In this thesis was designed, manufactured and tested the fourth evolution of a slit-flow rheometer with another necessary parts, eg. rheometer`s holder, drive frame and important jig tools. The rheometer is able to measure rheological properties of magnetic and non-magnetic fluids at very high shear rates, which commercial rheometers can not reach. It is designed for 200 bar pressure and maximum load 15 kN. The construction of the slit-flow rheometer with it`s holder and drive frame improves user friendliness, accelerates change of the fluid sample and expands research opportunities thanks to a big space for additional adjustments. It is possible to use different length of the slit and thanks to a changeable inserts it is possible to change parameters of the slit (roughness of the walls, wall material, thickness of the slit). A part of this thesis was focused on illation of necessary equations for planning calibration measurements. Aim of these measurements is to obtain minor pressure losses dependence on Reynolds number for specific slit.

This thesis reports recent numerical investigation of the rheological behavior of fresh concrete using the Distinct Element Method (DEM). Some relevant questions of the concrete rheology e.g. the influence of the concrete composition on the rheological behavior of the fresh concrete, the experimental determination of the Bingham rheological constants as well as the use of these constants in the numerical simulation were discussed thoroughly. An important topic of the performed investigation was the development of the numerical model for fresh concrete which enables simple, fast and stable predictive simulation of different technological operations with fresh concrete. Firstly, in a literature survey, the state-of-the-art of the numerical simulation of fresh concrete was presented and critically discussed in order to show advantages and disadvantages of other methods and modeling approaches. Open (unsolved) questions were highlighted and the basis for their investigation is created within this thesis. Fundamental concepts of the rheology were then presented and the basic rheological models of viscoelastic materials were considered; the rheological behaviors of different types of concretes were presented and its influencing factors were discussed. Additionally main methods for scientific investigation and testing of the fresh concrete were shown. The test methods were critically discussed in order to select the test, which has been used as a reference experimental test for the numerical simulations. Chosen reference experimental test was the slump flow test. The slump flow test was thoroughly analyzed and an analytical solution was developed which helps to interpret the results of measurements and provides a link between rheological constants and measured quantities. In a further step an extensive experimental program was carried out in order to investigate the rheological behavior of fresh concrete and get the input data for numerical simulation. Firstly, the experiments on macrolevel were performed. Here the rheological behavior of the fresh concrete flow in different tests was investigated (slump and slump flow tests, L-Box). Further, the experiments on mesolevel with polymer on Carbopol basis and mortar were developed and performed in order to investigate the interaction between distinct particles suspended in a fluid matrix. The necessary material parameters, especially those representative of the fluid suspension micromechanical behavior, i.e. the force-displacement relationship, yield force and bond strength, were determined by these experiments. The slump flow test was used as the basic test to calibrate the model for fresh concrete (key data: slump value, slump flow diameter (for concretes with a soft consistency) and the time of spreading). Thus, the decisive phenomena of the fresh concrete flow were highlighted, control points for a contact model were selected and the initial input data for the development of the contact model was obtained. Next, the user-defined contact model was developed and implemented into the Particle Flow Code ITASCA. The contact model was completely described and its limitations discussed. Then, the set of numerical tools was developed, which enable simplified and stable numerical simulation of the fresh concrete with particular behavior, i.e. automatic generation of the concrete with given particle grading, amount of fibers and air, automatic recalculation of the micromechanical parameters of the contact model from given initial yield stress and plastic viscosity. The model was calibrated by slump flow test simulations and validated by corresponding analytical approach. Further, the role of different model parameters was investigated by simulating the slump flow test. Furthermore, for verification of the model several additional experiments were simulated, i.e. L-Box and LCPC-box test. The results of modeling were compared with experimental results and discussed in detail. All numerical simulations provide qualitatively as well as quantitatively correct results and hence adequately represent the phenomena observed in real experiments. The thesis closes with general conclusions and outlook of the work. In the future, the developed contact model and tools of the “Virtual concrete laboratory” could be modified in order to extend the potential of the laboratory to cover such properties as thixotropic behavior of fresh concrete or simulating hardening of the concrete and behavior of the hardened concrete.

No description available.

