Melt index measurement

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... 

Melt Index measurements were made per ASTM D1238, Condition... 

Whereas melt index measures flow (shear) rate under constant shear stress, fluidity measures shear stress at constant shear rate (0.1 s 1). Fluidity varies inversely with MW. 

ASTM Method 1238, Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer [6], completely defines the melt index, both the instrument and the experimental procedure. Temperatures and instrument configurations for common materials are given along with recommended calibration procedures and round-robin results. This method must be strictly followed if consistent melt index results are to be obtained. A melt index measurement is performed at low stress levels compared to capillary rheometers measurements (typical weights are in the range of 1.2-21.6 kg) and is sensitive to variations in operating procedure, instrument cleanliness (between tests), and operator bias (items such as packing and sample preparation). 

The most important advantage that the rheometer holds over the indexer, however, is the shear rate at which the test occurs. The melt index measurement occurs at shear rates that fall into the lower ranges of a capillary rheometer s capabilities (see Fig. 9). In most cases, these shear rates are also considerably below the shear rate range of the process for which the polymer is intended (see Fig. 11). Two materials with differently shaped viscosity curves could easily have the same viscosity at low shear rates and different viscosities at high rates. They would have the same melt index, pass QC inspection, and behave completely differently on the production floor. The ability of the rheometer to test at shear rates pertinent to the process allows the development of more relevant quality control test procedures. 

Quite often, the melt index test results simply do not provide sufficient information because the melt index is a single-point test. The prespecified test temperature is not necessarily the actual processing temperature. The test is conducted at a low shear rate, which is significantly lower than the actual processing shear rate. The flow rates are measured at a single shear stress and shear rate performed at one set of temperatures and geometric conditions. Furthermore, since the melt index measurement takes account of the behavior of the polymer at only one point, it is quite... 

By far the most famous implementations of Shewhart s basic logic come where the plotted statistic is either the mean, the range, or, less frequently, the standard deviation. Such charts are commonly known by the names x bar charts, R charts, and s charts, respectively. As a basis of discussion of Shewhart charts, consider the data given in Table 4.4. These values represent melt index measurements of... 

Melt index measures how well a molten polymer will flow. This same information can be determined from rheology data. Figure 1 plots the pressure versus piston speed for several of... 

The melt index measurement, I2, in grams per 10 minutes, was performed in accordance with ASTM D 1238 at 190 °C and 2.16 kg load. The molecular weight... 

As a binder material. Exact 5361 from ExxonMobil Chemical was used. It is an ethylene octene copolymer made with metallocene catalysist. The density and melt index measured at standard condition were 0.860 g/cm and 3g/10min, respectively. As a filler material Dechlorane Plus 25 Ifom OxyChem was used. It is a hydrophobic flame retardant and has average particle diameter of 5 p m. The SEM microscopy is shown in Fig. 1. It is seen that the particle size of Dechlorane ranges from 1 to 10 p m. 

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