Effect of crystallinity on gas permeation in miscible polycarbonate–copolyester blends

Permeation rates of helium, methane, and carbon dioxide in miscible blends of polycarbonate and a copolyester were measured at 35°C. The permeabilities for semicrystalline blends having copolyester cyrstallinity induced by annealing were compared to fully amorphous blends. Crystallinity caused a slightly greater impedance to carbon dioxide transport than it did for helium or methane. The relative rates of permeation of one gas compared to another, an issue important for membrane separations, varied greatly with blend composition; however, the effect of crystallinity was not large.     

Effect of crystallinity on mechanical properties of miscible polycarbonate–copolyester blends

Normally amorphous miscible blends of a copolyester and polycarbonate in the form of injection molded bars and extruded film were thermally annealed above the blend T_g to cause the copolyester component to crystallize, and the resulting mechanical properties were evaluated. The properties were found to depend in a complex way on blend composition, annealing conditions employed, the initial state of molecular orientation, and the process history.     

Mechanical relaxation in polycarbonate–polysulfone blends

Lexan polycarbonate and polysulfone P-1700 were blended to various weight percentages by dissolution in methylene chloride. The blended material was reclaimed in the form of evaporated thin films which were dried, ground, and molded. Low-frequency mechanical relaxation tests were run on specimens machined from this material as a function of composition and thermal treatment. In addition to the β-peak, a second peak, β′, was resolved in unannealed 75 wt/o P-1700 specimens. These results are presented and a possible interpretation is discussed and compared with previously proposed mechanisms.     

Melting and crystallization behavior of miscible copolyester–polycarbonate blends

The melting and crystallization behavior of Kodar, a copolyester formed from 1,4-cyclohexanedimethanol and a mixture of terephthalic and isophthalic acids, and its miscible blends with polycarbonate was examined. The results of the melting behavior are discussed in terms of crystallization-induced chemical rearrangements and the copolymeric character of Kodar and interchange reactions between components when polycarbonate is present in the blend. For various reasons, the melting behavior cannot be extrapolated to infinite crystal size using the Hoffman–Weeks approach. Crystallization kinetics follows the Avrami equation, with rates being higher when the crystallization temperatuare is approached from the glass rather than from the melt. The kinetic data are discussed in terms of modern theories. An approximate melting point depression analysis is used to estimate the interaction parameter for the blend, and the result obtained is compared to a value from another technique.     

Thermal and mechanical behavior of polycarbonate–poly(ethylene terephthalate) blends

Melt blends of polycarbonate and poly(ethylene terephthalate) were formed by continuous extrusion and injection-molded into bars for mechanical testing. Thermal analysis was used to ascertain transitional behavior and the level of PET crystallinity at various points in the fabrication and testing process. The mechanical properties showed little departure from additivity except for the percent elongation at break which was substantially larger for certain blends than expected. Glass transition behavior suggests two amorphous phases for PC rich mixtures and only one mixed phase in the PET rich region. Crystallizability of the PET after the blend was held for prolonged times in the melt state suggests that interchange reactions do not occur to any great extent.     

Thermal behavior,morphology, and the determination of the Flory–Huggins interaction parameter of polycarbonate–polystyrene blends

Blends of bisphenol-A polycarbonate (PC) and polystyrene (PS) prepared by screw extrusion and solution casting have been investigated with weight fractions of PC in the blends varying from 0.95 to 0.05. From the measured glass transition temperatures (T_g) and specific heat increments (ΔC_p) at the T_g, the polystyrene appears to dissolve more in the PC phase than does the PC in the PS phase. The blend appears to be near eqilibrium under extrusion conditions so that the polymer–polymer interaction parameter of PC/PS blends was calculated and found to be 0.038±0.004 for extruded blends at 250°C. Scanning electron microscopy supports the conclusion that the compatibility increases more in the region of PS-rich compositions than in the regions of PC-rich compositions of the PC/PS blends.     

