Role of capillary end correction in flow analysis of molten polyethylene

Abstract

SynopsisThe role of the capillary end correction in flow analysis of molten lowdensity polyethylenes has been analyzed. In spite of limitations of accuracy a quantitative approach has been undertaken. The results are much more complicated than predicted by Bagley in his early reports. The elastic component of the end correction is controlled by shear stress and shear modulus. The latter is affected by the size of the subchain between entangles, M e , and by the degree of long-chain branches. Both are eventually dependent on the length of the chain, i.e., its molecular weight. In addition shear stress and temperature affect the process of disentanglement. Capillary end correction increases with increasing molecular weight and shear stress and with decreasing temperature. The available analysis of branching is still in controversy, and therefore no numerical parameters are yet proposed. A consistent theory of the response of entanglement couplings to shear forces and temperature is evaluated.

Rheological properties of polypropylenes with different molecular weight distribution characteristics

“…As a large tendency, ν is higher as MFI is lower or the molecular weight is higher. This tendency is also generally reported for PP7, 18–21 and other polymers 12, 14, 17, 22–24. Compared at a similar MFI (molecular weight), cat.‐B PPs with generally broader molecular weight distribution tend to show higher ν.…”

“…Although the slope of decrease in ν of cat.‐B PPs is higher than that of cat.‐A PPs below 280°C, it tends to level off or turn to increase at high temperatures. The fact that ν decreases with temperature is generally observed for PP6, 7 and other polymers 8–17. As a large tendency, ν is higher as MFI is lower or the molecular weight is higher.…”

Rheological properties of metallocene isotactic polypropylenes

“…The fact that ν is higher as the MFI is lower or the molecular weight is higher is generally reported for PP6, 12, 13, 24–26 and other polymers 10, 15, 16, 27–29. The fact that comparing at an equivalent MFI (molecular weight), ν is higher as the molecular weight distribution is broader is reported for PP by Kamide and Fujii,24 Fujiyama and Awaya,21 and Fujiyama et al,6 for HDPE by LaMantia et al,30 and for chloroprene by Kawasaki et al10, 16 The experimental results for ν's of MET‐PPs and ZN‐PPs can be explained from the viewpoint of the difference in molecular weight distribution.…”

Flow behavior of partially crosslinked low‐density polyethylene

“…At about 80% gel content the sol viscosity is onethird to one-fifth of that of the original polyethylenes which is an indication of the importance of the viscosity ratio qW. This decrease in sol viscosity becomes more pronounced as the melt flow index decreases, but this effect is not due exclusively to molecular weight change, since the tertiary carbons from which the chain branches originate are potential sites of degradation, and it was found that the frequency of long-chain branching increases with molecular weight ( 10). In addition, measurements on irradiated hydrocarbons showed that branched hydrocarbons undergo more carbon-carbon bond scissions than normal alkanes ( 5 ) .…”