Orientation polymers

The stretching properties of polymers are investigated by examining the effect of polymer orientation, polymer chain length, stretching rate, and temperature. Homogeneity of polymer films and consistency between lots of polymer films also are investigated. Statistical analysis of data includes Q-tests and f-tests. 

Applications. The polyamides have important appHcations. The very high degree of polymer orientation that is achieved when Hquid crystalline solutions are extmded imparts exceptionally high strengths and moduli to polyamide fibers and films. Du Pont markets such polymers, eg, Kevlar, and Monsanto has a similar product, eg, X-500, which consists of polyamide and hydra2ide-type polymers (31) (see High performance fibers Polyamides, fibers). 

The processes of ordering in polymer systems consisting of linear polymers are related, at least on one level of supermolecular organization, to the development of a predominant localization of macromolecules (or their parts) along some directions the orientation axes, i.e. to the transition of the system into the oriented state. The most simple and most widely spread type of polymer orientation is the uniaxial orientation, i.e. the one-dimensional orientation in the direction of the axes of macromolecules. 

In summary, therefore, processing, and in particular injection moulding, can introduce limited chemical degradation, local polymer orientation, orientation of short fibre reinforcements, internal stresses, warpage, shrinkage and defects such as weld lines and voids. 

As expected, the third order susceptibilities vary significantly with polymer orientation. It seems unlikely however that this feature alone will ever increase the values by more than an order of magnitude and further significant improvements will probably require more highly polarizable substituents, the introduction of... 

Most of the systems described in Chapter 5 contain small- or medium-sized or multinuclear benzenoid and non-benzenoid arenes. In Chapter 6, Hoger gives an overview over the mastery of the synthesis of macro- and megacycles. He shows different approaches towards shape-persistent macrocycles and carefully examines and discusses selected examples that display the advantages and disadvantages of macrocycle synthesis under kinetic and thermodynamic control. The template approach (both supramolecular and covalent) towards functionalized rings is also discussed and introduces a strong motif of supramolecular chemistry, which is much further developed but in a more polymer-oriented topic, in the next chapter. 

Fig. 2.7 holds for non-oriented polymers. Orientation in semi-crystalline polymers gives the material a long-range order, which is important for many product properties. 

Orientation has a pronounced effect on the physical properties of polymers. Oriented polymers have properties, which vary in different directions, i.e. they are anisotropic. 

Measurements of optical birefringence and density were obtained in an attempt to determine if total polymer orientation and the amount of fiber crystallinity would correlate with aging behavior. These values are presented in Table III. Because the secondary wall of cotton comprises... 

Polymer orientation varies through the thickness of the injection-molded part owing to the fountain flow of the melt in the mold cavity. The flow at the center of the cross-section is deformed through extension and the highly stretched flow front rolls up to the cold mold surface, where orientation is frozen in a thin surface layer. The rest of the melt required to fill the cavity flows under this stationary frozen layer in more or less a plug fashion, with minimum orientation. Surface orientation in an injection-molded part can be significantly different from that in the core of the part. 

However, SWCNT orientation in PAN/SWCNT gel spun fiber was less than polymer orientation in fibers like Kevlar, Zylon, and Spectra where typical orientation factor value was 0.99. 

The relationship between stress and polymer orientation implies that there is a proportionality between the polymer stress tensor optical anisotropy or birefringence. This proportionality is called the stress-optic law (Janeschitz-Kriegl 1983) and is expressed as (Section 1.6.3)... 

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