Back SearchTitle: FOAMING POLYSTYRENE WITH MIXTURES OF CARBON DIOXIDE AND HFC-134a
Page Range: p.75-87
Author(s): Vachon C; Gendron R
File size: 95K
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Issue Year: cp
Volume: 22
Issue No: No. 2
Abstract
Mixtures of blowing agents are becoming widely used in the industry either for economical reasons or for achieving better control of processing conditions. Despite the fact that they are commonly used for foaming, the literature is fairly scarce on that particular subject and the fundamentals are not very well understood. The effect of blending carbon dioxide and 1,1,1,2-tetrafluorethane (HFC-134a) in PS is studied. Ultrasonic monitoring and online rheology provide information on the solubility and plasticising effect of the gases. Results show that, on an equivalent molar basis, HFC-134a is slightly more soluble than CO2 and is a more effective plasticiser. Moreover, HFC-134a generates samples with a higher nucleation density than CO2 using similar processing conditions. Blending the two gases generates nucleate cell densities, which are intermediate to the pure gases but do not follow a log-additivity rule. It is hypothesised that blending gases affect their mutual diffusion coefficients, which in turn, largely dictates the final foam morphology. 15 refs.
Title: MODELING DIFFUSION-INDUCED BUBBLE GROWTH IN POLYMER LIQUIDS
Page Range: p.89-101
Author(s): Venerus D C
File size: 91K
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Issue Year: cp
Volume: 22
Issue No: No. 2
Abstract
Accurate modelling of diffusion-induced bubble growth is essential for the development of efficient polymer foaming processes. Consequently, a large number of transport models of this complex phenomona have been formulated. In previous studies, one or more simplifying approximations have been invoked to reduce mathematical complexity. Several models of bubble growth in liquids are presented and compared and the effects of blowing agent concentration, liquid viscosity and elasticity on bubble growth are examined. In addition, predicted and measured bubble growth behaviour in two polymer foaming systems is compared. 21 refs.
Title: ELONGATIONAL MIXING IN FOAM EXTRUSION
Page Range: p.103-115
Author(s): Rauwendaal C
File size: 94K
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Issue Year: cp
Volume: 22
Issue No: No. 2
Abstract
The development of elongational mixing technology is described, from the early inception of the basic ideas behind the technology, the first commercial applications, subsequent developments, to the current status. Future developments currently underway are described together with how these developments will likely impact the polymer processing industry. 15 refs.