No description available.

No description available.

The project set out to investigate the relative effectiveness of thermal conductive heating (from external resistance heaters) and viscous heating in the heating (and melting) of low density polyethylene. A model system was used in order to simplify the mathematical analysis. A theory was developed to describe both processes in the model apparatus. The results showed large differences between the experimental and predicted results at low melt temperatures (the predicted results were much greater than the experimental) . Analysis of the results indicated that the apparatus was probably not producing the required shear rates in the sample. The theory appeared to be satisfactory, in that it did not over estimate the viscous heating to any significant extent. The theoretical results could therefore be considered to be a reasonable estimate of the viscous heating.

The main aim of this work was two fold, firstly to investigate the effect of a highly reactive comonomer, divinylbenzene (DVB), on the extent of melt grafting of glycidyl methacrylate (GMA) on ethylene-propylene rubber (EPR) using 2,5-dimethyl-2,5-bis-(tert-butyl peroxy) hexane (Trigonox 101, T101) as a free radical initiator, and to compare the results with a conventional grafting of the same monomer on EPR. The effect of processing conditions and chemical composition including the concentration of peroxide, GMA and DVB on the extent of grafting was investigated. The presence of the comonomer (DVB) in the grafting process resulted in a significant increase in the extent of the grafting using only a small concentration of peroxide. The extent of grafting increased drastically with increasing the DVB concentration. Interestingly, in the comonomer system, the extent of the undesired side reaction, normally the homopolymerisation of GMA (polyGMA) was shown to have reduced tremendously and in most cases the level of polyGMA was immeasurable in the samples. Compared to a conventional EPR-g-GMACONV (in the absence of a comonomer), the presence of the comonomer DVB in the grafting system was shown to result in more branching and crosslinking and this was paralleled by an increase in DVB concentration. In contrast, the extent of grafting in conventional system increased with increasing the peroxide concentration but the level of grafting was much lower than in the case of DVB. Homopolymerisation of GMA and excessive crosslinking of EPR became dominant at high peroxide concentration and this reflects that the side reactions were favourable in the conventional grafting system. The second aim was to examine the effect of the in-situ functionalised EPR when used as a compatibiliser for binary blends. Blending PET with functionalised EPR (f-EPR) gave a significant improvement in terms of blend morphology as well as mechanical properties. Blending PET with f-EPRDVB (prepared with DVB) was much more effective compared to the corresponding PET/f-EPRCONV (without DVB) blends in which f-EPRDVB having optimum grafting level of 2.1 wt% gave the most pronounced effect on the morphology and mechanical properties. The presence of high polyGMA concentration in f-EPRCONV was found to create damaging effects on its morphology. However, the use of commercial terpolymers based on ethylene-methacrylate-glycidyl methacrylate (EM-GMA) or a copolymer of ethylene-glycidyl methacrylate (E-GMA) containing various GMA levels as compatibilisers in PET/EPR blends was more efficient compared to PET/EPR/f-EPR blends with the former blends showing finer morphology and high elongation at break.

Ten grades of ABS and four grades of polypropylene have been plated with various copper + nickel + chromium coatings and subjected to a variety of tests. In corrosion studies the pre-electroplating sequence and plastics type have been shown to influence performance. One ABS pre-electroplating sequence was consistently associated with better corrosion performance; two factors were responsible for this, namely the more severe nature of the etch and the relatively more noble electroless nickel. Statistical analysis has indicated that order of severity of the corrosion tests was static-mobile-CASS, the latter being the least severe. In mechanical tests two properties of ABS and polypropJylene, ductility and impact strength, have been shown to be adversely affected when electrodeposited layers were applied. The cause of this is due to a complex of factors, the most important of which is the notch sensitivity of the plastics. Peel adhesion has been studied on flat panels and also on ones which had a ridge and a valley moulded into one face. High adhesion peaks occurred on the flat face at regions associated with the ridge and valley. The local moulding conditions induced by the features were responsible for this phenonemon. In the main programme the thermal cycling test was shown to be more likely than the peel adhesion test to give an indication of the service performance of electroplated plastics.

