Thermal mechanical analysis results

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

With requenching and reaging, expansivity above Tg again increases with reaging time (96.6 % increase), demonstrating once again the thermoreversibility of physical aging. Table 2 summarizes the results of the thermal mechanical analysis. 

The pure components, as well as IPNs produced at various ratios, were characterized by density measurements, dynamic thermal mechanical analysis, and electron microscopy. Results are presented and discussed below. 

Dynamic mechanical thermal analysis, a non-sample-destructive technique in which an oscillatory stress is applied to the sample and the resultant strain determined as a function of both frequency and temperature. Examples of this technique include thermal-ramped oscillatory rheometry and conventional dynamic thermal mechanical analysis. 

The glass transition temperature of ice cream can be measured by thermal mechanical analysis. A sample of unaerated frozen ice cream mix approximately 0.5 mm thick and 1 cm in diameter is placed between two plates. One of the plates is attached to a probe that measures the expansion of the sample as it is warmed up from below the glass transition temperature. Unaerated samples are used because aeration affects the thermal expansion. However, since the glass transition temperature is a property of the composition of the matrix, the absence of air does not affect the result. The glass transition temperature is indicated by a change in the rate of expansion that occurs at about — 30 °C for a typical ice cream. 

Thermal mechanical analysis affords a method of obtaining precision results on a small test piece as a function of temperature. A procedure for plastics using DMA is given in a draft ISO standard, ISO DIS 11359-2 [9]. 

Characterization by thermal mechanical analysis indicated that the incorporation of the fibers cause a decrease of the mechanical loss factor. This results in better damping capabilities. Scanning electron microscope (SEM) studies of the impact fractured surfaces of the composites with cotton linter showed a debonding cavitation at the matrix fiber interface. 

Our sincere thanks to J. P. Heeschen of the Dow Analytical Laboratory for his help in proton and 13c NMR determinations to R.A. McDonald of Dow Systems Research for providing us with the scanning differential calorimetry results, and to F. E. Towsley, our colleague, for providing us with the results of thermal mechanical analysis. 

Figure 4.4-5 DEA results of a second clean silicon wafer sample 4.5 Thermal Mechanical Analysis... 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

A difunctional bisphenol-A-based benzoxazine has been synthesized and characterized by GPC and 1II NMR (Fig. 7.39). A small of amount of dimers and oligomers also formed. Thermal crosslinking of bisphenol-A benzoxazine containing dimers and oligomers resulted in networks with relatively high Tgs. Dynamic mechanical analysis of the network showed a peak of tan 8 at approximately 185°C. 

Glass transition temperature (Tg), measured by means of dynamic mechanical analysis (DMA) of E-plastomers has been measured in binary blends of iPP and E-plastomer. These studies indicate some depression in the Tg in the binary, but incompatible, blends compared to the Tg of the corresponding neat E-plastomer. This is attributed to thermally induced internal stress resulting from differential volume contraction of the two phases during cooling from the melt. The temperature dependence of the specific volume of the blend components was determined by PVT measurement of temperatures between 30°C and 270°C and extrapolated to the elastomer Tg at —50°C. 

Thermal gravimetric analysis shows that the increase in phosphorus content results in char yield increases which are correlatable with the self-extinguishment time decreases. This led to the conclusion of phosphorus "rich" barrier shielding the surfaces as a mechanism of the flammability decrease. 

An appropriate cure cycle was established based on the results obtained from the thermal analysis and cure rheology studies of the resin and cured BCB bar and dogbone shaped samples were fabricated for testing. Bar shaped specimens had the dimensions of 3.5 x 0.5 X 0.125 and were used to stake compact tension specimens for fracture toughness studies and for dynamic mechanical analysis of a torsion bar. Dogbone shaped specimens for tensile tests had a gauge area of 1 x 0.15 and were approximately 0.040 thick. 

Thermal analysis, moisture uptake and dynamic mechanical analysis was also accomplished on cured specimens. Thermal analysis parameters used to study cured specimens are the same as those described earlier to test resins. The moisture uptake in cured specimens was monitored by immersing dogbone shaped specimens in 71 C distilled water until no further weight gain is observed. A dynamic mechanical scan of a torsion bar of cured resin was obtained using the Rheometrics spectrometer with a temperature scan rate of 2°C/minute in nitrogen at a frequency of 1.6Hz. The following sections describe the results obtained from tests run on the two different BCB resin systems. Unless otherwise noted all tests have been run as specified above. 

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