Thermomechanical analysis glass transition temperature

The dynamic mechanical properties of VDC—VC copolymers have been studied in detail. The incorporation of VC units in the polymer results in a drop in dynamic modulus because of the reduction in crystallinity. However, the glass-transition temperature is raised therefore, the softening effect observed at room temperature is accompanied by increased brittleness at lower temperatures. These copolymers are normally plasticized in order to avoid this. Small amounts of plasticizer (2—10 wt %) depress T significantly without loss of strength at room temperature. At higher levels of VC, the T of the copolymer is above room temperature and the modulus rises again. A minimum in modulus or maximum in softness is usually observed in copolymers in which T is above room temperature. A thermomechanical analysis of VDC—AN (acrylonitrile) and VDC—MMA (methyl methacrylate) copolymer systems shows a minimum in softening point at 79.4 and 68.1 mol % VDC, respectively (86). 

The glass transition temperatures (Tg) of both modified and unmodified PSs were determined by DSC analysis, and thermomechanic analysis was controlled by TMK. The results are given in Table 8. It is seen from Table 8 that the highest glass transition temperature (410 K) was obtained with chlorohydrinated PS and that of the lowest (370 K) with olefinic PS. The lowest glass transition temperature in the alkenylated PS caused to elasticity properties on polybutadien and polyisopren fragments. 

DSC helps in determining the glass-transition temperature, vulcanization, and oxidative stability. TG mainly is applied for the quantitative determination of major components of a polymer sample. TMA or DLTMA (dynamic load thermomechanical analysis) measures the elastic properties viz. modulus. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

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. 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

Electron irradiation causes chain scission and crosslinking in polymers. Both of these phenomena directly affect the glass transition temperature (Tg) of the materials. Thermomechanical (TMA) and dynamic-mechanical analysis (DMA) provide information about the Tg region and its changes due to radiation damage. Therefore, DMA and TMA were performed on all irradiated materials. 

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to measure the glass transition temperatures (Tgs) of the uncured and cured AT-resins respectively (Figure 6). 

More recently [79], a carboxy-terminated PBZT ([r ] = 4.8 dL/g) was reacted with m-phenoxybenzoic acid via a Friedel Craft procedure in a meth-anesulfonic acid/P2Os mixture. This provided an ABA block copolymer in which the outer blocks (A) are composed of flexible coil polyetherketone (PEK) and a center block (B) which contains the rigid-rod PBZT. Thermomechanical analysis showed that 20 PBZT/80 PEK and 10 PBZT/90 PEK compositions exhibited glass transition temperatures of 157 °C and 135°C respectively. Consolidation studies have not been investigated to date. 

ISO 11359-2, 1999. Plastics - Thermomechanical analysis - Determination of coefficient of linear thermal expansion and glass transition temperature. 

Thermomechanical studies have indicated that the glass transition temperature of synthesized copo-lymers is decreased as the volume of cyclosiloxane ring in the chain is increased. The results of X-ray structural analysis indicate that the copolymers represent amorphous systems, and increase of cyclic fragment volume leads to an insignificant increase of the interchain distance. 

As the loading rate increases, thermal effects need to be accounted for and the analysis is extended to a coupled thermomechanical framework. Evidence of a temperature effect in glassy polymer fracture is found (e.g., in [2,3]) with a temperature increase beyond the glass transition temperature Tg. The influence of thermal effects on the fracture process is also reported. 

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. 

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

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. 

Glass transition temperatures are most often determined by DSC and by thermomechanical analysis (TMA) (Goff, 1994). Table 7.5 shows the T of some food products. Tg is strongly affected by the composition of the matrix also depends on the procedure used to determine its value. In the case of ice creams, for example, depends on the recipe, particularly on the level of sugars. As Brake and Fennema... 

Thermomechanical Analysis. A thermomechanical analyzer (Perkln-Elmer TMS 2) was used to measure glass transition temperature (Tg) and coefficient of thermal expansion (a ) of completely cured samples In the penetration and expansion modes respectively. Experimental conditions are listed In Table I. 

Properties relating to performance of completely cured adhesive were determined by mechanical spectroscopy and thermomechanical analysis. Measurement of glass transition temperature and coefficient of thermal expansion was obtained from temperature scanning. 

Thermal analysis has been used extensively to characterize resin composites, which have been under development for several decades. Conventional DSC is an excellent method for investigating polymerization of the composites [53-57]. The glass-transition temperature, which is highly relevant for the mechanical properties of the composites, can be readily foimd by dynamic mechanical analysis (DMA) [58-61], as shown in Figure 22, and by thermomechanical analysis (TMA) [62,63], where there is a discontinuity in the slopes of the plot of length change as a function of temperature below and above Tg. 

Duske [6] discussed the use of thermomechanical analysis (TMA) in assessing the quality of wire insulation materials. This is particularly important for characterization of the polymer glass transition temperature, Tg, and for curing process control. TMA has been known to be a very sensitive technique for the... 

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... 

Plastics - Thermomechanical analysis (TMA) - Determination of linear thermal expansion coefficient and glass transition temperature Plastics - Thermomechanical analysis (TMA) - Determination of softening temperature Plastics - Determination of dynamic mechanical properties -General principles Plastics - Dynamic mechanical analysis - Determination of glass transition temperature Plastics - Dynamic mechanical analysis - Calibration... 

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. 

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