Woo Nyon Kim

Properties of blends of a thermotropic liquid crystalline polymer with a flexible polymer (Vectra/PET)

Blends of Vectra A900, a thermotropic liquid crystalline polymer (LCP), and poly(ethylene terephthalate) (PET) were studied over the entire composition range using scanning electron microscopy, differential scanning calorimetry, and rotational rheometry. There is some interaction between the polymers, as evidenced by melting‐ and crystallization‐point depression in the PET phase. The shear rheology deviates substantially from simple mixing laws and from predictions of an emulsion model of dispersed blends. The viscosity of LCP‐rich compositions exceeds that of either component at low rates and frequencies. The viscosity of PET‐rich compositions falls below that of either component at low rates and frequencies. The latter observation cannot be explained by deformation and orientation of the LCP phase, since the dispersed LCP inclusions remain spherical following steady shear.

Properties of crosslinked polyurethanes synthesized from 4,4′-diphenylmethane diisocyanate and polyester polyol

Polyurethanes were synthesized using the high functional 4,4′-diphenylmethane diisocyanate (MDI), polyester polyol, and 1,4-butane diol. The synthesized polyurethanes were analyzed using differential scanning calorimeter (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectrometer, and swelling measurement using N,N′-dimethylformamide. From the result of thermal analysis by DSC and DMTA, single Tgs were observed in the polyurethane samples at all the formulated compositions. From this result, it is suggested that the polyurethanes synthesized in this study have crosslinked structure rather than the phase-separated segmented structure because of the high functionality (f = 2.9) of the MDI. By annealing the polyurethane samples using DSC, the Tgs were increased by 4.7∼16.0°C at the various annealing temperatures. From the results of FTIR and swelling measurement of polyurethanes, it is suggested that the increase of Tg of the polyurethanes by annealing is not due to increase of the hydrogen bond strength but mainly due to the increase of the crosslink density.

Determination of the Flory‐Huggins interaction parameter of polystyrene—polybutadiene blends by thermal analysis

Blends of polystyrene (PS) and polybutadiene (PBD) were investigated by differential scanning calorimetry. From the phase composition diagram of the blends, it appears that PBD dissolves more in the PS-rich phase than does PS in the PBD-rich phase. This result is consistent with the behavior of the specific heat increment at the glass transition temperature of PBD in the PS-PBD blends. From the measured glass transition temperature and apparent weight fractions of PS and PBD dissolved in each phase, values of the Flory—Huggins polymer—polymer interaction parameter (χ12) were determined to be 0.0040–0.0102 depending on the composition and molecular weights of the PS and the PBD. No significant difference in χ12 was observed among the blending methods. The composition-dependent value of the Flory—Huggins polymer—polymer interaction parameter was found to be similar to the value of χ12. The polymer—polymer interaction parameter appears to depend on the degree of polymerization of the polymers as well as on the apparent volume fraction of the polymers dissolved in each phase.

Compatibility studies of blends of a thermotropic liquid crystalline polymer and flexible chain polymers by application of Flory's lattice theory

Abstract Florys lattice theory has been applied to the polymer blends containing a thermotropic liquid crystalline polymer (LCP) and flexible chain polymers. The phase behavior of blends of a thermotropic LCP and a flexible chain polymer at melt processing temperature can be evaluated by two quantitative parameters: the polymer–polymer interaction parameter ( χ 12 ) and the degree of disorder ( y / x 1 ). From the results of the model calculation, it has been found that the miscibility is increased with the increase of the degree of disorder ( y / x 1 ) of the LCP and with the decrease of the degree of polymerization ( x 1 m and/or x 2 ). The simulated spinodal curve of ternary polymer blends containing a thermotropic LCP and two flexible chain polymers has been calculated using the lattice theory. When three pairs of binary polymer blends are immiscible, the coexistence curve of the three phases appears for the ternary blend having similar values of χ ij among component polymers. When the LCP is immiscible with two flexible chain polymers, and also when the two flexible chain polymers are miscible with each other, the strong effect of anisotropy of the LCP is observed in the simulated spinodal curve. When three pairs of binary polymer blends are miscible, a phase separation is also observed due to the |Δ χ | effect.

Properties of flame-retarding blends of polycarbonate and poly(acrylonitrile-butadiene-styrene)

Abstract Limiting oxygen index (LOI) value, glass transition temperature (Tg), thermal degradation profile, morphology, and tensile strength and elongation at break of the flame-retarding polycarbonate (PC)-poly(acrylonitrile- butadiene-styrene) (ABS) (7/3) blends were studied. The flame retardants used were huntite-hydromagnetite compounds (HHM), triphenyl phosphate (TPP), zinc stannate, and antimony trioxide. The LOI values were increased with the increase of TPP content, but they did not change significantly when the HHM was used as a flame retardant Glass transition temperatures of the flame-retarding PC-ABS (7/3) blends were decreased significantly when TPP was added to the blends. This is mainly due to the plasticizing effect of the TPP on the PC-ABS (7/3) blends. In the flame-retarding PC-ABS (7/3) blends, the LOI value, tensile strength, and elongation at break were measured and found to be 24.6 - 31.6%, 41.4 - 50.3 MPa, and 2.16 - 33.7%, respectively. These LOI values and mechanical properties were achieved when the TPP, zinc stannate, and antimony trioxide were used as flame retardants, and when dodecylbenzenesulfonic acid sodium salt and dimethylsulfone were used as additives into the PC-ABS (7/3) blends.