Crystallization yield stress, effect

The modification of crystal morphologies of 35 wax induced by the addition of PEB-7.5 and PEB-10 random copolymers are compared in Fig. 68 as a function of polymer concentration in solution a clear decrease of the crystal size with increasing the polymer amount is visible, an observation in accordance with the yield stress trend from Figs. 66 and 67. At the highest concentration (0.8%) both morphologies and yield stress effects shown by PEB-7.5 and PEB-10 are similar numerous crystallites are forming a gel at the same time the increased yield stress observed. 

Yield Stress The effect of hydrogen on the yield stress of iron and steels is unpredictable. For very pure iron single crystals and polycrystals the yield stress is frequently found to be decreased by hydrogen, but it may increase or stay the same, depending on the dislocation structure, crystal orientation and purity of the iron . Little information is available for steels. 

Low-temperature distillate fuel pumpability and viscosity can be reduced below that of an untreated fuel. Below the cloud point, fuel which does not contain a wax crystal modifier is difficult to handle and pump effectively. Wax crystal modifiers help minimize pumpability problems related to yield stress and viscosity. 

This hypothetical effective concentration is certainly higher than that required for colloidal crystallization, so we should expect the suspension to have a yield stress. To estimate the magnitude of the yield stress we use Eq. (6-69) ... 

It is proposed that the nylon 6 molecules nucleate and grow as lamellar crystals on the microfibrils in a chain-folded manner shown in Figure 7.4. Overall the effect is highly desirable as increased modulus, heat distortion temperature and yield stress result due to the resultant morphology and increased crystallinity. 

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