Effect of Temperature on Polymer Viscosity

As a starting point it is useful to plot the relationship between shear stress and shear rate as shown in Fig. 5.1 since this is similar to the stress-strain characteristics for a solid. However, in practice it is often more convenient to rearrange the variables and plot viscosity against strain rate as shown in Fig. 5.2. Logarithmic scales are common so that several decades of stress and viscosity can be included. Fig. 5.2 also illustrates the effect of temperature on the viscosity of polymer melts. 

For dilute polymer solutions, the effect of temperature on the viscosity can be described with Andrade s equation ... 

The effect of temperature on melt viscosity is illustrated in Fig. 14. Here the viscosity of a typical S-B-S polymer is shown at three shear rates. It is important to note the long plateau followed by a rapid increase in viscosity on cooling. Through control of application temperature, either long or short open times followed by rapid setup can be achieved. These characteristics are advantageous in high speed packaging where rapid hot tack buildup is de-... 

The effect of temperature on the viscosity is of primordial importance in polymer processing, where tight control of temperatures is required for a successful... 

Many amorphous homopolymers and random copolymers show thermorheologically simple behavior within the usual experimental accuracy. Plazek (23,24), however, found that the steady-state viscosity and steady-state compliance of polystyrene cannot be described by the same WLF equation. The effect of temperature on entanglement couplings can also result in thermorheologically complex behavior. This has been shown on certain polymethacrylate polymers and their solutions (22, 23, 26, 31). The time-temperature superposition of thermorheologically simple materials is clearly not applicable to polymers with multiple transitions. The classical study in this area is that by Ferry and co-workers (5, 8) on polymethacrylates with relatively long side chains. In these the complex compliance is the sum of two contributions with different sets of relaxation mechanisms the compliance of the chain backbone and that of the side chains, respectively. 

Eq. (15.35) gives a fair description of the effect of temperature on viscosity for a number of polymers. For some other polymers, however, considerable deviations are found. According to Eq. (15.35), ri(T)/ri(Tg) should be a universal function of (T — Tg), which is not confirmed by experimental data. 

For a number of polymer solutions experimental data on the effect of temperature on viscosity are available. By way of example, Fig. 16.4 shows log t] against 1/T for polystyrene in xylene, together with the curve for the melt and the straight line for the pure solvent. 

Macromolecules in solution, melt, or amorphous solid states do not have regular conformations, except for certain very rigid polymers described in Section 4.6 and certain polyolefin melts mentioned on page 139. The rate and ease of change of conformation in amorphous zones are important in determining solution and melt viscosities, mechanical properties, rates of crystallization, and the effect of temperature on mechanical properties. 

Effect of Temperature on Viscosity. The viscosity of mobility control polymers decreases with increasing temperature and an Arrhenius type relationship is obeyed ... 

Effect of Temperature on the Solution Behavior of Carhoxylate and Sulfonate lonomers. Based on the results above, a substantial difference in the solution behavior of carhoxylate and sulfonate ionomers might be expected as a function of temperature. Figure 10 illustrates the effect of temperature on the solution viscosity of carboxylated and sulfonated ionomers at very low sulfonate and carhoxylate content. At low polymer concentrations it is seen that the sulfonate system manifests a higher viscosity level in 1% hexanol/xylene solution. This is consistent with the dilute solution viscosity behavior. More importantly, at high polymer concentrations it is seen from Figure 10 that the 5% S-PS curve actually goes through a maximum, while the carhoxylate system decreases mono-tonically. These results are apparently attributable to the weaker ionic association in the carhoxylate case as compared to the sulfonate system. 

Other equations have been developed to describe the shear thinning behavior of polymer melts, for instance, the Yasuda-Carreau equation, which is written here as Equation 22.19 [41]. In this equation, as in the power-law model, the effect of temperature on viscosity of the system can be taken into account by means of an Arrhenius-type relationship ... 

