CO2 foaming of poly(ethylene glycol)/polystyrene blends: Relationship of the blend morphology, CO2 mass transfer, and cellular structure
✍ Scribed by Kentaro Taki; Kouei Nitta; Shin-Ichi Kihara; Masahiro Ohshima
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 328 KB
- Volume
- 97
- Category
- Article
- ISSN
- 0021-8995
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✦ Synopsis
Abstract
When polymer blends are foamed by physical foaming agents, such as CO~2~ or N~2~, not only the morphology and viscosity of the blend polymers but also the solubility and diffusivity of the physical foaming agents in the polymers determine the cellular structure: closed cell or open cell and monomodal or bimodal. The foam of poly(ethylene glycol) (PEG)/polystyrene (PS) blends shows a unique bimodal (large and small) cellular structure, in which the large‐size cells embrace a PEG particle. Depending on the foaming condition, the average size of the large cells ranges from 40 to 500 μm, whereas that of small cells becomes less than 20 μm, which is smaller than that of neat PS foams. The formation mechanism of the cellular structure has been investigated from the viewpoint of the morphology and viscosity of the blend polymer and the mass‐transfer rate of the physical foaming agent in each polymer phase. The solubility and diffusivity of CO~2~, which determine the mass‐transfer rate of CO~2~ from the matrix to the bubbles, were measured by a gravimetric measurement, that is, a magnetic suspension balance. The solubility and diffusivity of CO~2~ in PS differed from those in PEG: the diffusion coefficient of CO~2~ in PEG at 110°C was 3.36 × 10^−9^ m^2^/s, and that in PS was 2.38 × 10^−10^ m^2^/s. Henry's constant in PEG was 5600 cm^3^ (STP)/(kg MPa) at 110°C, and that in PS was 3100 cm^3^ (STP)/(kg MPa). These differences in the transport properties, morphology of the blend, and CO~2~‐induced viscosity depression are the control factors for creating the unique cellular structure in PEG/PS blends. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1899–1906, 2005