Mass flow rate, polymers

In polymer processing practice, we need to ensure that the particulate gravitational mass flow rate of the hopper exceeds, over the complete operating range, the extruder open discharge rate (i.e., the rate without any die restriction). That is, hoppers must not be the production-rate limiting factor. Second, and more importantly, it is necessary for stable extrusion operations and extruded product quality that the flow be steady and free of instabilities of the particulate flow emerging from the hoppers. Finally, as we will see in Chapter 9, we need to know the pressure under the hopper in order to determine the pressure profile in a SSE. 

The overall polymer conversion ratio is given by kg times the total surface area. The temperature dependence of polymer deposition for various monomers (of difierent molecular weights) under difierent discharge conditions is best expressed in terms of the normalized deposition rate kg rather than deposition rate ki or k2 because the actual deposition rate observed under a set of conditions is dependent on the mass flow rate (see Chapter 8). 

In general plasma polymerization processes it has been established that the deposition rate and properties of a plasma polymer primarily depend on the value of the normalized energy input parameter WjFM, as described in Chapter 8. In LPCAT polymerization processes, as described in Chapter 16, the deposition rate of a plasma polymer primarily depends on the value of the normalized energy input parameter, which is given by W FM)J FM). In this composite parameter, W is the power input applied to arc column, FM) is the mass flow rate of carrier gas (argon), and FM) is the mass flow rate of monomer that is injected into the cascade arc torch. The quantity of W FM)J FM) can be considered as the energy, which is transported by carrier gas plasma, applied to per mass unit of monomers. 

In LCVD, the simplest parameter that can be correlated with the flow rate of monomer is the polymer deposition rate, which is generally and most logically expressed by (mass)/(area)(time). As long as the dependence of polymer deposition rate on monomer flow rate is sought for a given monomer only, the monomer flow rate given by seem can be used without difficulty when such a correlation is extended to different monomers and the polymer deposition characteristics are compared, however, the flow rate based on cubic centimeters per minute cannot be used because the mass of a mole of gas depends on the molecular weight of the monomer. The polymer deposition rates of various monomers should be compared on the basis of the mass flow rate otherwise, polymer deposition rates are not directly proportional to the polymerization rates. 

Bulk density, as well as the physical shape of the polymer, influences the solid material flow in hoppers and in the feed section of screws. Low bulk density results in low mass flow rate, possibly causing solids conveying rates too low to feed enough solids to the plasticating section. In this situation, specially designed force-feed... 

A power-law non-Newtonian solution of a polymer is to be heated from 288 K to 303 K in a concentric-tube heat exchanger. The solution will flow at a mass flow rate of 210 kg/h through the inner copper tube of 31.75 mm inside diameter. Saturated steam at a pressure of 0.46 bar and a temperature of 353 K is to be condensed in the armulus. If the heater is preceded by a sufficiently long unheated section for the velocity profile to be fully established prior to entering the heater, determine the required length of the heat exchanger. Physical properties of the solution at the mean temperature of 295.5 K are ... 

As has been seen in Table 4.1, the polymer microstructure influences the application properties of the polymer, such as melt flow index (MFI). The MFI is the mass flow rate [in g (10 min) ] of a HIPS melt that flows through a capillary, when forced by a piston loaded by a constant weight. It indicates the processability of the polymer and it is an important quality control variable in the polymerization process. MFI mainly depends... 

This equation provides an estimate of the polymer melt density based on the solid density. It can be used for calculations of mass flow rate. 

In devolatilization, one or more volatile components are extracted from the polymer. The polymer can be either in the solid state or in the molten state. Two processes occur in the devolatilization process. First, the volatile components diffuse to the polymer-vapor interface then the volatile components evaporate at the interface and are carried away. Thus, the first part of the process is a diffusional mass transport and the second part a convective mass transport. If the diffusional mass flow rate is less than the convective mass flow rate, the process is diffusion-controlled. In polymer-volatile systems, the diffusion constants are generally very low, and, therefore, in many polymer devolatilization processes the process is diffusion-controlled. 

Many extruder screws are designed such that the drag flow is considerably larger than the pressure flow. In these cases, the approximate output of the extruder is determined from Eq. 7.199. If the mass flow rate is required, the volumetric flow rate is simply multiplied with the polymer melt density. The reason that many... 

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-... 

The measurement of melt mass-flow rate and density is usually the first step in the specification and identification of polyethylene materials. It should be noted that the density of the base polymer differs from the density of the finished geomembrane mixed with carbon black. The confusion, which can occur in the classification of the PE resin, has briefly been dealt with in Sect. 2.1. As a rule, only geomembianes coloured black by carbon black, and not their natural-coloured resin, reach a density which properly meets the classification of HOPE plastic material (see Sect. 2, Tables 2.2 and 2.3). However, one may not consider these classification limits as strict technical criteria even if the density of the black geomembianes is just below 0.940 g/cm, it may correspond to what is ealled HOPE geomembrane over the whole spectrum of its characteristics. 

If the molten polymer is cooled, the resultant data take the form shown in Figs. 4-34-4.37 for polyethylene (Phillips Marlex 6001). Once again, the curves come together as mass flow rate is increased because of decreased residence time (compare Fig. 4-34 at 191.0 g/min to Fig. 4-37 at 338.9 g/min although it is not obvious that there is a definite effect of viscous dissipation in cooling. 

A polymer solution (n of 0.5 K at 90 F of 51 Ibm fT viscosity activation energy of 14,900 Btu/lb mole) is fed into a 1-in. i.d. stainless steel tube (10 ft long) at a mass flow rate of 750 Ibm/h and a temperature of 90 F. The velocity profile is fully developed before the solution enters the heated tube. Heat is supplied by steam condensing at 20 psia. 

The polymer solution in the preceding problem can be processed in one of two different systems. For each case, the solution s mass flow rate (0.5 kg/s) and inlet and outlet temperatures (65.6 and 26.7°C) are the same. Which pipe diameter (0.02 m,wall at 21°C or 0.01 mg, wall at 5°C) will give the lower pressure drop ... 

Thermally softened polystyrene is heated in a circular tube (diameter of 0.03 m) that is 3 m long. The mass flow rate of the polymer is 400 g/min. What wall temperature will be needed if the polymer s average inlet and exit temperature are 490 and 513 K Rheological data for the polymer are n = 0.22 K = 2.2 X 10" N s7ml... 

Fig. 11-33 Surface temperature (open circles) and filament diameter (solid circles) vs z, distance from spinneret. Polymer spun is polypropylene, initially at 260°C (air at 25 C). Mass flow rate and spin speed are (a) 2 g/min, 200 m/min and (b) 4 g/min, 100 m/min [38,93,94].

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