Analysis torsional braid

There are other supports used in torsional braid (or perhaps, more strictly termed, supported dynamic mechanical) measurements. These include solid substrates (solids that are free of mechanical transitions under the testing conditions), which have been shown to improve the precision of results over those obtained using conventional glass braids (Wetton, 1986). However, these solid substrates generally require thick coatings. Also wire-mesh 

TDA applications have been reviewed for inorganic compounds (4,11.13) clays (12), metallic glasses (14), metallurgy (15), ceramic science (16), and zeolites (17). Since numerous applications of this technique have been described, only a few illustrative examples will be discussed here. 

TDA has provided useful information on the tempering process and iie influence of individual alloying elements in steel (15). Complications irise due to the fact that while the decomposition of martensite produces a. ontraction, decomposition of any retained y-iron is accompanied by expan- 

Almost all the applications of TMA have been to polymeric systems. It is used to measure the thermal expansion characteristics of the polymer and hence to determine the glass transition temperature, Tfl, a temperature at 

From penetration produced by a hemispherical quart probe, Finklin (23) showed that Young s modulus of the sample is given by 

Reviews on the application of TMA to polymers include those by Miller (48), Chiu (25), Ogilvie (26), Barton (22), and numerous others. TMA has also been used to characterize oil shales (27) but its use in clay mineralogy appears to be slight (12). 

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The cure of novolaks with hexa has been studied with differential scanning calorimetry (dsc) and torsional braid analysis (tba) (46) both a high ortho novolak and a conventional acid-cataly2ed system were included. The dsc showed an exothermic peak indicating a novolak—hexa reaction ca 20°C higher than the gelation peak observed in tba. Activation energies were also calculated. 

Table IV shows the data on rigidity changes of the end-sealing compounds at two dose levels. Rigidity was determined by torsional braid analysis (5). These data indicate that the blend of cured and uncured isobutylene-isoprene copolymer was softened most by the irradiation treatment, the blend of polychloroprene and butadiene-styrene copolymer softened the least, and the blend of polychloroprene and the uncured isobutylene-isoprene copolymer was intermediate. Increasing the irradiation dose from 3-4 Mrad to 6-7.5 Mrad decreased the rigidity of the three end-sealing compounds. The irradiation temperature did not significantly influence rigidity.

Probably most of these investigators were studying poly(dichlorophosphazene) in the partially crosslinked state. Most of this was summarized by Allcock (.9). More recently, highly purified, uncrosslinked II has been examined in the solid state (21). The unstressed polymer is amorphous at room temperature, but crystallization can be induced by cooling or stretching techniques. The glass transition temperature, measured by Torsional Braid Analysis, is -66°C (22). 

The formation of essentially linear polymers from N3P3C16 and/or N4P4C18 is catalysed by water147 and by (CF3S03)2Hg.148 Torsional braid analysis on... 

A representative sample of many of the polyimide films that were produced were subjected to thermo-mechanical analysis (TMA), torsional braid analysis (TBA), thermal gravimetric analysis (TGA), infrared spectral analysis and weight loss on prolonged heating (e.g. isothermal studies), TABLE II. The softening temperature as measured by TMA and TBA are in general... 

TGA analysis shows that polymer degradation starts at about 235°C which corresponds to the temperature of decomposition of the cellobiose monomer (m.p. 239°C with decom.). Torsion Braid analysis and differential scanning calorimetry measurements show that this polymer is very rigid and does not exhibit any transition in the range of -100 to +250 C, e.g. the polymer decomposition occurs below any transition temperature. This result is expected since both of the monomers, cellobiose and MDI, have rigid molecules and because cellobiose units of the polymer form intermolecular hydrogen bondings. Cellobiose polyurethanes based on aliphatic diisocyanates, e.g. HMDI, are expected to be more flexible. 

Major instrumentation involved with the generation of thermal property behavior of materials includes thermogravimetric analysis (TG, TGA), DSC, differential thermal analysis (DTA), torsional braid analysis (TBA), thermomechanical analysis (TMA), thermogravimetric-mass spectrometry (TG-MS) analysis, and pyrolysis gas chromatography (PGQ. Most of these analysis techniques measure the polymer response as a function of time, atmosphere, and temperature. 

