Effect of environmental and molecular factors on viscous flow properties

2 Effects of environmental and molecular factors on viscous flow properties 

The viscous shear properties at any given shear rate are primarily determined by two factors, the free volume within the molten polymer mass and the amount of entanglement between the molecules. An increase in the former decreases the viscosity whilst an increase in the latter, i.e. the entanglement, increases viscosity. The effects of temperature, pressure, average molecular weight, branching and so on can largely be explained in the these terms. 

Let us first consider temperature. An Arrhenius equation of the form 

however, consider that viscosity is inversely related to the fractional free volume, which increases from a small value at the glass transition temperature Tg linearly with temperature above this figure, then it is possible to derive an equation. 

There is some evidence to show that/g and Oj are constant for many polymers so that the above equation may simplify to 

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