A few studies considered the effect of pH on the viscosity of xanthan solutions. Jeanes et al. observed a rapid increase in the viscosity of xanthan solution at pH 9-11 [28]. Whitcomb and Macosko [29] and Philips et al. [30] found the viscosity of xanthan to be independent of pH. Szabo examined the stability of various EOR polymers in caustic solutions at room temperature, including Kelzan MF (a biopolymer) [6]. He found a fast initial drop in the viscosity of a xanthan solution containing 2 wt% sodium chloride and 5 wt% sodium hydroxide, at 12.5 s", which virtually stopped after 10 days. Krumrine and Falcone found that the effect of alkali (sodium silicates) on the viscosity of xanthan solution depended on the concentration of sodium and calcium ions present [31]. Ryles examined the thermal stability of bio-polymers in alkaline conditions [16]. He found that xanthan was totally degraded (in anaerobic conditions) upon the addition of 0.8 wt% sodium hydroxide at temperatures from 50 to 90°C (in a 1 wt% sodium chloride brine). Seright and Henrici observed total biopolymer degradation at pH > 8 and a temperature of 120°C [26]. 

To examine the effect of alkalis on the viscosity of HPAM, the viscosity of polymer solutions was measured as a function of shear rate at various alkali concentrations. Viscosity measurements were repeated on the same solutions after two weeks (336 h) and four weeks (696 h) from initial mixing. Figure 13 depicts the variation of the low-shear relative viscosity with sodium hydroxide concentration at polymer concentration = 1,000 ppm and a temperature of 20°C. After approximately one hour from initial mixing, the low-shear relative viscosity decreased with sodium hydroxide concentration to a limiting value. This result is similar to the trend previously observed with sodium chloride and is due to the shielding effect of the sodium ion. The influence of sodium hydroxide on the low-shear viscosity measured two weeks (336 h) from initial mixing was more dramatic where higher viscosities were obtained at low alkali concentrations. Low-shear viscosity measurements after four weeks (696 h) were very similar to those obtained after two weeks. 

This chapter is organized in the following way. First, we present some common techniques for characterizing the dispersion of nanoclays in polymer blends. The dispersion level has been shown to have a fundamental effect on the fire performance of polymer-clay nanocomposites (PCNs), as an exfoliated or intercalated polymer-clay system seems to enjoy reduced flammability. Second, the effects of nanoclays on the viscosity of polymer blends are discussed. With increased temperature in the condensed phase during combustion, most polymers (and hence polymer blends) have sufficiently low viscosity to flow under their own weight. This is highly undesirable, especially when the final products will be used in vertical orientation, because the melt can drip, having the potential to form a pool fire, which can increase fire spread. The results on thermal stability are presented next, followed by those for the cone calorimeter. The quantitative effects of nanoclays on the... 

In a study of the effects of temperature on the melt viscosities of copolyesters of terephthalic acid, i sophthalic acid, and methylhydroquinone, McFarlane and Davis observed that minima in the melt viscosity versus temperature curves occurred at about 340 to 360°C in compositions containing 40 to 60 mol % isophthallc acid (total diacids equal 100 mol %). The increase in the melt viscosities with increasing temperature after the minima presumably is due to the Increase in the isotropic content of the polymers and the decrease in the degree of liquid crystallinity. We did not observe this phenomenon in the rigid-rod, all-aromatic, liquid crystalline polyesters that did not contain any meta component because of the high temperatures involved (above the decomposition temperatures of the polyesters). A poly(terephthalate-Isophthalate) of methylhydroquinone containing 70 mol % isophthallc acid was not liquid crystalline and, therefore, did not exhibit a minimum in a plot of melt viscosity versus temperature... 

Often, one is interested in comparing the viscosities of flexible, amorphous homopolymers with different molecular weights and which have the same chemical structure or different chemical structures. Since the viscosities of polymers depend on both temperature and molecular weight, it is essential to suppress, if not eliminate completely, the effect of temperature on viscosity for such purposes. When the... 

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