Dynamic mechanical techniques

Dynamic techniques are used to determine storage and loss moduli, G and G respectively, and the loss tangent, tan 5. Some instmments are sensitive enough for the study of Hquids and can be used to measure the dynamic viscosity T 7 Measurements are made as a function of temperature, time, or frequency, and results can be used to determine transitions and chemical reactions as well as the properties noted above. Dynamic mechanical techniques for sohds can be grouped into three main areas free vibration, resonance-forced vibrations, and nonresonance-forced vibrations. Dynamic techniques have been described in detail (242,251,255,266,269—279). A number of instmments are Hsted in Table 8. Related ASTM standards are Hsted in Table 9. 

Dynamic mechanical techniques for studying polymers are described in detail in Chapter 7. For the moment we will restrict ourselves to a simple outline of the method of DMTA as it is applied to the determination of Tg. 

The effect of temperature on microhardness at low temperatures (for PE between —60 and 25 °C and for isotactic polypropylene (i-PP) between -20 and 25 °C) has also been studied (Perena et al, 1989 Martin et ah, 1986). While for i-PP it is possible to detect accurately the glass transition temperature, for PE it is concluded that the use of only H for recognizing the secondary relaxations in PE does not allow their precise temperature location. Here the joint use of dynamic mechanical techniques and microhardness is recommended (Perena etal, 1989). 

Dynamic mechanical techniques have been widely employed in the polymer and related industries however, the applications of such techniques for the characterization of pharmaceutical and certain biomedical systems have not received similar attention. Therefore, in this section, an overview of reported and future applications of these techniques for the characterization of pharmaceutical and biomedical systems is provided. 

The a relaxation observed by dynamic mechanical techniques is attributable in part to an ionic-phase mechanism. The existence of this relaxation is suggested as evidence for the presence of phase-separated clusters in these materials. The temperature at which the fi relaxation occurs is found to result from the complex interaction of crystallinity and ionic group concentration. 

In contrast to other Tg methods, dynamic measurements easily detect glassy state relaxations and have been extensively applied to their study. These include dynamic mechanical methods, dielectric relaxation, and nuclear magnetic resonance (NMR). Since we are primarily concerned with viscoelastic response at this point, we shall confine the discussion to the dynamic mechanical technique and delay our consideration of dielectric and NMR methods until Chapter 7. 

Samples of poly(4-methyl-l-pentene) (P4MP1) prepared from mats of dilute solution-crystallized polymer have been investigated by NMR and dynamic mechanical techniques. Dynamic mechanical data for crystal mats of P4MP1 were obtained with a vibrating reed apparatus by J. A. E. Kail of Imperial Chemical Industries, Ltd., Plastics Division, on a... 

STUDY ON ADHESIVES PERFORMANCE BY DYNAMIC MECHANICAL TECHNIQUES... 

Other uses of dynamic mechanical analysis on epoxy resins, or epoxy resin adhesives, are reviewed by Kaelble and by Lewis and Saxon. Eddy et al have proposed that dynamic mechanical techniques be used in evaluating new polymers as structural adhesives.Beckwith and Crabtree have demonstrated a relationship between G and the lap shear strength of bonds made with various commercial structural adhesives. ... 

The effects of cure temperature and amount of catalyst on the rheokinetical behavior of an MF resin can be followed using dynamical mechanical techniques (127), and time-temperature-transformation (TTT) cure diagrams can be constructed using the results of these methods (127-129) (see Dynamic Mechanical Analysis). 

Schoff [2] has described the use of dynamic mechanical techniques in the characterisation of commercial organic coatings. Such techniques have become valuable methods for the determination of basic viscoelastic properties, following and measuring cure, and... 

Polymers are viscoelastic materials, whose mechanical behavior exhibits characteristics of both solids and liquids. Thermal analysts are frequently called on to measure the mechanical properties of polymers for a number of purposes. Of the different methods for viscoelastic property characterization, dynamic mechanical techniques are the most popular, since they are readily adapted for studies of both polymeric solids and liquids. They are often referred to collectively as dynamic mechanical analysis (DMA). Thermal analysts often refer to the DMA measurements on liquids as rheology measurements. 

Woo, L., Study on Adhesive Performance by Dynamic Mechanical Techniques, paper presented at the National meeting of American Chemical Society, Seattle, Washington, March 1983. 

In terms of thermal properties, Aspler and Gray (1982) reported the glass transition temperature (Tg) of 10 °C for bulk HPC by using inverse chromatography. Later this results was sustained by Suto et al. (1982), by means of Dynamic Mechanical techniques in which a broad endotherm ranging from 160 to 210 °C with a peak at 180 °C was described. This broad endotherm was related to the thermotropic toward isotropic liquid crystal around 200 °C. 

Dynamic mechanical techniques are important in the characterization of the rheological properties of polymers. In dynamic mechanical analysis, a small-amplitude oscillatory strain is applied to a sample, and the resulting dynamic stress is measured as a function of time. The dynamic mechanical technique allows the simultaneous measurement of both the elastic and the viscous components of the stress response. Typically, the temperature and deformation frequencies are changed in order to determine the mechanical relaxation spectrum of the system. The molecular basis of changes in the dynamic mechanical properties can be investigated using dynamic IR dichroism. 

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