This paper reports on specific open and interconnected CO 2 foams of poly(L-lactic acid). The effect of varying gas concentration and hence physical changes induced by CO 2 has been investigated and thus used to generate specific structures. The developed morphologies have a skin core structure with larger pores in the core and open and interconnected smaller pores in the skin.
This study reports the glass transition temperature (T g ), and sorption and diffusion of subcritical CO 2 gas in polymethyl methacrylate (PMMA) nanocomposites containing organically modified smectite clay, Cloisite 20A (C20A). A range of methods for preparing the PMMAclay nanocomposites was investigated and a solution coprecipitation method was selected as the most appropriate. Using this method, PMMA nanocomposite containing 2, 4, 6, and 10 wt% nanoclay loadings were prepared. Wide-angle X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) indicated that the 2 wt% nanocomposite materials had a well-dispersed intercalated clay structure. The T g for PMMA-C20A nanocomposites, as measured by differential scanning calorimetry (DSC), was found to be independent of the clay loading. CO 2 solubility studies from 0 to 65°C and pressures up to 5.5 MPa using an in situ gravimetric technique were performed on compression-molded films. The organoclay was found to have no effect on the solubility of CO 2 in PMMA, and therefore the solubility of CO 2 in the nanocomposite can be determined from the solubility of CO 2 in the matrix polymer alone. Diffusion coefficients were determined using the appropriate transport models for these test conditions and the diffusion coefficients for CO 2 in PMMA-C20A composites were found to increase with organoclay loading. It is believed that the processing path taken to prepare the nanocomposites may have resulted in the agglomeration of the C20A organoclay, thereby preventing the polymer chains from fully wetting and intercalating a large number of clay particles. These agglomerations are responsible for the formation of large-scale holes within the glassy nanocomposite, which behave as low resistance pathways for gas transport within the PMMA matrix. POLYM. ENG. SCI., 45: 904 -914, 2005.
The sorption of compressed gases in polymers causing a reduction in the glass transition temperature (T g ) is well established. There is, however, limited information on polymer-gas systems with favorable interactions, producing a unique retrograde behavior. This paper reports on using a combination of established techniques of in situ gravimetric and stepwise heat capacity (C p ) measurements using high-pressure differential scanning calorimetry (DSC) to demonstrate the occurrence of this behavior in acrylonitrile-butadiene-styrene copolymer (ABS)-CO 2 and syndiotactic poly(methyl methacrylate) (sPMMA)-CO 2 systems. The solubility and diffusion coefficient of CO 2 in the range 0 to 65• C and pressures up to 5.5 MPa were determined, which resulted in a heat of sorption of −15.5 and −15 kJ mol −1 , and an activation energy for diffusion of 28.3 and 32.1 kJ mol −1 in the two systems, respectively. The fundamental kinetic data and the changes in C p of the polymer-gas systems were used to determine the plasticization glass transition temperature profile, its relationship to the amount of gas dissolved in the polymer, and hence the formation of nano-morphologies.
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