<p>In recent years, cellulose nanocrystals (CNCs) isolated from natural cellulosic sources through an acid hydrolysis treatment have garnered significant interest in both academia and industry. CNCs have attracted attention not only because they stem from an abundant, renewable resource and are biodegradable, but also because of their low density, light weight, high aspect ratio, high tensile strength and a specific Young’s modulus comparable to steel and Kevlar. These properties make CNCs ideal for use as reinforcing agents in nanocomposites, as well as stabilizing agents in foams and gels. However, due to the high surface area and hydrophilic nature of CNCs, unmodified nanocrystals are difficult to disperse in non-polar materials. The lack of interfacial compatibility between components causes CNCs to agglomerate and thus their incorporation into conventional polymer matrices has been challenging at best, and unsatisfactory in most cases.</p> <p>In this work, CNCs have been rendered pH and temperature-responsive by surface-initiated graft polymerization of 4-vinylpyridine and <em>N</em>-isopropylacrylamide, respectively, using ceric (IV) ammonium nitrate as the initiator. The resultant suspensions of poly(4-vinylpyridine)-grafted cellulose nanocrystals (P4VP-<em>g</em>-CNCs) and poly(<em>N</em>-isopropylacrylamide)-grafted cellulose nanocrystals (PNIPAM-<em>g</em>-CNCs) show reversible hydrophilic to hydrophobic responses with changes in pH and temperature, respectively. The presence of grafted polymer and the tunable hydrophilic/hydrophobic properties were characterized via Fourier transform infrared spectroscopy, elemental analysis, electrophoretic mobility, mass spectrometry, transmittance spectroscopy, contact angle measurements, thermal analysis and various microscopies.</p> <p>The intention of this work has been to shift towards more industrially viable surface modification routes for CNCs by using a one-pot, water-based synthesis to produce a low cost and functional nanomaterial. Moreover, sonication is used throughout the polymerization reaction to avoid particle aggregation and ensure that individual CNCs are surface-functionalized. As a result, reproducible and uniform material properties have been measured in both suspensions and films of modified CNCs. The responsive nature of P4VP-<em>g</em>-CNCs and PNIPAM-<em>g</em>-CNCs may offer new applications for cellulose nanocrystals in hydrophobic nanocomposites, biomedical devices, as clarifying agents, and in industrial separation processes.</p> / Master of Applied Science (MASc)

An experimental and analytical study of the process of blown film extrusion was carried out. On-line measuring techniques were used to follow the dynamics and temperature profiles occurring in the process. The applicability of a mathematical model which includes a non-isothermal crystallization rate equation was tested. Subsequently, a new simplified model derived from a modified force balance was proposed and examined. Linear low density polyethylene, LLDPE, (melt flow index 1.0) provided by Dow Chemical Company was used in the experimental part of the study. On-line measurements for radius, thickness, velocity and temperature as a function of distance from the extrusion die were carried out, and their reliability was examined. The results indicated that these measuring techniques were sufficiently accurate to make the collection of on-line data a useful analytical tool. The measured profiles of radius, thickness, velocity and temperature were used to test the theoretical model for the tubular film blowing process. The apparent elongational viscosity, a key parameter for the theoretical simulation, was estimated and calculated from experimental data taken on a melt spinline and an inversion procedure developed for obtaining apparent elongational viscosities for melt spinning. This gave a Newtonian, temperature-dependent apparent viscosity equation. The heat transfer coefficient was estimated from measured temperature profiles on the blown film process. A computer simulation for semi-crystalline materials was carried out using the mathematical analysis for film blowing which appears in the literature plus a non-isothermal crystallization rate equation. The analysis was carried out by using the fourth-order Runge-Kutta method to solve the resulting differential equations. The predicted results were in qualitative agreement only with the experimental data. At the same time, several unexpected phenomena appeared in the simulation. Some of them have also been reported in the previous literature, but still no satisfactory interpretation is available. A modified physical approach based on a force balance led to the derivation and proposal of a new simplified model. From this modified analysis, an important and useful relationship between the external forces (i.e., the net takeup force and the inflation pressure) and the variation of radius and thickness of the bubble were determined. Based on the same initiaI conditions as that of the original model, the new model gave predictions which were in fair quantitative agreement with the on-line measurements. Finally, it was also found that the development of crystallinity strongly influences the final values of radius and thickness of the tubular film, two of the important specifications in industrial film processing. In other words, the effect of crystallization is so significant that it should not be neglected in modelling the tubular film blowing process.

