Thermomechanical tests glass-transition temperature

ASTM E 1545-00, ASTM Book of Standards 2002. Standard Test Method for Assignment of the Glass Transition Temperature by Thermomechanical Analysis . ASTM International, Conshohocken, PA. 

CHARACTERIZATION. Melting points were determined on an E. I. DuPont Series 99 Thermal Analyzer at 20°C/min. Inherent viscosities of polyamic acid solutions were obtained at a concentration of 0.5% (w/w) in DMAc at 35°C. Glass transition temperatures (T ) of the fully cured polymer films were measured by thermomechanical analysis (TMA) on a DuPont 943 Analyzer in air at 5°C/min. Films fully-cured at 300°C were tested for solubility at 3-5% (w/w) solids concentration in DMAc,N,N-dimethylformamide (DMF), and chloroform (CHCl-j). Solubilities at room temperature were noted after periods of 3 hours, 1 day and 5 days. Refractive indices of 1 mil thick films were obtained at ambient temperature by the Becke line method (11) using a polarizing microscope and standard immersion liquids obtained from R. P. Cargille Labs. 

Earnest, C.M. Assignment of glass transition temperatures using thermomechanical analysis. In Assignment of the Glass Transitions Seyler, R.J., Ed. American Society for Testing and Materials Philadelphia, U.S.A., 1994 ASTM STP 1249, 75-87. 

C. M. Earnest, Assignment of Glass Transition Temperatures Using Thermomechanical Analysis , in R. J. Seyler (ed.). Assignment of the Glass Transition, ASTM STP 1249, American Society for Testing and Materials, Philadelphia, 1994, pp. 75-87. 

E 1782 (1998) Vapour pressure by DSC/DTA E 1824 (1996) Standard Test Method for Assignment of a Glass Transition Temperature using Thermomechanical Analysis under Tension... 

Thermomechanical-analysis (TMA) testing is used to measure a material s expansion coefficient above and below the glass-transition temperature or Tg. Thermomechanical analysis continuously monitors the expansion of a probe on a sample as a function of temperature. The standard test method for TMA is ASTM D3386, Coefficient of Linear Thermal Expansion of Electrical Insulating Materials.In addition to the glass-transition temperature or Tg, the expansion coefficients above and below Tg are reported. 

The glass transition temperatures were estimated from deformation tests performed on the very same pellets which were used for x-ray studies. The tests were made by means of a Perkin-Elmer Thermomechanical analyzer TMS-l, calibrated with polystyrene and polymethylmethacrylate. C-13 NMR Spectra were run in deu-terated chloroform at 10wt% concentration and at 450C. A JEOL PFT-100 spectrometer was used (resolution ... 

The absorption of moisture critically affects other important resin properties, particularly those associated with low-dielectric and thermomechanical applications. Results of a 96-h boiling water immersion test are presented in Table 2.2. The moisture absorbed decreased substantially with fluoromethylene chain length from n = 3 to n = 6, followed by only modest decreases for n = 8 and 10. This latter behavior was somewhat unexpected and may be the effect of decreased cross-link density counteracting the increased fluorine content. These 100°C measurements are just above the glass transition and the situation may be different at room temperature. These measurements are in progress. 

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. 

The thermomechanical tests of synthesized BSN showed, that the temperature magnitudes of glass transition and fluidity greatly depend on the composition and construction of the initial substances and are in in the interval 207-217 °C and 250-350 °C correspondingly. 

Interestingly, it was found that the thermodynamic glass transition matched not only the change in coefficient of expansion which accompanies the glass transition found by thermomechanical analysis (TMA), but also the heat distortion temperature as measured on macroscopic test bars. This finding permitted the use of DSC data with confidence for cure checks, in preference to the more complex and time-consuming preparation of heat distortion test bars. 

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