A polymer is rarely used as a pure material and the baseline physical, chemical and rheological properties such as molecular weight, strength, stiffness and viscosity are often modified by the addition of fillers or by blending with another polymer. However, as many polymers are immiscible, compatibilisation and graft processing polymer blends are very important techniques to increase miscibility of the blends as well as to improve chemical, physical and mechanical properties. Reactive extrusion, or melt-state processing, is one of the most appropriate techniques for improving polymer properties. Compatibilisation and graft polymer processing are often carried out under reactive extrusion conditions. This technique is an efficient approach because it is easy, inexpensive and has a short processing time. Although reactive extrusion has numerous advantages one of the limitations is degradation of the polymer under the high temperatures and mechanical stresses encountered. In the polymer industry, because of increasing customer demand for improved product quality, optimising the polymerisation process by decreasing product costs and controlling the reaction during polymerisation has become more important. It can be said that any method used for monitoring the polymerisation process has to be fast, accurate and reliable. Both in-line and on-line methods may be involved in in-process monitoring. The primary information from in-process monitoring is used for identifying and understanding molecular structure and changes, optimising and improving process modelling and understanding whether the process is under control. This also involves considering whether the products have the required properties. This thesis describes research in a number of aspects of melt processing of polymers, including examination of extruded products, an in situ spectroscopic study of the reaction of MAH and PP, a study of the melt processing of TPU, and a study of the use of nitroxide radicals as probes for degradation reactions. As mentioned previously, a suitable method for improving polymer properties is polymer blending. Starch is a hydrophilic biodegradable polymer which may be blended with other polymers to produce biodegradable products. In spite of its benefits, it is immiscible with most synthetic polymers, such as polyesters. The main technique for improving the miscibility of starch with the other polymer is a grafting reaction. The reactive extrusion technique was applied to the production of starch and polyester blends, the product of which was a biodegradable aliphatic polyester. In this process dicumyl peroxide (DCP) and maleic anhydride (MAH) were used as an initiator and cross-linker, respectively. Extruded samples were investigated by infrared microscopic mapping using the attenuated total reflectance (ATR) technique. Measurement of various band parameters from the spectra allowed IR maps to be constructed with semi-quantitative information about the distribution of blend components. IR maps were generated by measuring the band area ratio of O-H and C=O stretching bands which are related to starch and polyester, respectively. This was the first time this method has been used for understanding the homogeneity of a polymer blend system. This method successfully indicated that the polyester/starch blend was not a homogenised blend. It was concluded that to improve the homogeneity the reaction conditions should be modified. Another important compatibilisation reaction is the reaction between a polyolefin and MAH. This was investigated by combining a near infrared (NIR) spectrometer with a small laboratory scale extruder, a Haake Minilab. The NIR spectra were collected in situ during melt processing by the use of a fibre optic cable. In addition to this the viscosity of the polymer melt was measured continuously during processing through two pressure transducers within the Minilab extruder. The vinyl C-H stretch overtone of the MAH was clearly seen in the NIR spectra near 6100 cm-1 and diminished over time as the MAH reacted with PP. The spectra obtained were analysed by two techniques: principal component analysis (PCA); and peak area ratios. The peak area ratios were calculated using the =C-H first overtone of MAH with respect to the band observed between 6600 and 7400 cm-1. This band corresponds to a combination band of CH2 and CH3 in PP and was unchanged during the reaction. These data facilitated interpretation of the reaction kinetics and experiments at different temperatures allowed determination of the activation energy of the reaction. These results have thrown new light on the PP-MAH reaction mechanism. It was also shown that although the presence of DCP causes production of a high concentration of macro-radicals it does not have any effect on the rate and kinetics of the reaction. As mentioned previously, one of the limitations of reactive extrusion is degradation of the polymer under high temperatures and shear rates. Hindered amine stabilisers (HAS) are often used as inhibitors to control the thermal-oxidative degradation of polymers. They are used in various polymeric materials but were primarily developed for polyolefins, particularly PP. The stabilisation mechanism of HAS involves interaction firstly with the alkyl peroxyl radicals produced during oxidative degradation so that the hindered amine converts to the corresponding nitroxide. The nitroxide is then able to capture a carbon-centred radical and so retard the subsequent degradation chain reaction. 1,1,3,3- tetramethyldibenzo[e,g]isoindoline-2-yloxyl (TMDBIO) was used as a probe for investigation of PP during reactive extrusion conditions. The TMDBIO is a profluorescent compound that has been used previously to identify polymer degradation. In the radical form, there is no fluorescence since the unpaired spin on the nitroxide quenches the fluorescence of the phenanthrene moiety. When the radical is removed (by radical trapping or reduction) fluorescence is observed. As a result, the location and intensity of fluorescence can be used as a probe for identification of degradation and to determine the concentration of carbon-centred radicals produced during thermal or mechanical degradation such as occurs during reaction processing. This novel method shows that, the degradation of PP started at the early stage of processing. Also this method can be used as a useful technique to modify the processing conditions to decrease degradation of the polymer during processing. The second system investigated using in situ monitoring via the NIR fibre optic was the melt processing of a TPU nano-composite. This was the first time that the in situ monitoring of TPU nano-composite had been examined. In this investigation the effect of temperature during processing on the TPU molecular structure and rheological behaviour was again investigated. In addition, dispersion of clay nano-particles through the TPU matrix and rheological changes due to this was investigated. This investigation was successful in that it was found that several factors affected the viscosity of the nano-composite. However, to fully understand the degradation mechanism and viscosity changes further studies must be performed.