Effect of new curing and toughening agents

This dissertation describes research performed using siloxane polymers. This includes the reactions of siloxane polymers with inorganic oxide surfaces to form covalently attached monolayers, and the electrical properties of crosslinked silicone composite films fabricated by compounding with nickel particles. In addition to these topics, the use of contact line pinning as a practical and controllable method for the deposition of materials on superhydrophobic and chemically patterned surfaces is also described The first chapter provides a general review of siloxane polymer chemistry, focusing in particular on the relationship between molecular structure and physical properties. The use and fabrication of silicone composite materials is also discussed, including typical methods for crosslinking siloxane polymers and the effects of filler materials. Finally, contact angle hysteresis and contact line pinning phenomena are presented. Following this introduction, four separate but interrelated projects are presented. First, the surface modification of titania via hydridomethylsiloxanes is discussed. This work represents an extension of the reaction of hydridosilanes and provides an environmentally clean method for the hydrophobization of titania. Linear and cyclic hydridomethylsiloxanes, as well as hydridomethylsiloxane-co-dimethylsiloxane polymers, are used as reagents and the resulting surfaces are discussed. Unpredicted results from this method lead to the consideration of poly(dimethylsiloxane) as a previously unconsidered reagent presented in the next project. The second project discusses the covalent attachment of siloxane polymers, particularly poly(dimethylsiloxane), to a range of inorganic oxide surfaces, including titania, nickel oxide, alumina, and silica. This reaction is presented as a thermally activated equilibrium process, and offers insight into certain aging processes found in silicone materials. Particular focus is made on the development of a highly reproducible method for the fabrication of low contact angle hysteresis surfaces. Furthermore, this reaction is shown to be general for the siloxane bond through the reaction of functional and cyclic siloxanes. The third project describes the preparation of electrically conductive silicone coatings, containing nickel and titania particles. The effect of nickel concentration and geometry on the electrical properties of these coatings is examined and the effects on the percolation threshold are presented. In addition to this, the addition of titania nanoparticles to diminish electrical conductance is also investigated. The fourth project discusses the contact line pinning of liquids on hydrophobic surfaces. In this chapter, the use of ionic liquids exhibiting no vapor pressure is used to experimentally determine the de-wetting process of liquids from pillared, superhydrophobic surfaces through micro-capillary bridge rupture. Furthermore, this technique is used as a preparative technique for the fabrication of individual salt crystals supported on pillared surfaces.

