Controlling sandwich‐structure of PET microcellular foams using coupling of CO₂ diffusion and induced crystallization

Abstract

Controlling sandwich‐structure of poly(ethylene terephthalate) (PET) microcellular foams using coupling of CO2 diffusion and CO2‐induced crystallization is presented in this article. The intrinsic kinetics of CO2‐induced crystallization of amorphous PET at 25°C and different CO2 pressures were detected using in situ high‐pressure Fourier transform infrared spectroscopy and correlated by Avrami equation. Sorption of CO2 in PET was measured using magnetic suspension balance and the diffusivity determined by Fick's second law. A model coupling CO2 diffusion in and CO2‐induced crystallization of PET was proposed to calculate the CO2 concentration as well as crystallinity distributions in PET sheet at different saturation times. It was revealed that a sandwich crystallization structure could be built in PET sheet, based on which a solid‐state foaming process was used to manipulate the sandwich‐structure of PET microcellular foams with two microcellular or even ultra‐microcellular foamed crystalline layers outside and a microcellular foamed amorphous layer inside. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2512–2523, 2012

CO2‐blown nanocellular foams

“…The sorption conditions are maintained until the CO 2 concentration in the sample reaches the solubility limit at the soaking conditions. The minimum soaking time has to be determined either empirically or by calculation using the CO 2 diffusion coefficient in the particular polymer at the soaking conditions and the sample thickness. It varies from less than an hour for thin samples (100 μm or less) to several days for thick samples at low temperature.…”

“…Sparse cells with size of 150–300 nm were produced, with low porosity ( <25%). Li et al used PET, saturated with CO 2 for up to 15 days at 6 MPa and 25°C, followed by a foaming step at 235°C to produce a nanocellular foam with 193 nm cells and 3.4 × 10 13 cells/cm 3 . Expansion was very limited ( <20%).…”

Influence of Microphase Morphology and Long-Range Ordering on Foaming Behavior of PE-b-PEO Diblock Copolymers

“…The samples were immersed in liquid nitrogen for 10 min and then fractured. 41 The volume expansion ratio (R v ), the volume-average diameter (D v ), and the cell density (N 0 ) with respect to the original (unfoamed) material were calculated from the same method as Bao et al 40 Similar to the SEC analysis, number-average diameter (D n ) and polydispersity index (PDI D ) were respectively defined by eqs 1 and 2 to quantitatively indicate …”

Microcellular injection molding of in situ modified poly(ethylene terephthalate) with supercritical nitrogen

“…This low melt strength makes them unable to resist the intensive elongational deformations during the foaming process. Only a few studies have been conducted on the microcellular foaming of PET over the past 20 years, and these studies were predominantly done by batch forming and thermoforming .…”

“…Currently, environmentally benign gases such as supercritical carbon dioxide, CO 2 , and nitrogen, N 2 , are attractive alternatives as physical blowing agents because of their unique properties such as being nonflammable, nontoxic, quick dissolving, and having high self‐nucleating characteristics. Furthermore, blending supercritical fluid (SCF) in a polymer melt can effectively reduce the viscosity and glass transition temperature of the polymer melt, as well as the interfacial tension . Thus, the foaming process can be conducted at low temperatures and the degree of polymer degradation can be reduced.…”