The glass transition temperatures, specific for each thermosetting resin, are used to characterize cure kinetics. They can be measured by many techniques, of which the widely used are Differential Scanning Calorimetry (DSC) and Torsional Braid Analysis (TBA)... 

Torsional braid analysis indicates that the —Si—O—Si— flexible chain is present and persists, although its flexibility is somewhat impaired, even when the material is fully cured. This indicates that there is a substantial proportion of the R—Si—O— units which are neither crosslinked nor involved in ring formation. However, a spiral structure with the hydroxyl groups enclosed along the core meets the requirements. Such a structure has been suggested by Birchall et al. [12] for silanol-terminated poly(oxymethylenes). 

One of most popular techniques for dynamic mechanical analysis is the torsion pendulum method. In a modification of this method designed to follow curing processes, a torsion bar is manufactured from a braid of fibers impregnated with the composition to be studied this is the so-called torsional braid analysis (TBA) method.61 62,148 The forced harmonic oscillation method has been also used and has proven to be valuable. This method employs various types of rheogoniometers and vibroreometers,1 9,150 which measure the absolute values of the viscoelastic properties of the system under study these properties can be measured at any stage of the process. The use of computers further contributes to improvements in dynamic mechanical analysis methods for rheokinetic measurements. As will be seen below, new possibilities are opened up by applying computer methods to results of dynamic measurements. 

Figure 6.2 Torsional braid analysis (TBA) during isothermal reaction of a diepoxy, DGEBA, with a diamine, bis(p-aminocyclohexyl) methane, from -15°C to 220°C (a) relative rigidity (b) logarithmic decrement (Tg0 =-19°C, Tgoo = 170°C, and Tgge = 49°C). (Enns and Gillham, 1983 -Copyright 2001 - Reprinted by permission of John Wiley Sons, Inc.)...

Dynamic testing DMTA, DMA, torsional braid analysis (Enns and Gillham, 1983) is first used as a thermal analysis method to detect the transitions, using dissipation peaks. Certain commercial DMTA instruments have a relatively low accuracy in measuring forces and/or strains. In contrast, they give relatively accurate values of the damping factor tan 5, so that dissipation spectra tan 8 = f (oo, T), are very useful analytical tools. 

In addition, Seferis and Wedgewood have pointed out the many pitfalls that should be avoided when using dynamic mechanical analysis (DMA) to determine thermal properties in epoxy systems [134]. However, Sanz, et al. have investigated Tg of epoxy systems via DMA for a myriad of epoxy compositions and compiled large amounts of reasonable data using this technique [ 135]. Zukas has done the same using torsional braid analysis (TBA) on many epoxy systems and produced similar conclusions to Sanz [129]. 

Topological limit of the reaction 24 Torsion pendulum (TP) 88 Torsional braid analysis (TBA) 88 Transesterification 48... 

The changes which occur in thermosetting resins undergoing cure have been studied by a variety of techniques. Supported sample methods have been used to monitor the relative changes modulus and damping behavior from the initial low viscosity liquid to the fully cured rubbery or glassy state. Torsional braid analysis (TBA) employs a resin sample impregnated on a... 

Torsional braid analysis (TEA) is a particular case where the sample supported by a fiberglass braid is subjected to a torsional strain. 

A variation of the torsion pendulum, torsional braid analysis (TBA), utilizes a supported specimen so that the dynamic mechanical properties of a sample can be monitored in the liquid as well as the solid states (1, 2). An inert multifilamented glass braid is impregnated with the sample (usually in its liquid state or in solution). The observed dynamic mechanical properties are relative due to the composite nature and complex geometry of the specimen. 

Torsional Braid Analysis Curve Fitting by Least Squares". 

Viscoelasticity Torsional Braid Analysis (TBA), DMA, Dynamic Spring Analysis (DSA) A—>C 37-39... 

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