Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Vesiculated beads consist of aerated microvoids encapsulated in a solid spherical
continuous polymeric shell. The difference in refractive index between the voids and
polymer granules causes effective scattering of incident light on the particles,
presenting it with a white appearance. The size of these beads generally range in the
region of 0.5 – 40 μm, making it suitable for use as pigment extender in the surface
coatings or paint industry.
Currently, titanium dioxide pigment is predominantly used as opacifying agent in
paint formulations, but due to the high cost associated in purchasing this pigment, as
well as fluctuation in import prices, paint manufacturers are looking for alternative
products to replace or at least partially replace this pigment. As an alternative, opaque
vesiculated polymer particles can be produced locally at a cheaper price and in
existing vessels available in the paint industry.
Approximately five years ago a paint company in Mexico and member of the Nova
Club, started research in developing vesiculated beads for production in their
factories. However, it was found extremely difficult to scale-up the production to
industrial size, since the system was very sensitive to process variables. A local paint
company and member of the Nova Club acquired this technology and continued
further research in developing vesiculated beads on large scale in existing Cowles
disperser systems found in the paint industry.
The beads consist mainly of an organic phase comprising of unsaturated carboxylated
polyester and styrene. A polyamine is also added to assist the formation of vesicles in
the organic phase. This phase is slowly added under agitation to an aqueous phase
consisting of deionised water, a thickener and colloid stabilisers to form an oil-inwater
emulsion. Agitation is continued for a specified period of time, also known as
the emulsification period, to allow sufficient time for the organic globules to break-up
to smaller particle sizes. These globules are subsequently catalysed with a freeradical
initiator and redox activator and left static overnight to allow formation of the
solid beads. To determine the most important process parameters during production of vesiculated
beads, a fully integrated laboratory scale Cowles reactor system was designed and
constructed, geometrically analogous to the vessels found in the paint industry.
The system measures and controls production temperature, mixing speed and
component addition rates. Production runs were performed where various process
parameters were varied to investigate the effect on properties, which include average
particle size and particle size distribution, pH, viscosity and opacity. The most
important process parameters that were found to play a significant role include
production temperature, organic phase addition rate, emulsification time, the Cowles
impeller diameter and mixing speed.
Production runs were performed in geometrically similar 5l and 20l vessels on the
laboratory-scale system to investigate the effect of scale-up. A model presented by
Klein et al. (1996) was used as basis for describing the average particle size as a
function of mixing speed, impeller diameter, vessel diameter and emulsification time.
The applicability of this model was tested on average particle size data obtained from
industrial scale runs performed on the plants and proved to be reasonably accurate. / AFRIKAANSE OPSOMMING: Sferiese polimeerpartikels met klein lugholtes vasgevang in ‘n harde omhulsel word
al jare in die verf industrie aangewend as pigment. Weens die verskil in
brekingsindeks tussen die soliede polimeerpartikel en die vasgevange lugholtes, word
invallende lig versprei op so ‘n manier dat die partikels ondeursigtig (of wit)
voorkom. Hierdie partikels kan geproduseer word met deursneë wat strek van 0.5 –
40 μm, wat dit geskik maak vir gebruik in verf formulasies.
Tans word titaandioksied poeier hoofsaaklik gebruik in verf as pigment, maar weens
die hoë koste van die invoer en aankoop van hierdie produk, het verfmaatskappye
begin soek na goedkoper alternatiewe. Aangesien hierdie ondeursigtige
polimeerpartikels plaaslik goedkoper vervaardig kan word in bestaande mengvate
beskikbaar in verf aanlegte, dien dit as moontlike plaasvervanger.
Ongeveer vyf jaar gelede het ‘n Mexikaanse verfmaatskappy, wat lid is van die Nova
Klub, navorsing begin doen om hierdie polimeerpartikels in hul fabrieke te produseer.
Dit was egter vir hulle onmoontlik om die produksie op te skaal na industriële
vervaardiging aangesien die proses baie sensitief was vir produksieveranderlikes.
Sekere eienskappe soos die gemiddelde partikelgrootte, partikelverspreiding, pH,
viskositeit en deursigtigheid van die partikels kon nie van lot tot lot herhaal word nie
en verdere navorsing is gestaak. ‘n Plaaslike verfmaatskappy (ook lid van die Nova
Klub) het die tegnologie oorgeneem en die proses verder ontwikkel. Die proses is
aangepas sodat “Cowles” mengers, wat wydverspreid in die verf industrie beskikbaar
is, gebruik kan word om dit te vervaardig.
Die partikels bestaan hoofsaaklik uit ‘n organiese fase wat ‘n onversadigde
gekarboksileerde poliëster en stireen insluit. ‘n Poli-amien word ook bygevoeg en is
verantwoordelik vir die vorming van die lugholtes in die partikels. Hierdie fase word
stadig onder menging by ‘n tweede water fase, bestaande uit gedeïoniseerde water, ‘n
verdikker en kolloïdale stabiliseerders gevoeg om ‘n olie-in-water emulsie te vorm.
Menging word voortgesit vir ‘n bepaalde emulsifiseringsperiode om die oliedruppels
verder op te breek. Gevolglik word hierdie druppels gekataliseer met ‘n vry-radikaal inisieerder en redoksaktiveerder en oornag staties gelos om vorming van die soliede
partikels toe te laat.
Aangesien eienskappe van die polimeerpartikels so sensitief is vir
prosesveranderlikes, is besluit om aanvanklik ‘n ten volle geïntegreerde laboratorium
skaal “Cowles” reaktorsisteem te ontwerp en bou. Hierdie sisteem is geometries
gelykvormig aan die mengvate wat in verffabrieke gevind word. Die
produksietemperatuur, stuwergrootte, mengspoed en materiaal toevoertempo kan
effektief gemeet, verstel en beheer word. Eksperimentele lopies is gedoen en die
effek van verskeie produksieveranderlikes op eienskappe is ondersoek. Die
belangrikste veranderlikes wat die proses beïnvloed, is die
emulsifiseringstemperatuur, die toevoertempo van die organiese fase,
emulsifiseringsperiode, stuwerdeursnit en mengspoed.
Eksperimentele lopies is gedoen op twee geometriese gelykvormige mengvate (5l en
20l kapasiteit) om die effek van opskaling op eienskappe te ondersoek. ‘n Model wat
deur Klein et al. (1996) voorgestel is, is as basis gebruik om die gemiddelde
partikelgrootte te bepaal as ‘n funksie van mengspoed, stuwerdeursnit, mengvat
deursnit en emulsifiseringstyd. Hierdie model is getoets op partikelgrootte data wat
verkry is van groot industriële skaal lopies uitgevoer in die fabrieke onder bekende
produksie kondisies en daar is gevind dat hierdie model bevredigend gebruik kan
word om die gemiddelde partikelgrootte te voorspel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16447 |
| Date | 04 1900 |
| Creators | Terblanche, Johannes C. |
| Contributors | Knoetze, J. H., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxi, 200 leaves : ill. |
| Rights | University of Stellenbosch |
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