Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Desired behaviour of paint during processing, storage, application and after application is of great
importance in the coatings industry. Rheology (the study of flow and deformation behaviour) is
used as a method to investigate the behaviour of the flow and deformation properties of the paint
during these stages. Some of the more important phenomena that can occur during these stages,
which were examined rheologically, are:
1. The rheological behaviour of certain complex raw materials during processing - vesiculated
beads suspensions
11. The paint behaviour during storage - in-can stability, e.g. phase separation and
sedimentation of particles;
Ill. The paint during application - ease of application, spatter, etc.;
IV. The paint behaviour after application - sag, layer thickness, levelling (ability to hide brush
marks), etc.
A rheometer was used to obtain rheological curves from a paint sample (± 1 ml). Correct
interpretation of these curves, which display rheological properties of the sample such as the
viscosity, shear stress, structural strength and many more, produced information about the
properties mentioned in i, ii, iii and iv above. It was found that the rheological data correlated well
with empirical tests carried out in the laboratory for spatter, sag, levelling behaviour and in-can
stability of the paint.
A wide variety of paints were studied ranging from tough/durable outdoor paints to smooth/velvety
indoor paints. The rheological behaviour explained the specific end-use properties of the paints.
Paints from two different companies were compared on a rheological basis. In some cases large
differences in rheological behaviour were observed. Rheology modifiers were tested on a new paint.
It was found that specific rheology modifiers could be incorporated into the formulation to give the
specific rheological behaviour required. Rheological modelling was performed and it was found
that the flow behaviour of paint cou1d be modelled accurately with existing viscosity models
(Ostwald/de Waal, Bingham, Casson, Herschel-Bulkley, Cross and Philips-Deutsch). Other
rheological properties of paint were also modelled successfully with a simple linear regression
model. Rheology was also used as a method to examine the flow and deformation properties of vesiculated
beads, a component of paint with very complex rheology. The most important factors that influence
the rheological behaviour of the vesiculated beads were determined. It was found that the type of
manufacturing process for the beads affected the rheological behaviour. The effect of the raw
materials used to manufacture the vesiculated beads were rheologically determined. / AFRIKAANSE OPSOMMING: Dit is baie belangrik dat verf die gewenste gedrag moet toon tydens berging, vervaardiging, tydens
aanwending en direk na aanwending. Reologie (die studie van vloei- en vervorming) word gebruik
as a metode om die vloei- en vervormingseienskappe van verf gedurende bogenoemde stadia te
ondersoek. Sommige van die belangriker verskynsels wat gedurende hierdie stadia kan plaasvind, is
d.m.v reologiese toetse ondersoek. Die verskynsels is as volg:
i. Die reologiese gedrag van komplekse grondstowwe soos gevesikuleerde partikel
suspensies.
ll. Verfgedrag tydens berging - stabiliteit van verf in die blik, bv. faseskeiding en sedimentasie
van partikels
lll. Verfgedrag tydens aanwending - gemak van aanwending, spatsels
IV. Verfgedrag direk na aanwending - afsakking, dikte van verflaag, vloei-eienskappe
'n Reometer is gebruik om die reologiese kurwes te bepaal deur gebruik te maak van ± 1 ml
monster. Korrekte interpretasie van hierdie kurwes, wat onder meer eienskappe soos viskositeit,
spanning en struktuursterkte insluit, lei tot inligting wat die verskynsels in i, ii, iii en iv kan
verklaar. Daar is gevind dat inligting wat verkry is i.v.m die verskynsel van spatsels, afsakking,
vloei en die stabiliteit van verf in die blik, goed korreleer met empiriese toetse wat in die
laboratorium uitgevoer is.
'n Groot verskeidenheid van verwe, wat wissel van duursame/sterk buitemuurse verf, tot
fluweelsagte binnenshuise verf, isondersoek. Die reologiese toetse het daarin geslaag om die
eienskappe van die eindproduk suksesvol te verduidelik. Verf van twee verskillende maatskappye is
ook met mekaar vergelyk op 'n reologiese grondslag. Daar is by sommige van die verwe
aansienlike verskille in die reologiese gedrag gevind. 'n Nuwe verf is gebruik om die uitwerking
van reologie modifiseerders te ondersoek. Daar is gevind dat daar spesifieke reologie
modifiseerders bestaan wat unieke reologiese gedrag verseker. Reologiese modellering is gedoen op
verf en daar is gevind dat die vloeigedrag van die verf akkuraat gemodelleer kan word deur van die
bestaande viskositeitsmodelle gebruik te maak (Ostwald/de Waal, Bingham, Casson, Herschel-
Bulkley, Cross en Philips-Deutsch). Ander reologiese eienskappe is gemodelleer deur gebruik te
maak van eenvoudige regressie modelle.
Daar is ook van reologiese tegnieke gebruik gemaak om die vloei en vervormingseienskappe van
gesuspendeerde gevesikuleerde partikels, wat as 'n grondstof vir verf gebruik word, te ondersoek.
Die belangrikste faktore wat die reologiese gedrag beïnvloed het, was onder meer die verskillende
prosesse waarmee die gevesikuleerde partikels vervaardig is. Die effek van sekere van die
grondstowwe wat gebruik word om die gevesikuleerde partikels te vervaardig, is ook reologies
ondersoek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53577 |
| Date | 03 1900 |
| Creators | Moolman, Pieter Lafras |
| Contributors | Knoetze, J. H., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 290 p. : ill. |
| Rights | Stellenbosch University |
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