Melt Flow temperature relationship

Calibration and Standards. Thermal analysis methods are not absolute and calibration is needed to record the correct abscissa value of temperature T (in Kelvin) and time t (in seconds or minutes). On the ordinate, calibration is necessary for the amplitude of deflection, AT, expressed as the difference in temperature (in Kelvin) for DTA or as heat flux, dQldT (in joules per second or watts) for DSC. Each instrument manufacturer provides methods and standard materials for these calibrations. In addition, ICTAC, in collaboration with the National Institute of Standards and Technology (NIST), has developed a series of materials as calibration standards for DSC/DTA. These reference materials can be used to calibrate both the temperature scale (K, abscissa) and heat flow (J/g, ordinate) on the basis of the integrated area under the curve. Figure 4 shows the heat flow-temperature relationship for various solid-solid and solid-liquid melting standards. Table 3 lists the solidi-to-solid2 transitions, melting points, and Curie temperatures of various pure metals, and also their transition enthalpies (J/g) (11). 

Fig. 12.9 Melt surface temperature rise at the capillary exit, calculated for ABS Cycolac T and measured ( ) with an infrared pyrometer Tq = 505 K, Dq = 0.319 cm, L/Dq — 30. The relationships Nu = C(GZ) 3 are used to estimate h. [Reprinted by permission from H. W. Cox and C. W. Macosko, Viscous Dissipation in Die Flow, AIChE J., 20, 785 (1974).]...

Fluoropolymer manufacturers and suppliers have developed time-temperature-shear-rate data for melt viscosity or melt flow rate (index) to provide an assessment of the thermal stability of these polymers. Figures 6.1 and 6.2 show the melt viscosity of a few commercial grades of polyvinylidene fluoride as a function of temperature at a fixed shear rate. The relationships between melt viscosity and shear rate, and shear stress versus shear rate, are presented in Figs. 

Many processes are available for the production of plastic products and the choice depends upon the relationship between material properties, processing method and end-product properties, in addition to the choice of forming method, which all have technical and economic aspects. Three important features of plastic melts during processing are shear viscosity, melt flow index (MFI) and melt elasticity. MFI is the quantity of polymer extruded under specific load and temperature conditions in a given time. The elastic properties of the melt are a major factor in determining the residual strain and moulding defects [8]. 

Compositions with terephthalate levels of over 60% would not be as desirable, however, since flow was not measurable above this level (Table 1). The polyesters which were examined all can be prepared with melt flow characteristics similar to those of commercial polysulfone resins as indicated by Figure 2. While the viscosity/temperature relationships for the two types of polymers are different this should not be a serious problem in the utilization of the aromatic polyesters. 

The melt-flow index is an extremely simple test, and essentially consists of measuring the amount of polymer melt flowing through a tube of specific dimensions under a specific pressure over a specified amount of time. Experimentally, the apparatus is a small extruder. The index obtained has a sort of inverse relationship to viscosity at any given temperature, and is indirectly related to polymer molecular weight. 

Figure 9.75 Relationship between surface temperature and melt flow index for a polymer blend in hot melt adhesive formulation. (From Ref. 67.)...

Combs, R. L. and Nation, R. G., Relationships among melt flow, glass transition temperature and inherent viscosity of tfamnoplastic polyestms, J. Pofym, ScL, 30, 407-414 (1970). 

The spiral test is used for classifying injection molding resins with respect to their melt flow behavior. By plying dimensional analysis to measured flow curves of thermoplastic resins a relationship was obtained to predict the flow length as a function of melt temperature, mold temperature, injection speed, injection pressure and spiral geometry. 

In order to understand potential problems and solutions of design, it is helpful to consider the relationships of machine capabilities, plastics processing variables, and product performance (Fig. 1-10). A distinction has to be made here between machine conditions and processing variables. For example, machine conditions include the operating temperature and pressure, mold and die temperature, machine output rate, and so on. Processing variables are more specific, such as the melt condition in the mold or die, the flow rate vs. temperature, and so on (Chapter 8). 

Short shot can be avoided by proper mold design and control of polymer melt conditions—namely, temperature and injection pressure. This relationship is shown in Figure 7.76. Within the area bounded by the four curves, the specific polymer is moldable in the specific cavity. If the pressure and/or temperature are too low, short shot will result. If the temperature is too high, thermal degradation of the polymer can occur. If the temperature is too low, the polymer will not be molten. If the pressure is too high or the polymer is too fluid, the melt can flow into the gaps of the mold, creating thin webs of polymer attached to the molded article in an undesirable part... 

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