Melt viscosity dynamic

Dynamic melt viscosity studies on the star blocks and a similar triblock were carried out using a Rheometric Mechanical Spectrometer (RMS) (Rheometrics 800). Circular molded samples with -1.5 mm thickness and 2 cm diameter were subjected to forced sinusoidal oscillations (2% strain) between two parallel plates. The experiment was set in the frequency sweep mode. Data were collected at 180 and 210 °C. 

The dynamic melt viscosity measurements of select star blocks and a similar triblock were carried out on a rheometric mechanical spectrometer, RMS. Circular molded samples of 2 cm diameter and -1.5 mm thickness were subjected to forced sinusoidal oscillations. Dynamic viscosities were recorded in the frequency range of 0.01-100 rad/s at 180 °C. Figure 10 shows the complex viscosities of two select star blocks and a similar linear triblock. The plots showed characteristic behavior of thermoplastic elastomers, i.e., absence of Newtonian behavior even in the low frequency region. The complex viscosity of the star block... 

Fig. 32 Master curve of the dynamic melt viscosity (/] ), storage modulus (G ) and loss modulus (G") of a poly(ethylene/butylene) copolymer (Mn = 3500gmol ). Reprinted with permission from [131]...

FIGURE 1 Size-exclusion chromatography and rheology of various polymers made with the three common commercial catalysts. Above Molecular weight distribution. Below Dynamic melt viscosity versus shear (frequency) at 190 °C. 

In the case of the irradiated neat PA-6, no gel fraction was observed. A comparison of the dynamic melt viscosity versus frequency for the non-irradiated and irradiated (200 and 400 kGy) PA-6 showed that the behavior of the irradiated samples was non-Newtonian, which was... 

Rheology. Every process used to convert LLDPE into a finished product involves melting. Therefore, polymer viscosity is a very important resin parameter that must be considered when selecting a resin for use. LLDPE melts in the normal processing range of 150-300°C exhibit non-Newtonian (shear thinning) behavior as their apparent viscosity is reduced when melt-flow speed is increased (82-85). Figure 23 shows a plot of dynamic melt viscosity for LDPE, gas-phase... 

Tifi of similar numerical values have been obtained by other methods such as torsional braid analysis and dynamic melt viscosity. ... 

The Rheometric Scientific RDA II dynamic analy2er is designed for characteri2ation of polymer melts and soHds in the form of rectangular bars. It makes computer-controUed measurements of dynamic shear viscosity, elastic modulus, loss modulus, tan 5, and linear thermal expansion coefficient over a temperature range of ambient to 600°C (—150°C optional) at frequencies 10 -500 rad/s. It is particularly useful for the characteri2ation of materials that experience considerable changes in properties because of thermal transitions or chemical reactions. 

Within the Rouse model for polymer dynamics the viscosity of a melt can be calculated from the diffusion constant of the chains using the relation [22,29,30] ... 

As known from the broad crossover phenomena observed in the macroscopic chain dynamics (such as the molecular weight dependence of the melt viscosity) very important limiting mechanisms must exist that affect the confinement limit of the reptation process. These processes increase in importance as the chain length decreases. The two main mechanisms are [62] ... 

A series of different hydroxyfunctional hyperbranched polyesters (H1-H6) with increasing ratio TMP bis-MPA was studied. The tests were made on samples quenched from melt. As discussed previously, the molar masses for these polymers are difficult to determine and the results ate therefore presented as a function of the ratio bis-MPA TMP, which can be directly related to the theoretical molar mass. The complex dynamic viscosity (r ) of hyperbranched polyesters show an increase in viscosity with size which levels out at a certain value (Figure 11). The corresponding linear polymers would exhibit a linear relationship q versus log molar mass and hence have a higher melt viscosity. The hydroxyfunctional polyesters exhibit a Newtonian behavior within a medium shear range (10 -10 rad s ). 

In the production of a condensation polymer the melt viscosity of the final polymer (Y) was measured every 15 minutes by an on-line viscometer. This viscosity could be kept near its target value by manipulating a variable (X). By performing a very simple plant test in which the input (manipulated) variable was perturbed in a pseudo-random binary manner and the resulting viscosity recorded every 15 minutes by the on-line viscometer, the following dynamic-stochastic model was identified for the process ... 

Rheological Experiments. Melt viscosity and low-strain oscillatory experiments were performed on a Rheometrics RDS-7700 dynamic spectrometer equipped with a 0.2-2.0-g-cm torque transducer. The samples were mounted on 25-mm-diameter parallel-plate fixtures with a gap of 0.5 mm. Prior to each scan, samples were heated to 50 °C and then cooled slowly to room temperature. Steady-shear... 

The growth of bubbles is controlled by the rates at which volatiles in the melt can diffuse towards the bubbles, and the opposing viscous forces. Near a bubble, volatiles are depleted such that melt viscosity increases dramatically, and diffusivities drop, making it harder for volatiles to diffuse through and grow the bubble. These opposing factors are described by the nondimensional Peclet number (Pe), which is the ratio of the characteristic timescales of volatile diffusion (T(1 = r lD, where r is the bubble radius and D the diffusion coefficient of the volatile in the melt) and of viscous relaxation (t = 17/AP where 17 is the melt dynamic viscosity and AP the oversaturation pressure, i.e., Pe = Dingwell... 

The thermal properties (DSC second cycle), melt viscosities, and properties of test bars injected into unheated molds in a 1-oz Watson-Stillman injection-molding machine were determined as described earlier for the SDA copolyesters <2. 7. 81. The glass transition temperatures (Tg s) were determined on 1/16-in. thick injection-molded bars at 4°C/min and a frequency of 0.3 Hz with a Mark IV Dynamic Mechanical Thermal Analyzer from Polymer laboratories, Inc. 

Another fundamental state variable that can be regulated during the cycle is cavity pressure. Closed loop control of cavity pressure could automatically compensate for variations in melt viscosity and injection pressure to achieve a consistent process and consistency of molded products. Adaptive control methods have been developed to track the cavity pressure profile at one location in the mold. In these earlier works, cavity pressure control was handicapped by the absence of actuators for distributed pressure control, as conventional molding machines are equipped with only one actuator (the screw), which prevents the simultaneous cavity pressure control at multiple points in the mold. This problem has been solved with the development of dynamic melt flow regulators that allow control of the flow and pressure of the polymer melt at multiple points in the mold.[ °l... 

Despite the relative simplicity of most ionomers, questions about them remain. One of the key questions is how structure and dynamics on different length scales connect. Specifically, how does the metal coordination to the neutralized acid groups (which is on an angstrom level) correlate with the size, shape, and distribution of the ion-iich aggregates in the hydrophobic matrix (which is on a nanometer length scale) Furthermore, how does the microscopic structure control the macroscopic properties like melt viscosity or elastic modulus ... 

The bulk rheological properties of the PFPEs, including the melt viscosity, storage modulus, and loss modulus at several different temperatures, have been widely reported via steady shear and dynamic oscillation tests. In this entry, the focus is on the confined geometry effects on viscosity. 

Using melt viscosity measurements, Lundberg et al. (107) showed that one could selectively plasticize either the ion-rich phase or the nonpolar hydrocarbon phase of SPS lonomers by varying the chemistry of the diluent used. Fitzgerald et al. (108) studied the effects of dioctyl phthalate (DOP) and glycerol on the dynamic mechanical properties of SPS lonomers. The addition of DOP lowered... 

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