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No description available.

The project involved the production of, conductive polyanilines and their blending with elastomers to make new conducting' rubbers. Conductive elastomers already have commercial applications such as antistatic coatings, artificial muscles, sensors and electromagnetic screening. These have been based on carbon black or metal fillers, or more recently conducting polymer powders incorporated into natural or synthetic rubbers. A number of polyaniline-rubber blends have been reported in the literature. A key aim of this project was to improve the compatibility, mechanical, thermal stability and electrical properties of this type of blend through different mixing methods such as solution and thermo-mechanical with more systematic mixing procedures and better optimised mixing conditions. The first part of the work was to optimise the synthesis of conducting polyanilines (P Ani), polyanisidines (poAnis), and copolymers of the latter two, in the presence of a variety of protonating agents under a range of conditions, in order to study the influence of the synthetic conditions on the physical, chemical and morphological characteristics of the polymers. PAnilPoAnis products were prepared via solution polymerisation (simple oxidation at low pH) or via emulsion polymerisation using sulfonic acids (surfactants). Syntheses yielded the emeraldine salts (ES), which were either kept as such, or deprotonated using ammonia solution. There were noticeable differences in the behaviour of the two families of polymers. P Anis display better conductivity and a higher thermal stability than PoAnis due to their less hindered structure. These differences in physical characteristics tend to fade when the compounds are synthesised using a protonic surfactant such as dodecylbenzenesulfonic acid (DBSA). Here, the surfactant-induced order of the final polymeric particles becomes dominant over that of the pendant methoxy-group of PoAnis. Scanning electron microscopy (SEM) revealed the strong influence of the protonic acid used for the synthesis onthe shapes of the final particles. Hence, P Ani-DB SA has a monoclinic appearance and rhombic shape particles while P Ani-ß-naphthalenesulfonic acid (ß-NSA) has a "flakey" morphology. It was shown that a very small quantity of co-monomer could change drastically the physical characteristics of P Ani; hence, when anisidine (Anis) is added to the aniline-acid complex, a different crystalline structure is achieved. The chosen polymer (P Ani-DB SA) was matched with two individual elastomers, one based on an ethylene oxide co-polymer and the other on a nitrile butadiene co-polymer, both of which had suitable solubility parameters. The polymers were solution-blended and studied for compatibility by means of microscopy, electrical conductivity measurements and thermal analysis. Blends of poly (epichlorohydrin-co-ethylene oxide) rubber (Zeon Hydrin" C2000L) and polyaniline doped with dodecylbenzenesulfonic acid (P Ani-DB SA), containing different weight fractions of P Ani, were cast from solution. Solubility parameters for both P Ani¬DBSA and Hydrin® were calculated and found to be comparable, favouring some degree of miscibility. Conductive transparent films were formed by casting onto PTFE substrates. Conductivities of the cast films were found to be in the region of 10-7 Scm" for 1 wt% P Ani¬DBSA. Electrical conductivities increased with the proportion of P Ani-DB SA, showing a percolation threshold as low as I wt%, with highest conductivity achieved at, 50wt%. Decomposition steps of conductive blends were investigated using thermogravimetric analysis (TOA) and differential scanning calorimetry (DSC). The thermal stability of the blends was influenced by the ratio ofPAni-DBSA to Hydrin'". The effect of composition on the glass transition in the blends was determined using thermomechanical analysis (TMA). Thin films of the blends of dodecylbenzenesulfonic acid (DB SA) doped polyaniline (P Ani) and pure grade of Poly[(acrylonitrile-co-butadiene)/poly vinylchloride] (Zeon Nipol® DN171) were prepared via co-dissolution, at varying ratios of conducting filler (0.5-50)wt %. The electrical conductivity correlated with the concentration ofP Ani-DB SA. At a percolation threshold ofO.9% (wt/wt), an increase in electrical conductivity of approximately eight orders of magnitude was observed, with a recorded conductivity of 1.21xlO-4 S.cm-1 for the most conductive blend (consisting of 50wt% PAni). Characterisation by UV-visible spectroscopy indicated the retention of the doped state of the conductive P Ani-DB SA in each elastomer blend. Morphological studies by optical microscopy, showed the presence of P Ani-DB SA agglomerate networks (or interpenetrating networks) at higher concentrations; however, at lower concentrations of P Ani-DB SA, the dispersion and encapsulation of the conductive species was observed. Due to the double phase morphology of Nipol® DN 171, the encapsulating phenomenon was attributed to the presence of the thermoplastic (poly vinylchloride). Solubility parameter calculations confirmed the compatibility ofP Ani-DB SA with the constituents of the Nípol" DN171 elastomer. This was supported by the infrared spectrum, which shows the presence of functional groups specific to the reacting components of each blend. Thermal studies, performed by DSC and TOA, indicated an increased thermal stability with increasing concentration of the elastomer.

