Effects Of Ionic Liquid On The Structure And Foaming Behavior Of Polymer By Using Supercritical CO₂

Microcellular polymer is a novel material prepared by supersaturation method with using the supercritical fluid as a blowing agent, with the foam size of order 10μm. Supercritical carbon dioxide (scCO₂) has been widely used production of microcellular foams and porous materials obtained by the saturation of polymers with compressed or supercritical carbon dioxide and a desorption at elevated temperature.Ionic liquids (ILs) are composed of organic cation and organic/inorganic anion with relative low melting point. They exhibit excellent thermal and chemical stability and have very low vapor pressure (practically non-detectable) which have been described as novel environmentally benign solvents. One of the promising applications with ILs is a nonvolatile solvent for capturing unwanted compounds. CO₂ is remarkably soluble in imidazolium-based ionic liquids however the solubility of ILs in CO₂ is immeasurably low, which opens up the possibility of absorbing CO₂ with ILs. Besides, imidazolyl ionic liquid also have attracted much attention and gained recognition as potential high quality promoters.In this study, ionic liquids were incorporated into polymer matrix by melting or solution blending, and the aim of this work is to investigate the influences of foaming behavior of polymer by using supercritical CO₂ in the presence of ionic liquids. The main conclusions obtained as following:1. Ionic liquid, 1-n-tetradecyl-3-methylimidazolium bromide ([C₁₄MIM][Br]), has significant effect on the foaming behavior of Poly(propylene)(PP), compared to pure PP foamed under the same saturation conditions, the foamed PP/[C₁₄MIM][Br] samples exhibit close cell structure, increased cell size and decreased un-foamed region. [C₁₄MIM][Br] has little effect on the crystallinity, melting point and the mass uptake of CO₂ of PP. Therefore ionic liquid will not change the mechanical properties of PP due to the crystallization.2. Ionic liquid ,1-alkyl-3-methylimidazolium hexafluorophosphate ([CnMIM][PF₆]) has obvious effect on the foaming behavior of polyvinyl chloride(PVC). As the amount of ionic liquid [C₁₄MIM][PF₆] increases, the foaming property of PVC decrease and then increase, with the phase separation gradually appeared between ionic liquid and PVC. Different length of 1-alkyl groups in ionic liquid [CnMIM][PF₆] has different effects on the foaming behavior of PVC, with different size and density of ionic liquid dispersed phase.3. The effect of ionic liquid [C₁₄MIM][PF₆] on the foaming behavior of polystyrene (PS) is not obvious. [C₁₄MIM][PF₆] forms a well-dispersed phase, whose size increases with its content, in the PS matrix. The ionic liquid has a negative effect on the foaming property of PS when the amount of [C₁₄MIM][PF₆] is high.