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This thesis describes a series of studies of the physical behaviour of commercially important stabilizing additives in polyolefins. A series of nickelthiocarbamates have been synthesised and their solubilities measured as a function of temperature in linear hydrocarbon solvents, low density polyethylene and isotactic polypropylene. The results are compared with predictions from a regular solution model. The loss of three benzophenone UV-stabilizers from supersaturated solution has been investigated with the aim of determining whether the loss is a diffusion controlled blooming or involves phase separation. Our data shows this phenomenon is a diffusion controlled blooming process. The volatilities of these same UV-stabilizers have been measured as a function of temperature. The solubility of a typical hindered amine (Tinuvin 770) has been investigated in hydrocarbon solvents and in polypropylene by infrared methods. Low solubility values were obtained in all cases. The diffusion of Tinuvin 770 in polypropylene has been monitored by an infrared method developed for the purpose and the diffusion coefficient estimated over a range of temperatures. Litp.rature data on solubility of additives together with our own data are critically reviewed and the effect of structure on solubility is analysed. Data on the benzophenone additives allows prediction of loss times and mechanisms to be made for the first time.

No description available.

Over the past couple of decades interest in particle-stabilised emulsions or Pickering emulsions has greatly increased. When using particles as stabilisers, as opposed to surfactants, the interface becomes more rigid and this can lead to interesting physical properties. In addition, the resulting emulsions are found to be longer-lived garnering commercial interest. This thesis aims to explore the mechanical properties of some specific systems containing particle-stabilised interfaces. The main system investigated was the bicontinuous interfacially jammed emulsion gel or bijel. The bijel has two continuous interpenetrating liquid phases separated by a particle-stabilised interface. Therefore, the structure has a very large interface in a fairly small volume and the pore size is under the experimentalist's control giving it promise in a variety of applications, particularly those based on catalysis. The response of bijels stabilised by either spherical particles or anisotropic rod-shaped particles to centrifugal compression has been investigated in this thesis. It was found that, in both cases, the structure was distorted to create anisotropic particle-stabilised sheets orientated perpendicular to the force. The original method for fabricating bijels involves the arrested spinodal decomposition of partially miscible liquids. This method requires partially miscible liquid pairs and particles that are equally wetted by each phase. Due to these requirements, a new method for making bijels using mixing was developed by others and the bijel made by mixing has been tested with oscillatory rheology combined with imaging and squeeze flow experiments. It was found that at low strain the bijel displayed solid-like behaviour and the structure remained intact until well past the yielding point. In addition, two further systems were investigated. The first system was rod-shaped particle-stabilised emulsion droplets that stick together by particle bridging. Bridging is where one particle can stabilise two droplet interfaces, preventing coalescence and leading to droplet clusters. Particle bridging was found to occur regardless of shear rate, particle volume fraction and to some extent aspect ratio with these anisotropic rod-shaped particles. This behaviour is hypothesised to be a consequence of the charged nature of the silica surface above pH 2. The second system was large particle-stabilised water droplets that can sprout tubes by the partitioning of solute from a bath into the droplet. By using different solutes and mixtures of different alcohols, the key requirements for sprouting behaviour have been ascertained. The most important requirement was found to be achieving the correct balance between the interfacial tension and the amount of solute partitioning into the droplet.

This study explores the role of design as a force that may stabilise cultural identity in a cultural climate of globalisation through the use of visual rhetoric and narrative. It focuses specifically on the heritage and face of a German culture in South Africa. Objects that are found amongst the South African German community are analysed in an attempt to uncover the rhetoric and narrative of the culture’s heritage in a country far removed from their Heimat. The study deals with terms such as Sehnsucht and belonging, of maintaining a sense of cultural difference while being integrated and socially accepted. It uses visual rhetoric as a means to discover elements that may be used by design in order to adequately represent the Germanness of the South African German community in a way that it can be maintained in today’s way of life. / Dissertation (MA)--University of Pretoria, 2012. / Visual Arts / unrestricted

The main purpose of this thesis was to find ways to maintain a low level of light‐induceddiscolouration at an increased addition of mechanical and chemimechanical pulps in coated highqualityfine paper and magazine paper grades. Current technology allows the production of highyieldpulps such as thermomechanical and chemimechanical pulps with properties suitable formanufacturing high‐quality paper or paperboard with a low basis weight. Coating of woodcontainingpaper will probably be necessary for photo‐stability reasons if lignin‐containing pulps areto be used as the main fibre furnish in long‐life and high‐value products.In order to find the most suitable pulp for this purpose, light‐induced discolouration of a variety ofpaper samples from unbleached and bleached softwood and hardwood pulps was studied under bothaccelerated and long‐term ambient light‐induced ageing conditions. Hardwood high‐yield pulps,especially aspen pulps, were proven to be more photo‐stable compared to softwood pulps. Hardwoodpulps should therefore be the first choice for applications where a high permanence is desirable.Evaluating ageing characteristics using the CIELAB colour system showed that accelerated ageingconditions tend to mainly increase the b* value and decrease the L* value (i.e. yellow the pulp),whereas long‐term ambient ageing also increases the a* value, which makes the pulp more reddish.A new method for studying the influence of the UV‐screening properties of coating layers on abase paper was developed, and used to investigate the effect of pigment, pigment size distribution,binder and UV‐absorbing additives. The coat weight and pigment type were found to be the mostimportant factors for reducing the transmittance of UV‐radiation. Coating colours containing kaolinpigments had a lower UV‐transmittance than calcium carbonate pigments. Of the calcium carbonates,precipitated calcium carbonates were better than ground calcium carbonates and the difference wasgreater at higher coat weights. The particle size distribution should preferable be narrow. When thebest pigment (bleached kaolin) and the best binder (styrene butadiene latex) were combined withtitanium dioxide, the UV‐transmittance could be reduced by about 90% at a coat weight of ~10 g/m2.At a coat weight close to 20 g/m2, the transmittance was close to zero. This shows that it is possible tomore or less fully protect a double coated base paper from harmful UV‐radiation, when the coatinglayer has an optimum composition for that purpose. A prerequisite to reach so far is that the coatinglayer has an even coat weight.

Klasická lineární regrese a z ní odvozené testy hypotéz jsou založeny na předpokladu normálního rozdělení a shodnosti rozptylu závislých proměnných. V případě že jsou předpoklady normality porušeny, obvykle se užívá transformací závisle proměnných. První část této práce se zabývá transformacemi stabilizujícími rozptyl. Značná pozornost je udělena náhodným veličinám s Poissonovým a negativně binomickým rozdělením, pro které jsou studovány zobecněné transformace stabilizující rozptyl obsahující parametry v argumentu navíc. Pro tyto parametry jsou stanoveny jejich optimální hodnoty. Cílem druhé části práce je provést srovnání transformací uvedených v první části a dalších často užívaných transformací. Srovnání je provedeno v rámci analýzy rozptylu testováním hypotézy shodnosti středních hodnot p nezávislých náhodných výběrů s pomocí F testu. V této části jsou nejprve studovány vlastnosti F testu za předpokladu shodných a neshodných rozptylů napříč výběry. Následně je provedeno srovnání silofunkcí F testu aplikovaného pro p výběrů z Poissonova rozdělení transformovanými odmocninovou, logaritmickou a Yeo Johnsnovou transformací a z negativně binomického rozdělení transformovaného argumentem hyperbolického sinu, logaritmickou a Yeo-Johnsnovou transformací.