The effect of molecular composition on the properties of polyolefin-wood composites

Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Polymer composites, and in particular wood-polymer composites have become commercially and environmentally important materials. Studies in polyolefin-wood composites have mostly focused on polypropylene (PP) and polyethylene (PE). To our knowledge, no study has been undertaken on advancing impact polypropylene copolymer (IPPC)-wood composites as a suitable alternative to using PP and PE. IPPC have proven to be a suitable alternative to PP at low temperatures to improve impact resistance for manufactured polymer products, and could be a great addition to improved properties for wood polymer composites. This study shows that the physical properties of IPPC-wood composites can be markedly improved when compatibilizer(s) are used to improve the distribution of the wood within the matrix, as well as improving the interaction between the wood and the polymer matrix.. The use of different compatibilizers, vi polypropylene-graft-maleic anhydride (PPgMA) and poly(ethylene-co-vinyl alcohol) (EvOH) results in different physical properties. Using simple admixtures of the PPgMA and EvOH in IPPC-wood composites result in a large spread of results, while pre-reacting the PPgMA and EvOH to form a joint compatibilizer gives reproducible results w.r.t the physical testing. A study of the fundamental interactions of the compatibilizer(s) with the molecular components of the IPPCs was undertaken. The IPPCs used were fractionated by preparative temperature rising elution fractionation, and the fractions were mixed with the compatibilizers. To this end, fluorescence microscopy was utilized to study the interaction. The results clearly indicate that the interaction of the PPgMA with the fractions differ from that of the EvOH. These differences can be explained in terms of the chemical composition distribution within the IPPC fractions. Atomic force microscopy (AFM) was used to study adhesive forces between compatibilizer, polymer and cellulose and lignin. Successful coating of AFM tips with PPgMA and EvOH was achieved. Whilst interactions based on chemical force microscopy (CFM) could not be quantified, the AFM results in conjunction with fluorescence spectroscopy provided meaningful insight in the way that compatibilizers interact with both the wood and the impact copolymers used in this study.AFRIKAANSE OPSOMMING: Polimeer saamgestelde material, en meer spesifiek hout-polimeer saamgestelde material het die afgelope tyd belangrike produkte geword, beide kommersieel en in verband met omgewingvriendelikheid. Navorsing op die gebied van poli(olefien)-hout komposiete het tot op hede meestal gefokus op die grbruik van poli(propileen) (PP) en poli(etileen) (PE). Sover dit on kennis strek is daar nog geen studie gedoen om die gebied van impak polipropileen kopolimere (IPPK)-hout komposiete uit te bou nie. IPPKs is ‘n geskikte alternatief vir PP in veral laetemperatuur aanwendings. Die gebruik van IPPKs as matriks vir die hout komposiete kan ‘n groot staqp vorentoe beteken. Hierdie studie wys dat die fisiese eienskappe van iPPK-hout komposiete merkwaardig verbeter kan word waneer versoeningmateriale gebruik word om die verspreiding van die hout in die polimeermatriks sowel as die interaksie tussen die hout en polimeer te verbeter. Die gebruik van verskillende versoenings material, t.w poli(propileen-ent-maleinsuur anhidried) (PPeMA) en pol(etlieen-ko-viniel alkohol) (EVOH). Deur gebruik te maak van eenvoudige mengsels van PPeMA en EVOH in IPPK-hout composite het ‘n geweldige wye verpreiding van resultate tot gevolg gehad, terwyl ‘n voorafgaande reaksie tussen die PPeMA en die EVOH om ‘n saamgestelde versoeningmateriaal te maak tot gevolg gehad het dat reproduseerbare resultate verkry kon word. ‘n Studie van die fundamentele interaksies van die versoeningsmateriale met die molkulêre komponente van die IPPKs is uitgevoer. Die IPPKs is gefraksioneer deur preparatiewe temperatuur-stygende uitloog frakasionering en die fraksies is gemeng met die versoeningmateriale. Fluoressensie mikroskopie is gebruik om hierdie interaksies te bestudeer. Die resultate dui duidelik daarop dat die interaksie van die PPeMA met die fraksies verskil met die van die EVOH. Die verskille kan verduidelik word aan die hand van die chemiese samestelling verspreiding van die IPPK fraksies. Atoomkrag mikroskopie (AKM) is gebruik om die adhesive-kragte tussen die versoeningmateriale, polimere, sellulose en lignien. AKM tippe is suksesvol bedek met PPeMA en EVOH, onderskeidelik. Alhoewel interaksies gebaseer op chemiese krag mikroskopie (CKM) nie gekwantifiseer kon word nie, lewer hierdie resultate tesame met die fluoressensie spektroskopie unieke insig in die manier wat versoeningmateriale met beide die hout en die polimeer reageer

