Melt index ratio

Dividing HLMI by MI affords the melt index ratio (MIR), a dimensionless number which gives an indication of breadth of molecular weight distribution. As MIR increases, MWD broadens. 

MIR melt index ratio (HLMI/MI) an indicator of the breadth of MWD of a polymer, used mostly with PE... 

Table 1. Heptane slurry polymerization at 80 C, 8 bar ethylene pressure. Effect of ILB on melt index and melt index ratio with cocatalyst triethyl and trihexylaluminium [Al] = 3 mM.l ...

Table 3. Effect of ILB and ELB on productivity nelt-index and melt-index ratio in gas phase ethylene polymerization at 95 C.

A erude measure of the shear sensitivity of a polyethylene resin can be obtained if it is extruded from a melt indexer under two different loads. It is conventional to make this determination using the standard load of 2.16 kg and one of 10.0 kg. The ratio of the mass of extrudate in 10 min at high load relative to that at low load is a dimensionless number known as the melt index ratio (MIR) or fiow rate ratio (FRR). The higher the number, the greater is the sample s propensity to undergo shear thinning. 

Fig. 12. Tensile strength vs draw ratio (6) 0.42 melt index spun at 50 m /min, B, and 500 m /min, A, A 12.0 melt index spun at 100 m /min, , O and 500 m /min, , <). Open symbols = cold drawn and annealed at 140°C filled symbols = drawn at 140°C. To convert GN/m to dyne/cm, multiply by...

The width of molecular weight distribution (MWD) is usually represented by the ratio of the weight—average and the number—average molecular weights, MJM. In iadustry, MWD is often represented by the value of the melt flow ratio (MER), which is calculated as a ratio of two melt indexes measured at two melt pressures that differ by a factor of 10. Most commodity-grade LLDPE resias have a narrow MWD, with the MJM ratios of 2.5—4.5 and MER values in the 20—35 range. However, LLDPE resias produced with chromium oxide-based catalysts have a broad MWD, with M.Jof 10—35 and MER of 80-200. 

The molecular weight distribution of LLDPE resins is usually characterized in industry by the ratios of melt indexes measured in the same apparatus using different loads (2.16, 10.16, and 21.6 kg). The commonly used ratios are melt flow ratio, MFR) and I q/I2. Both of these ratios... 

Experiments were conducted with a dual catalyst chain shuttling system in a continuous solution polymerization reactor. A series of ethylene-octene copolymers of similar melt index were produced with a composition of ca. 30% (by weight) hard and 70% soft blocks. The level of DEZ was systematically varied to study the effects of CSA ratio on polymer microstructure. 

An LDPE resin was used for this study. The resin had a melt index of 2.0 dg/min (2.16 kg, 190 °C) and a solid density of 0.922 g/cmT The shear viscosity was reported previously [37] thermal properties are provided in Chapter 4 bulk density as a function of temperature and pressure is provided in Fig. 4.4 and the coefficients of dynamic friction are provided in Appendix A5. The lateral stress ratio was measured at 0.7 [38] using the device shown in Fig. 4.8. 

Entry Ti/Mg Ratio Catalyst Efficiency (g PE/g catalyst) Polymer Bulk Density (g/cm3) Melt Index (g/10 min)... 

MFR defined as the ratio of the high load melt index to the low load melt index... 

First, the rate of shear, which is not linear with the shearing stress due to the non-Newtonian behaviour, varies with the different types of polymer. The processability of different polymers with an equal value of the MI may therefore differ widely. An illustration of this behaviour is given in Fig. 15.14. Furthermore the standard temperature (190 °C) was chosen for polyethylenes for other thermoplastics it is often less suitable. Finally, the deformation of the polymer melt under the given stress is also dependent on time, and in the measurements of the melt index no corrections are allowed for entrance and exit abnormalities in the flow behaviour. The corrections would be expected to vary for polymers of different flow characteristics. The length-diameter ratio of the melt indexer is too small to obtain a uniform flow pattern. 

MI = Melt index (ASTM D 1238, condition E) HLMI = Flow rate (ASTM D 1238, FR = Flow ratio ratio of melt index HLMI to melt index MI... 

The Gyna-ir Correlation can be sharpened by the two-phase argument. With the crosslinking agents confined to their own phase, the quantity of gel should be determined by the total surface area of that phase and, hence, the dispersion of the E/ABP in the polyethylene matrix. If we assume that better blending is achieved by matching the component melt viscosities, then Qninv should be dependent on the sensitizer melt index (MI), the relative volumes of the components -blend ratio, BR - and the total sensitizer concentration (Co). From least squares analyses of our results, we find ... 

FIGURE 76 The response of the molten polymer to shear stress, indicated here as the HLMI/MI ratio, is shown as a function of melt index. The addition of CO to the reactor diminishes the shear thinning ability of the resin because of lowered LCB levels. 

FIGURE 79 Response to shear stress, here as the polymer HLMI/MI ratio, as a function of ethylene concentration in the reactor for three series of polymers of constant melt index. 

FIGURE 82 Response to shear stress, shown here as the polymer HLMI/MI ratio, as a function of catalyst activation temperature for polymers made in the slurry process with Cr/silica-titania catalyst. Reaction temperature was varied (102-110 °C) to produce three series of polymers of constant melt index. (Compare with Figure 83.)... 

FIGURE 137 The polymer s response to shear stress, expressed here as the HLMI/MI ratio, is usually lowered for a given melt index by the presence of fluoride on the catalyst. Cr/silica-alumina was impregnated with (NH4)2SiF6 and activated at 540 °C. The reaction temperature (120-140 °C) was adjusted to maintain constant Ml. 

In order to overcome the shortcomings of the melt index method, high load MI (HLMI) has been introduced to indicate the grams of polymer pushed out of the barrel under the action of a heavier weight, usually 10 kg (or 21.6 kg). The ratio of the HLMI/MI indicate how shear thinning the resin is. The higher the ratio, the more shear thinning the polymer [8]. 

Now let us consider the so-called polymer processability, which is represented by the MFl ratio measured at 10 and 2.16 kg loads, namely HLMI/Ml (high load melt index over melt index) (Table 17.21)... 

With this much interest in polyethylene, many attempts have been made to use low frequency NMR in either the time domain or frequency domain to monitor and control the production more rapidly. Auburn International (now part of Oxford Instruments) developed a widely adopted system based on the time domain spectrometers [21]. In this case, sample preparation is no longer an issue since the system accepts either powder or pellets and no solvent is used. The Auburn systems determine crystalline and amorphous ratios, viscosity, melt index and molecular weight For other types of polymers, the list of advertised measurements include tacticity, rubber content, copolymer analysis, and various rheological properties. These values are determined by correlating several routine but laborious methods with the decay of the NMR signal under various pulse sequences. The man-hours... 

Approximate melt index of Ig(lOmin)" and density 0.920gcm". Extrusion conditions blow-up ratio = 2 1 die gap = 2.03 mm output = 32kgh film thickness = 31.75 pm die size = 63.5mm frost line height — unknown melt temperature = 466 K. 

The molecular weight distribution (MWD), also discussed earlier, is an indication of the relative proportions of molecules of different weights/ lengths. It shows the breadth of distribution, or the ratio of large, medium, and small molecular chains in the resin. If most of the molecules have about the same MW, the MWD is classified as narrow. A wide or broad MWD implies a large variation in MW. Figure 1-5 compares wide and narrow MWDs. The MWD is independent of both density and melt index (MI) (see Chapter 10), and must be taken into account in considerations of both processing and product performance. A narrow MWD enables much better. 

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