Plateau modulus region

At still longer times a more or less pronounced plateau is encountered. The value of the plateau modulus is on the order of 10 N m", comparable to the effect predicted for cross-linked elastomers in Sec. 3.4. This region is called the rubbery plateau and the sample appears elastic when observed in this time frame. 

The plateau modulus is determined by the region in which these two relaxation modes cross. The plateau modulus, the low shear viscosity and the tube disengagement time are given in Section 6.4.3 as... 

The early attempts to interpret the dynamic mechanical behaviour in structural terms include that of Smith et al. where the plateau modulus was correlated with the fraction of non-crystalline material f, determined by NMR. Plots of the plateau compliances at —60 °C and —160 °C as a function of f suggested a modified Takay-anagi series model, with a constant amount of non-crystalline material in parallel with the simple series model. The modd showed good internal consistency, with values for the compliances of the non-ciystalline regions which were acceptable in physical terms. 

Apart from a reduction in the width of the plateau region and a lower plateau modulus, (G blend = 0.5 g pure polymer), the blend exhibits a shift... 

At intermediate fi equendes, monodisperse polymers exhibit a well-defined "plateau region" where G = constant Gn (Figure 2). For a given macromolecular species, the value of the plateau modulus is a characteristic feature that does not depend on molecular weight. The only way to lower the plateau modulus is to add small compatible molecules, either of the same species or not this is, for example, what is done for Hot-Melt Adhesives (HMAs) when adding a "tackifying resin" which softens the polymer and improves the "tack". 

Doi and Edwards were able to develop an equation for the stress relaxation modulus G(t) of monodisperse entangled linear chain liquids in the terminal region without resorting to the independent alignment approximation From G(t), expressions can be obtained for the plateau modulus, the steady-state viscosity and steady-state recoverable compliance. The following dependences on chain length are obtained ... 

The central region of the curve, comprising the drop to the ionic plateau, the plateau modulus, and its drop-off towards the rubbery plateau, is determined by the form of Equation 1, K, EQ, Ef and b. 

The plateau modulus (Gp ) for starch-POClg gel was determined by mechanical oscillation measurements. Figure 16 represents the values of the storage moduli in the plateau region as a function of the reaction rate of starch-POClg gel. Gel formation takes several hours to reach completion this time requirement points to a very slow condensation during phosphate formation. 

This approach to viscoelastic theory is reasonably successful in the low modulus regions, but it requires considerable modification if the high modulus and rubbery plateau regions are to be described. 

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