African Journals Online
South African Journal of Chemical Engineering

Volume 14, Issue 1, March 2002
Abstracts

Characterisation of the pervaporative separation of water and acetonitrile by PVA membranes
Scholtz, J.J.Grimsehl, U. 1-15

Abstract: Acetonitrile can be successfully dried by means of pervaporation with PVA membranes. A substantial amount of data is required to describe the behaviour of the system with the solution-diffusion model. Wijmans and Baker have formerly proposed a method to describe pervaporation systems with permeation data only. This method was used to attempt to describe the pervaporative behaviour of acetonitrile-water systems in the vicinity of the thermodynamic azeotrope. The method was found to be sufficiently accurate for interpolation between experimental data.

Evaluation of commercial plastics purging compounds on a laboratory film blower
Govender, MorganFocke, Walter W.Tolmay, Andries T.Graeffe, Dagmar 15-26

Abstract: Application of purge compounds allows rapid colour and material changes in plasics converting machines. They have both a cleaning and a purging action. In this paper we postulate that slip flow patterns can contribute to a purging action. This implies that the cleaning and purging functions can have conflicting requirements with respect to the wall shear stress. Commercial purge products function according to additional methods including filler abrasion, solvent dissolution and the dislodging of deposits with the aid of surfactants. Six different commercial purge compounds were tested for their colour change efficiency using polyethylene and switching from blue to clear in a laboratory film blower. The products based on a scuffing mechanism in combination with surfactants clearly outperformed the other types.

Reinigingsmiddels bewerkstellig vinnige oorskakeling na 'n nuwe kleur of materiaal in plastiekverwerkingsmasjienerie. In hierdie artikel postuleer ons dat glipvloeipatrone moontlik die purgeeraksie mag aanhelp. Dit impliseer egter dat die skoonmaak- en purgeeraksies botsende vereistes stel ten opsigte van die wandskuifspanning. Kommersiële purgeermiddels funksioneer ook nog volgens addisionele meganismes soos vulstofskuur- of skraapaksies, solvering deur oplosmiddels, en die losmaak van neerslae deur oppervlakaktiewe middels. Ses verskillende kommersiële reinigingsmiddels is getoets vir hulle effektiwiteit om vinnige kleuromskakeling in 'n laboratoriumfilmblaasmasjien te bewerkstellig. Produkte met 'n skraapaksie het beter resultate gelewer.