Geometrically hindered motions of a single large solute (particle or polymer) can be imaged in real time via optical microscopy. The dynamics of fluorescent colloidal particles near surfaces and in porous membranes were monitored using confocal microscopy. A method of analysis to estimate diffusivity of particles in the axial direction by observing their intensity fluctuations was developed. The intensity fluctuations correspond to the Brownian motion of the particles in the axial direction. The method was successful in capturing the hindered diffusion of particles close to surfaces and in pores. This study provides a novel route to monitor the dynamics of particles, including biomacromolecules, near surfaces, through porous substrates and biological tissues. Ionic liquid (IL) as a medium for room temperature preservation of biomacromolecules has been proposed and, to investigate the possibility, physicochemical and enzymatic properties of proteins in the neat hydrophilic IL, ethylmethyl imidazolium ethyl sulfate [EMIM][EtSO4] were studied. Spectroscopic techniques were employed to probe the secondary and tertiary structure of proteins whereas light scattering and viscometry were used to estimate the hydrodynamic size. The secondary structure of the protein was retained in the ionic liquid but the tertiary structure was found to change. Alterations in protein conformation/activity were investigated after transfer of the dissolved protein from the IL to buffer. Further, suitability of ionic liquid gels as protein encapsulation and preservation media was assessed.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Various companies produce waxes, which are used extensively in various applications, either as produced or as chemically or physically modified value-added products. They are used in the traditional candle industry and applications including hot melt adhesives, inks, plastics, polishes and emulsions for rust prevention or fruit coating. Insight into the properties of these waxes is required to assist the applications chemist in understanding the role of the wax component in a specific formulation. Analytical techniques such as differential scanning calorimetry (DSC), thermogravimetry (TG), rheometry, gel permeation chromatography (GPC), high temperature gas chromatography (HTGC) and infra-red spectroscopy (IR) were used to characterise Fischer Tropsch, polyethylene, natural and petroleum waxes. Property profiles were formulated by integrating the results from the various techniques. The results of traditional wax analyses (e.g. congealing point, melting point, penetration, density and viscosity) were also correlated to relevant analytical results obtained from the instrumental techniques. Structure-property relationships have been proposed. / AFRIKAANSE OPSOMMING: Verskeie maatskappye vervaardig wasse, wat in menige toepassings gebruik word - of direk, of as chemies- of fisies- veranderde produkte van hoër waarde. Benewens die tradisionele kersbedryf, word die wasse in toepassings soos warmsmeltkleefmiddels, ink, plastiek, roeswerende- en vrugtebedekkings- emulsies en politoere gebruik. Wetenskaplikes betrokke by die formuleering van wasse vir verskillende toepassings sal baat vind by beter inligting van waseienskappe en die rol van waskomponente in formulasies. Tegnieke, bv. differensialeskandeerkalorimetrie (DSC), termogravimetrie (TG), reologie, gelpermeasiechromotografie (GPC), hoëtemperatuurgaschromatografie (HTGC) en infrarooispektroskopie (IR), is gebruik om Fischer Tropsch-, polietileen-, petroleum- en natuurlike wasse te karakteriseer. Profiele van waseienskappe is geformuleer deur die integrasie van die data verkry van die verskillende analitiese tegnieke. Die resultate van tradisionële wasanalises (bv. stolpunt, smeltpunt, penetrasie, digtheid, viskositieit en olie-inhoud) word ook in verband gebring met die resultate van die instrumentele analises. Verbande tussen struktuur en waseienskappe word ook voorgestel.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: In this study, the feasibility of the non-conjugated 1,5-hexadiene as monomer in metallocene catalised cyclopolymerizations was considered. Homopolymers and copolymers with ethylene, propylene, 1-pentene, 1-hexene and 2-methyl-1,5- hexadiene as comonomers were synthesised in the presence of Cp2ZrCh and rac-Et(lnd)2Zrh. The microstructure (stereoregularity and cyclisation) and number-average molecular weight were determined from NMR analysis. Crystalline oligomers with functional (eg -OH) and vinylidene end groups were obtained. / AFRIKAANSE OPSOMMING: Die studie behels die ondersoek rakende die gebruik van ongekonjugeerde 1,5- heksadieen as monomeer in metalloseengekataliseerde polimerisasies. Homopolimere, sowel as kopolimere van etlieen, propileen, 1-penteen, 1- hekseen en 2-metiel-1,5-heksadieen, is in die teenwoordigheid van Cp2ZrChen rac-Et(lnd)2ZrCI2 gepolimeriseer. Die mikrostruktuur (stereochemie en siklisering) en die getal-gemiddelde molekulêre gewig van die gesintetiseerde polimere is met behulp van KMR spektroskopie ondersoek. Die studie het getoon dat kristallyne oligomere met funksionele (bv -OH) en vinilideen endgroepe gesintetiseer is.

No description available.