No description available.

Ces travaux ont pour objectif d’améliorer les propriétés physico-chimiques et la réaction au feu du polylactide pour des applications durables. Le manuscrit commence par un état de l’art des propriétés et des méthodes d’ignifugation du polylactide. Ensuite, un procédé par extrusion réactive a été développé et optimisé pour la polymérisation de différents polylactides, stéréocomplexés ou non, à partir des isomères L et D du lactide. Le polylactide stéréocomplexe multibloc ainsi obtenu possède des propriétés supérieures à celles du polylactide commercial (température de fusion et taux de cristallinité augmentés), mais une stabilité thermique plus faible à cause de la présence du catalyseur de polymérisation résiduel. Le protocole d’extrusion réactive est ensuite modifié afin d’améliorer la stabilité thermique des polylactides et de former des nanocomposites. L’ajout d’un ligand (α tropolone) pour désactiver le catalyseur de polymérisation résiduel améliore la stabilité thermique. Les polylactides chargés en nanotubes de carbone montrent une faible amélioration de leur réaction au feu. De ce fait, des polylactides intumescents ont été élaborés en combinant des retardateurs de flamme conventionnels (polyphosphate d’ammonium et mélamine) avec des nanoparticules (argile organomodifiée). La réaction au feu des polylactides intumescents est fortement améliorée, en particulier avec l’ajout d’argile organomodifiée. Un mécanisme réactionnel expliquant la synergie se produisant entre l’argile organomodifiée et les retardateurs de flamme est proposé. / The aim of this work is to enhance the physical and chemical properties and the fire reaction of polylactides for durable applications. A state of the art first reviews the properties and fire retardancy of polylactide. Then, a reactive extrusion process to polymerize L and D lactides monomers into various polylactides, including stereocomplexes polylactides (PLA), has been developed and optimized. The multibloc stereocomplexed polylactide shows enhanced properties compared to commercial PLA (increased fusion temperature and crystallinity rate), but less thermal stability due to residual catalyst of polymerization. Reactive extrusion process is thereafter updated in order to enhance thermal stability and to make PLA nanocomposites. The thermal stability is increased by catalyst deactivation with a ligand (α-tropolon). The polylactides filled with carbon nanotubes exhibit slight improvement in terms of fire retardancy. To overcome this issue, intumescent polylactides have been processed by combination of conventional fire retardants (ammonium polyphosphate and melamine) and nanofillers (organoclay). The fire retardancy of these materials is dramatically enhanced, especially when organoclay is used as synergist. A mechanism of action explaining synergy between fire retardant and organoclay is then proposed.

Novel conducting polyanilines which are thermoplastic and have mesogenic side-chains have been synthesised and investigated in order to study the use of liquid crystal alignment to produce higher conductivity. The backbone was based on ortho-substituted aniline polymers. A large variety of suitable ortho-substituted nitrobenzene precursors with liquid crystalline properties were synthesised and investigated by microscopy and differential scanning calorimetry. A study of the 4-methoxyphenyl 4-[x-(2-nitrophenoxy)alkoxy] benzoate series (x = 2-10) showed that only the molecules with even spacer lengths were liquid crystalline whereas the ones with odd spacer lengths were not. All the even molecules were nematic in character. Some substituted biphenyl nitrobenzenes were also synthesised and 4-cyano 4'-[6-(2-nitrophenoxy)hexoxy]biphenyl exhibited a monotropie nematic phase. A large variety of ortho-substituted nitrobenzenes with transition temperatures above 100°C were also synthesised. Depending on their structure, nematic as well as smectic phases were characterised. The ortho-substituted nitrobenzene molecules were subsequently reduced to the required anilines. Their liquid crystal properties were similar to their respective nitro-compounds.These liquid crystalline aniline monomers were chemically polymerised by use of an emulsion system. The polymers obtained were fully characterised by spectroscopic analysis, and were a head-to-tail emeraldine type substituted polyaniline. The physical properties of these potentially liquid crystalline conducting polymers were fully investigated. They were found to be soluble in DMF, DMSO, THF and CHCI3• UV/visible study revealed an average band gap of 3.4 eV. Gel permeation chromatography analysis showed the presence of oligomers and higher polymers in smaller proportion for each samples. These polymers were also structurally stable up to 300°C. Polarising hot-stage microscopy and differential scanning calorimetry showed the existence of liquid crystal properties for two of these polymers namely : poly[2-(hexoxy)-6-(4- biphenyloxy-4' carboxylic acid)]aniline and poly[2-[4-cyanophenyl-4-carboxylate 6-(4'-oxybiphenyl)hexoxy aniline. In fact, a nematic phase was exhibited for the carboxylic acid polymer between 225 and 261°C and between 120 and 175°C for the ester polymer. Study of their electrical conductivities showed some semi-conducting characteristics with values as high as 1.2xlO-3 S ern" for the H2S04 vapour doped carboxylic acid polymer and equal to 8xlO-6 S cm" for the HCI doped ester poÍymer. An increase in conductivity values was also observed as the temperature reaches the nematic liquid crystal transitions, demonstrating the effect of the mesogenic groups on the ordering of the polymer backbone. Laser alignment of these two liquid crystal semi-conducting polymers was also carried out. A conductivity anisotropy was observed along the laser written samples. This technique could also be of great potential interest as a method of localised conductivity enhancement.