In rubber product manufacturing the processability of a compound is highly dependent upon the internal mixing operation. The mixer operating variables and the ingredients of the compound influence strongly the quality of the compound coming out from the mixer. In this study, which is based on a natural rubber compound, a total of eight variables, comprising five mixer variables and three material variables were changed systematically using a statistical experimental design technique; and the resulting rheological properties and carbon black dispersion levels of the mixed batches were evaluated. A prototype variable speed rotational viscometer known, as the TMS rheometer, was used in investigating the flow properties and wall slip behaviour of the rubber compounds. Rheological characterization of these compounds was based on the power-law dashpot Maxwell mechanical model. In addition, dark field reflected light microscopy (DFRLM) system was utilised in determining the carbon black dispersion level of the compounds. A second order polynomial function was used to model the relationship between the measured properties of the rubber mixes and the independent variables. A statistical computer package performed curvilinear regression analysis for such a multivariable process. A newly developed technique, known as Interactive Graphics for Process Simulation, enables the measured responses to be represented pictorially in the form of shading diagrams. By inspecting the shading diagrams, the responses can be correlated with one another, consequently establishing an optimum level of the mixer operating variables and the material variables, for meeting both the process productivity and mixed product specification objectives.

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No description available.

A study has been made of the effect of single extensions and continuou fatigue on the structures of various natural rubber networks. The change in network structure of a conventional vulcanisate on a single extension manifests itself as permanent set. The change in network structur e has been as s es sed by the us e of the chemical probes, propar 2 -thiol/piperidine, hexane-thiol/piperidine and triphenyl phosphine, which determine the polysulphide and disulphide crosslink densities and main chain modification respectively. The permanent set induced on a single extension of a conventional sulphur vulcanisate has been shown to result from the destruction and reformation of polysulphide crosslinks. The magnitude of the effect was dependent upon the degree of extension and showed a maximum at extensions corresponding to the onset of stress -induced crystallisation. The incorporation of a reinforcing fille.r, HAF - carbon black, magnified the effe ct. Vulcanis ates that poss es s ed only monO and disulphide cros s links did not show any significant permanent set. The continuous changes in network structure during fatigue have also been determined, and the effects of carbon black and antioxidants on these changes and the fatigue life have been assessed. During' fatigue the ove rall cros s link density incr eas ed slightly, which resulted from the destruction of polysulphide cro$slinks. and their replacement by principally disulphide cros$links. Antioxidants reduced the rate of destruction of polysulphide cros slinks and increased the fatigue life of the rubber network. The fatigue life of the network als 0 depended upon the conc entration of free chain ends. Thes e chain ends were incorporated into the network by masticating rubber under nitrogen in the presence of bis (diis opropyl)thiophosphoryl dis ulphide, which improved the fatigue resistance by up to 9%.

An investigation of the effects of various water-soluble polymers upon some properties of natural rubber latex has been carried out. All the polymers, which were of two principal types, distinguished according to the rate of addition of polymerisation reactants, were prepared by free-radical initiated solution polymerisation. Two types of monomers, namely, ionisable hydrophilic monomers and hydrophobic monomers were used in the preparation of polymers. Both types of polymers, referred to as Type 1 and Type 2, were principally characterised by viscometry, hydrophilicity assessment and infra-red analyses. It has been found that such characteristics of these polymers as molecular weight, composition distribution and hydrophilicity are dependent upon the method used for their preparation. Explanations which have been suggested for this dependence accord with theoretical predictions. It has also been found that certain properties of natural rubber (NR) latex such as mechanical stability (MST), viscosity, zinc-oxide thickening, heat- sensitivity and creaming can be modified with the addition of watersoluble polymers and that the extent to which each of these properties is modified depends upon the characteristics of the added polymer. The extent of the modification of MST and viscosity of NR la tex greatly depended upon both the molecular weight and composition of the added polymer. The influence of composition of the added polymer in modifying zinc-oxide thickening was found to be more important than that of molecular weight. Even though the effects of polymers of Type 1 and Type 2 upon the properties of NR latex were generally similar it has not been able to make proper comparisons between the effects of these two types of polymers as their characteristics were different.

A comparison has been made of the vulcanization of NR in the latex form and in the dry form. In latex form, NR wa s found to vu Lcani ze at a much f asterra t ethan in the dry form. The faster rate of reaction in latex prevulcanization is attributed to the presence of the aqueous phase which acts as a medium for the dissolution of ZDBC and sulphur, and provides a suitable environment for the two vulcanizing ingredients to react to form the active sulphurating agent. A comparison has also been made of the prevulcanization behaviour of NR latex and synthetic cis-polyisoprene latex. It has been suggested that the indigenous vulcanization accelerators and activators present in NR latex act as additional vulcanizing accelerators and therefore increase the rate of prevulcanization. Experiments have been carried out to determine the solubilities of sulphur and ZDBC in the aqueous phase of the latex during prevulcanization. Sulphur was found to dissolve to an appreciable extent; ZDBC was found to have a solubility of ca. 0.011%. The effects of varying the levels of sulphur and ZDBC upon NR latex prevulcanization was investigated. The variations of the following properties with time of prevulcanization were investigated: free and network-combined sulphur, disappearance of ZDBC, crosslink insertion, and tensile strengths of cast films. Information was also obtained concerning the polymer-solvent interacticn parameter for the cast films swollen in n-decane at 23°C. Investigations of the different types of sulphidic crosslinks as a function of prevulcanization time for vulcanizate obtained from prevulcanized latex have also been carried out. Tne crosslinks were found to be mainly of the polysulphidic type. The effect of varying the dialkyl chain-length and metal counterion of the dithiocarbamate accelerator upon NR latex prevulcanization have been studied. The molal effectiveness of the zinc dialkyl dithiocarbamates appears to pass through an optimum as tbe dialkyl chain-length of the accelerator is increased. PbDEC was found to be of very low activity as an accelerator and the water soluble SDEC has poor. accelerating properties when compared to ZDEC. Plausible hypotheses to account for the observations have been postulated.

No description available.