Melt flow ratio

Molecular Weight Distribution. In industry, the MWD of PE resins is often represented by the value of the melt flow ratio (MER) as defined in Table 2. The MER value of PE is primarilly a function of catalyst type. Phillips catalysts produce PE resins with a broad MWD and their MER usually exceeds 100 Ziegler catalysts provide resins with a MWD of a medium width (MFR = 25-50) and metallocene catalysts produce PE resins with a narrow MWD (MFR = 15-25). IfPE resins with especially broad molecular weight distributions are needed, they can be produced either by using special mixed catalysts or in a series of coimected polymerization reactors operating under different reaction conditions. 

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 Flow Ratio 230°C/2.16kg Tensile Yield g/lOmin ISOI133 30 48 48... 

Disclosed is a crossUnked ethylenic polymer foam structure of an ethylenic polymer material of a crosslinked, substantially linear ethylenic polymer. The ethylenic polymer in an uncrossUnked state has (a) a melt flow ratio greater than or equal to 5.63 (b) a molecular weight distribution defined by a given equation and (c) a critical shear rate at onset of surface melt fracture of at least 50% greater than the critical shear rate at the onset of surface melt fracture of a linear ethylenic polymer having about the same melt flow ratio and molecular weight distribution. Further disclosed is a process for making the above foam structure. 

The polymer material contains a linear ethylenic polymer having a melt flow ratio, 11012, of 5.63 or above, a MWD, Mw/Mn, defined by the equation Mw/Mn less than or equal to (I10/I2)-4.63 and a critical shear rate at onset of surface melt fracture of at least 50% greater than that of a linear olefin polymer having about the same 12 and Mw/ Mn. The foam structures have toughness and elasticity similar to those formed from conventional LLDPE without the poor dimensional stability and foam quality associated with those structures and foam quality similar... 

The ethylenic polymer has, in the uncrosslinked state, specified melt flow ratio, MWD and critical shear rate at the onset of surface melt fracture. 

The test is sometimes performed at two loads, making it possible to calculate the melt flow ratio (MLR), which is the ratio of the MI values at the two loads. MLR can been related to the molecular weight distribution, MWD. 

In addition, the volume of the polymer melt discharged through the nozzle per time interval can also be calculated from the piston movement. This test quantity, with a unit of cmVlO min, is called melt volume-flow rate. Usually, the abbreviation MFR is used for the test quantity of melt mass-flow rate and MVR for the melt volume-flow rate. However, the old abbreviation, MFI (melt flow index) is also often used. Another parameter is the ratio of MFR measured with a large test weight to that measured with a small test weight. This quantity designated as melt flow ratio is unfortu-... 

Flow Rate Ratio. The FR ratio is used as a rough estimate of the MWD of a resin. Molecular weight distribution can be measured directly by gel permeation chromatography, but this is a time-consuming, technically challenging measurement that is not commonly found in quality control laboratories. Melt-flow ratio measurements are easily done, since the MFR of a resin is the flow index of the sample divided by the melt index of the sample. 

Melt-flow ratios for LDPE resins can range from very narrow [20] to very broad [100], and can be controlled by reactor conditions and reactor type. Resins with narrow MWD give stronger products but are more difficult to extrude than resins with broad MWD. 

Melt Flow Ratio of the FI and MI values is a relative measure of the polymer MWD where MFR values between 24-28 indicate that the MWD is relatively narrow. Melt Index, Flow Index, MFR and density are only approximate values for each application. 

Index range from 1.25-6.12, which would be suitable for polyethylene film and injection molding applications. The polyethylene molecular weight distribution was relatively narrow as indicated by Melt Flow Ratio values (HLMI/Ml) reported between 26.0 and 33.5. The narrower MWD exhibited by the polymer samples would offer improved film and injection molding properties. 

