THERMORHEOLOGICAL PROPERTIES

Anandhan, S., De, P.P., De, S.K., Swayajith, S., and Bhowmick, A.K., Thermorheological properties of thermoplastic elastomeric blends of nitrile rubber and poly(styrene-co-acrylonitrile) containing waste nitrile rubber vulcanizate powder, Kautsch. Gummi Kunst., 11, 2004. 

The rheological properties of insitu polymerized nanocomposites with end-tethered polymer chains were first described by Krisnamoorti and Giannelis [33]. The flow behavior of PCL- and Nylon 6-based nanocomposites differed extremely from that of the corresponding neat matrices, whereas the thermorheological properties of the nanocomposites were entirely determined by the behavior of the matrices [33]. The slope of G (co) and G"(co) versus flxco is much smaller than 2 and 1, respectively. Values of 2 and 1 are expected for linear mono-dispersed polymer melts, and the large deviation, especially in the presence of a very small amount of layered silicate loading, may be due to the formation of a network structure in the molten... 

There have been several studies of the thermorheological properties of polymeric systems of pharmaceutical and biomedical importance. However, rather than describing all studies in detail, some selected examples have been described in the... 

FIGURE 10.18 Thermorheological properties of polymethacrylate ester. (Reprinted from Wetton, R.E. et al., Thermochim. Acta 175, 1, 1991. With permission.)... 

FIGURE 10.21 Thermorheological properties of poly(e-caprolactone) as determined using dynamic mechanical thermal analysis (film geometry, 50-pm amplitude, and 1 Hz). 

Journal of Applied Polymer Science 87, No.6, 7th Feb.2003, p. 1016-26 SOLUTE AND SOLVENT EFFECTS ON THE THERMORHEOLOGICAL PROPERTIES OF POLYOXYETHYLENE-POLYOXYPROPYLENE BLOCK COPOLYMERS. IMPLICATIONS FOR PHARMACEUTICAL DOSAGE FORM DESIGN Jones D S Brown A F Woolfson A D Belfast,Queen s University... 

Details are given of the equilibrium thermorheological properties of oxyethylene-oxypropylene copolymers. The effect of molecular weight, solute and solvent composition on the structural properties was investigated. The efficacy of these copolymers in drug delivery systems is discussed. 32 refs. 

Few examples of the homogeneous diblock-incompatible homo-polymer behavior have been reported. One that has received considerable attention is the system polystyrene-poly-a-methylstyrene (2). Block copolymers of styrene and a-methylstyrene exhibit a single loss peak in dynamic experiments (2,3) and have been shown to be thermorheologi-cally simple (4) hence they are considered to be homogeneous. Mechanical properties data on these copolymers also has been used to validate interesting extensions of the molecular theories of polymer viscoelasticity (2,3,4). 

Calculation of Master Curves from Mechanical Models. The only way to obtain valid master curves for the thermorheologically complex systems (75/25 and 50/50 blends) is to calculate the moduli of the blends as a function of time, using an appropriate mechanical model. This method requires knowledge of the time and temperature dependence of the mechanical properties of the constituent phases. 

Lest one ignore the important role of rheological behavior and properties of fluid foods in handling and processing foods, they are covered in Chapter 8. Here, the topics covered include applications under isothermal conditions (pressure drop and mbcing) and under non-isothermal conditions (heat transfer pasteurization and sterilization). In particular, the isothermal rheological and nonisothermal thermorheological models discussed in Chapters 3 and 4 are applied in Chapter 8. 

A fundamental characteristic of the so-called thermorheologically simple systems is that consecutive isotherms have similar habits, so they overlie each other when they are shifted horizontally along the log t axis. In other words, the time-temperature correspondence principle holds. This property in creep experiments can be expressed by the relation (2,3)... 

However, for thermorheologically simple materials, that is, for those materials for which the time-temperature superposition principle holds, the mechanical properties data can be shifted parallel to the time or frequency axis. This fact suggests an additional hypothesis that can be very useful in solving some specific thermoviscoelastic problems. According to this hypothesis, the net effect of temperature in the response must be equivalent to a variation in the rates of creep or relaxation of the material. Thus for T > Tq the process occurs at a higher rate than at Tq. 

In the first experiments over an extended frequency range, the biaxial viscoelastic as well as uniaxial viscoelastic properties of wet cortical human and bovine femoral bone were measured using both dynamic and stress relaxation techniques over eight decades of frequency (time) [Lakes et al, 1979]. The results of these experiments showed that bone was both nonlinear and thermorheologically complex, that is, time-temperature superposition could not be used to extend the range of viscoelastic measurements. A nonlinear constitutive equation was developed based on these measurements [Lakes and Katz, 1979a]. 

The rheological properties of polymeric solution highly depend on temperature. Therefore, its variation affects the bubble pulsations. Thermorheological features in bubble dynamics have been studied on the basis of temperature superposition principle, using relations [7.2.30], [7.2.31]. It was shown that the temperature rise leads to decrease of the decrement and this effect is enhanced with the increase of nj. Note that the higher is the equilibrium temperature of the liquid, the less sensitive are the Aj values to variations in nj. It is explained by narrowing of the relaxation spectrum of the solution. ... 

The disparity between the temperature dependences of t and % [Eqs. (41) and (42)] depends on the size of the couphng parameter n. Polystyrene has a larger n (= 0.63) than polyisobutylene (= 0.45) [19, 96, 97]. Hence we expect the degree of breakdown of thermorheological simplicity is lesser in polyisobutylene (PIB) than polystyrene (PS).This expectation, as well as other predicted differences in viscoelastic properties of PIB and PS, were confirmed... 

It should be noted that the use of creep and shear compliances as material property input allows Poisson s ratio to be time-dependent. Hence, the present formulation is applicable to any thermorheologically simple isotropic viscoelastic material over any length of time. 

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