Dissertation (Ph.D.)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Self-emulsifiable and self-assembling nano-particle phosphated and siloxane-modified polyurethane dispersions, for use in metal coatings, were synthesised from a new phosphate monomer, a carboxylate monomer, a polysiloxane macroglycol and a . cycloaliphatic diisocyanate, and characterised. Crosslinked nano-particles of acrylic-modified, self-assembling, phosphated polyurethane dispersions with better water swell resistance were obtained using the phosphated nanoparticles as the 'seed' to polymerise monofunctional and multifunctional acrylic monomers in the dispersed phase. This was done by reacting 2-hydroxyethyl methacrylate end-capped polyurethane with monofunctional and multifunctional acrylate monomers in the dispersed phase. Phase inversion of the polyurethane resin from an organic solvent into dispersion was accompanied by three stages, as studied by viscosity and conductivity measurements. In an attempt to modify existing synthesis procedures of the traditional polyurethane acrylic dispersions for which organic solvents are used, polymerisable acrylic monomers were used as diluents during the urethane-forming reaction. This resulted in overcoming the limitations of the existing process. Particle-size analysis indicated that the above dispersions had smaller particle sizes, narrower distributions and better hydrophobicity than any reported to date. Aqueous vinylterminated phosphated polyurethane dispersions were studied for their viscosity behaviour under shear and showed Newtonian behaviour. The polyurethane dispersions were evaluated for their hydrolytic stability with respect to the location of the ionic groups on the segments. Greater hydrolytic stability was obtained when the ionic groups were on the urethane hard segment. The polyurethane dispersionsresponded well to UV curing, a curing technique that has not received much attention to date. The surface and interface analyses of the self-assembling coatings obtained from the phosphated and siloxane-modified polyurethane dispersions showed increased silicon enrichment at the coating/air interface and phosphorus enrichment at the metal/coating interface. Results of dynamic contact angle studies proved the poor wettability of the coatings, as shown by the increase in contact angle by probe liquids. Dynamic thermogravimetry studies of the phosphate-containing polyurethanes showed a decrease in activation energy with increasing phosphate content. This is a good indication that phosphate-containing polyurethanes could be used as fire retarding coatings that comply with fire limit regulations. / AFRIKAANSE OPSOMMING: Self-emulgeerbare en selfsamestellende, nanopartikel, fosfaat- en siloksaanbevattende poliuretaandispersies, vir gebruik as deklae vir metale, is gesintetiseer en gekarakteriseer. Die uitgangstowwe vir die ~ bereiding was 'n splinternuwe fosfaatmonomeer, 'n karboksilaatmonomeer, 'n polisiloksaanglikol en 'n siklo-alifatiese diisosianaat. Deur die polimerisasie van die monofunksionele en multifunksionele akriel-monomere in die dispergeerde fase in te ent met die fosfaat-bevattende nanopartikels, is kruisgebinde nanopartikels van akrielgemodifiseerde, selfsamestellende, fosfaatbevattende poliuretaandispersies met goeie waterswelweerstand berei. Dit is bewerkstellig deur poliuretaan, met reaktiewe hidroksietiel-endgroepe, te reageer met monofunksionele akrilaatmonomere in die gedispergeerde fase. Fase-omkering van die poli-uretaanhars uit die organiese oplosmiddel, tot in dispersie, het in drie stappe plaasgevind. Dit is bepaal deur viskositeit en konduktiwiteit. Bestaande metodes van sintese Vir tradisionele poli-uretaanakrieldispersies, waarvoor organiese oplosmiddels gebruik is, is gewysig om die beperkinge van die bestaande metodes te oorkom. Suskes is behaal met die gebruik van polimeriseerbare akrielmonomere as verdunningsmiddels in die uretaanvormingsreaksie. Partikelgrootte-analises het getoon dat die verkreë dispersies kleiner partikelgroottes, nouer verspreidings en beter hidrofobisiteit gehad het as enige wat tot dusver beskryf is. Die viskositeit van die wateroplosbare, vinielgetermineerde, fosfaatbevattende poliuretanandispersies is onder afskuiwing bepaal en het Newtoniese gedrag getoon. Die hidrolitiese stabiliteit van die poli-uretane, met betrekking tot die posisie van die ioniese groepe in die segmente, is bepaaL ..Die polimere met die ioniese groepe in die harde segment van die poli-uretaan het hoër hidrolitiese stabiliteit vertoon. Kruisbinding (verharding) deur middel van UV, wat tot dusver min aandag geniet het, was baie suksesvol. Analises van die oppervlakte en die tussenvlak van die selfsamestellende deklaag, wat van die fosfaat- en siloksaanbevattende dispersies berei is, het verhoogde siloksaanverryking by die deklaag/lug tussenvlak en verhoogde fosfaatverryking by die metaal/deklaag tussenvlak getoon. Resultate van dinamiese kontakhoekstudies het bewys dat die deklae swak benat is, dws daar was 'n toename in die kontakhoek deur peilvloeistowwe. Termogravimetriese studies het getoon dat daar 'n afname was in die aktiveringsenergie van die fosfaatbevattende poli-uretane met 'n toenemende fosfaatinhoud. Hierdie feit dui daarop dat hierdie poli-uretane moontlik as brandvertragende deklae gebruik kan word.

No description available.