Gas transport properties of polycarbonate–polyurethane membrance

Polyurethanes (PU) were prepared using polymeric diols, containing polar groups, as ? O? C(O)? O? (carbonate) groups, carbonate and ether (? O? ) groups, or carbonate and ester groups [? C(O)? O? ]. PUs were prepared by the prepolymer two-step technique using ethyl acetate (EA) as the solvent; the diol was reacted at about +80°C with TDI (ratio 1:2) to give the prepolymer terminated with NCO, which was then cross-linked with triisopropanolamine (TIPA). The membranes were prepared using a Gardner knife and were characterized by differential thermal analysis (DSC). Most of the polymers prepared from low and medium molecular weight diols were amorphous and elastomeric at the temperature of gas transport measurement (35°C). The permeabilities (P) and the diffusion coefficients (D) of different gases (O₂, N₂, CO₂, CH₄, CO) were measured by a modified Lyssy apparatus, the solubility coefficient (S) was also calculated. The water-vapor transport properties D and S were measured according to ASTM. Diffusivity data follow the Fujita model and the solubility coefficients the regular solution theory, as developed by Prausnitz and Shair. © 1993 John Wiley & Sons, Inc.     

Catalytic transesterification in polycarbonate–polycaprolactone systems

Bisphenol A polycarbonate (PC)–poly-ε-caprolactone (PCL) blends have been prepared by melt mixing in the presence of different catalysts using a Brabender plastograph and single-screw extruder at 240–260°C. Increased crystallizability [detected by differential scanning calorimetry (DSC)] of the PC component was observed in the blends obtained in the presence of p-toluenesulfonic acid. Acceleration of carbonate-carbonate exchange reactions is suggested as the main reason for the crystallizability enhancement. Results of solubility tests, DSC, and infrared (IR) spectroscopy evidence ester-carbonate transesterification taking place during PC–PCL blending in the presence of tetrabutoxy titanium and dibutyltin dilaurate. © 1994 John Wiley & Sons, Inc.     

Miscibility and thermooxidative degradation of poly(vinyl chloride)/biodegradable aliphatic–aromatic copolyester blends

The miscibility of poly(vinyl chloride) (PVC) and a biodegradable aliphatic–aromatic copolyester (AAC) was investigated by differential scanning calorimetry. The thermooxidative degradation of the blends was investigated thermogravimetrically. The blends were prepared by dissolution in 1,2‐dichloroethane and precipitation with methanol. The investigated blends were completely miscible with the glass‐transition temperatures best predicted by the Fox equation. Fourier transform infrared analysis showed that the interactions responsible for miscibility were the hydrogen bonds between the blend components. The thermooxidative stability of the PVC/AAC blends was improved compared to that of pure PVC. Furthermore, when AAC was added, the dehydrochlorination rate of PVC decreased, and the maximum rate shifted to a higher temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2158–2163, 2006     

Mechanical properties of miscible polycarbonate-copolyester blends

Miscible blends of polycarbonate and the copolyester based on 1,4-cyclohexane-dimethanol and a mixture of terephthalic and isophthalic acids were melt processed into film and injection moulded into test bars. Wholly amorphous specimens of each type were mechanically tested directly after fabrication and after a variety of annealing conditions. As processed blends exhibited nearly additive responses versus blend composition for modulus, strength, elongation at failure, and notched lzod impact strength. Various annealing protocols caused maxima to appear in plots of modulus versus composition. Similar responses were observed for blend density, and good correlations were noted between density and modulus as both composition andhistory were varied. Sub-T_g annealing of injection moulded specimens was demonstrated to involve simultaneous relaxations of volume and molecular orientation. The individual effects of this combined process were separated by sequential super-T_g (or T_m) and sub-T_g annealing steps.     

