Four different fabrication procedures were used for casting thin films of syndiotactic polypropylene (sPP). A hot press system operated at 200°C and 30 MPa pressure was used to melt polypropylene powder and make the cast films. Different cooling procedures were used to anneal the films, including cooling in liquid nitrogen (LN), ice water, and air at room temperature (RT). The morphological and mass transfer properties of the films were studied with XRD, polarized optical microscopy, bulk flow, and diffusion experiments. All sPP films contained amorphous and crystalline phases. The crystalline phase was determined to be disordered Form I. The sPP films annealed with LN had the lowest crystallinity whereas the sPP films cooled in air at RT had the highest crystallinity. Diffusion of toluene in the films and comparison with Maxwell's equation indicated that the crystalline phase mass permeability is much lower than the amorphous phase, which causes films with low crystallinity to have a higher effective diffusion constant and permeability compared with high crystallinity films. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
The coagulation size of a solvent bound in an isotactic polypropylene (iPP)/o-dichlorobenzene gel was estimated by thermal analysis and small-angle neutron scattering (SANS), and it was examined with respect to the molecular morphology of the gel. The melting process of the solvent frozen in the iPP/o-dichlorobenzene gel showed an endothermic peak below the melting temperature of pure o-dichlorobenzene. This temperature decrease is closely related to the coagulation size of the freezable bound solvent. The relationship between the decrease in the melting temperature and the coagulation size of o-dichlorobenzene was estimated by using porous silica gel. Then, an equation was applied to estimate the coagulation size of the solvent in the iPP gel. The 20-wt% gel showed a coagulation radius of 6.1 nm, whereas for the 50-wt% gel, the radius decreased to 4.1 nm. Next, a SANS measurement was taken for comparison purposes (to be compared with the coagulation size determined by the thermal analysis). The coagulation dimension was estimated using the scattering profile of iPP/o-dichlorobenzene-d 4. The coagulation radius of the freezable bound solvent decreased from 4.8 nm for the 20-wt% gel to 4.0 nm for the 50-wt% gel. This result showed good agreement with the estimations from the thermal analysis.
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