Dynamic mechanical data

Characterization Methods. Stress-strain experiments were carried out with an Instron model 1122. Dogbone samples of 10mm in length were used, and the initial strain rate was 2 mm/min. Dynamic mechanical data were obtained utilizing a DDV-IIC Rheovibron Dynamic Viscoelastometer. Most samples were tested within the temperature range of -100°C to 220°C with a heating rate of 2-3°C/min. A frequency of 11 Hz was selected for all the dynamic mechanical experiments. 

The dynamic mechanical experiment has another advantage which was recognized a long time ago [10] each of the moduli G and G" independently contains all the information about the relaxation time distribution. However, the information is weighted differently in the two moduli. This helps in detecting systematic errors in dynamic mechanical data (by means of the Kramers-Kronig relation [54]) and allows an easy conversion from the frequency to the time domain [8,116]. 

Dynamic mechanical data near the gel point allow easy determination of the parameters of the critical gel, Eq. 1-1. Tan 8, as shown in Fig. 26, gives the relaxation exponent n... 

Master curves are important since they give directly the response to be expected at other times at that temperature. In addition, such curves are required to calculate the distribution of relaxation times as discussed earlier. Master curves can be made from stress relaxation data, dynamic mechanical data, or creep data (and, though less straightforwardly, from constant-strain-rate data and from dielectric response data). Figure 9 shows master curves for the compliance of poly(n. v-isoprene) of different molecular weights. The master curves were constructed from creep curves such as those shown in Figure 10 (32). The reference temperature 7, for the... 

Figure 14. Dynamic mechanical data plotted as tan d versus temperature for Nation in various forms.

Figures 3-5 that the dielectric relaxation again reveals only a single a relaxation for the mixtures. These are, however, noticeably broader than the a relaxation of the pure polymers. The temperatures of the loss maxima, when plotted (Figure 7) as a function of wu the weight fraction of PPO in the mixtures, do not display the smooth monotonic increase in T0 vs. Wi that was shown by both the Vibron and the DSC results. Instead, there is a pronounced increase in Tg above = 0.5 to give a sigmoid curve for this relation. Some reservations should be attached to this observation inasmuch as data for only three polyblend compositions are available nevertheless a qualitatively similar phenomenon is observed in the analysis of the intensity of the y peak (below). Further, if only the stronger maxima in the dynamical mechanical data are considered— i.e.y if the secondary peaks and shoulders which led to the identification of two phases are omitted—then a similar sigmoid curve is found. The significance of this observation is discussed later.

The upper and lower curves for the dynamical mechanical data (110 Hz) correspond to the maxima in the resolvable loss curves. Dielectric data at 100 Hz. 

It is important to note that stress softening is also present during dynamic stress-strain cycles of filled rubbers at small and medium strain. In particular, this can be concluded from the dynamic mechanical data of the S-SBR samples filled with 60 phr N 220 as shown in Fig. 48. In the framework of the above model, the observed shift of the center point of the cycles to smaller stress values with increasing strain amplitude or maximum strain and the accompanied drop of the slope of the hysteresis cycles can be related to a de-... 

Detailed analysis of the isothermal dynamic mechanical data obtained as a function of frequency on the Rheometrics apparatus lends strong support to the tentative conclusions outlined above. It is important to note that heterophase (21) polymer systems are now known to be thermo-rheologically complex (22,23,24,25), resulting in the inapplicability of traditional time-temperature superposition (26) to isothermal sets of viscoelastic data limitations on the time or frequency range of the data may lead to the appearance of successful superposition in some ranges of temperature (25), but the approximate shift factors (26) thus obtained show clearly the transfer viscoelastic response... 

In the present case, all of our dynamic mechanical data could be reduced successfully into master curves using conventional shifting procedures. As an example, Figure 7 shows storage and loss-modulus master curves and demonstrates the good superposition obtained. In all cases, the shifting was not carried out empirically in order to obtain the best possible superposition instead the appropriate shift factors were calculated from the WLF equation (26) ... 

Electron micrographs of compositions D and E are shown in Figures 9 and 10. It is evident that in E polybutadiene is the continuous phase (with some rubber in the polystyrene domains) while D represents a transition from lamellar to polybutadiene-continuous morphology. Again the dynamic mechanical data (Table II) are consistent with these obser-... 