The survival of Heliothis Armiger (Hübner) (Lepidoptera: Noctuidae) eggs on cotton plants in relation to simulated rain and overhead irrigation

Crop pests are known to be adversely affected by rain. Because limited information on this aspect was available for Heliothis spp. occurring on cotton, this study was undertaken to examine the effect of water droplets from overhead irrigation and simulated rain on the survival of H. armiger eggs on cotton. Three aspects were examined: the effects of submersion, the physical impact of droplets on the eggs and the washing off of the eggs from cotton plants in the field. The first two aspects were examined in terms of the structure and respiratory system of the eggs, confirming that H. armiger eggs are able to survive initial wetting in the field. The wash-off of H. armiger eggs from cotton plants is explained in the light of the selection of oviposition sites by the moths, adhesion of the eggs to the plant parts and the dislodging and wash-off by water from simulated rain and overhead irrigation. The data are discussed in terms of the other mortality factors which occur in commercial cotton fields. All in all, it was found that while overhead irrigation should be taken into account in surveys of H. armiger for pest management purposes, it does not offer a viable control strategy and should not be investigated furthe

In vitro antimicrobial comparison of three commercially available chlorhexidine-based oral rinses

INTRODUCTION: Commercially available chlorhexidine (CHX) formulations differ in their CHX concentrations (0.2% and 0.12%) as well as in various additives including alcohol, antimicrobials such as cetylpyridinium chloride and antidiscolouration chemicals such as ascorbic acid and sodium metabisulphite. AIMS AND OBJECTIVES: To compare in vitro the antimicrobial efficacies of three different CHX preparations (Corsodyl ®, Curasept® and GUM® Paroex®) using 0.2% and 0.12% CHX concentrations as controls METHODS: A disk diffusion test was performed using pure cultures of the organisms Streptococcus mutans and Candida albicans, and mixed cultures (facultative and strict anaerobes) prepared from oral rinse samples of 14 study participants. The means and standard deviations of the diameters of inhibition zones were calculated. RESULTS: A statistically significant difference (p value = 0.0001) was found only in Candida albicans cultures between the mean inhibition zones of the CHX preparation disks. Pure CHX preparations and Corsodyl® showed higher antifungal efficacy than Curasept® and GUM® Paroex Conclusion: Both CHX preparations (0.12% and 0.2%) and the 0.2% CHX preparation containing alcohol (Corsodyl®) have more potent antifungal properties against C. albicans than alcohol-free 0.12% CHX preparations such as Curasept® and GUM® Paroex®.DHE

Antimicrobial activity of two South African honeys produced from indigenous Leucospermum cordifolium and Erica species on selected micro-organisms

<p>Abstract</p> <p>Background</p> <p>Honey has been shown to have wound healing properties which can be ascribed to its antimicrobial activity. The antimicrobial activity can be effective against a broad spectrum of bacterial species especially those of medical importance. It has also been shown that there is considerable variation in the antimicrobial potency of different types of honey, which is impossible to predict. With this in mind we tested the antimicrobial activity of honeys produced from plants grown in South Africa for their antibacterial properties on selected standard strains of oral micro-organisms.</p> <p>Methods</p> <p>The honeys used were produced from the blossoms of <it>Eucalyptus cladocalyx </it>(Bluegum) trees, an indigenous South African plant <it>Leucospermum cordifolium </it>(Pincushion), a mixture of wild heather shrubs, mainly <it>Erica </it>species (Fynbos) and a <it>Leptospermum scoparium </it>(Manuka) honey. Only pure honey which had not been heated was used. The honeys were tested for their antimicrobial properties with a broth dilution method.</p> <p>Results</p> <p>Although the honeys produced some inhibitory effect on the growth of the micro-organisms, no exceptionally high activity occurred in the South African honeys. The carbohydrate concentration plays a key role in the antimicrobial activity of the honeys above 25%. However, these honeys do contain other antimicrobial properties that are effective against certain bacterial species at concentrations well below the hypertonic sugar concentration. The yeast <it>C. albicans </it>was more resistant to the honeys than the bacteria. The species <it>S. anginosus </it>and <it>S. oralis </it>were more sensitive to the honeys than the other test bacteria.</p> <p>Conclusion</p> <p>The honeys produced from indigenous wild flowers from South Africa had no exceptionally high activity that could afford medical grade status.</p

