Melt Viscosity MFI

The melt viscosity of polymers is usually measured as the melt flow index (MFI), also known as melt viscosity index (MVI) and melt flow rate (MFR). A pressure is applied to force the molten polymer through a hole at a controlled temperature [24]. All three parameters are set out in standards appropriate to the polymer being measured [24]. The measured value is in grams of polymer extruded through the hole in a set period of time, e.g., ten minutes. This of course, is actually the reciprocal of the viscosity, so a high MFI means low viscosity and vice versa. 

The viscosity of a very dilute dispersion of rigid spherical particles in a Newtonian fluid is described by the Einstein equation (Equation 8.2) [26]. Where q is the viscosity of the dispersion, qi is the viscosity of the fluid alone, ( is the volume fraction of particles and kg is the Einstein coefficient, which is 2.5 for spherical particles, k depends upon both particle shape and orientation. 

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The effect of MW and MWD on the solid state properties have been extensively studied [11,12,82]. These studies have been made both on fractionated and whole polymer samples. Attempts have also been made to correlate the solution viscosity, melt viscosity, MFI and other related parameters, which represent the MW and MWD of the polymers, with the solid state properties. Table 6 summarizes the results of various studies on effect of MW and MWD on the properties of PEs. 

FIGURE 14 The dependences of melt viscosity MFI on nanofiller mass contents IF for nanocomposites PP/CaCOj. 1—the experimental data 2-4—calculation according to the Eq. (3.43) without accounting for (2) and with accounting for (3) nanofiller particles aggregation and at the condition p =const (4). 5—calculation according to the Eq. (49). 

The fibers produced from the polymer with low melt viscosity (MFI = 35 g/10 min) possess a paracrystalline structure with low orientation. The X-ray diffraction patterns of these fibers show halos indicating poor orientation. The overall molecular orientation as shown by the birefringence values decreases with increasing extrusion temperature. 

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