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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.

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The purpose of this study is to identify and quantify factors governing extrudate swell and melt fracture. In the first part, the factors which control the extrudate swell of carbon black (N330) filled styrene-butadiene rubber (SBR) compounds at various states-of-mix were investigated. State-of-mix is quantified by effective filler volume fraction (EFVF), based on an estimate of the amount of rubber immobilised in the carbon black agglomerates. Extrudate swell was found to be dominated by recoverable strain and relaxation time, which are controlled by EFVF. In contrast, shear rate and the rubber-carbon black tridimensional transient network were not found to influence extrudate swell significantly. In the second part, melt fracture of the rubber compounds was investigated in terms of surface texture wavelength. The longer the wavelength, the greater the severity of the surface disruption. It was found that wavelength was controlled strongly by state-of mix (or by EFVF). In addition, a mechanism for melt fracture of the compounds studied has been proposed, based on average energy at the extrudate surface (t.E). Lastly, the influences of additives; paraffinic processing oil, stearic acid or a mixture of predominantly calcium fatty acid soaps on extrudate swell and melt fracture were investigated. For the rubber compounds with paraffinic processing oil or stearic acid, EFVF was found to play an important role in extrudate swell. The mixture of fatty acid soaps was shown to reduce significantly extrudate swell due to the presence of wall slip. The influence of the fatty acid soaps on extrudate swell is more noticeable for extrudates obtained from long dies, in which flow is dominated by shear. The major factors shown to exert a significant influence on melt fracture for the compounds with paraffinic processing oil or stearic acid are EFVF and green strength of the extrudate. Wall slip, promoted by a mixture of fatty acid soaps, was also found to decrease the melt fracture severity, particularly for long dies in which shear stresses are dominant.

No / Flows of complex fluids need to be understood at both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: Orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22474号 / 工博第4735号 / 新制||工||1740(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 山本 量一, 教授 渡辺 宏, 准教授 谷口 貴志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The basic understanding of mixing in the process of polymer melt extrusion by twin screw extruder is limited by their geometrical complexity and the interactions of the process parameters. Mixing and flow in a 100mm diameter, trapezoidal channeled, intermeshing co-rotating twin-screw extruder have been characterised by determination of residence time distribution (RTD) and of the paths taken by tracers added to the melt. The axial mixing and the effects of varius parameters on it were established by studying RTD using tracer techniques. As the tail of the distribution is of paramount importance, the reproducibility of the RTD curve was extensively studied. Radioactive NnO2 was used as a tracer and detected by gamma ray spectroscopy giving more reproducible results than added barytes estimated gravimetrically after ashing. Shock cooling of the extruder and sectioning of the solidified compound in the screw channels was used to-study the flow mechanism. The maximum throughput achieved, polymer melting mechanism, filled volume and axial mixing Are interrelated, and are dependent on the configuration and position of segmented mixing discs present in the screw profile. In the upstream position these act as melting discs and their efficiency is increased in a closed configuration. Initial melting is achieved over a remarkably short distance along the screw profile. The screw speed affects the axial mixing which is shown to be related to the net relative pressure change at the screw tips. A flow model is proposed such that the overall material flow taking place in an anticlockwise direction along the screw channel comprises two separate flow regimes. The upper regime rotates anti-clockwise and is made up of main and small tetrahedron flow and calender flow. The lower flow regime rotates clockwise and is made up of main and small side leakage flows and a portion of the main tetrahedron flows together with a central flow. The flow studies show conclusively that the melt from a particular site ahead of the intermeshing zone occupies a predestined site after passing through the intermeshing zone.

A filament stretching extensional rheometer was used to investigate the effect of uniaxial flow on the crystallization of polypropylene. Samples were heated to a temperature above the melt temperature to erase their thermal and mechanical histories. The Janeschitz-Kriegl protocol was applied and samples were stretched at various extension rates to a final strain of e = 3.0. Differential scanning calorimetry was applied to crystallized samples to measure the degree of crystallinity. The results showed that a minimum extension rate, corresponding to a Weissenberg number of approximately Wi = 1, is required for an increase in percent crystallization to occur. Below this Weissenberg number, the flow is not strong enough to align the tubes of constrained polymer chains and as a result there is no change in the final percent crystallization. An extension rate was also found for which percent crystallization is maximized. The increase in crystallinity is likely due to flow-induced orientation and alignment of tubes of constrained polymer chains. Polarized-light microscopy verified an increase in number and decrease in size of spherulites with increasing extension rate. Small angle X-ray scattering showed a 7% decrease in inter-lamellar spacing at the transition to flow-induced increase in crystallization. Crystallization kinetics were examined by observing the time required for melts to crystallize under uniaxial flow. The crystallization time decreased with increasing extension rate, even for extension rates where no increase in percent crystallization was observed. These results demonstrate that the speed of crystallization kinetics is greatly enhanced by the application of extensional flow.

The Langevin equation is a stochastic differential equation frequently used in molecular dynamics for simulating systems with a constant temperature. Recent developments have given rise to wide uses of Langevin dynamics at different levels of spatial resolution, which necessitate time step and friction parameter choices outside of the range for which many existing temporal discretization methods were originally developed. We first study the GJ--F, BAOAB and BBK numerical algorithms, originally developed for atomistic simulations, on a coarse-grained polymer melt, paying close attention to the large time step regime. The results of this study then inspire our search for new algorithms and lead to a general class of velocity Verlet-based time-stepping schemes designed to perform well for all parameter regions, by ensuring that they faithfully reproduce statistical quantities for the case of a free particle and harmonic oscillator. This family of methods depends on the choice of a single free parameter function and we explore some of the methods defined for certain choices of this parameter on realistic coarse-grained and atomistic molecular systems relevant in material and bio-molecular science. In addition, we provide an equivalent splitting formulation of this one-parameter family which allows for enhanced insight into the hidden time scaling induced by the choice of the free parameter in the Hamiltonian and stochastic time scales. / Mathematics