Tg-Composition analysis of miscible polymer blends

Several authors have suggested a monotonic variation of the glass transition temperature (T_g) of miscible polymer blends as a function of composition. They usually express the results in terms of equations proposed by Couchman-Karasz, Gordon-Taylor, Fox, and several others. However, we have noticed that numerous systems exhibit a cusp when T_g is plotted as a function of composition (after correction for the presence of crystallinity when semi-crystalline polymers are involved). This cusp cannot appear when the T_g's of the two homopolymers involved are separated by less than about 52 degrees., It will be shown that this observation is quite general since it has been observed with several polyester/chlorinated polymer blends, polycaprolactone/nitrocellulose blends, and polystyrene/poly(vinylmethylether) blends; It will also be shown that this behavior is predicted in the framework of the free volume theory, with equations derived by Kovacs. According to this theory, above a critical concentration ?c (relative to the plasticizer) and below a critical temperature T_c, the high-T_c, polymer no longer contributes to the free volume of the mixture whereas it does above T_c. This difference leads to a T_g-composition variation which has to be expressed by two different equations, one below T_c and the other above T_c, the cusp defining the limit of applicability of each equation.     

Styrene/N-phenylmaleimide copolymer miscible blends

The morphological changes that occur in molded phenolic specimens during long-term heat aging tests have been observed in optical and scanning electron microscopy. The changes in morphology include shrinking and the formation of both cracks and charred zones in the phenolic matrix. The relationship of these morphological changes to weight losses and flexural strength losses was demonstrated.     

Molecular transport of alkanes through thermoplastic miscible blends of ethylene–propylene random copolymer and isotactic polypropylene

A new experimental protocol based on the measurements of sorption (S), desorption (D), resorption (RS), and redesorption (RD) has been used to study the molecular transport of aliphatic alkanes through the miscible blends of an ethylene–propylene random copolymer and an isotactic polypropylene over the temperature interval 25–70°C. Diffusion and activation parameters are evaluated and their dependencies on solvent size, shape, and nature are discussed. Estimated values of the molar mass between chain entanglements, kinetic rate constants, and overshoot index parameters have been influenced by the polymer–solvent interactions. The sorption–diffusion mechanism is found to be of anomalous type. © 1995 John Wiley & Sons, Inc.     

Flammability resistance synergism in BPA polycarbonate–silicone block polymers

The synergism in limiting oxygen index found in BPA carbonate–dimethylsiloxane block polymers (BPAC/DMS) is correlated with a rise in yield of pyrolytic char and an improvement in char oxidation resistance. These changes in turn are related to a peaking of fractional silicon retention in the char at a resin composition of 50 mole % DMS. This behavior, the fine dispersion of silicon in the char, and analyses of the pyrolysates suggest that an important feature of char formation in the block polymers is a polycondensation reaction between pyrolysis products from the two blocks. In addition to the role of chars in withholding fuel from the flame, they are thought to function effectively as thermal insulators.     

Baroplastic behavior of miscible block copolymer blends

Pressure dependence of various phase transitions for the miscible block copolymer (BCP) blends was evaluated by depolarized light scattering (DPLS) and small-angle neutron scattering (SANS) measurements, in which the blends consist of a polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and a deuterated polystyrene-b-poly(n-hexyl methacrylate) (dPS-b-PnHMA). Excellent baroplasticity was observed in nearly symmetric blends of PS-b-PnBMA/dPS-b-PnHMA, leading to the most outstanding pressure coefficients, |dT/dP|, in a closed-loop type phase behavior between a lower disorder-to-order transition (LDOT) and an order-to-disorder transition (ODT) type phase behavior. Together with the estimated pressure coefficients based on the values of enthalpic and volumetric changes at phase transitions, we demonstrate that the entropic compressibility for the miscible BCP blends is a baroplastic indicator, which was characterized by the negative volume change on mixing (ΔV_mix) at transitions.     

Orientation of miscible and immiscible polymer blends

Polystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress-strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the system.