The role of competition for glucose amongst oral species in the maintenance of Candida albicans homeostasis in a mixed microbial habitat

Dissertation (Ph.D.)--University of Stellenbosch, 1999.ENGLISH ABSTRACT: Oral candidosis is one of the commonest fungal infections of man and manifests itself in a variety of ways. The widespread use of antibiotics, immunosuppressive drugs, the increasing proportion of the elderly population and the increasing number of AIDS patients, all resulted in an increased awareness of oral candidosis amongst clinicians. This led to the large number of studies on candidosis and the pathogenic mechanisms of Candida albicans that has been done. However, little is known about the mechanisms that control the opportunistic behaviour of C. albicans in the oral cavity and especially of the role of the autochthonous bacteria in this regard. Over recent years it has become clear that the autoch~honous species throughout the digestive tract have a barrier effect against allochthonous species and acts as an important defence mechanism against such species. It has been hypothesised that one of the primary mechanisms that affords a colonisation resistance by the indigenous populations is a competition for growth limiting substrates, specifically for glucose, amongst the species. The well-defined theory of the chemostat, together with its benefits as an open system, allows long-term quantitative studies of the behaviour and composition of microbial communities. The chemostat can be used to study the conditions required for the coexistence of stable populations of more than one species competing for common substrates. With this study the chemostat was used as an in vitro model to investigate the role of competition for glucose amongst oral species in preventing the growth of C. albicans in a mixed culture of oral bacteria. A chemostat model comprising a mixture of oral bacteria that suppressed the growth of C. albicans under growth conditions similar to that of the oral cavity was first established. This model was used to grow oral bacteria with the yeast under glucose limiting and glucose excess conditions in order to establish under what conditions washout or growth of the yeast occurred. The growth parameters of the organisms were estimated and their theoretical saturation curves plotted in order to identify the bacteria that competed against the yeast. The theoretical saturation curves were used to predict the outcome of competition amongst the species at different glucose concentrations. Seven bacterial species including Streptococcus sanguis, Streptococcus sobrinus, Streptococcus mitis, Lactobacillus rhamnosus, Veillonella parvula, Eubacterium saburreum and Fusobacterium nucleatum were able to establish in the chemostat under glucose limiting conditions. The yeast was unable to compete with these bacteria under glucose limitation but could establish under glucose excess conditions. The three species S. sanguis, S. mitis and S. sobrinus were identified as the organisms able to afford a colonisation resistance. At glucose concentrations below 3 mg/ml a change in glucose concentration would not have an effect on the outcome of competition between the bacteria and the yeast. In conclusion, at glucose concentrations found in the oral cavity, at a neutral pH and under anaerobic conditions, S. sanguis, S. mitis and S. sobrinus will afford a colonisation resistance or prevent the growth of C. albicans. This colonisation resistance will be afforded through competition for glucose amongst the oral species and the yeast when grown in a mixed community of the species.AFRIKAANSE