Density, melt index, and molecular weight

Table 2.3 Density, melt index, and molecular weight influence PEs performances...

Three basic characteristics of PEs determine their processing and end-use properties their density, melt index, and molecular weight distribution (see Chapter 2). Their range in density, from 0.890 to above 0.96 g/cm, is a result of their crystalline structure. This difference accounts for their property variations seen in Chapter 2. As one example, reducing PE s crystallinity increases its impact resistance, cold flow, tackiness, tear... 

Table 6-8. The Effects on PEs of Increases in Density, Melt Index, and Molecular Weight... 

Direct comparisons between melt index and molecular weight of polyethylene should be made with caution. Such comparisons are only appropriate when the polymers have similar histories (made using the same catalyst, by the same process, at near identical densities, etc.). An example of the relationship between melt index and molecular weight for a series of LLDPEs with similar histories is... 

FIGURE 39 High-load melt index and molecular weight (Mw) values of polymers made at three densities by adjusting the amounts of 1-hexene added to the reactor. The addition of comonomer tended to decrease the polymer MW (raise HLMI). 

Polyethylene and polypropylene are semitransparent plastics made by polymerization. They are produced from ethylene and propylene in a variety of grades. Their mechanical properties are determined mainly by density (degree of crystallinity) and molecular weight, characterized by the Melt Index (MI). 

Description A variety of polymers are produced on these large reactors for various applications. The melt index, polymer density and molecular weight distribution are controlled with temperature profile, pressure, initiator and comonomer concentration. Autoclave reactors can give narrow or broad molecular weight distribution depending on the selected reactor conditions, whereas tubular reac-... 

First, wc purify the compound and determine its physical properties melting point, boiling point, density, refractive index, and solubility in various solvents. In the laboratory today, we would measure various spectra of the compound (Chap. 13), in particular the infrared spectrum and the nmr spectrum indeed, because of the wealth of information to be gotten in this way, spectroscopic examination might well be the first order of business after purification. From the mass spectrum we would get a very accurate molecular weight. 

Melting involves a change from the crystalline solid state into the liquid form. For low-molecular-weight (simple) materials, melting represents a true first-order thermodynamic transition characterized by discontinuities in the primary thermodynamic variables of the system such as heat capacity, specific volume (density), refractive index, and transparency. Melting occurs when the change in free energy of... 

You should list physical constants such as melting points, boiling points, densities, and molecular weights in the notebook when this information is needed to perform an experiment or to do calculations. These data are located in sources such as the CRC Handbook of Chemistry and Physics, The Merck Index, Lange s Handbook of Chemistry, or Aldrich Handbook of Fine Chemicals. Write physical constants required for an experiment in your notebook before you come to class. 

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. 

The Fracture behavior of Medium Density Polyethylenes (MDPE) with different melt flow indexes (1.9 to 5.0 dg/min) employed in rotational molding were studied by Essential Work of Fracture (EWF). The EWF parameters obtained were equivalent for all samples examined regardless of their differences in comonomer content and molecular weights. Annealing of samples resulted in lower ductility values according to EWF parameters, in spite of minimum crystallinity changes. 

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