Thermomechanical system, sample

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

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. 

After final chromatographic purification, samples of the AT-systems were cured in air at 288°C (550°F) for eight hours. Samples chosen for curing included pure monomers, monomer/oligomer mixtures produced by the stoichiometry outlined In the previous section, and In one case (the bisphenol-A based resin) pure oligomer. This set of samples was selected to provide data showing the effect of oligomer concentration on thermomechanical properties. 

As the first step, we have tried to acylate wood in a triflu-oroacetic anhydride (TFAA)-higher aliphatic acid system at 30 or 50 °C (TFAA method) and in a higher aliphatic acid chloride-pyri-dine-DMF system at 100 °C (Chloride method) (15). Both the methods resulted in thermally meltable products. An example of the thermomechanical diagram for the products is shown in Fig. 11. In this figure, the diagram for a lauroylated wood sample prepared by the TFAA method is compared with that for untrated wood. The lauroylated wood shows thermal behavior with a sharp drop caused by complete flow of the sample at 195 °C. 

The Mettler TMA 40 thermomechanical analyzer is illustrated in Figure 11.3. A measuring sensor applies a user-definable force to the sample of -0.05-0.5 N. The position of the sensor is continuously monitored by a LVDT. TMA measurements can be made in the temperature range -100-1000 C. This module is part of the Mettler TA 3000 thermal analysis system. 

In equation 2.14, the non-equilibrium solute chemical potential is calculated through the use of equation 2.12 and of an appropriate EoS for the polymer-penetrant system under consideration. The pseudo-equilibrium penetrant content in the polymer, can be easily calculated whenever the value of the pseudo-equilibrium polymer density Pp i is known. Such a quantity represents, obviously, a crucial input for the non-equiUbrium approach, since it labels the departure from equilibrium it must be given as a separate independent information, and cannot be calculated simply from temperature and pressure since it depends also on the thermomechanical history of the sample. 

This system is expanded to the thermomechanical analysis capability which requires the measurement of length in a penetration, expansion, or extension mode. The basis of this analysis has been discussed in the literature. The relationships of the thermal expansivity a and the length 1 of a sample with respect to temperature and tensile force f are expressed as follows... 

The three resins above were tested by thermomechanical analysis (TMA) on a Met-tler 40 apparatus. Triplicate samples of beech wood alone, and of two beech wood plys each 0.6 mm thick bonded with each resin system were tested. Sample dimensions were 21 mm x 6 mm x 1.2 mm. The samples were tested in non-isothermal mode from 40°C to 220°C at heating rates of 10°C/min, 20°C/min and 40°C/min with a Mettler 40 TMA apparatus in three-point bending on a span of 18 mm. A continuous force cycling between 0.1 N and 0.5 N and back to 0.1 N was applied on the specimens with each force cycle duration being 12 s. The classical mechanics relation between force and deflection E = [L /(4bh )][AF/(Af)] (where L is the sample length, AF the force variation applied and A/ the resulting deflection, b the width and h the thickness of the sample) allows calculation of the modulus of elasticity E for each case tested and to follow its rise as functions of both temperature and time. The deflections A/ obtained and the values of E obtained from them proved to be constant and reproducible. 

The creation of the triple-shape capability for an AB polymer network system by a simple one-step process similar to a conventional dual-shape progranuning process was shown for networks based on PCL and PCHMA [24] (see Sect. 2.4). In these materials a stress-controlled cyclic, thermomechanical experiment was used to quantify the triple-shape effect. The sample was deformed at 150°C (liigh) to 50% (Ein) and subsequently cooled to —10°C (Tio ). The large temperature interval of around 160 K led to a strong reduction of the strain. When the sample was heated... 

This system measures dimensional changes as a function of temperature. The dimensional behavior of a material can be determined precisely and rapidly with small samples in any form— powder, pellet, film, fiber, or as a molded part. The parameters measured by thermomechanical analysis are the coefficient of linear thermal expansion, the glass-transition temperature (see Figs. 9-10 and 9-11), softening characteristics, and the degree of cure. Other applications of TMA include the taking of compliance and modulus measurements and the determination of deflection temperature under load. 

Table 2.5 summarises the main applications of thermal analysis and combined techniques for polymeric materials. Of these, thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) provide only physical properties of a very specific nature and yield very little chemical information. DMA was used to study the interaction of fillers with rubber host systems [40]. Thermomechanical analysis (TMA) measures the dimensional changes of a sample as a function of temperature. Relevant applications are reported for on-line TMA-MS cfr. Chp. 2.1.5) uTMA offers opportunities cfr. Chp. 2.1.6.1). The primary TA techniques for certifying product quality are DSC and TG (Table 2.6). Specific tests for which these techniques are used in quality testing vary depending upon the type of material and industry. Applications of modulated temperature programme are (i) study of kinetics (ii) AC calorimetry (Hi) separation of sample responses (in conjunction with deconvolution algorithms) and (iv) microthermal analysis.

A systematic discussion is given of the actual experimental response of an amorphous polymer sample to particular thermomechanical histories. For a system subjected to a constant stress, S, the creep strain is given by ... 

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