Apparent melt viscosity

Rheology. Both PB and PMP melts exhibit strong non-Newtonian behavior thek apparent melt viscosity decreases with an increase in shear stress (27,28). Melt viscosities of both resins depend on temperature (24,27). The activation energy for PB viscous flow is 46 kj /mol (11 kcal/mol) (39), and for PMP, 77 kJ/mol (18.4 kcal/mol) (28). Equipment used for PP processing is usually suitable for PB and PMP processing as well however, adjustments in the processing conditions must be made to account for the differences in melt temperatures and rheology. 

Stepto (1997) focused on the injection molding of potato starch including the basis of the process. In addition, the rheological behavior of starch/water melts during the refill part of the injection molding cycle was analyzed quantitatively to give apparent melt viscosities. Finally, the mechanical properties of molded starch materials and the dmg-delivery behavior of starch capsules were also discussed. 

Figure 11.1. Apparent melt viscosity as a function of shear rate.

Among the many different classes of thermotropic polymers, only a limited number of polyesters based on aromatic ester type mesogenic units have been studied by rheological methods, beginning with the publication by Jackson and Kuhfuss of their work on the p-oxybenzoate modified polyethylene terephthalate, PET, copolymers. They prepared a series of copolyesters of p-hydroxybenzoic acid, HBA, and PET and measured the apparent melt viscosity of the copolymers as a function of their composition by use of a capillary rheometer. On inclusion of low levels of HBA into PET, the melt viscosity increased because of partial replacement of the more... 

Jn recent years, there has been a considerable amount of interest in high-molecular-weight polyarylsulfone polymers (1-3). These polymeric materials possess heat-deflection temperatures of 165°-260°C plus excellent thermal stability at the high processing temperatures required. This paper deals with the synthesis and the physical and mechanical properties of a new heat-resistant polyarylsulfone. This new polyarylsulfone thermoplastic exhibits a significant reduction in apparent (melt) viscosity with only a slight reduction in heat deflection temperature when compared with the polyarylsulfone based on bis(4-chlorophenyl)sulfone and 2,2-bis (4-hydroxyphenyl) propane. 

Figure 6.1 Apparent melt viscosity of PVDF vs temperature at 100 l/sec.i >...

An unplasticized PVC formulation usually contains at least one other lubricant, which is mainly intended to improve the flow of the melt, i.e., to reduce the apparent melt viscosity. Such materials are known as internal lubricants. Unlike external lubricants they are reasonably compatible with the polymer and are more like plasticizers in their behavior at processing temperatures, whereas at room temperature this effect is negligible. Among materials usually classified as internal lubricants are montan wax derivatives, glyceryl monostearate, and long-chain esters such as cetyl palmitate. 

Mixing flows in an extruder influence the heat transfer process, and conversely, the flow of a viscous fluid generates heat according to Eq. (5.8). The resulting rise in the melt temperature reduces the apparent melt viscosity... 

Figure 12.1.9. Apparent melt viscosity of original PET and PET containing 20% 1-methyl naphthalene vs. shear rate. [Adapted, by permission, from S Tate,...

Pitches are thermoformable and suitable, in the molten state, to be melt extruded through the orifices of a spinneret. Upon heating, the apparent melt viscosity of a pitch initially decreases within a narrow temperature range (the softening range), then passes through a broad minimum, and increases sharply above 450-500 C as bulk mesophase is formed [23]. 

Even at low usage levels, the additive allows the processor to work at lower extrusion pressures. Additionally, Dynamar PPA FX 5922 reduces the apparent melt viscosity, permitting easier processing of high-strength, high-molecular weight resins. 

Figure 3.241. Relationship between apparent melt viscosity and molecular weight of the polymer.

FI/MI is directly proportional to the molecular weight distribution of the polyethylene sample. Higher FI/MI values indicate the polyethylene will experience a greater degree of shear thinning (lower apparent melt viscosity) as the polymer is extruded under shear. 

Schott and Kaghan [36] observed that a plot of log fractional decrease of apparent melt viscosity, against the number of extrusion passes gave straight lines at each temperature. Considering also that the dwell time is proportional to n/Q (where Q is the volumetric flow rate and n the number of passes). 

Figure 6.5 Apparent melt viscosity as a function of shear rate at 285°C for poly(butylene terephthalate). Drawn after data from Engberg et al (1994b).

Apparent Melt Viscosity ( 100 sec" ), Pa-sec High Viscosity Medium Viscosity 2800-3800 2800-3100 2500-4000 1300-2500... 

Hylar Apparent Melt Viscosity 232°C, 100 sec, kpoise Melting Point, °C Specific Gravity Tensile Strength at 23°C, MPa Elongation at Break at 23°C, % Flex Modnlns, GPa Impact Resistance at 23°C, J/m ... 

Figure 10.24 Apparent melt viscosity of fluoroplastics and engineering polymers.f ...

The sample material is placed in the barrel of the extrusion assembly, brought to temperature, and forced out through a capillary. The force required to move the plunger at each speed is detected by a load cell. Shear stress, shear rate, and apparent melt viscosity are calculated as follow (6) ... 

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