A novel sol-gel process has been developed for producing transparent conductive tin dioxide films and for their application to polymer substrates. Initially, tin oxide was produced by hydrolysis of tin tetrachloride using amended versions of methods found in the literature. The tin oxide produced from the procedure did not adhere well to glass and was not transparent. The procedure was also very time consuming. Preliminary experiments using tin bis (acetylacetonate) dichloride as a precursor were very promising and all efforts were soon concentrated on that route. After a lot of experimentation optimising the method, it was found that colloids capable of producing conductive transparent tin oxide coatings were obtained approximately 10 days after beginning the procedure. Indium and antimony dopants were added to the tin oxide at the sol-gel stage in order to investigate their effect on the DC conductivities of the tin oxide coatings. Bulk conductivities in the ranges 1 to 100 Sm[sup]-1 and 13 to 800 Sm[sup]-1 were obtained for p- and n-type doped annealed tin oxide coatings on glass substrates respectively. The percentage transparencies of the coatings remained high for unannealed coatings (~80%) but decreased to ~ 40% after annealing. Polymer pre-treatments were carried out on the poly (methyl methacrylate), polycarbonate and poly (ethylene terephthalate) substrates. The contact angles and surface energies of the substrates were studied to investigate the effects of the surface pre-treatment techniques. Treatment of the poly (methyl methacrylate) and poly (ethylene terephthalate) substrates consisted of hydrolysis by aqueous sodium hydroxide. A combination of UV/ozone oxidation was used for the polycarbonate substrates. The tin oxide coatings were applied to the polymer substrates by spin-coating, solvent casting and spray coating. From optical microscopy studies, it was shown that the spin-coated films were the most uniform and least cracked. To further increase the adhesion of the coatings on the polymeric substrates, a systematic study was made of the effects of coupling agents, both on the substrate surfaces and in the sol-gel solutions themselves. Short pulses of heating were given to the coatings in an infrared furnace. The annealing did not increase the bulk conductivities greatly but the coatings retained a very high transparency (greater than 90%). To investigate the effect of infrared annealing on tin oxide powder, it was shown from X-ray diffraction that the crystallinity of the tin oxide increased significantly as a result of annealing in the infrared furnace.

