Glass transition dynamic mechanical testing

Ta = glass transition temperature determined in a dynamic mechanical test, K... 

Dynamic mechanical testing was conducted in uniaxial extension with an Imass Corp. Dynastat Mark II instrument. Specimens were typically 35 mm in length and 12 mm wide. The measurements were made over a frequency range of from 0.01 to 100 s" at various temperatures down through the glass transition temperature of the sample. 

Thin-films of Resin 5208 with specific isothermal cure histories exhibit three dispersion regions upon heating. The first is attributed to softening, followed by further chemical reaction and finally a peak due to the glass transition of the fully cured resin. Dynamic mechanical testing on thin-films shows that significant reaction takes place between the two DSA loss tangent peaks and that the second DSA peak is associated with vitrification. 

From Reference 37 with permission from Elsevier Ltd.] Glass-transition temperature determined by dynamic mechanical tests. Degree of crystalhnity in volume fraction estimated using density data. Long period evaluated by SAXS. 

Dynamic mechanical tests provide useful information about the viscoelastie nature of a polymer. It is a versatile tool for studying the effects of molecular structure on polymer properties. It is a sensitive test for studying glass transitions and secondary transitions in polymer and the morphology of crystalline polymers. 

The principles of time-temperature superposition can be used with equal success for dielectric measurements as well as dynamic mechanical tests. Analysis of the frequency dependence of the glass transition of the adhesive in the system described above shows that it follows a WLF type dependence whereas the transition of PET obeys Arrhenius behaviour. This type of study can be used to distinguish between different types of relaxation phenomena in materials. 

In this communication we present the results of an FTIR study of the blend system poly(bis-phenol A-carbonate) (PC) - PCL. This is a complex blend system which contains two crystallizable polymers with large differences in the crystalline melting points (T ) and glass transition temperatures (Tg). Cruz, et al.have demonstrated from thermal analysis and dynamic mechanical testing that blends of PC and PCL have a single Tg which is dependent only on the composition of the blend and conclude that the amorphous phase is miscible. These authors also concluded that the miscible amorphous phase results primarily from physical rather than chemical interactions between the polymers. 

The glass transition temperature can be determined readily only by observing the temperature at which a significant change takes place in a specific electric, mechanical, or other physical property. Moreover, the observed temperature can vary significantly, depending on the specific property chosen for observation and on details of the experimental technique (for example, the rate of heating, or frequency). Therefore, the observed Tg should be considered to be only an estimate. Ifhe most reliable estimates are normally obtained from the loss peak observed in dynamic mechanical tests or from dilatometric data (ASTM D-20). 

Earlier measurements on the moist transitions of extracted hemicelluloses were made by differential scanning calorimetry (DSC) (4). This enables the glass transition to be studied from a thermodynamic point of view, but information relevant for mechanical considerations such as the effect of load frequency is lacking. Some measurements in temperature scans in dynamic mechanical tests have been performed on carbohydrates such as amylopectin (13-15). The problem with such measurements on moist samples is the evaporation of water at the high temperatures. To avoid such problems, a technique for humidity scans... 

Much work has been published on the physical structure of thermoplastic rubber. Two glass transition temperature T peaks are found in dynamic mechanical tests with an S-B-S block copolymer. In contrast, only one peak is found in a random SBR copolymer with the same sty-rene/butadiene ratio. This difference is shown in Fig. 4. 

The dynamic mechanical tests over a wide temperature range are very sensitive to the physical and chemical structure of polymers and composites. They allow the study of glass transitions or secondary transitions and yield information about the morphology of polymers. Experimental results of dynamic tensile tests (DMTA) conducted on nanocomposites are shown in Table 2 for selected temperatures (20 °C, 100 °C, 220 °C, and glass transition, T ). 

ASTM E 1640-99, ASTM Book of Standards 2002. Standard Test Method for Assignment of the Glass Transition Temperature by Dynamic Mechanical Analysis . ASTM International, Conshohocken, PA. 

The first data on polymer systems were collected via (laser-) light-scattering techniques [1] and turbidity measurements, further developed by Derham et al. [2,3]. Techniques based on the glass-transition of the polymer-blend constituents were also tested, such as DSC, Dynamic Mechanical Spectroscopy, and Dielectric relaxation [4]. Films made from solutions of... 

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