Thesis (M.S.)--Rochester Institute of Technology, 1981. / Typescript. Includes bibliographical references (leaves 56-57).

An effort concerned with the feasibility of achieving melt-processable polyacrylonitrile copolymer system precursors for producing high modulus carbon fibers is detailed. High molecular weight poly(acrylonitrile-ran-methyl acrylate) (PAN-MA) copolymer with high acrylonitrile content were mixed with various water containing binary melting point modifiers to produce systems that formed stable melts at temperatures below the temperature corresponding to the onset of PAN-MA crosslinking. The structure of the copolymer was found to be 96.5 ± 0.13 mole % acrylonitrile and 4.40 ± 0.13 mole % methyl acrylate by 1H-NMR with an Mw ]= 238 kDa and dispersity of 1.9 determined by size exclusion chromatography. A reduction in the Tm of the copolymer of 200 C was established for a copolymer/melting point modifier system containing copolymer mixed with water and acetonitrile with the following composition: PAN-MA/ACN/H2O 55/25/20 wt:wt:wt. This corresponds to the greatest reduction in a PAN-based copolymer melting temperature yet reported. From isothermal DSC and pressurized capillary rheometry experiments it was found that the stability of the resulting melts shows a strong temperature dependence, but does not show a strong dependence on shear rate. Copolymer mixtures with H2O and acetonitrile or H2O and adiponitrile were found to be suitable for melt-extrusion at 170 C with viscosities ranging from 1800-2000 Pa*s with stabilities greater than 1 hour. The modification of membranes to improve gas separation properties is of considerable interest. Crosslinking is one route to modify membranes, but the resulting effects on thin membranes have yet to be investigated to understand the impact of such modification at thicknesses that are relevant to industrial membranes. In this study, the influences of UV irradiation and physical aging on O2 and N2 gas permeation properties of thin (~ 150 nm) glassy poly(arylene ether ketone) (PAEK) films at 35 C and 2 atm were investigated. Thin PAEK films prepared from tetramethyl bisphenol A and 4,4'-difluorobenzophenone were UV irradiated on both sides in air or N2 at wavelengths of 254 nm or 365 nm. This induced crosslinking and, in some cases, photooxidation. Gas permeability decreased and O2/N2 selectivity increased as UV irradiation and aging time were increased. At 254 nm, samples irradiated in air had lower permeability coefficients and higher selectivities than samples irradiated in N2, and this was ascribed to additional decreases in free volume due to photooxidation in air-irradiated samples. Additionally, air-irradiated samples at 254 nm exhibited less physical aging than non-crosslinked and N2-irradiated samples at 254 nm, possibly due to interactions among photooxidative polar products that may restrict polymer chain mobility, thereby lowering the aging rate. The influence of water vapor on physical aging of air-irradiated samples was examined. Finally, irradiation at 254 nm leads to more extensive crosslinking and/or photooxidation than irradiation at 365 nm, possibly due to greater UV absorption by the polymer and the higher probability of radical formation at the lower wavelength. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is utilized for gas separation membranes. It has a relatively high free volume with high gas permeabilities but suffers from low selectivities. PPO polymers with Mn's from 2000-22,000 g/mole were synthesized and blended with a poly(arylene ether ketone) derived from bisphenol A and difluorobenzophenone (BPA-PAEK). DSC showed that the blends with all but the lowest molecular weight PPO had two Tgs, thus suggesting that two phases were present. The ketone carbon and benzylic methyl groups on the BPA-PAEK and the PPO polymers crosslinked upon exposure to UV light. The gel fractions after UV exposure were high and the tensile properties were similar to the PPO control polymer that is currently used as a gas separation membrane. The crosslinked blends had improved gas selectivities over their linear counterparts. The 90/10 wt/wt 22k PPO/BPA PAEK crosslinked blends gained the most O2/N2 selectivity and maintained a high permeability. Two series of high molecular weight disulfonated poly(arylene ether sulfone) random copolymers were synthesized as proton exchange membranes for high temperature water electrolyzers. These copolymers differed based on the position of the ether bonds on the aromatic rings. One series was comprised of fully para-substituted hydroquinone comonomer and the other series incorporated 25 mole % of a meta-substituted comonomer, resorcinol, and 75 mole % hydroquinone. The influence of the substitution position on water uptake and electrochemical properties of the membranes were investigated and compared to the state-of-the-art membrane, Nafion. Mechanical properties of the membranes were measured for the first time in fully hydrated conditions at room and elevated temperatures. While submerged in water, these hydrocarbon-based copolymers had moduli an order of magnitude higher than Nafion membrane. Selected copolymers of each series showed dramatically increased proton conductivity at elevated temperature and fully hydrated conditions while their H2 gas permeabilities were well controlled over a wide range of temperatures. These improved properties were attributed to the high glass transition temperature of poly(arylene ether sulfone)s. / Ph. D.