We thank the Union Carbide Corp. for permission to publish this work. Acknowledgment also goes to J. J. Bohan and L. B. Conte for thgir technical assistance to A. D. Hammerich for the NMR measurements and to L. M. Robeson for the dynamic mechanical data. 

Tip (13C), the rotating frame spin-lattice relaxation time can partially be correlated with dynamic mechanical data. It has been shown to characterise qualitatively the... 

Equilibrium Dynamic Mechanical Data. Dynamic mechanical properties of both the DGEBA-TETA and the N-5208 epoxy systems exhibit characteristic transitions observed in many polymeric materials. Figures 2a and 2b Illustrate "equilibrium" dynamic mechanical tan 6 as a function of temperature for samples saturated at different moisture levels. 

The Increase in magnitude of the low temperature tan 6 associated with the 0-transltlon peak can be rationalized due to a plasticization of the epoxy network. However, the significant differences in the tan 6 magnitudes which arise above the 25"C for both epoxies are not attributable to plasticization. This shift is in fact a tertiary u dynamic mechanical transition (3, 4). This ti) transition is highly sensitive to the presence of polar solvents. Chu and Seferls (6) obtained dynamic mechanical data which demonstrate formation of such a tertiary u transition in a T(3)DM-DDS epoxy system from residual amounts of acetone in the network. Keenan, et al (4) present data for the N-5208 epoxy system which indicate a slight drop in the temperature location of the u transition with Increased moisture content. Broadening of the peak was also observed. 

Figure 6 plots transient Isothermal tan 6 dynamic mechanical data for a 25 PHR-DDS N-5208 epoxy sample. This sample was Initially exposed to a dry 50 C environment. This temperature was selected since It coincides with the vicinity of the dynamic mechanical u transition. Hence, differences between properties In the dry and wet states could be maximized. Behavior of the Initial dry to wet state transient cycle was previously discussed for DGEBA-TETA epoxy sample of Figure 5. Similar behavior Is noted for this N-5208 epoxy sample. There Is an Initial rise In the tan 5 followed by a "blocking" and gradual reduction. After the tan 6 appeared to approach a stable value, the environment In the sample chamber was switched from one of a 50 C liquid environment to a 50°C desiccated environment. Once again, a rapid Increase In the mobility of the system occurred. After the sharp Increase In tan 5, a gradual decrease followed.

Dynamic mechanical data of Figure 8 conforms with this behavior since additional plasticization occurs immediately after the initial 20°C to 30°C temperature change. The rapid rise is then followed by a decrease in the tan 6 corresponding to a "blocking" of the network structure created by the 20°C - 50°C hygrothermal sequence. 

Transient dynamic mechanical data on the DGEBA-TETA and high performance M-5208 epoxy based systems have been obtained and compared with "equilibrium" data.. The transient data have demonstrated that moisture can act not only to plasticize an epoxy network but also to restrict and stiffen molecular chain movement. The behavior observed was explained by examining the synergistic effects that moisture and temperature have on the particular epoxy network structure. 

An analysis of the dielectric data similar to that for the dynamic mechanical data was undertaken. The natural logarithm of the time to peak maximum vs. 1/T was plotted for the two peak maxima observed in the dielectric loss tangent as shown in Figure 11. The activation energies derived from linear least squares fit of the data in these plots are listed in Table II. 

Baumgartel M and Winter HH (1989) Determination of discrete relaxation and retardation time spectra from dynamic mechanical data. Rheol Acta 28 511-9. 

Winter HH (1997) Analysis of dynamic mechanical data inversion into a relaxation time spectrum and consistency check. J Non-Newtonian Fluid Mech 68 225-39. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

Figure 8. Dynamic mechanical data for the two component materials as well as a blend which contains 75 weight percent of component (1).

Using a computerized data reduction scheme that incorporates a generalized WLF equation, dynamic mechanical data for two different polymers were correlated on master curves. The data then were related to the vibration damping behavior of each material over a broad range of frequencies and temperatures. The master curves are represented on a novel reduced temperature nomograph which presents the storage modulus and loss tangent plots simultaneously as functions of frequency and temperature. ... 

The dynamic mechanical data (Figure 6) point to enhanced phase separation as a result of annealing, as shown by the flatter storage modulus curves. The data show that a similar Improvement Is obtained by annealing without PEDA and by addition of PEDA without annealing. A similar conclusion Is also derived from the heat sag data. 

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