Amorphous necking

One-step heat-set 500 mL tea-drink bottles, amorphous neck. 

Amorphous polymers may be cold drawn only below their glass transition temperatures above this temperature, they stretch but without forming a well-defined neck region. Crystalline polymers, by contrast, can be cold drawn at all temperatures up to almost their melting points. 

PET flakes have different crystallinities. The wall particles are oriented and crystallized, while the flakes from the neck and bottom of non-heat-set bottles are amorphous and require crystallization to prevent sintering before they can be subjected to SSP. Separating the thick amorphous PET flakes before SSP to circumvent the sticking risk and to improve the uniformity of the product has also been suggested [122], However, this may only be commercially acceptable if the separated flakes can be used in a final application. 

It can be assumed that the orientation of the amorphous regions is a result of the deformation of a rubber-elastic network. Therefore, it can be expected that crystallization during spinning occurs at the neck, where the deformation is maximal. The amorphous phase develops into a load-bearing factor which is related to its orientation, as expressed by Hermans orientation factor. 

Neck, V., Muller, R., Bouby, M., Altmaier, M., Rothe, J., Denecke. M. Kim, J. I. 2002. Solubility of amorphous Th(lV) hydroxide - application of L1BD to determine the solubility product and EXAFS for aqueous speciation. Radiochimica Acta, 90, 485 -494. 

To a 12 L, 3-neck round bottom flask fitted with a mechanical stirrer, thermometer and an addition funnel was added the (Z)-l-bromo-2-carbomethoxy-3-phenyl-2-propene (400.0 g, 1.57 mol) and methanol (4 L). The mixture was warmed to 50°C and a solution of sodium sulfite (199.0 g, 1.57 mol) dissolved in water (4 L) was added over 75 min while the internal temperature of the flask was maintained at 50°C. After the addition was complete, the clear solution was allowed to stir at 50°C for an additional 45 min. The reaction mixture in solution was taken to the next step without additional purification. The (Z)-2-carbomethoxy-3-phenyl-2-propene-l-sulfonic acid sodium salt may be isolated by concentration to an amorphous powder. 

The lamellae slip rigidly past one another. Lamellae parallel to the direction of draw cannot slip thus, spherulites become anisotropic. At this stage, at which necking begins, the strain is accommodated almost entirely by the interlamellar amorphous component. 

Finally, stress whitening after neck formation in tensile bars of crystalline polymers imder plane stress conditions may be associated with some kind of craze-II-formation, in analogy to the corresponding observations in amorphous PC. 

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