Dma 7

A Perkin Elmer DMA7 (Perkin Elmer Corp., Waltham, MA, USA) in three-point bending mode was used to measure the viscoelastic properties of the materials. For a specimen of known geometry, if L = distance between the two supports, b = width, and t = depth, the oscillating strain (ε_o) is given by,
where, y⁰ is the displacement amplitude. The maximum oscillating stress (σ_o) occurs on the upper and lower surfaces and was given by, where, F₀ is the axial force amplitude. Therefore, by substituting for stress and strain, the complex modulus (E*) was given by,
The support separation in three-point bend test was 20 mm and the specimen length was about 24 mm. Prior to testing, the exact dimensions (width and depth) for each specimen were measured at three different points and averaged. Testing was performed in the temperature scan mode using the parameters and conditions shown in Table 3. The temperature was measured with a thermocouple positioned approximately 1 mm away from the sample. Helium gas at a rate of 30 mL min⁻¹ was used in the furnace and cooling water maintained the isothermal environment outside the furnace. The measured data were automatically saved at the end of each test using the Pyris Manager software. One way ANOVA statistical test was used to check the significance level between samples for each time period. A p value ≤0.05 was regarded as being significant.

The experiments were perfomed on samples mounted in metallic holders and clamped in a PerkinElmer DMA 7.A minimum pre-estress of 1.5 MPa was applied to keep the samples straight and stable during the heating process. The creep experiment was not started until the temperature reached a stable value. Once the temperature was stable a constant stress was applied and the elongation as a function of time was measured. The DMA7 was placed in a glove box in N₂ atmosphere to avoid oxidation of the samples.