There are many existing and developing commercial applications for electrically-conductive elastomeric blends. 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, often with poor electrical conductivities have been reported in the literature. Interest was found in this project to improve the compatibility, mechanical and electrical properties of this type of blend through different mixing methods (i.e. solution and thermo-mechanical) with more systematic mixing procedures and better optimised mixing conditions. Poly(butadiene-co-acrylonitrile) rubber (NBR) and polyaniline dodecylbenzenesulfonate (PAni.DBSA) were chosen for study as blends in the present work, because their solubility parameters were calculated to be compatible (NBR with 48.2 wt% of acrylonitrile content had the best compatibility with PAni.DBSA) and also because the polymers were thermally stable and readily available. No literature work was found relating to the electrical properties of natural rubber-PAni.DBSA blend. Therefore, epoxidised natural rubber (with 50 mole% of epoxide level) was also selected in this work in order to investigate a novel usage of this natural resource. Non-vulcanised NBR-PAni.DBSA and non-vulcanised ENR-PAni.DBSA blends with useful electrical conductivities (up to about 10[sup]-2 and 10[sup]-3S.cm[sup]-1 respectively) were successfully prepared by solution mixing for the first time in this work. Peroxide-vulcanised NBR-PAni.DBSA blends with similar electrical conductivities (up to x 10[sup]-2S.cm[sup]-1) were also successfully prepared for the first time by thermo-mechanical mixing (with an internal mixer). The conductivities of all these blends were much higher than those of comparable materials reported in the literature due to the reasonably good compatibility between the two polymers and the high mixing efficiency of the two chosen mixing methods (i.e. solution and thermo-mechanical mixing). The electrical conductivities of the peroxide-vulcanised blends were found to be unaffected by the presence of dicumyl peroxide vulcanising agent. The FT-IR spectra of both non-vulcanised and peroxide-vulcanised NBR-Pani.DBSA blends (either prepared by solution or thermo-mechanical mixing) resembled a superposition of the spectra of the constituent materials. However, some notable peak shifts were observed, providing evidence of the bonding interaction between the two polymers. For ENR-PAni.DBSA blends, the ring opening of ENR with increasing PAni.DBSA content was successfully quantified by NMR and FT-IR spectroscopic (based on the intensities of all spectroscopy bands assigned to the functional groups relating to ENR ring opening). The non-vulcanised and peroxide-vulcanised NBR-PAni.DBSA blends with up to 30 wt% of PAni.DBSA, (produced either by solution or thermo-mechanical mixing) showed the largest temperature shifts for their thermal events in both the sub- and above-ambient temperature DSC thermograms, strengthening the evidence of interaction between the two polymers. Progressive glass transition temperature (Tg) shifts with increasing PAni.DBSA content were observed for the ENR-PAni.DBSA blends from both the sub- and the above-ambient temperature DSC thermograms, supporting the proposition that there was further ring opening of the ENR. Optical and electron micrographs of all NBR- and ENR-PAni.DBSA blends showed that the higher the content of PAni.DBSA, the greater the phase separation (dark-green regions with larger proportion of PAni.DBSA) between the rubber and conductive filler. However, the thermo-mechanically mixed NBR-PAni.DBSA blends (made by high temperature-processing, [tilde]140[sup]oC), produced more well-blended regions (seen as rubber-rich pale-green regions) between the two polymers, even with a high level of PAni.DBSA content, i.e. [greater than or equal to]40 wt%. Transmission electron micrographs of all NBR- and ENR-PAni.DBSA blends prepared in this work revealed numerous small PAni.DBSA particles (of colloidal dimensions, 50-1000nm), which were also likely to have contributed to the electrical conductivities of all these blends (especially for those that were below their percolation thresholds). The effect of PAni.DBSA. polymer chain alignment on the peroxide-vulcanised NBR-PAni.DBSA blends prepared by thermo-mechanical mixing was also studied in this work. It was found that both the mechanical properties (i.e. tensile properties and tear strength) and the electrical conductivities of the blends were enhanced, when they were strained along the orientation axis of elongated PAni.DBSA polymer chains (the orientation tended to be parallel to the flow direction when the blends were passing through a two roll-mill). Both FT-IR spectroscopy and optical microscopy successfully revealed a higher level of inter-chain interaction among the elongated PAni.DBSA particles for the blends strained along this particular orientation axis. All the peroxide-vulcanised blends also exhibited a good historical memory in terms of their electrical conductivities (99% retention of the original non-strained sample's value) during the multi-cycles of strain loading and unloading. This was attributed to the high proportion of well-blended regions in all the blends prepared by thermo-mechanical mixing.