ASTM D7028-07 Glass Transition Temperature of Polymer Matrix Composites

Scope:

ASTM D7028-07 test method defines the procedure to evaluate the dry and wet transition temperature (T_g) for polymer matrix composites. The polymer matrix composites contain high modulus, 20 GPa fibers that are analyzed using the dynamic mechanical analyzer (DMA). Experimental parameters, apparatus used, and the physical property measured affect the glass transition temperature. This test method is primarily intended for polymer matrix composites reinforced by continuous, oriented, high modulus fibers. The values are reported in SI units.

Test procedure:

In ASTM D7028-07 the specimen thickness, width, length, and weight are recorded. A flat rectangular strip of laminate is placed in the dynamic mechanical analyzer (DMA). It is then oscillated at a nominal frequency of 1Hz. The test specimen is heated at 5 °C/min. The same parameters are used for both dry and wet specimens to facilitate comparison. The glass transition temperature (DMA T_g) is noted when a significant drop in the storage modulus is observed during the method. The run is set to begin at room temperature or a temperature at least 50 °C below the estimated DMA T_g` and end at a temperature at least 50 °C above DMA T_g but below the decomposition temperature. Load and displacement data are recorded as a function of temperature. The specimen under test needs to be examined for any visual oddity such as blisters, cracks, etc. post completion of the test.

Specimen size:

Depending on the analyzer, typical specimen size can range from 56 ± 4 × 12 ± 1 × 2.0 ± 0.5 mm (L × W × T) to 22 ± 1 × 3 ± 1 × 1.0 ± 0.5 mm

Data:

Plot logarithm of storage modulus (E’) and linear tangent delta (tan δ) versus the linear temperature. The DMA T_g is determined to be the intersection of two tangent lines from the storage modulus by this test method. The figure below shows a typical plot for determining the DMA T_g–