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Molecular orientations during

The reason for the activity of the above named classes of liquids is not fully understood but it has been noted that the most active liquids are those which reduce the molecular cohesion to the greatest extent. It is also noticed that the effect is far more serious where biaxial stresses are involved (a condition which invariably causes a greater tendency to brittleness). Such stresses may be frozen in as a result of molecular orientation during processing or may be due to distortion during use. [Pg.226]

One obvious weakness in the derivation of (4) is that the reacting molecules are represented by spheres with surfaces of uniform reactivity the question of molecular orientation during reaction does not then arise. This is obviously a very crude approximation for the reaction of many complex molecules. Some recent studies (Sole and Stockmayer, 1971, 1973) have employed a more realistic model in which the representation as spheres is retained but with the assumption that only part of the area of the sphere is reactive. The contact of two spheres involving both reactive areas is then taken as a necessary and sufficient condition for reaction. [Pg.7]

The answer lies in the molecular orientations during collisions. We can illustrate this effect by using the reaction between two BrNO molecules, as shown in Fig. 15.13. Some collision orientations can lead to reaction, and others cannot. Therefore, we must include a correction factor to allow for collisions with nonproductive molecular orientations. [Pg.737]

Problem 7 Molecular orientation during flow increases with the polymer melt elasticity and the flow rate. If the polymer molecular weight is kept to a minimum, the melt elasticity is minimised. Polycarbonate has a low melt elasticity compared with polystyrene. For CD manufacture the mould is filled in between 0.2 and 0.4 s, which is a low flow rate. The skin thickness can be reduced by having a very hot melt at 340 °C and a mould temperature of 95 °C, to reduce the solidification during mould filling. [Pg.505]

FIGURE 13.9 Molecular orientation during dry-jet wet spinning. (From Yang, H.H., Aramid fibers, in Fibre Reinforcement for Composite Materials, Bunsell, A.R., Ed., Elsevier, Amsterdam, 1988. With permission.)... [Pg.1008]

The changes in the molecular orientation during these tests can be expressed by means of optical anisotropy. The path-difference between the ordinary and the... [Pg.666]

It is well known that the extent to which isothermal crystallization in polymers occurs can be profoundly influenced by molecular orientation. Recently Nakamura et al. (275) have performed a detailed theoretical analysis of the relationships between crystallization temperature, crystallinity, orientation and cooling conditions for nonisothermal processes. These investigators have also evaluated the crystallization rates under molecular orientation during melt spinning experiments and... [Pg.88]

Figure 6.14 Picture of molecular orientation during shear-thinning process. Reprinted from B. J. Edwards et al, J. of Non-Newtonian Fluid Mechanics,... Figure 6.14 Picture of molecular orientation during shear-thinning process. Reprinted from B. J. Edwards et al, J. of Non-Newtonian Fluid Mechanics,...
Intermittent electric fields have been suggested in the past as a way to reduce the average molecular orientation during an experiment, with... [Pg.595]

PA-IR " provides information about molecular orientation during and after fast irreversible deformations with a time resolution in the order of microseconds and a low data scatter [37],... [Pg.8]

Most polymer processes involve heat transfer. Polymers must usually be heated above their melting points before shaping and then cooled to maintain the desired shape. It is during the cooling phase of the process that the physical properties of the polymer can drastically be altered. Because the thermodynamic and thermal properties of most polymers are rather similar to other materials, it is not necessary to develop any new laws as it was for the flow of polymers. Hence, this chapter serves mostly as a review of heat transfer with emphasis on those topics pertinent to polymer processing. The main aspects that require additional discussion and that set polymers apart from other materials are their crystallization behavior and the ability to control molecular orientation during processing. [Pg.111]


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Molecular orientation

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