Cold drawing process

As noted in Fig. 14.1 (a), commercial fibers of semicrystallme polymers are always cold-drawn after spinning to achieve further structuring through further macromolecular orientation and crystalline morphological changes, many of which are retained because of the low temperature of the cold-drawing processes. A typical stress-strain curve for a polycrystalline polymer at a temperature Tg < T < Tm appears in Fig. 14.6. 

Chapter 3(57) discusses the reduced permeability commonly observed when crystallinity is added to either a rubbery or glassy matrix. The reduction in permeability results from reductions in both the solubility and diffusivity parameters (58-62). This chapter also reviews the important effects of combined orientation and crystallinity which are dependent on whether orientation occurs during the formation of the barrier, or subsequent to it in a cold drawing process (62-66). The effects of process-induced orientation of several commercial barrier resins is considered in further detail in Chapter 12(67). 

Figure 5. Cold drawing process of a semicrystalline material. The dispersed crystal lamellae (a) under stress are arranged in a tilted stack formation (b).

In order to understand the stress-strain behavior of the SMPFs and strain-hardening during the cold-drawing process, MTS (Alliance RT/5, MTS Inc., USA) equipped with a 250 N load cell was used to test the fibers by tension at room temperature. The loading rate was 20 mm/min as per the ASTM D76/D76M standard. The fiber was stretched until failure to determine the maximum tensile strength. Figure 7.8 shows the test setup. 

During this cold-drawing process, vegetable oil is applied to the yarn as a lubricant and is washed off afterwards. In the case of nylon 6 melt-spinning is also used. The filaments are normally drawn to 350 00%. If the molecular weight of nylon 6 is between 20 000 and 25 000, hot-drawing is used. Unlike PET, both nylon fibers are fairly crystalline as spun. The crystal structures of nylon 66 and 6 fall into the categories of a, ji and 7. Almost all the commercially important nylons exist in either the a or the /3 form. 

It is appealing to view the cold-drawing process as the result of a loss of mechanical stability of the homogeneously deformed undrawn state. The existing theories of which I am aware use this idea in some way. These theories relate kinematic variables like strain, the rate of strain or the history of strain to the stress. To compare with observations it would be convenient, if not... 

The first nylon to be produced industrially was Nylon-6,6. The remarkable fact about the discovery of this polymer is not how it was first prepared from the two monomers, but how it was first prepared in a form suitable for a textile fiber. This depended on iiwention of the cold-drawing process, and this technique was discovered almost completely by accident, as we shall see. 

Fig. 1.5 Schematic of cold drawing process with transformation of the lamellar texture into a microfibrillar structure. (From Peterlin [24] used with permission.)...

Bekichev, V. 1. (1974). About Poly (ethylene terephthalate) Crystallinity in its Cold Drawing Process. Vysokomolek. Soed. A, 16(7), 1479-1485. 

Figure 10.17 demonstrated that the development of orientational order during a cold-drawing process can be followed by the registration of X-ray scattering patterns. These contain information about both the orientational texture of the crystallites and the orientational distribution of the chain axes in the amorphous regions. These orientational distributions show up in the azimuthal... 

Fig. 10.26. PEVA12 Azimuthal variation of the 110 reflection intensity Ino ip) top) and of the intensity at the halo maximum /haio(A) bottom), deduced from X-ray scattering patterns obtained at different stages of the cold-drawing process [125]...

COLD DRAWING PROCESS CAPABILITY CHART FOR COPPER AND COPPER ALLOYS... 

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