Polymer threading

Prior to deposition on a moving belt or screen, the molten polymer threads from a spinnerette must be attenuated to orient the molecular chains of the fibers in order to increase fiber strength and decrease extendibiUty. This is accompHshed by hauling the plastic fibers off immediately after they have exited the spinnerette. In practice this is done by accelerating the fibers either mechanically (18) or pneumatically (17,19,20). In most processes, the fibers are pneumatically accelerated in multiple filament bundles however, other arrangements have been described wherein a linearly aligned row(s) of individual filaments is pneumatically accelerated (21,22). 

J. W. Hoyt and R. H. J. Sellin. Polymer threads and drag reduction. Rheol Acta, 30(4) 307-315, July-August 1991. 

Fig. 1.5.9 Soft-shell poly(/>-fer-butylstyrene) particles connected by polymer threads. The monomer and initiator flow rates were 2.7 dm3 min-1 and 9 cm3 min-1 and the boiler and initiator reservoir temperatures were 50°C and 92°C, respectively. (From Ref. 67.)...

In his experiments with centrally injected polymer solutions, Bewersdorff (1984) showed in flow visualization experiments that the injected polymer solution formed a liquid thread which remained intact down the entire length of the pipe (1/d = 270), provided that the concentration of the injected polymer solution exceeded 0.3%. This polymer thread is deformed by turbulent flow, i.e., it can undergo elongation by stretching and even from loops (see Fig. 4). 

This was in contrast to a glycerine solution having the same zero-shear-viscosity which was dispersed after a few pipe diameters at a relatively low Reynolds number. For injection concentrations of 0.25% and 0.3%, the polymer thread did not remain... 

Fig. 4. Examples of the behaviour of a polymer thread (c, = 500 ppm, Re = 70000) in turbulent pipe flow. Pictures taken on a high speed camera at a frequency of 1000 exposures per second serve to illustrate this effect (Bewersdorff 1984)...

Bewersdorff HW (1982) Effect of centrally injected polymer thread on drag in pipe flow Rheol Acta 21 587... 

Vleggaar J, Tels M (1973) Drag reduction by polymer threads Chem Eng Sci 28 965... 

Keywords Additives, Blends, Complexation processing, Cyclodextrins, Polymers, Threading... 

It was in 1976 that Ogata et al. reported the synthesis of inclusion polyamides [78]. When /1-cyclodextrin was stirred with aliphatic diamines in water, precipitates were formed and they were characterized as inclusion compounds. Condensation of these inclusion amides with isophthaloyl or terephthaloyl chloride yielded polyamides encircled by many of the cy-clodextrins, i.e., the first pseudopolyrotaxanes. Ogata et al. likened them to a train passing through many tunnels . The solubility and water absorption of the pseudorotaxanes were greater than those of the naked polymer threads. Differential thermal analysis experiments showed that the thermal properties of the pseudorotaxanes were different both from the naked threads and from /1-cyclodextrin. 

Anderson s group reported the synthesis of cyclo dextrin-encapsulated conjugated polyrotaxanes that were the first examples of conjugated polyro-taxanes, i.e., conjugated polymers threaded through macrocyclic units with bulky stoppers (Scheme 21) [123]. The conjugated polyrotaxane was pre-... 

Figure 23 Helical ID polyiotaxane 20. (a) Overall Structure of 20 showing cucurbituril beads threaded on a helical ID coordination polymer. Counter anions are omitted for clarity, (b) The helical ID coordination polymer threading cucurbituril beads (omitted) in 20.

Smith, R. E., and Tiederman, W. G., The mechanism of polymer thread drag reduction, Rheol. Acta,30, 103-113(1991). 

Experiments are reported in which.a concentrated polymer solution is injected into the centre of a turbulent pipe flow. Drag reduction is obtained even if the polymer forms a liquid thread which is conveyed in the core region of the flow, i.e. no significant part of the injected polymer is present in the near-wall region. This type of drag reduction differs from that found in homogeneous solutions and seems to be due to an interaction between the polymer thread and the large-scale structure. 

If the concentration of the injected polymer solution is decreased, drag reduction increases much more quickly from the injection point. This may be explained by the fact that no polymer threads or strings are observed. Therefore the polymer is transported very quickly to the wall region. 

In these experiments the interaction between the polymer thread... 

Vleggaar, J. and Tels, M. Drag reduction by polymer threads. Chem. Engin. Sc. 28 (1973) 965-968. 

A wide range of experimental techniques has been proposed through the years to measure the interfacial tension. Most popular has been the pendent drop technique but there has been increasing interest in techniques based upon breaking molten polymer threads. Methods of measurement of interfacial tension are summarized in Table 6.1 and values of the interfacial tension for different polymer-melt pairs are summarized in Table 6.2. The larger the polarity difference is, the larger the interfacial tension. Thus the greatest interfacial tension in Table 6,2 is for polyethylene and polyamide 6,... 

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