Doctor of Philosophy / Department of Grain Science and Industry / Yong Cheng Shi / To realize the full potential of waxy wheat flours in food applications, six advanced hard waxy wheat lines were studied. Pasting properties of waxy wheat flours as well as factors governing the pasting properties were investigated. Waxy wheat starch granules swelled more extensively and were more prone to α-amylase degradation than normal wheat starch. A combination of endogenous α-amylase activity and protein matrix contributed to a large variation of pasting properties of waxy wheat flours. Bi-axial extension properties classified dough from waxy wheat as in-elastic. Waxy wheat flour had higher water absorption and lower mixing time than normal wheat flour. Waxy wheat starch affected protein hydration but not protein extractability after optimum dough mixing. Presence of some non-protein free thiol contents and some gliadins acting as chain terminators could be the underlying reasons for waxy wheat flours producing slack dough. In an effort to improve functionality of waxy wheat flours, hydro-thermal processing was used. Two temperatures (140 and 160°C), three moisture contents (0, 12.4 and 20%), and four exposure times (0, 5, 15, 30 and 60 min) were employed. Hydrothermal processing resulted in non-cohesive waxy wheat flours with high viscosity and greater acid stability than native waxy wheat flour. A closer investigation revealed the possible role of endosperm proteins in improving pasting properties of waxy wheat flours. Upon thermal processing, waxy wheat flours demonstrated a long hydration time before forming dough. Heating decreased protein solubility while no changes in starch molecular weight distribution were observed. Our results indicate that hydro-thermal processing results in increased starch protein interaction. As part of application of waxy wheat, bread was baked by replacing normal wheat flour with two hard waxy wheat flours at 15, 30, and 45% levels. Substitution with waxy wheat flour resulted in higher loaf volume and softer loaves. However, substitution at > 30% resulted in excessive post-bake shrinkage and a ‘key-hole’ shape with an open crumb structure. Bread crumb microstructure indicated a loss of starch granule rigidity and fusing of starch granules. Soluble starch content was significantly higher in bread 1-day old crumb containing waxy wheat flour than in control bread.

Doctor of Philosophy / Department of Grain Science and Industry / Hulya Dogan / Jon Faubion / Bread quality and final crumb grain are reflective of the ability for wheat flour dough to retain and stabilize gas cells during the baking process. The visco-elastic properties of dough allow for the incorporation of air cells and expansion during fermentation and baking. The gluten-starch matrix provides the backbone support. However, following the end of proofing and during the beginning of baking, the structure weakens due to over-extension and expansion and the matrix begins to separate and eventually break down. Native wheat lipids, which are found in small quantities in wheat flour, provide a secondary support for gas cell stabilization because of their amphiphilic characteristics and ability to move to the interface and form condensed monolayers. The objectives of this research were to evaluate the influence of native wheat lipids on the rheological properties of dough and the microstructure of bread. Native wheat lipids were extracted from straight-grade flour and separated into total, free, bound, nonpolar, glycolipids, and phospholipids using solid-phase extraction (SPE) with polar and nonpolar solvents. Defatted flour was reconstituted using each lipid fraction at a range of levels between 0.2% and 2.8%. Dough and bread were made following AACC Method 10-10.03. Rheological testing of the dough and evaluation of the microstructure of the bread was conducted using small and large deformation testing, C-Cell imaging, and x-ray microtomography analysis to determine changes in visco-elastic properties and gas cell structure and distribution. Rheological assessment through small amplitude oscillatory measurements demonstrated that nonpolar, phospholipids, and glycolipid fractions had a greater interaction with both proteins and starch in the matrix, creating weaker dough. Nonpolar, phospholipids, and glycolipids, varied in their ability to stabilize gas cells as determined by strain hardening index. C-Cell imaging and x-ray microtomograpy testing found that treatments containing higher concentrations of polar lipids (glycolipids and phospholipids) had a greater effect on overall loaf volume, cell size, and distribution. This illustrates that level and type of native wheat lipids influence the visco-elastic properties of dough and gas cell size, distribution, cell wall thickness, and cell stability in bread.

