Temperature sweep tests

Dynamic temperature sweep tests, in the linear viscoelastic range, were conducted at 1 °C/min and 1 % strain, at 2 constant frequencies 6.28 and 10 rad/s (AASHTO-TP5). 

Temperature sweep tests were performed in the linear viscoelastic region at 1 Hz, using synthetic binders and binary blends (Table 10.2) with the same ratio, in order... 

This new model is more simple and accurate than the previous one. However, the fitting parameters are interaction parameters as they don t reflect a simple dependence. Parameter Ci multiplies the complex viscosity of the resin, but depends on the oil concentration. This dependence could be due to the influence of the oil-resin fraction, which determines the cohesion of the synthetic binder. Parameter C2 multiplies the complex viscosity of the oil-polymer blend, but depends on the resin-polymer ratio, perhaps due to the interaction between the resin and the vinyl-acetate groups present in the EVA copolymer [20]. And finally, parameter C3 is independent of complex viscosity, but depends on the polymer concentration, probably due to the strong influence of the polymer on the fluidity of the samples, which is clearly present in a rheological test such as the temperature sweep test. 

Rheological tests of epoxy resin were performed using a TA Instruments Discovery Hybrid Rheometer with a peltier plate fixture of 25-mm disposable parallel plates. Similar to DSC tests, batches of approximately 50 g of epoxy resin, with GO contents of 0,0.05,0.1, and 0.2 wt%, and the appropriate amount of hardener were mixed. Samples of approximately 2 mL of mixed resin samples were pipetted onto the rheometer bottom plate. Rheological tests were performed with a 0.5-mm plate gap at a constant shear rate of 2.5 s Temperature sweep tests were completed for the determination of temperature-dependent viscosity evolution and were performed on all samples from 25 to 95 °C. Isothermal rheology tests were conducted at 80 °C to determine the viscosity evolution with respect to time. This temperature was selected after investigating the dynamic DSC scans in which peak temperature was approximately 82 °C. 

Figure 40. Storage and loss moduluses G and (/") of glutenin at different water content in a temperature sweep test (5 K min" heating rate 0,5% strain 1 Hz frequency). For each data series, moisture content (%) decreases from the left to the right hand side (modified from [258], where further details are given).

Figure 45. Storage and loss moduluses (O and G ) of different varieties of wheat gluten observed in a temperature sweep test at 1 K min heating rate, and 5% strain (modified from [262]).

Figure 47 Storage and loss moduluses ((/, upper, and O ", lower) of different gluten - starch - water mixtures with a starch content (w/w dry basis) of 75 ( ), 50 ( ), 25 (A), 10 (O), and 0 %( ), in a temperature sweep test (2 K min heating rate, 10% strain, and 1 Hz frequency), (modified from [263]).

For investigating the effect of temperature on viscosity, dynamic shear measurements were performed using the Rheometric Scientific ARES-RDAIII, with a parallel-plate fixture. Disc-shaped samples were prepared by compression molding for the measurements using the compounded pellets, or the as-received base polymers. Dynamic temperature sweep tests were carried out with temperatures ranging from 250 °C to 110 °C at a cooling rate of 5 °C/min, while the frequency was set at 1 rad/s. The plate gap was actively controlled at 1 mm to compensate for the thermal expansion of the fixtures. 

It is clear that this data treatment is strictly valid providing the tested material exhibits linear viscoelastic behavior, i.e., that the measured torque remains always proportional to the applied strain. In other words, when the applied strain is sinusoidal, so must remain the measured torque. The RPA built-in data treatment does not check this y(o )/S (o)) proportionality but a strain sweep test is the usual manner to verify the strain amplitude range for constant complex torque reading at fixed frequency (and constant temperature). 

The strain temperature sweep measurement is conducted with a preselected amplitude for the applied strain (y) and a constant frequency (f). The changing parameter is the temperature T, which is given in a temperature-time profile [T = T(t)]. This test method serves to illuminate the structural build-up, the softening, the melting and the gelation of pectins influenced when the temperature changes. 

Figure H3.1.3 For oscillatory (sweep) testing, four control parameters can be varied amplitude, frequency, time, and temperature.

The sample is loaded onto the instrument and the time reference is noted by starting a timer or resetting a timer in the software. A dynamic test for viscoelastic structure is then used to monitor changes in the sample that could result from mechanical relaxation, drying, or thixotropy. A time sweep test is usually performed at a constant temperature. The test is also run at a constant frequency that is comparable to real-time observation (typically 1 Hz) or at a constant angular frequency (10 rad/sec or 1.6 Hz). 

The four variables in dynamic oscillatory tests are strain amplitude (or stress amplitude in the case of controlled stress dynamic rheometers), frequency, temperature and time (Gunasekaran and Ak, 2002). Dynamic oscillatory tests can thus take the form of a strain (or stress) amplitude sweep (frequency and temperature held constant), a frequency sweep (strain or stress amplitude and temperature held constant), a temperature sweep (strain or stress amplitude and frequency held constant), or a time sweep (strain or stress amplitude, temperature and frequency held constant). A strain or stress amplitude sweep is normally carried out first to determine the limit of linear viscoelastic behavior. In processing data from both static and dynamic tests it is always necessary to check that measurements were made in the linear region. This is done by calculating viscoelastic properties from the experimental data and determining whether or not they are independent of the magnitude of applied stresses and strains. 

FIGURE 2.12 Rheometric frequency sweep test of slurries conducted at 5-30 °C. G, G", and complex = rj + if]" reduce as temperature increases. 

Frequency sweep studies in which G and G" are determined as a function of frequency (o)) at a fixed temperature. When properly conducted, frequency sweep tests provide data over a wide range of frequencies. However, if fundamental parameters are required, each test must be restricted to linear viscoelastic behavior. Figure 3-31... 

Mechanical Properties. Dynamic mechanical properties were determined both in torsion and tension. For torsional modulus measurements, a rectangular sample with dimensions of 45 by 12.5 mm was cut from the extruded sheet. Then the sample was mounted on the Rheometrics Mechanical Spectrometer (RMS 800) using the solid fixtures. The frequency of oscillation was 10 rad/sec and the strain was 0.1% for most samples. The auto tension mode was used to keep a small amount of tension on the sample during heating. In the temperature sweep experiments the temperature was raised at a rate of 5°C to 8°C per minute until the modulus of a given sample dropped remarkably. The elastic component of the torsional modulus, G, of the samples was measured as a function of temperature. For the dynamic tensile modulus measurements a Rheometrics Solid Analyzer (RSA II) was used. The frequency used was 10 Hz and the strain was 0.5 % for all tests. 

Dynamic-shear measurements are of the complex viscosity rj ) as a function of the dynamic oscillation rate (o), at constant temperature. These tests are defined as isothermal dynamic frequency sweeps. Since the dynamic frequency sweeps are conducted at a given amplitude of motion, or strain, it is necessary to ensure that the sweeps are conducted in the region where the response is strain-independent, which is defined as the linear viscoelastic region. This region of strain independence is determined by an isothermal strain sweep, which measures the complex viscosity as a function of applied strain at a given frequency. This ensures that a strain at which the dynamic frequency sweep may be conducted in the linear viscoelastic region is selected. 

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