Dynamic Mechanical Analysis, loss modulus

Dynamic Mechanical Analysis. The modulus loss tangent data for FPE-2 and -3 are shown In Figures 7 and 8. The data for FPE-2 were obtained from a compression molded film and those for FPE-3 were obtained from a film cast from methylene chloride. 

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. 15. Dynamic mechanical analysis of 100 minutes-aged Thornel 300/Fiberite 934 composite showing the loss tangent and the dynamic storage modulus...

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. 

The dynamic mechanical analysis method deter-minesl l elastic modulus (or storage modulus, G ), viscous modulus (or loss modulus, G"), and damping coefficient (tan A) as a function of temperature, frequency or time. Results are usually in the form of a graphical plot of G, G", and tan A as a function of temperature or strain. DMA may also be used for quality control and product development purposes. 

The dynamic mechanical analysis of virgin PP, untreated sisal/PP composites and MAPP treated sisal PP composites revealed an increase in the storage modulus (E ) in the PP matrix with the addition of fibers and MAPP (Figure 9.5a) [71]. The loss modulus displayed three relaxation peaks at -80°C (y), 8°C (P), and 100°C (a), respectively. The temperature of P relaxation maximum corresponds to the Tg of the matrix, while the a relaxation peak is related to the slip mechanism in the crystallites. The y relaxation peak is due to the... 

Elastomeric systems are quite commonly monitored by thermal techniques. Mohler [5] has discussed how DSC is used to characterize the quality of blends of elastomers. Changes in polymer Tg can point to miscible phases that might otherwise require a microscopic techmque to establish. The cold crystallization of a polymer in a blend can also be examined using the relaxation enthalpy of the sample. Vacuum TG can look at plasticizer content separate from polymer degradation. Dynamic mechanical analysis (DMA) is always a powerful technique with elastomers. Dimensional stability, storage modulus, loss modulus and loss factor are all important for this class of materials and are... 

Pakalapati et al [115] investigated some carbon/thermoplastic laminates. The materials were pultruded and they consisted of 50 v/o unidirectional continuous polyacrylonitrile-based carbon fibres in DuPont J-2 aromatic polyamide-based thermoplastic matrix. They were subjected to anodic and cathodic currents in sea water. Dynamic mechanical analysis was carried out in situ to measure the shear storage modulus (G ) and shear loss modulus (G") of 1.27mm diameter rod shaped samples, subjected to small amplitude torsional oscillations. The moduli were constant with time in air. 

S.3.2 Dynamic Mechanical Analysis (DMA) Storage and Loss Modulus Dynamic mechanical analysis (DMA) is typically performed to measure the viscoelastic behavior of polymer networks. A sinusoidal force (stress) is applied to a material and the resulting displacement (strain) is measured, allowing one to determine the complex modulus. 

Mechanical property characterization involves measurement of fiacture energy, stress intensity, tensile strength and modulus, and tan. Tan (9) can be defined as the ratio of the loss modulus, E", to the in-phase or storage modulus, E. Tan = E7E. Values for tan obtained from dynamic mechanical analysis can be related to epoxy structure. 

Dynamic mechanical analysis curve Graphical representation of the data collected by a dynamic mechanical analyser, where the dynamic loss modulus, dynamic storage modulus and tan 5 are plotted as a function of temperature (scanning mode) or time (isothermal mode). 

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