Melt viscosity also molecular weight, relation

Typical of thermoplastics (see Chapter 8) the melts are pseudoplastic and also in common with most thermoplastics the zero shear rate apparent viscosity of linear polyethylene is related to the weight average molecular weight by the relationship... 

MFR tests are used to detect degradation in fabricated products where comparisons, as an example, are made of the MFR of pellets to the MFR of product.3 143 MFR has a reciprocal relationship to melt viscosity. This relationship of MW (molecular weight) to MFR is an inverse one as the MFR increases, the MW drops. MW and melt viscosity is also related as one increases the other increases. 

As shown above, EHD instability manifests itself at high temperatures at which the viscosity of the LC melt is not too high. The influence of the molecular weight of the polymer on the temperature Tguj) seems also to be related to the viscosity. If in the polymer la with of about 100-150 the EHD process takes place in a wide temperature range (Fig. 4), DSM in the polymer with P V/ISOO in an electric field of f 50 Hz appears only a few degrees below TqX. 

Many different molecular weight grades of VP-based polymers, characterized by viscosity, are available commercially. The determination of viscosity is historically satisfactory for quality assurance purposes however, most physical properties of polymers are directly related to molecular weight. For example, the glass transition temperature and tensile strength of amorphous polymers are known to depend on molecular weight. The melt viscosity of polymers and the bulk viscosity of concentrated polymer solutions are also known to depend on molecular weight. 

The physical properties of polymers are also related to their molecular weights. Melt viscosity, hot strength, solvent resistance, and overall toughness increase with molecular size. Table 2.4 illustrates the effect of molecular weights (size) upon physical properties of polyethylene [64]. 

Polymer modification through additives is ultimately related to the affinity of the additive to the matrix which is controlled by physical and chemical interactions. The selection of mixing configuration which in turn, depends on the nature of the additive (low viscosity liquid, low molecular weight solid, melt, liquid) also affects the performance of the additive. Additives forming distinct dispersed morphologies may be deformable or rigid... 

Broadline nmr, relating melt order with polymer composition and temperature, also provided evidence supporting the thermotropic nature of these materials. The physical properties of molded parts of certain compositions showed a definite mechanical anisotropy. Strength and modulus values in the machine direction were considerably higher than those values transverse to the machine direction, that is, perpendicular to the direction of flow. Again, facile and high molecular orientation was noted for these polymers in the flow direction and this became more pronounced as part thickness was reduced. Further, the melt viscosities of the X7G copolyesters, at about equivalent molecular weights, were... 

As the flow velocity relates to the disentangling time, this also holds for the melt viscosity. Indeed, po and the disentangling time for entangled melts show the same dependence on the molecular weight. Figure 5.13 collects the results of viscosity measurements for various polymers. As should be noted, a power law behavior... 

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