Polymers melt flow index

Polymerization conditions solvent hexane temperature 75 °C pressure 1100 Pa i-BujAl as cocatalyst and hydrogen as molecular weight regulator (Polymer Melt Flow Index 0.1-0.2 g/10 ) > G.P.C. data... 

Polybond Base polymer Melt flow index (190°C/2.16 kg) Maleic anhydride level (%)... 

Figure 6 Viscosity stabilization of SIS polymer. Melt flow index (MFI), days at 80°C (176°F) MFI (g/10 min)-200°C/5 kg.

The Influence of some Important Industrial parameters such as the hydrogen/ethylene ratio, the 1-butene content In the polymerization mixture and polymerization temperature on the behaviour of the catalysts, has been evaluated by measuring polymer productivity after 4 hours, polymer melt flow Index (MFI), shear sensitivity (SS), Intrinsic viscosity and molecular weight distribution. 

Figure 9.1 Effect of reaction temperature on polymer melt flow index. (From Ref. 1.)...

Polymers ranging in melt flow index (an inverse measure of molecular weight) from less than 0.1 to greater than 600 can be obtained by this process but commercial products have a melt flow index of only 0.2-5 and have the highest density of any commercial polyethylenes ( 0.96 g/cm ). 

With the availability of the higher density polymers the value of the melt flow index as a measure of molecular weight diminishes. For example, it has been found that with two polymers of the same weight average molecular weight (4.2 X 10 ), the branched polymer (density = 0.92 g/cm ) had only 1/50 the viscosity of the more or less unbranched polymer (density = 0.96 g/cm ). This is due to long chain branches as explained above. 

The commercial grades available in the 1970s used either zinc or sodium as the cross-linking ion and ranged in melt flow index from 0.4 to 14. The main application of the ionomer resins has been for packaging film. The polymer is particularly useful in composite structures to provide an outer layer with good heat sealability. The puncture resistance of film based on ionomer film has the puncture resistance of a LDPE film of twice the gauge. 

Important physical properties include the density, melt flow index, crystallinity, and average molecular weight. Mechanical properties of a polymer, such as modulus (the ratio of stress to strain), elasticity, and breaking strength, essentially follow from the physical properties. 

The melt flow index describes the viscosity of a solid plastic. It is the weight in grams of a polymer extruded through a defined orifice at a specified time. The melt viscosity and the melt flow index can measure the extent of polymerization. A polymer with a high melt flow index has a low melt viscosity, a lower molecular weight, and usually a lower impact tensile strength. 

In an alternate synthesis, the formation of thermoplastic vulcanizate (TPV) is accomplished with two polymers, wherein one polymer is grafted with a carboxylic acid anhydride, which then is reacted with an aminosilane, which reacts with the acid anhydride and then cross-links with moismre. The vulcanizates exhibit good mechanical properties and lower melt-flow index than the starting polymers. 

In the past three decades, industrial polymerization research and development aimed at controlling average polymer properties such as molecular weight averages, melt flow index and copolymer composition. These properties were modeled using either first principle models or empirical models represented by differential equations or statistical model equations. However, recent advances in polymerization chemistry, polymerization catalysis, polymer characterization techniques, and computational tools are making the molecular level design and control of polymer microstructure a reality. 

Table 1 Glass transition temperature (7 gi), melting temperature (V m) and melt flow index (MFI) of polymers...

Oilfields in the North Sea provide some of the harshest environments for polymers, coupled with a requirement for reliability. Many environmental tests have therefore been performed to demonstrate the fitness-for-purpose of the materials and the products before they are put into service. Of recent examples [33-35], a complete test rig has been set up to test 250-300 mm diameter pipes, made of steel with a polypropylene jacket for thermal insulation and corrosion protection, with a design temperature of 140 °C, internal pressures of up to 50 MPa (500 bar) and a water depth of 350 m (external pressure 3.5 MPa or 35 bar). In the test rig the oil filled pipes are maintained at 140 °C in constantly renewed sea water at a pressure of 30 bar. Tests last for 3 years and after 2 years there have been no significant changes in melt flow index or mechanical properties. A separate programme was established for the selection of materials for the internal sheath of pipelines, whose purpose is to contain the oil and protect the main steel armour windings. Environmental ageing was performed first (immersion in oil, sea water and acid) and followed by mechanical tests as well as specialised tests (rapid gas decompression, methane permeability) related to the application. Creep was measured separately. 

Too little has been published about the flow properties of PET as a criterion for processing. The results of melt flow index (MFI) testing conditions do not correlate with the processing behavior in the case of PET. This may be caused by the discrepancy between the shear rates in testing and processing. MFI is defined as the amount of polymer melt (in g) extruded within 10 min through an orifice of specified diameter at a standard load and temperature. In the case of PET, this method was not very popular until recently due to the sensitivity of this material to hydrolytic degradation. 

Two main types of viscometers are suitable for the determination of the viscosity of a polymer melt The rotation viscometer (Couette viscometer, cone-plate viscometer) and the capillary viscometer or capillary extrusiometer. The latter are especially suitable for laboratory use since they are relatively easy to handle and are also applicable in the case of high shear rates. With the capillary extrusiometer the measure of fluidity is not expressed in terms of the melt viscosity q but as the amount of material extruded in a given time (10 min). The amount of ex-trudate per unit of time is called the melt index or melt flow index i (MFI). It is also necessary to specify the temperature and the shearing stress or load. Thus MFI/2 (190 °C)=9.2 g/10 min means that at 190 °C and 2 kg load, 9.2 g of poly-... 

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