OPSOMMING: Kandidose van die mondholte is een van die algemeenste fungale infeksies wat by die mens voorkom. Dit manifesteer in 'n verskeidenheid van vorms en word in die meeste gevalle deur die gis Candida albicans veroorsaak. Die algemene gebruik van antibiotika, immuunonderdrukkende middels, die verhoging van die populasie van bejaardes en die toename in VIGS gevalle is almal faktore wat vir 'n verhoogde bewustheid van mondkandidose onder klinici verantwoordelik is. Dit het daartoe gelei dat 'n aantal studies oor kandidose en oor die meganismes waardeur die siekte veroorsaak word, gedoen is. Alhoewel dit algemeen bekend is dat C. albicans 'n opportunistiese patogeen is, is daar nog weinig bekend oor die meganismes wat die opportunistiese optrede van die gis beheer en die rol wat die outochtone mondbakteriee in die verb and speel. Dit het oor die laaste aantal jare duidelik geword dat die outogtone spesies van die spysverteringskanaal as 'n skans teen kolonisering deur allogtone spesies optree en sodoende as 'n belangrike verdedigingsmeganisme funksioneer. Daar is ook voorgestel dat 'n kompetisie vir groei-beperkende faktore soos glukose tussen die outogtone spesies en die allogtone spesies, een van die primere meganismes is waarvolgens so 'n skans bewerkstellig word. Die welbekende teorie oor die werking van die chemostaat tesame met die voordeel van 'n "oop sisteem" maak die chemostaat geskik vir langtermyn kwantitatiewe studies wat betref die gedrag en die samestelling van mikrobiale populasies. In hierdie studie is die chemostaat as 'n in vitro model gebruik om die toestande wat nodig is vir die samebestaan van C. albicans in 'n gemengde populasie van mondbakteriee wat vir dieselfde gemeenskaplike substraat kompeteer, te ondersoek. Eerstens is 'n model wat uit 'n verskeidenheid van mondbakteriee bestaan onder toestande soortgelyk aan die van die mondholte gevestig. Die model moes in staat wees om die groei van C. albicans te kan onderdruk en is gebruik om vas te stel onder watter toestande die uitwas van die gis plaasvind en onder watter toestande die gis groei. Vervolgens is die groeiparameters van die organismes bepaal om hul teoretiese versadigingskurwes op te stel. Die kurwes is gebruik om te bepaal watter organismes teen die gis kompeteer en om te voorspel wat die uitkoms van kompetisie tussen die spesies by verskillende glukose konsentrasies is. Sewe mondbakteriee insluitende, Streptococcus sanguis, Streptococcus sobrinus, Streptococcus mitis, Lactobacillus rhamnosus, Veillonella parvula, Eubacterium saburreum en Fusobacterium nucleatum het onder toestande van glukose tekort in die chemostaat gevestig. Die gis kon nie onder die toestande met die bakteriee kompeteer nie. Die gis kon egter wei onder toestande van oormaat glukose, waar daar slegs drie mondbakteriee voorgekom het, in die chemostaat vestig. Die drie spesies S. sanguis, S. mitis en S. sobrinus is geldentifiseer as die organismes wat die vestiging van die gis onderdruk. 'n Verandering in die glukose konsentrasie (O-20mglml) sal geen effek op die uitkoms van die kompetisie tussen hierdie drie bakteriee en die gis uitoefen nie en die gis sal altyd in hul teenwoordigheid geelimineer word. Die gevolgtrekking van die studie is dat by glukose konsentrasies soortgelyk aan die van die mondholte, by 'n neutrale pH en anaerobiese toestande, die organismes S. sanguis, S. mitis en S. sobrinus die kolonisering en groei van C. albicans in 'n gemengde kultuur sal voorkom. Hierdie onderdrukking van groei is as gevolg van die onvermoe van die gis om in 'n gemengde kultuur met die bakteriee vir glukose te kompeteer

