Forced vibrational experiments and stress relaxation experiments have been performed on acetate rayon, viscose rayon, nylon, and polyethylene over a range of humidities at both 2°C and 25°C. Forced vibrational experiments have also been carried out on acetate rayon, viscose rayon, and raw silk over the temperature range -80°C to 0°C. Interpretation of previous experiments is discussed in terms of both Newtonian viscosity and Eyring viscosity. The apparatus employed is described and a method for calibrating the solenoid of the forced vibrator is outlined. An inverse relation has been found between ηω and the negative slope of the stress relaxation curve, E°. Since the equation ηω = π/(4.606) E° derived on the basis of Newtonian viscous units predicts a direct relation between ηω and the slope E°, it is assumed that the flow in stress relaxation must be non-Newtonian* Preliminary calculations indicate that a more satisfactory relation between ηω and E° may exist if the flow units involved in stress relaxation follow the Eyring law of viscous flow. An outline for determining such a relation is given. The experimental 1y observed increase with decreasing temperature of dynamic modulus, stress relaxation modulus, and energy loss, as measured by ηω, is interpreted in terms of increasing order of chain segments. A maximum found at -55°C in the ηω vs. temperature curve for viscose rayon is attributed to a "freezing in" of segment motions as the result of a second order transition. / Science, Faculty of / Chemistry, Department of / Graduate

Please read the abstract in the section 00front of this document Copyright 2000, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bisschoff, J 2000, Oxygenated hydrocarbon compounds as flame retardants for polyester fabric, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-01122007-112752 / > H 81/th / Dissertation (M Eng (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Concrete is used in most of the modern day infrastructure. It is a building material for which there exist various design codes and guidelines for its use and construction. It is strong in compression, but lacks tensile strength in its fresh and hardened states and, when unreinforced, fails in a brittle manner. The structural use of synthetic fibres in concrete is investigated in this study to determine its effect on enhancing the mechanical properties of concrete. Slabs on grade are used as the application for which the concrete is tested. The material behaviour is investigated in parallel with two floor design theories. These are the Westegaard theory and the Yield-Line theory. The Westegaard theory uses elastic theory to calculate floor thicknesses while the Yield-Line theory includes plastic behaviour. Conceptual designs are performed with the two theories and material parameters are determined from flexural tests conducted on synthetic fibre reinforced concrete (SynFRC) specimens. Large scale slab tests are performed to verify design values from the two theories. Higher loads till first-crack were measured during tests with concrete slabs reinforced with polypropylene fibres than for unreinforced concrete. It is found that the use of synthetic fibres in concrete increases the post-crack ductility of the material. The Westegaard theory is conservative in its design approach by over-estimating design thicknesses. This was concluded as unreinforced slabs reached higher failure loads than predicted by this theory. The Yield-Line theory predicts design thicknesses more accurately while still accounting for the requirements set by the ultimate- and serviceability limit states. By using SynFRC in combination with the Yield-Line theory as design method, thinner floor slabs can be obtained than with the Westegaard theory. / AFRIKAANSE OPSOMMING: Beton word gebruik as boumateriaal in meeste hedendaagse infrastruktuur. Daar bestaan verskeie ontwerp kodes en riglyne vir die gebruik en oprig van beton strukture. Alhoewel beton sterk in kompressie is, het beton ‘n swak treksterkte in beide die vars- en harde fases en faal dit in ‘n bros manier indien onbewapen. Die gebruik van sintetiese vesels in beton word in hierdie projek ondersoek om die invloed daarvan op die eienskappe van die meganiesegedrag van beton te bepaal. Grond geondersteunde vloere word as toepassing gebruik. Parallel met die materiaalgedrag wat ondersoek word, word twee ontwerpsteorieë ook ondersoek. Dit is die teorie van Westegaard en die Swig-Lyn teorie. Die teorie van Westegaard gebruik elastiese teorie in ontwerpsberekeninge terwyl die Swig-Lyn teorie ‘n plastiese analise gebruik. ‘n Konseptuele vloerontwerp is gedoen deur beide die ontwerpsmetodes te gebruik. Materiaalparameters is bepaal deur buig-toetse uit te voer op sintetiesevesel-bewapende beton. Grootskaalse betonblaaie is gegiet en getoets om die akkuraatheid van die twee metodes te verifieer. Die betonblaaie wat bewapen was met polipropileen vesels het groter laste gedra tot by faling as die blaaie wat nie bewapen was nie. Die vesels verbeter die gedrag van beton in die plastiese gebied van materiaalgedrag deurdat laste ondersteun word nadat die beton alreeds gekraak het. Die Westegaard teorie kan as konserwatief beskou word deurdat dit vloerdiktes oorskat. Hierdie stelling is gegrond op eksperimentele data wat bewys dat onbewapende betonblaaie groter laste kan dra as wat voorspel word deur die Westegaard teorie. Die Swig-Lyn teorie voorspel ontwerpsdiktes meer akkuraat terwyl daar steeds aan die vereistes van swigting en diensbaarheid voldoen word. Deur gebruik te maak van sintetiese vesels en die Swig-Lyn teorie kan dunner betonblaaie ontwerp word as met die Westegaard teorie.