Ultra High Molecular Weight Polyethylene (UHMw-PE) is an engineering polymer that is widely used in demanding applications because of its un-paralleled properties such as high abrasion resistance, high-modulus and high-strength tapes and fibres, biaxial films etc. In common practice, to achieve the uniaxial and the biaxial products, the solution processing route is adopted to reduce the number of entanglements per chain, such as found in Dyneema(R) from DSM(R). Another elegant route to reduce the number of entanglements to ease solid-state processing is through controlled polymerisation using a single-site catalytic system. In this theses, how different polymerisation condition, such as temperature and time control molecular weight and the resultant entangled state in synthesised disentangled UHMw-PE is addressed. Linear dynamic melt rheology is used to follow entanglement formation in an initially disentangled melt. With the help of rheological studies, heterogeneity in the distribution of entanglements along the chain length and the crystal morphology produced during polymerisation is considered. For the understanding of influence of large shear flow on melt dynamics large amplitude oscillatory shear (LAOS) is used and the non-linear viscoelastic regime is explored. A remarkable feature of overshoot in loss (viscous) modulus with increasing deformation (strain) in UHMw-PE melt in the LAOS is observed. This observation is characteristic of colloidal systems. The role of entanglement density in the amorphous region of the synthesised disentangled UHMw-PE (semi-crystalline polymers) on the melting and crystallisation is presented. To understand the effect of topological differences on melting behaviour, nascent entangled, nascent disentangled and melt-crystallised samples have been used. The role of superheating on the melting process is also addressed. Preliminary results on characteristic melting time of a crystal using TM-DSC are also presented.

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Magnesium alloys, as the lightest of all structural metallic materials, and aluminium-based particulate metal matrix composites (PMMCs), offering unified combination of metallic and ceramic properties, have attracted increased interest from the automotive, aerospace, electronic and recreation industries. Current processing technologies for PMMCs do not achieve a uniform distribution of fine-sized reinforcements and produce agglomerated particles in the ductile matrix, which are detrimental to the ductility. At the same time, molten magnesium alloys contain impurities and oxides and when cast conventionally, the final components usually exhibit a coarse and non-uniform microstructure with various casting defects. The key idea in this thesis has been to adopt a novel intensive melt conditioning process, allowing the application of sufficient shear stress that would disperse solid particles present in the melt and offer unique solidification behaviour, improved fluidity and die-filling during casting. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, where intensive shearing is directly imposed on the alloy melt, which is then cast by the conventional HPDC process, has been used to produce PMMC and magnesium alloy castings. The MC-HPDC process for PMMCs leads to a uniform dispersion of the reinforcement in the matrix, confirmed by quantitative statistical analysis, and increased mechanical performance as indicated by an increase in the hardness and the tensile properties of the composites. We describe a solidification path for aluminium containing magnesium alloys, where intensive shearing prior to casting leads to effective dispersion of solid oxide particles, which then effectively act as nucleation sites for magnesium grains, resulting in significant grain refinement. The MC-HPDC processed magnesium castings have a significantly refined microstructure, with reduced porosity levels and casting defects. Evaluation of the mechanical properties of the castings reveals the beneficial effect of intensive shearing. After careful optimization, the MC-HPDC process shows promising potential for the direct recycling of high purity magnesium die casting scrap, producing casting with mechanical properties comparable to those of primary magnesium alloys.

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