Die geskiedenis van die Kaapse Burgermag-Mediese eenhede, 1889-1939

Thesis (MA (History))--University of Stellenbosch, 1988.Die doel met hierdie studie is tweeledig. Eerstens word gepoog om die Kaapse burgermag-mediese eenhede se rol binne die verdedigingstelsels waarvan hulle op sekere stadia van hul bestaan deel was te ondersoek, hetsy as deel van die Kaapse Koloniale Magte vir die tydperk 1889 - 1913 of as deel van die burgermag-element van die Unieverdedigingsmag, 1913 - 1939. Tweedens word hierdie eenhede se ontwikkelingsgang nagegaan : van die stigting van die Volunteer Medical Staff Corps (VMSC) in 1889 af tot met die uitbreek van die Tweede Wêreldoorlog in 1939. As 'n titel vir hierdie onderwerp is besluit op Die Geskiedenis van die Kaapse Burgermag-mediese eenhede, 1889 - 1939. Die rede daarvoor is dat dit die hele tydperk onder bespreking volledig omskryf die aanloop tot die stigting van die VMSC, sy stigting in 1889, sy rol as 'n vrywilligereenheid, sy omskakeling na twee burgermag-mediese eenhede in 1913 asook hul rol en ontwikkeling in daardie verband tot met die uitbreek van die Tweede Wêreldoorlog in 1939. Aangesien hierdie tydperk van vyftig jaar 'n duidelike beeld rakende hierdie eenhede se rol en ontwikkeling gee, het die keuse daarom geval op 1889 en 1939 as onderskeidelik die begin- en einddatum vir hierdie onderwerp. Met die uitbreek van die Tweede Wêreldoorlog in 1939 het daar in die Kaapprovinsie twee burgermag-mediese eenhede binne die Unieverdedigingsmag gefunksioneer, naamlik 2 Veldambulans en 3 Veldambulans. Beide kan egter hul ontstaansgeskiedenis terugvoer na 21 Oktober 1889, toe. soos hierbo aangedui, die VMSC as die eerste selfstandige mediese eenheid in die Kaapkolonie gestig is. Met sy stigting het die eenheid uit twee kompanies bestaan. te wete A-kompanie en B-kompanie wat onderskeidelik in King William's Town en Kaapstad gesetel was. Daarna het die VMSC by twee verdere geleenthede naamsveranderinge ondergaan. In 1889 is sy naam na die Cape Medical Staff Corps (CMSC) verander en van 1903 af het dit as die Cape Medical Corps (CMC) bekend gestaan. Met die totstandkoming van die Suid-Afrikaanse Geneeskundige Diens (SAGD) in 1913, is die twee kompanies in twee afsonderlike burgermag-mediese eenhede omgeskakel en in die SAGD opgeneem. Dit het eweneens 'n naamsverandering tot gevolg gehad. A-kompanie sou voortaan as 1 Berede Brigade Veldambulans (1 BBVA) bekend staan terwy1 B-kompanie tot No. 1 Kompanie herdoop is. tn 1935 het die twee eenhede weer eens 'n naamsverandering ondergaan toe 1 BBVA tot 2 Veldambulans en No. 1 Kompanie tot 3 Veldambulans herdoop is. Die doel van hierdie studie in ag genome, word die rol en ontwikkeling van hierdie eenhede oor die tydperk van vyftig jaar bespreek. In die eerste hoofstuk word daar, as inleiding, kortliks verwys na die onderskeie militê re organisasies in die Kaapkolonie gedurende die neëntiende eeu waarvan die vrywilliger-mag een was. Daar het egter 'n behoefte bestaan aan voldoende mediese steun vir sy lede waaruit voortgevloei het die stigting van die St John's Ambulance Association en die ambulansafdeling van die King William's Town Volunteer Artillery om hierdie leemte te vul. Vervolgens word gekonsentreer op die stigtingsproses van die VMSC in 1889 asook die groei en ontwikkeling van die eenheid in die jare onmiddellik daarna..

Die beginsels van taalverwerwing as teoretiese basis vir die onderrig van Xhosa in die primere skool

Proefskrif (M.A.) -- Universiteit van Stellenbosch, 1988.Full text to be digitised and attached to bibliographic record

Vestiging van lactobacilli op tande van kiemvrye rotte en op menslike tande in 'n kunsmatige mond

Proefskrif (M. Sc.)) -- -Universiteit van Stellenbosch, 1982.Full text to be digitised and attached to bibliographic record

Die toepassing van 'n karaktertoets op jeugmisdadigers in liggaamlike opvoeding-situasies

Proefskrif (M. Ed. Ph.) -- Universiteit van Stellenbosch, 1952.Full text to be digitised and attached to bibliographic record

Die invloed van liggaamsopvoeding op die geestelike prestasies van skoolkinders

Proefskrif (B. Ed. Ph.) -- Universiteit van Stellenbosch, 1945.Full text to be digitised and attached to bibliographic record