Single-site ethylene polymerization catalysts based on titanium or zirconium as the active center are primarily used in the low-pressure manufacture of polyethylene with a relatively very narrow molecular weight distribution to include high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and very low density LLDPE to include amorphous material. Table 4.1 summarizes a few examples of end-use applications for this type of polyethylene in terms of the density, molecular weight distribution and molecular weight for various applications. Note that in Table 4.1 a Melt Flow Ratio (MFR) value of 16 approximately corresponds to an polydispersity value of 2.0, which is indicative of a... 

Most LLDPE resins manufactured have a relatively narrow molecular weight distribution as indicated by Melt Flow Ratio values (MFR = FI/MI) of 16-30 or polydispersity values of 2-4. Films produced from this type of polyethylene have higher dart impact and tear properties as shown in the Table 6.5. However, LLDPE resin with a MWD broader than LDPE is used in geomembrane applications such as landfill covers and caps and other heavy-gauge film applications. 

Polymer Melt Index Apparatus (Provides relative polymer molecular weight 12.16 (Melt Index) and relative data on polymer molecular weight distribution by determining the Melt Flow Ratio (MFR), which is the ratio of I,. (Flow Index) value divided by the Melt Index.)... 

MFR) or Melt Flow Ratio FI/MI correlates with polyethylene MWD. 

These values determine the type of end-use application that this particular sample may be utilized for in a commercial application. The Melt Index (MI) value is a relative measure of the polyethylene molecular weight, while the Flow Index (FI) value is a relative measure of the processability of a sample and the Melt Flow Ratio (MFR) value is a relative measure of the shear-thinning behavior of the polyethylene sample which correlates with the MWD of the sample. A relative increase in the shearthinning characteristics denotes an increase in the MWD of the polymer. 

Commercial polyethylene manufactured with a low-pressure process can be classified in terms of molecular weight distribution (MWD) and falls into two categories polyethylene with a relatively narrow MWD as indicated by Melt Flow Ratio values of 15-30 and polyethylene with a relatively broad MWD as indicated by MFR values of 80-130. 

Gel permeation chromatography (GPC) is another important tool in the polyethylene characterization process. Although the Melt Flow Ratio (MFR) value obtained with an experimental sample of polyethylene... 

Melt Flow Ratio (MFR) melt index/flow index Comonomer content (IR method)... 

Table 8. Gas phase ethylene-butene copolymerization at 85 C. Effect of the catalyst and butene content on melt index and melt flow ratio ( 21. / 2.16) different comonomer content given by the number of ethyl branches. PTES, dpdms and DBF are respectively for phenyltrlethoxysllane, dlphenyl-dlmethoxysllane, dibutylphtalate.

Hydrogen was adjusted in order to maintain the 2.16 kg melt index near 1 g per 10 min. The effect of Lewis bases chosen in different chemical families is presented at different butene contents. Most of the ELB induces a MWD narrowing. Good results are obtained with ethers for instance. The best melt flow ratio indices are very low 22 to 24. 

Table 9. Gas phase ethylene butene polymerization (85 C 10 bar total pressure) effect of butene content and ELB on the melt-flow ratio. The solid catalyst used cotnains dlbutylphtalate as an internal Lewis base.

In Fig. 18.1, the molecular weight and color changes of PP as a function of times the polymer is processed are shown. Adding PAO-2 leads to a smaller increase of the melt flow ratio (MFR) the addition of phosphites leads to a larger decrease of the MFR increase. However, the smallest increase in color was found for the unstabilized PP and the largest with the PAO-2 only containing polymer, while the discoloration of the phenolic and phosphite containing samples is in between both. This discoloration can be ascribed to transformation products of the phenolic antioxidant. 

Abstract Polyethylene, PE, is characterized by molecular weight (MW), molecular weight distribution (MWD) and density. Melt index (MI2) is measured in the QC lab and is used as an indication of resin MW. Melt flow ratio (MFR or MI20/MI2) is a calculated QC lab number, which is used as an indication of MWD. Density is a measure of crystallinity. In polyethylene production, having fast reliable feedback on MW and MWD is critical for producing high quality resins. This article describes a novel/unique idea how a capillary rheometer can be used to predict MI2 and MI20. 

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