Polymer processing dynamic mechanical thermal analysis

Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) provides a method for determining elastic and loss moduli of polymers as a function of temperature, frequency or time, or both [1-13]. Viscoelasticity describes the time-dependent mechanical properties of polymers, which in limiting cases can behave as either elastic solids or viscous liquids (Fig. 23.2). Knowledge of the viscoelastic behavior of polymers and its relation to molecular structure is essential in the understanding of both processing and end-use properties. 

The relaxation methods employed are Dynamic Mechanical Thermal Analysis (DMTA) and Dielectric Thermal Analysis (DETA). Generally in both cases a single excitation frequency is used and the temperature is varied, typically over a range between — 100 °C and +200 °C. Changes in molecular motion, and hence 7, are detected by both techniques, but in the case of DETA the process has to involve movement of dipoles or fully developed electrical charges on the polymer in order to be detected. Thus the two techniques can be used to complement each other, since transitions can be detected on DMTA and assigned as due to dipoles according to whether or not they also occur with DETA. 

A novel process for the preparation of latex with high solid content, but maintaining the characteristics of microemulsion polymerisation latex, small particle size (less than 50 nm) and polymer with high molecular weight (more than 10 6) is presented. With the PS latex obtained by microemulsion polymerisation as seed, core shell, styrene-butyl acrylate polymers functionalised with itaconic acid are prepared. Materials were characterised by differential scanning calorimetry, dynamic mechanical thermal analysis and transmission electron microscopy. These polymers have better mechanical properties than the non functionalised or those prepared by emulsion polymerisation. 11 refs. 

One of the most popular methods of studying such transitions is dynamic mechanical thermal analysis, DMTA.The sample is subjected to some form of oscillatory distortion, as described in Chapter 10, and its response observed as a function of frequency and temperature. In aU cases, the scale of the motion being observed is relatively local, usually limited to the motion of eight to ten units of the polymer. The shape of the response curve conforms to that of a simple relaxation or a Hmited distribution of relaxation processes. It is only when the polymer is in the melt phase that the longer range motions become apparent. 

The glass-transition temperature, melting point, heat distortion temperature, thermal degradation temperature, ete. are important parameters affecting the application and processing of semicrystalline polymer materials. These thermal parameters can be obtained via differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, etc. 

Studies of the thermal and chemical stability of polymers are of paramount importance and instrumentation used in these studies discussed in Chapter 9 include thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry, thermal volatilisation analysis and evolved gas analysis. Monitoring of resin cure is another important parameter in polymer processing in which dynamic mechanical analysis, dielectric thermal analysis and differential scanning calorimetry is used (Chapter 10). 

Thermal analysis techniques are used to study the properties of polymers, blends and composites and to determine the kinetic parameters of their stability and degradation processes.Here the property of a sample is continuously measured as the sample is programmed through a predetermined temperature profile. Among the most common techniques are thermogravimetry (TG) and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) and dielectric spectroscopy are essentially extensions of thermal analysis that can reveal more subtle transitions with temperature as they affect the complex modulus or the dielectric function of the material. 

Nanoparticles, compared with traditional fillers, provide more reinforcement due to the higher interfacial area. Introduction of these particles into the mbber matrix improves many of its properties, in particular tensile strength, thermal stability, elasticity, processability or barrier improvement. The final properties of nanocomposites are determined by the filler-filler and polymer-filler interactions. Therefore, it is very important to have knowledge of the characteristics of nonlinear viscoelastic behavior for mbber reinforced systems, especially an analysis of the low strain dynamic mechanical properties (Payne effect). 

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