Master of Science / Department of Grain Science and Industry / Hulya Dogan / Kansas is the top wheat-producing state, providing about 1/5 of the yearly wheat crop in the U.S. Therefore, the quality of wheat grown in Kansas is a primary concern of the milling and baking industry. Quality of wheat flour is measured through analysis of protein, dough rheology, and baked product characteristics. This study characterized four commonly-grown Kansas hard red winter wheat cultivars chosen to span the largest possible range of protein contents and baking qualities. Flour protein content and moisture was determined by NIR, and composition was assessed using SE-HPLC. Dough empirical rheological and mixing characteristics were determined by farinograph and mixograph recording dough mixers. Rheological measurements of fundamental dough properties were performed through strain sweeps, frequency sweeps, temperature sweeps, creep-relaxation, and stress relaxation on a rheometer. All cultivar flours were baked to assess baking quality through evaluation of loaf volume, texture profile analysis (TPA), C-cell, and x-ray microtomography (XMT). Overley and Karl 92 have the two highest protein contents, respectively, and are not significantly different in percent of unextractable polymeric protein (UPP). Generally, cultivars with higher protein and percent UPP (Overley and Karl 92) gave larger loaves, much more expanded air cells, thinner cell walls, greater void fractions, and better mixing properties. Lower TPA firmness was found for Overley, corresponding with its larger XMT fragmentation index, existence of large air cells, and high void fraction. In contrast, 2137 gave the lowest XMT fragmentation index, low void fraction, larger cell wall thicknesses, and a significantly firmer (P< 0.05) crumb structure. Protein content was found to have an inverse relationship with the elastic nature of dough in fundamental rheological measurements since small amplitude measurements generally do not give good correlations to baking quality. Stress relaxation gave the most useful information about flour quality through its relaxation spectra. Flours with high total polymeric protein percentages could be identified through their higher relaxation spectra. Starch gelatinization properties of the flours were different for RVA and rheometer temperature sweeps. All of these tests have helped characterize the four Kansas wheat cultivars chosen for this study.

Résumé : Le climat local, le transport avec l’agitation entre l’endroit de bétonnage et le site de fabrication du béton influencent fortement les propriétés du béton frais et durci. Selon les particularités du béton autoplaçant (BAP), le maintien de l’homogénéité et l’ouvrabilité du BAP avant la mise en place est très important. Les propriétés des BAP sont généralement plus sensibles à la température et au transport par rapport à celles des bétons conventionnels. Une meilleure compréhension de l’effet de la température et de l’agitation sur la performance des BAP est nécessaire pour prévoir les conséquences du changement du climat (température) et de l’effet du transport (temps et vitesse d’agitation), puis pour donner des précautions à suivre afin de répondre à la demande des BAP pour un bon rapport performance-coût. De manière pragmatique, il s’avère nécessaire d’utiliser la méthode du mortier de béton équivalent (MBE) afin d’analyser rapidement les influences de la température et de l’agitation sur les propriétés rhéologiques, calorimétriques et mécaniques des BAP. Cinq températures (8, 15, 22, 29 et 36°C) et deux vitesses d’agitation (6 et 18 tr/min) ont été étudiées sur les MBE. Ensuite, quelques compositions spécifiques (type d’adjuvant et ajout cimentaire) ont choisies afin de vérifier avec des températures compasse entre 8 à 36°C et les agitations différentes (2 et 6 tr/min) sur les BAP destinés aux travaux de bâtiment (BAP-B) sans agent entraîneur d’air et sur des bétons semi-autoplaçant destinés aux travaux d’infrastructures (BSAP-I) avec agent entraîneur d’air. La fluidité initiale des MBE et BAP a été fixée en faisant varier la demande en SP, la température et l’agitation. Les résultats montrent qu’il y a un effet important de la température et de l’agitation sur l’efficacité des adjuvants, la fluidité, la teneur en air, les propriétés rhéologiques, calorimétriques et mécaniques des MBE et des BAP. Pour prévoir la performance de MBE à différentes températures, une équation mathématique est proposée pour déduire la demande en SP, la demande en AEA, le flux maximal et la résistance en compression à 1 jour en fonction des mêmes propriétés sur MBE à 22°C et de la température. Enfin, une corrélation linéaire a été trouvée entre les MBE et les BAP sur ces mêmes propriétés. / Abstract : The local climate, the transport of agitated concrete after manufacturing but before being cast strongly influence the properties of the fresh