Dynamic thermomechanical analysis

Dynamic properties are more relevant than the more usual quasi-static stress-strain tests for any application where the dynamic response is important. For example, the dynamic modulus at low strain may not undergo the same proportionate change as the quasi-static tensile modulus. Dynamic properties are not measured as frequently as they should be simply because of high apparatus costs. However, the introduction of dynamic thermomechanical analysis (DMTA) has greatly widened the availability of dynamic property measurement. 

The applied part of this study relied on a standard peel test in which closely set vertical and horizontal cut lines had been incised on the specimen surface, and on a dynamic thermomechanical analysis of finish flexibility at constant temperature [32,33,46]. 

DOP dioctyl phthalate DTMA dynamic thermomechanical analysis... 

Static and dynamic thermomechanical analysis of the commercial polymer separators (PP and PE) were made to understand their properties (Love, 2011). Anisotropic separators manufactured from a dry process showed limited tensile performance in the transverse direction. The separators prepared from a wet process displayed a uniform and biaxial structure and nearly showed identical mechanical strength on both directions. It was also found that small losses in mechanical integrity were observed after the separators were exposed to various electrolytes. 

A more common mechanical method is dynamic mechanical thermal analysis (DMTA). DMTA is also called dynamic mechanical analysis (DMA) or dynamic thermomechanical analysis. An oscillating force is applied to a sample of material and the resulting displacement of the sample is measured. From this the stiffness of the sample can be determined, and the sample modulus can be calculated. A plot of loss modulus as a function of temperature shows a maximum at Tg as shown in Figure 1.35. Figure 1.35 shows a series of blends of high-impact styrene (HIPS) and PPO. As the amount of PPO is increased, Tg increases. The single Tg indicates that these blends are miscible. 

Onic, L., Bucur, V., Ansell, M. P., Pizzi, A., Deglise, X., and Merlin, A., Dynamic Thermomechanical Analysis as a Control Technique for Thermoset Bonding of Wood Joints, J. Int. Adhesion Adhesives, 18 89-94 (1998)... 

Dynamic thermomechanical analysis was performed with film specimens obtained on a Orientech Rheovibron DDV-3-EP instrument at 11 Hz in the temperature range from —150° to 200°C at a heating rate of 2°C/min. 

PAS-8 were greater than those on SILASTIC 500-1, PAS-41, and 71. Although the surfaces of PASs and SILASTIC 500-1 were hydrophobic, the contact angle for PAS-8 was slightly lower than those for SILASTIC 500-1, PAS-41, and 71 (see Table 9). It was thought that the PAS-8 surface might have an influence on the aramid block. The phenomenon of the cell adhesion onto PAS-41 and 71 could not be explained by hydrophobicity alone. In former sections, the results of the gas-permeability measurement and the dynamic thermomechanical analysis of PAS implied the presence of a microphase-separated structure between PDMS and aramid phases in the PASs containing over 26 wt% of PDMS [14]. Moreover, a TEM study indicated that PAS films possessed microdomain structures in their bulk phases. That is, not only the hydrophobicity of the surfaces, but also the presence of a microphase-separated structure in the PASs may influence cell adhesion. 

The dynamic mechanical properties of VDC—VC copolymers have been studied in detail. The incorporation of VC units in the polymer results in a drop in dynamic modulus because of the reduction in crystallinity. However, the glass-transition temperature is raised therefore, the softening effect observed at room temperature is accompanied by increased brittleness at lower temperatures. These copolymers are normally plasticized in order to avoid this. Small amounts of plasticizer (2—10 wt %) depress T significantly without loss of strength at room temperature. At higher levels of VC, the T of the copolymer is above room temperature and the modulus rises again. A minimum in modulus or maximum in softness is usually observed in copolymers in which T is above room temperature. A thermomechanical analysis of VDC—AN (acrylonitrile) and VDC—MMA (methyl methacrylate) copolymer systems shows a minimum in softening point at 79.4 and 68.1 mol % VDC, respectively (86). 

DSC helps in determining the glass-transition temperature, vulcanization, and oxidative stability. TG mainly is applied for the quantitative determination of major components of a polymer sample. TMA or DLTMA (dynamic load thermomechanical analysis) measures the elastic properties viz. modulus. 

Other parameters which have been used to provide a measure of a include physical dimensions (thermomechanical analysis, TMA) [126], magnetic susceptibility [178,179], light emission [180,181], reflectance spectra (dynamic reflectance spectroscopy, DRS) [182] and dielectric properties (dynamic scanning dielectrometry, DSD) [183,184], For completeness, we may make passing reference here to the extreme instances of non-isothermal behaviour which occur during self-sustained burning (studied from responses [185] of a thermocouple within the reactant) and detonation. Such behaviour is, however, beyond the scope of the present review. 

Thermal and thermomechanical analyses44 are very important for determining die upper and lower usage temperature of polymeric materials as well as showing how they behave between diose temperature extremes. An especially useful thermal technique for polyurethanes is dynamic mechanical analysis (DMA).45 Uiis is used to study dynamic viscoelastic properties and measures die ability to... 

Dynamic mechanical anlaysis (DMA) measurements were done on a Rheometrics RDS-7700 rheometer in torsional rectangular geometry mode using 60 x 12 x 3 mm samples at 0.05% strain and 1 Hz. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) were performed on a Perkin-Elmer 7000 thermal analysis system. 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

Electron irradiation causes chain scission and crosslinking in polymers. Both of these phenomena directly affect the glass transition temperature (Tg) of the materials. Thermomechanical (TMA) and dynamic-mechanical analysis (DMA) provide information about the Tg region and its changes due to radiation damage. Therefore, DMA and TMA were performed on all irradiated materials. 

Other thermal techniques are Thermogravimetric Analysis (TGA) [55,68], High Pressure Calorimeter (HPC) [1], Thermomechanical Analysis (TMA) [1,141], and Differential (or Dynamic) Thermal Analysis (DTA) [74]. These are rarely used and will not be discussed here. 

The primary thermal characteristics of the polyimides were determined by dynamic thermogravimetric analysis (TGA) as well as thermomechanically. Although the data for dynamic TGA should be treated with some reservation, one can conclude the following ... 

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. 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

Three diblock copolymers of cis-1,4 polyisoprene (IR) and 1,4-polybutadiene (BR) have been studied in dynamic mechanical experiments, transmission electron microscopy, and thermomechanical analysis. The block copolymers had molar ratios of 1/2, 1/1, and 2/1 for the isoprene and butadiene blocks. Homopolymers of polybutadiene and polyisoprene with various diene microstructures also were examined using similar experimental methods. Results indicate that in all three copolymers, the polybutadiene and polyisoprene blocks are essentially compatible whereas blends of homopolymers of similar molecular weights and microstructures were incompatible. 

Thermomechanical Analysis (TMA) Dynamic mechanical analysis (DMA) Thermogravimetric analysis (TGA)... 

While TMA is one of the older and simpler forms of thermal analysis, its importance is in no way diminished by its age. Advances in DSC technology and the appearance of dynamic mechanical analysis (DMA) as a common analytical tool have decreased the use of it for measuring glass transitions, but nothing else allows the measurement of CTE as readily as TMA. In addition, the ability to run standardized material test methods at elevated temperatures easily makes TMA a reasonable alternative to larger mechanical testers. As the electronic, biomedical, and aerospace industries continue to push the operating limits of polymers and their composites, this information will become even more important. During the last 5 years a major renewed interest in dilatometry and volumetric expansion has been seen. Other thermomechanical techniques will also likely be developed or modernized as new problems arise. 

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