Analysis loss modulus

Similar information can be obtained from analysis by dynamic mechanical thermal analysis (dmta). Dmta measures the deformation of a material in response to vibrational forces. The dynamic modulus, the loss modulus, and a mechanical damping are deterrnined from such measurements. Detailed information on the theory of dmta is given (128). 

Linear regression analysis was performed on the relation of G"(s) versus PICO abrasion index. Figure 16.10 plots the correlation coefficient as a function of strain employed in the measurement of loss modulus. The regression results show poor correlation at low strain with increasing correlations at higher strains. These correlations were performed on 189 data points. 

Fig. 4 DMTA analysis of a PPC with a Mn of 46 kDa, showing storage modulus G, loss modulus G", and tan d as a function of temperature (Borchardt and Luinstra, unpublished data)...

The dynamic mechanical response of a material can be characterised through the loss modulus, the loss tangent, tan S, or the loss compliance, However, as already mentioned for Ar-Al-PA (Sect. 6), the loss compliance can be considered the most relevant parameter for quantitatively comparing different materials, at least for additive purposes. For this reason, the semi-quantitative analysis and the comparison of viscoelastic data determined for different systems have been performed [63] in terms of /", whereas the determination of activation energies and entropies are based on loss modulus data. 

The ft transition of a series of MGIMx copolymers has been investigated by dynamic mechanical analysis [80]. The temperature dependence of the loss modulus, E"y at 1 Hz is shown in Fig. 138. In the region of the a transition, when increasing the MGI content, a shift towards a higher temperature is observed. 

The physical properties of barrier dressings were evaluated using the Seiko Model DMS 210 Dynamic Mechanical Analyzer Instrument (see Fig. 2.45). Referring to Fig. 2.46, dynamic mechanical analysis consists of oscillating (1 Hz) tensile force of a material in an environmentally (37°C) controlled chamber (see Fig. 2.47) to measure loss modulus (E") and stored modulus (E ). Many materials including polymers and tissue are viscoelastic, meaning that they deform (stretch or pull) with applied force and return to their original shape with time. The effect is a function of the viscous property (E") within the material that resists deformation and the elastic property (E )... 

Fig. 11. Group contribution analysis leads to the determination of the effective area under the loss modulus-temperature curve. As in any spectroscopic experiment, background must be subtracted, and the instrument calibrated.

The importance of the concentration of polymer having a broad secondary loss maximum upon the loss modulus bandwidth of polymer blend materials is shown in Fig. 11 for the bulk polymerized IPN s of Huelck. (i ) The loss modulus temperature bandwidth constant is strongly dependent upon the concentration of methyl methacrylate, irrespective of whether methyl methacrylate is present in the matrix or the inclusions. Overall the Oberst type of analysis indicates that for a given type of polymer blend the area under the E" curve tends to be constant. In other words, one may have height or width but not both. 

Another possibility of determining the gel point with the help of rheological methods is dynamical mechanical spectroscopy. Analysis of change of dynamic mechanical properties of reactive systems shows that the gel point time may be reached when tan S or loss modulus G" pass a miximum [3,4,13], Some authors proposed to correlate the gel point with the intersection point of the curves of storage and loss moduli, i.e., with the moment at which tan 5 = 1 [14-16], However, theoretical calculations have shown that the intersection point of storage modulus and loss modulus meets the gelation conditions only for a certain law of relaxation behavior of the material and the coincidence erf the moment of equality G = G" with the gel point is a particular case [17]. The variation of the viscosity... 

When controlling the strain applied rather than the stress, a similar analysis can be undertaken to derive the storage modulus G and the loss modulus G", assuming that x = Tocos(ct)f - - (5) and y = yo cos cot, instead of using Eqs. (25) and (26). Such analysis shows that ... 

A torsion pendulum interfaced with a desktop computer form an automated instrument for dynamic mechanical characterization of polymeric materials. The computer controls the initiation of the oscillations, collects the digitized data and calculates the shear modulus and loss modulus from the damped oscillations, utilizing one of four methods of analysis ... 

In dynamic mechanical analysis for thermosetting systems the principal use is to monitor the glass-transition temperature (Tg). In a DMTA Tg is defined as the maximum in loss modulus, loss compliance or loss tangent. For example. Figure 3.57 (Prime, 1997a) shows the various transitions for a cured magnetic ink coating that had previously been cured under air and N2. 

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