and hard concrete. It’s important to keep the stability and workability of the self-consolidating concrete (SCC) because of its special characteristics. Compare to the normal concrete, the properties of SCC are generally more sensitive to the temperature and the transport. Therefore it’s necessary to understand the effects of the temperature and the agitation on the performance of the SCC in order to predict the consequences of climate change (temperature) and transport (time and speed of agitation), and then to give the better precautions with a good performance-cost report. In this study, the concrete mortar equivalent (CEM) method is used to quickly analyze the influences of the temperature and the agitation on the rheological, calorimetric and mechanical properties of the SCCs. Five temperatures (8, 15, 22, 29 and 36°C) and two agitation speed (6 and 18 tr/min) are varied in CEMs. And then, some compositions (type of adjuvant and supplementary cementing material) are chosen to be valued with the temperature (8-36°C) and the agitation (2 and 6 tr/min) in SCCs for the building without air-entraining admixture (AEA) and semi-flowable SCC for infrastructure with AEA. The initial slump flow of CEM and SCC is fixed, but the demand superplasticizer, the temperature and the agitation were varied. The results show that there are the effects of temperature and agitation on the effectiveness of admixture, the slump flow, the air content, the rheological, calorimetric and mechanical properties of CEM and SCC. A mathematical equation is proposed to predict the performance of SCC at different temperatures for the SP and AEA requirement, the maximum of heat flow and the compressive strength at one day by these same properties of SCC at 22°C and by the temperature. Finally, a good linear correlation is found between CEM and SCC for these properties.

The influence of low molecular weight additives containing polar groups and modified polyolefin-based compatibilisers on polypropylene (PP)-clay nanocomposites (PPCN) has been studied, in terms of intercalation and degree of exfoliation achievable by melt state mixing processes. PPCN were prepared by melt mixing of two commercial pp homopolymers with organically modified clay (OMMT) in the presence of maleic anhydride grafted pp (PP-MA). X-ray diffraction (XRD) analysis shows that the interlayer spacing of clay increases dramatically, whilst transmission electron microscopy (TEM) results show a significant improvement of clay dispersion in the PP matrix, when nanocomposites are prepared with commercial PP containing short chain organic additives with polar groups (amide-type slip and antistatic additives). Subsequent studies based upon customised PP formulations, with short chain amide molecules (AM), confirm the intercalation of this additive into clay galleries. The maximum interiayer spacing is achieved with low concentrations of this additive (0.5 wt. %). Contact angle measurements and low shear melt flow properties (MF!) further confirm the diffusion of this additive (AM) into the clay galleries rather than migrating away from the bulk of the PPCN. The interaction between the polar group (CONH2) of this additive and polar sites of the clay surface appears to be the driving force for the intercalation. Although this additive intercalates and allows the formation of an intercalated nanocomposite structure with non homogeneous dispersion of clay, an exfoliated PPCN structure is yet to be formed with this additive alone. A new preparation method for PPCN has therefore been developed by co-intercalation of AM and PP-MA. PPCN were prepared by this method with a significant reduction of overall PP-MA concentration in the nanocomposite structure, relative to conventional PPCN prepared with compatibiliser (PP-MA) only. XRD and TEM analysis showed that nanocomposite structures are formed with significantly improved clay dispersion, compared to PPCN prepared using the conventional method. Quantification of clay exfoliation, using image analysis software, showed that higher degrees of exfoliation can be achieved in PPCN from this new cointercalation method. Normalised melt flow index (n-MFI) data showed the relationship between low shear flow properties and clay structure and is an appropriate parameter to examine clay exfoliation and its interaction with pp in PPCN. Enhanced thennal stability of PPCN, in comparison to pure PP, further demonstrates the improved clay dispersion in nanocomposite structures prepared by the co-intercalation method. A possible mechanism for the co-intercalation of AM and PP-MA into clay galleries has been proposed, based upon hydrogen bonding between these additives and the silicate layers. Rheological characterisation of PPCN, using capillary rheometry experiments at high shear rates, shows a shear thinning, pseudoplastic behaviour similar to pure PP. However, a comparatively higher concentration