Experimental dynamic mechanical analysis

The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites. 

Various experimental techniques (dielectric relaxation, dynamic mechanical analysis, 1H, 2H and 13C solid-state NMR) have been used for investigating the secondary transitions of BPA-PC, and the block copolymers of BPA and TMBPA carbonates as well as compatible blends of BPA-PC and TMBPA-PC. They have provided lots of information on the motions of methyl, phenyl ring and carbonate units in bulk BPA-PC. The effect of intermolecular packing has also been clearly evidenced. 

The y transition observed from dynamic mechanical analysis at 1 Hz, is centred around - 150 °C. However, the temperature range available experimentally does not permit observation of the whole y relaxation. The temperature position is independent of the chemical composition of the xTy -y copolyamides. 

It is worth noticing that a molecular modelling approach is used to complement the experimental techniques of dynamic mechanical analysis, dielectric relaxation, solid-state 13C and 2H NMR. 

The approach developed in this paper, combining on the one side experimental techniques (dynamic mechanical analysis, dielectric relaxation, solid-state 1H, 2H and 13C NMR on nuclei at natural abundance or through specific labelling), and on the other side atomistic modelling, allows one to reach quite a detailed description of the motions involved in the solid-state transitions of amorphous polymers. Bisphenol A polycarbonate, poly(methyl methacrylate) and its maleimide and glutarimide copolymers give perfect illustrations of the level of detail that can be achieved. 

The main experimental methodology used is to directly characterize the tensile properties of CNTs/polymer composites by conventional pull tests (e.g. with Instron tensile testers). Similarly, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were also applied to investigate the tensile strength and tensile modulus. With these tensile tests, the ultimate tensile strength, tensile modulus and elongation to break of composites can be determined from the tensile strain-stress curve. 

Experimentally, these principles emphasize dynamic measurements that make possible the separation of the dissipative and the conservative components of energy Incident upon the system. Dynamic mechanical analysis has been an Important area of research for over 40 years. Computer-controlled experimentation now makes It possible to apply analogous techniques to the measurement of many other thermodynamic stresses. One example currently under Investigation, dynamic photothermal spectroscopy. Is expected to provide a new approach to predicting the long-term effects of ultraviolet radiation on materials [39]. 

Several experimental approaches have been applied for determining the fiber Tg under hot wet conditions [199-203]. Aiken et al. [199] compared the Tg of a commercial acrylic yarn in the dry state and in water using dynamic-mechanical analysis, and observed a reduction from 92 to 72°C. Bell and Murayama [200] observed that the Tg of a commercial AN-NA copolymer decreased from 128°C when dry to 80°C in a 100% relative humidity atmosphere. Gur-Arieh and Ingamells [201] related the extension in length of Acrilan filaments to a Tg reduction and showed a shift from a 90°C in air to 57°C in water. Finally, Hori et al. [202] used DSC to show that the Tg of four kinds of acryhc fibers decreased with increasing water content and approached an almost constant value for all four fibers. 

ASTM (1994) E1640-94. Standard Test Method for Assignment of the Glass Transition Temperature by Dynamic Mechanical Analysis, American Society for Testing and Materials, Philadelphia, PA. Tomblin, )., Salah, L., and Ng, Y. (2001) Determination of Temperature/Moisture Sensitive Composite Properties. DOT-FAA Report DOT/FAA/AR-01/40, Office of Aviation Research, Washington, DC. Bai, Y., Post, N.L, Lesko, J.J., and Keller, T. (2008) Experimental investigations on temperature-dependent thermophysical and mechanical properties of pultmded GFRP composites. Thermochim. Acta, 469, 28-35. 

Composition profiles generated by interdiffusion in the concentrated regime between polyphenylene oxide-polystyrene blend pairs were experimentally determined by two techniques. Three-point bending moment measurements over a convenient temperature range (dynamic mechanical analysis (DMA)) were used to determine interphase composition profiles. Confocal micro-Raman spectroscopy was also used to measure local compositions along a direction which was perpendicular to the original interface. The study included some limiting cases to test accuracy, precision and flexibility of the DMA method. 4 refs. 

The term thermal analysis (TA) is frequently used to describe analytical experimental techniques which investigate the behaviour of a sample as a function of temperature. This definition is too broad to be of practical use. In this book, TA refers to conventional TA techniques such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermogravimetry (TG), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA). A selection of representative TA curves is presented in Figure 1.1. 

Dias et al., used, what they called, a hyphenated rapid real-time dynamic mechanical analysis (RT DMA) and time resolved near-infi ared spectroscopy to simultaneously monitor photopolymerization of acrylate coating compositions. This allowed them to determine the rate of conversion and the mechanical properties of the finished films. It is claimed that up to 374 near infrared spectra and to 50 dynamic analysis points can be accumulated within a second. They observed that modulus buildup does not linearly follow chemical conversion of acrylate bonds. The gel point is detected after passing a certain critical acrylate conversion. Their experimental data revealed a critical dependence of the mechanical property development during the later stage of acrylate conversion. 

Both experimental and theoretical studies indicate the influence of nanoparticles boundary interactions on the dynamics of polymers within an interfacial layer because the size of nanometer particles is comparable to the relative size of a single polymer chain [44,45]. The degree of interaction between the nanoparticles and matrix polymer can be estimated from dynamic mechanical analysis (DMA) of PP and its nanocomposites using... 

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