo a self-assembly process in the continuous phase and were stabilized by their surrounding surfactant particles. The size of the latex particles could be easily adjusted by alternating the monomer addition speed, the reaction temperature, the amount of chain transfer agent applied and the type and the amount of surfactant introduced in the process. Not surprisingly, a small amount of chain transfer agent introduced into the DMP system might facilitate micellar nucleation and reduction of gel content in the polymer dramatically and may also aid increasing the size of the SBR latex particles. Owing to the small size of SBR latices prepared by the DMP method, the glass transition temperature (Tg) of the latices is much lower than the SBR latices generated by conventional technique. Furthermore, the increase of Tg was observed with an increase of the SBR particle size.

Pervaporation separation of aqueous ethanol solution has, for the first time ever, been investigated with natural rubber latex (NRL) base membranes which contained a hydrocolloid as a blend ingredient. Three different hydrocolloids viz. methyl cellulose, carboxy methyl cellulose (sodium salt) and alginic acid (sodium salt) of low or medium or high molecular mass were used and tested. The weight percent of a hydrocolloid in the blended layer of a membrane has been varied from 1.25 to 20 on a dry rubber basis. The composition of ethanol in the aqueous feed solution was varied within the range of 5 to 96 weight percent of ethanol. The temperature of operation was fixed in the range of 20 °C to 75°C. Fourier Transform Infrared / Attenuated Total Reflectance (FT-IR/ ATR) spectra and Scanning Electron (SE) micrographs have been used to study the distribution of hydrocolloids within the membrane. Morphological features of the cross section of a blended layer have been used to develop a probable mechanism of water transfer through the membrane. Water selectivity has been found to depend on the type, the molecular mass and the weight percent of the hydrocolloid used in the membrane. Both FT-IR/ATR and SEM techniques have proved that a high molecular mass hydrocolloid distributes itself uniformly throughout the membrane. Both techniques have, independently, shown that a low molecular mass hydrocolloid will be situated at or near the top surface of the membrane. A very strong link between a good distribution of the polymer bridged clusters of rubber particles within the membrane and the maximum increase in water selectivity has been established. For the first time ever, artificial neural networks have been used for the modelling and prediction of the pervaporation separation performance of NRL base membranes. Quantitative data about the distribution of hydrocolloids within the membranes was needed in order to train the neural net models. The correlation coefficients and rms errors between the predicted and experimental results were found to be greater than 0.89 and less than 0.086 respectively.

No description available.

The work is divisible into three interconnected areas, the first of which is concerned with the empirical modelling of the rubber internal mixing process. Here, the mixing machine variables were changed in a statistical experimental design, and several resulting dispersion dependent material responses monitored. The values of these were next combined into a composite function which related to the goodness of mixing. A response equation in terms of this function and the process variables was obtained by regression analysis. Other response equations derived were for relating mixing time and dumped stock temperature to the input variables. These graduating functions were tested for adequacy of fit; graphical representations of the predictions of the models are shown in the form of contour graphs and isometric projections (both hard copy and colour graphics). These show visual evidence of the influence of each machine variable (and interaction) on the mixing process as a whole. Also by these means, it was possible to establish optimum conditions of mixing. Next nominally identical carbon blacks from different manufacturing locations were mixed into rubber at defined processing conditions. From tests on these mixes the blacks were noted to have different dispersibilities. This was possibly attributable to the varying fines fractions and moisture contents in the test carbon blacks. To check this hypothesis, these factors were varied systematically in two common black types. The compounds resulting from mixing these experimental blacks were subjected to a wide range of tests to establish whether fines or moisture significantly affected dispersibility of blacks in rubbers. Ouring the preceding work, and also in the course of a critical review included here, it became evident that the commonly used methods for establishing dispersion (and thus mixing efficiency) were lacking, from several points of view. Therefore lastly a technique based on the analysis of an image of a cut rubber surface viewed by dark field reflected light microscopy was developed. Specimen preparation is simple and analysis is accomplished using a standard television system and oscilloscope. This method yields results which discriminate between all levels of black dispersion and also correlate admirably with a variety of processing, mechanical and microscopical properties. In the final stages of the work the capabilities of the method were expanded (in cooperation with Dunlop Ltd, Technology Division) by interfacing a computer and peripherals with the original equipment; such that data acquisition, manipulation and parameter output was made easier, faster and thus more effective than in the initial concept.

Tyre inner tubes made of butyl rubber have been found to have poor heat resistance when used in the environment of Iraq. Research investigations were undertaken to establish the causes of the problem: these consisted of examining the individual contributions of oxidative scission processes in both rubber hydrocarbon and the various processing oils. The principal method used to monitor the degradation processes was ageing in hot air using the reduction in strength for the rubber and change in chemical composition of the processing oils. This preliminary study established that the processing oil made in Iraq was found to be of different composition from the common European rubber processing oils and contributed considerably to the poor life of the butyl inner tubes. Analysis of the oil from Iraq identified the presence of trace amounts of copper (3 ppm) known, from the literature, to adversely affect the resistance of many rubbers to elevated temperatures and, as found in this work, to also degrade butyl rubber. Replacement of the butyl rubber by chlorobutyl rubber overcame the problem of inner tube degradation and an antioxidant system based on a combination of an acetone/diphenylamine (ADPA) plus mercaptobenzimidazole (MBI) with MgO was found effective in minimising chlorobutyl inner tube degradation. However, unexpectedly, the research also established that trace quantities of copper were useful as stabilisers in enhancing the heat ageing properties of chlorobutyl rubber and the addition of a particular copper salt (copper sulphatel in small proportions (3 ppm) as an anti-degradant was found beneficial. Another method studied to improve the resistance of halogenated butyl rubber to heat induced oxidative degradation tried to use ZnO as the curative, as recommended by the manufacturers of chlorobutyl rubber; however it was found that with this technique higher degradation was obtained in chlorobutyl than with the standard ZnO/ sulphurless curing system (i.e. ZnO/TMTDin proportions 5:1 phr). It was concluded from these studies that: 1. Reducing the oil level in butyl inner tubes from 25 phr to 15 phr enhances heat ageing properties of the rubber. Factory trials confirmed this finding. 2. Adding a copper inhibitor (ZDC) in the proportions 1-2 phr in butyl inner tubes was found successful in minimising oxidative degradation. 3. The existence of elemental copper in a chlorobutyl inner tube rubber formulation in the proportion 3 ppm improved the rubber properties at elevated temperatures.