CO2 Induced Foaming Behavior of Polystyrene near the Glass Transition

Salah Al-Enezi

doi:10.1155/2017/7804743

Abstract

This paper examines the effect of high-pressure carbon dioxide on the foaming process in polystyrene near the glass transition temperature and the foaming was studied using cylindrical high-pressure view cell with two optical windows. This technique has potential applications in the shape foaming of polymers at lower temperatures, dye impregnation, and the foaming of polystyrene. Three sets of experiments were carried out at operating temperatures of 50, 70, and 100°C, each over a range of pressures from 24 to 120 bar. Foaming was not observed when the polymer was initially at conditions below Tg but was observed above Tg. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites, with maximum radius of 0.02–0.83 mm. Three models were applied on the foaming experimental data. Variable diffusivity and viscosity model (Model C) was applied to assess the experimental data with the WLF equation. The model shows very good agreement by using realistic parameter values. The expansion occurs by diffusion of a dissolved gas from the supersaturated polymer envelope into the bubble.

Highlights

The use of high-pressure carbon dioxide as an efficient medium for polymer processing due to its chemical and economic advantages [1,2,3]
The sample transformed into a rubbery state and depressurized to atmospheric pressure to take the advantage of the swelling and plasticization of the polymer, which reduces the glass transition temperature (Tg) or melting temperature (Tm) due to its high solubility in polymers [4]
The bubble growth data are important for understanding the foam growth

Summary

Introduction

The use of high-pressure carbon dioxide as an efficient medium for polymer processing due to its chemical and economic advantages [1,2,3]. The sample transformed into a rubbery state and depressurized to atmospheric pressure to take the advantage of the swelling and plasticization of the polymer, which reduces the glass transition temperature (Tg) or melting temperature (Tm) due to its high solubility in polymers [4]. Bubble formation and foaming are caused by CO2, earlier dissolved in the polymer under pressure, to be released upon depressurization. This has been well reported in the literature and a number of models for bubble growth have been presented by many authors [14,15,16,17,18]. All three factors directly affect the growth of gas bubbles and will have an impact on the bubble-size and ultimate properties of the foamed product [16]

Methods

Results

Discussion

Conclusion