Crystalline and amorphous domains

From X-ray experiments it is known that the crystallinity of the PE fibres increases with stretching. In Figure 12.2 the NMR signal of 129Xe absorbed in the PE disappears with increasing stretching, which shows that the Xe is practically absorbed only in the amorphous domains, and possibly in the interface between crystalline and amorphous domains, of PE. 

If semi-crystalline polymers would just be a simple mixture of crystalline and amorphous domains, the following relationship would be valid (with xc = degree of crystallinity) ... 

Bombyx mori silk has both crystalline and amorphous domains. In the crystalline fraction, there is a high proportion of glycine (Gly), alanine (Ala) and serine (Ser) amino acid residues, present in the ratio of 3 2 1. This reflects the presence of hexapep-tide sequences, Gly-Ala-Gly-Ala-Gly-Ser. You ve probably forgot the structure of these amino acids, which we have therefore reproduced in Figure 9-16. 

What about semi-crystalline polymers Their viscoelastic behavior is much more complex, because of the superposition of the behavior of the crystalline and amorphous domains. This superposition is not necessarily linear, and coupling of the responses can occur, particularly as the degree of crystallinity of a sample is increased and the amorphous domains become constrained by the crystalline domains. Because of this, the behavior of semi-crystalline polymers is much less uniform than their amorphous counterparts, displaying individual idiosyncrasies that often have to be described separately. 

Each of the pure polymers, P(3HB), a-PVA, and s-PVA, shows only one Ti value, indicating that the crystalline and amorphous domains of these pure polymers are smaller than is the scale of effective spin diffusion. Figure 21.14 shows the variation of the Ti values with the blend composition [120]. In the blends, the Ti values of PHB and PVA approach each other with increasing... 

If there are different domains leading to distinguishable WAXS intensity profiles, e.g. crystalline and amorphous phases coexisting in separate regions of a sample, the amount of each phase can be determined simply by separating the integral intensities which contribute to the WAXS from the different phases. In the case of crystalline and amorphous domains this analysis will lead to the degree of crystallinity. 

The determination of the crystallinity of polymer stationary phases is based on the differential solubility of the solute in crystalline and amorphous domains. In effect the solute senses only the amorphous regions, leading to an increase in retention volume with decreasing crystallinity. 

Fig. 9.13 A montage of five AFM images from cleaved (100) surfaces of quasi-singlecrystalline HDPE having long-range coherence over several long periods and showing no apparent borders between crystalline and amorphous domains (from Schonherr et al. (1995) courtesy of Elsevier).

Fig. 9.25 Schematic representation of (a) a spherulite of HDPE (b) a composite inclusion of attached crystalline and amorphous domains (from Lee etal. (1993a) courtesy of Elsevier).

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