of AM appears to reduce the shear viscosity of PPCN. Die swelling behaviour revealed a reduction in melt elasticity in PPCN melts in comparison to unmodified PP. Reduced die swell occurs as a result, together with a delay in the onset of melt fracture. Sheet extrusion was used to produce PPCN products with increasing clay loading levels that were evaluated for a range of mechanical properties. Significant enhancement of modulus in PPCN is achieved in comparison to pure PP whilst maintaining similar strength characteristics. However, impact resistance of extruded PPCN sheets is not improved in comparison to unmodified PP. Results have been interpreted with reference to the degree of exfoliation, additive content and differences in PP crystallinity.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Heterophasic copolymers (also known as HECO polymers) or often referred to only as impact copolymers or block copolymers comprise a polymer matrix with a dispersed rubbery copolymer phase. The polymer under investigation in this study consists of a polypropylene homopolymer matrix and ethylene-propylene copolymers (EPCs). Due to its diverse range of applications and unique properties, polypropylene is the choice of polymer for a vast array of applications. This has led to the development of an entire class of polypropylene materials known as visbroken or controlled rheology polypropylene. By adding a suitable peroxide to the polymer in the presence of heat, radicals are formed which will attack the polymer chains in a random fashion. The resultant polymers generally have a higher melt flow rate (MFR), a narrower molecular weight distribution than the parent polymer, and good impact-stiffness balance. The main focus of this investigation was to determine if there exist any differences in the molecular structure and physical properties of controlled rheology HECO polymers and if differences do exist, how they influence the physical characteristics of the polymer. Eight HECO polymers with equal ethylene contents were visbroken to varying degrees by making use of two different types of organic peroxide. The effects of the amount of visbreaking on the molecular characteristics and physical properties were subsequently studied by making use various types of fractionation techniques, including preparative temperature rising elution fractionation (PTREF) and crystallisation analysis fractionation (CRYSTAF). Subsequent offline analysis was then done on the fractionated samples that included nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), high temperature size exclusion chromatography (HT-SEC), Fourier transform infrared spectroscopy (FTIR) and deposition of the SEC fractions via the LC Transform Interface (SEC-FTIR) as well as high temperature high performance liquid chromatography (HT-HPLC), a novel technique for the characterization of olefins according to their chemical composition. / AFRIKAANSE OPSOMMING: Heterofase kopolimere, ook bekend as HECO polimere, of dikwels na verwys net as impak kopolimere of blok kopolimere bestaan uit 'n polimeer matriks met 'n verspreide rubberagtige kopolimeer fase. Die polimeer wat in hierdie studie ondersoek was het bestaan uit 'n polipropileen homopolimeer matriks en etileen-propileen kopolimere (EPCs). As gevolg van sy veelseidigheid van toepassings en unieke eienskappe is polipropileen die keuse van polimeer vir 'n wye verskeidenheid van toepassings. Hierdie veelseidigheid het gelei tot die ontwikkeling van 'n hele klas van polipropileen materiaal bekend as gevisbreekte of beheerde reologie polipropileen. Deur die byvoeging van 'n geskikte peroksied tot die polimeer in die teenwoordigheid van hitte, word radikale gevorm wat die polimeerkettings in 'n ewekansige wyse sal aanval. Die gevolglike polimere in die algemeen het 'n hoë smelt vloeitempo (MFR), 'n smaller molekulêre gewig verspreiding as die moeder polimeer, en 'n goeie impak/styfheid balans. Agt HEKO polimere met gelyke etileen inhoude was gevisbreek in wisselende hoeveelhede deur gebruik te maak van twee verskillende tipes organiese peroksiedes. Die gevolge van die hoeveelheid van visbreeking op die molekulêre eienskappe en fisiese eienskappe was vervolgens gebestudeer deur gebruik te maak van verskillende fraksionasie tegnieke, insluitend preparatiewe TREF (P-TREF) en CRYSTAF. Daaropvolgende analiese is gedoen op die gefraktioneerde monsters en sluit in kernmagnetiese resonansie spektroskopie (KMR), differensiële skandeer kalorimetrie (DSC), 'n hoë temperatuur grootte uitsluitings chromatografie (HT-SEC), Fourier transform infrarooi spektroskopie (FTIR) met deponeering van die SEC fraksies via die LC transform koppelvlak (SEC-FTIR) sowel as 'n hoë temperatuur hoë werkverrigting vloeistof chromatografie (HT-HPLC), 'n nuwe tegniek vir die karakterisering van olefiene volgens hul chemiese samestelling.

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.