The development of vesiculated beads

Terblanche, Johannes C. (Stellenbosch : University of Stellenbosch, 2003-04)

Thesis (MScIng)--University of Stellenbosch, 2003.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/16447
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