Polymer/layered silicate nanocomposites: a review from preparation to processing

Biodegradable polymers and their layered silicate nanocomposites: In greening the 21st century materials world

Nylon 6 nanocomposites: the effect of matrix molecular weight

The entanglement concept in polymer rheology

Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions

Correlation of dynamic and steady flow viscosities

This study focuses attention on the relation between the glass transition temperature, Tg, of the amorphous phase of semicrystalline polymers and the morphological state of the polymer. By use of dynamic mechanical and thermal distortion tests, the influence of stereospecificity; crystallinity; and, orientation in the absence and presence of crystallinity, has been assessed for crystallizable polystyrene (CPS). These results, together with some analogous data on crystallizable polypropylene (CPP), are compared to published information on other polymers. Studies of quenched, oriented CPS by thermal distortion tests under load indicate that the retractive stress and external load are the prime factors in determining the glass temperature as measured by this type of test. The influence of Tg of the configurational state, sorted out from the other two factors, is shown to be small. For CPS, an increase in Tg of 5–15°C., depending on the method of test, is observed to accompany crystallization. An increase of 15–25°C. in Tg, relative to amorphous CPS, is noted for samples annealed in the stretched condition. The combined effect of crystallinity and orientation is significantly greater than the sum of the individual effects; a mechanism is postulated for this synergistic behavior. The breadth of the transition of oriented, annealed samples appears to depend on the direction of test relative to the direction of stretch. Stereo-specificity in polystyrene and polypropylene appears to have a negligible influence on Tg.

The glass temperature of semicrystalline polymers

The dynamic mechanical properties of several polystyrene fractions were measured in the frequency range 0.05–5 cycles per second and the temperature range 160–220°C. Data obtained at different temperatures with each fraction were superposed by means of Ferry's reduced variables. The empirical temperature shift factors involved in this superposition agreed well with values calculated from the universal function of Williams. The observed molecular weight dependence of the dynamic properties agreed qualitatively with the predictions of the Rouse theory as modified by Ferry, Landel, and Williams for application to polymer melts.

Dynamic viscosity and shear modulus of molten polystyrene as a function of molecular weight

A procedure is described for the measurement of number-average molecular weight Mn on a specimen in bulk form, utilizing a dynamic torsion pendulum. For both atactic and isotactic polystyrenes it has been found that the minimum value of the damping logarithmic decrement, δm, (above the glass temperature) is related to an measured osmometrically in dilute solution by Mn = δ × 105. The Mv/Mn ratio can also be estimated directly from the δ vs. temperature curve. A four-element spring-and-dashpot model yields similar 6 vs. T curves when the Williams-Landel-Ferry temperataure dependence is assigned to the viscosity of the dashpots.

W. P. Cox

Papers

Correlation of dynamic and steady flow viscosities

The glass temperature of semicrystalline polymers

Dynamic viscosity and shear modulus of molten polystyrene as a function of molecular weight

Dynamic mechanical measurement of ??n