Solidified filaments

Cellulose ucelate is converted into libers by solvating the polymer in an acetone solution which is ihen spun by a process called tin spinning. In ihe spinning process, the polymer solution is metered through a spinneret into a column cimuiining warm air which evaporates the acetone. The solidified filaments are oiled and package collected al the base uf llte spinning lube. 

In melt spinning, polypropylene in powder or pellet form is heated above the melting point and then is extruded through fine orifices of a spinneret into the air. Below spinneret in the air thin streams are intensively cooled and subjected to an intense stretching. During cooling the liquid streams sohdify. Finally, solidified filaments are taken by final take-up device. 

Filament yarn in the spinning of manufactured filaments, fiber-forming substances in the plastic or molten state, or in solution, are forced through the fine orifices in a metallic plate called a spinneret, or jet, at a controlled rate. The solidified filaments are drawn-off by rotating rolls, or godets, and wound onto bobbins or pirns. There are several methods of spinning manufactured filaments ... 

The group had constructed a molecular still and chose the polyester derived from propylene glycol and hexadecamethylene dicarboxylic acid for the first experiment. A waxy polyester was prepared and heated in the molecular still for an extended period. Tbe product was now tough with a chain length of about forty repeating units. Filaments of the ester could easily be drawn "taffy-like" from the melted product. When stress was applied to the solidified filaments, the thin opaque cylinder of filament separated into two sections joined by a thinner section of transparent fiber. As pulling continued, the transparent section grew till the opaque sections disappeared. 

The solidifying filament was drawn through the coagulation bath and onto the winder. The tale-up speed varied from 20 m/min to 60 m/min. Next, the bobbins with collected filaments were washed in runnning water for 24 h, dried in a vacuum oven at room temperature for 4 h and then at 90 ""C for 24 h. No postspinning treatments were performed. 

Two different in situ fibril formation techniques can be employed to create the reinforcing microfibrils cold drawing of the solidified filament at a temperature below the... 

Semi-crystalline samples, on the other hand, deposited at high speeds produce thinner filaments due to the inherent stretching of the crystallising polymer at the tip of the nozzle. However, in this case study (Fig. 7.16), where the variation of speed was relatively low, there were no significant variations in the crystals orientation (i.e. (P2)i0nmi/s = 0.04 to (P2)30mm/s = 0-057) ui thc Solidified filament. 

Two different in situ fibril formation techruques can be employed to create the reinforcing fibrils cold drawing of the solidified filament at a temperature below the melting temperature (7) ) of each blend constituent [61-75] or hot-stretching directly from the melt at a temperature above both polymers glass transition temperatures [76-80]. Cold drawing generally results in a better molecular orientation. 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

X The nascent acetate lilamems leav ing ihe jet are carried through the vertical spinning tube which may he 10-20 leei (3-6 meters) long and from 6 io 12 inches I5 lo 30 centimeters) in diameter. Hot air moving concurrent or countercurrent lo the path of the filaments evaporates most of the aceione anti solidifies the liquid stream into the acetate filament. 

The filaments which grow from a dirt particle are reminiscent of dendrites which often form near a surface at which liquid solidifies. The beautiful patterns of snowflakes seen under magnification are dendritic structures, for example. It is now generally believed that when a solidifi-... 

Dopes like these exhibit mesomorphic behaviour they are solid at room temperature, but at higher temperature become less viscous and show optical anisotropy. If heated further, the clearing temperature (Td) is reached at which a phase transformation takes place from an anisotropic solution to an isotropic solution. With increasing polymer concentration both Ta and the melting point of the dope (T ) increase. Fibres of the highest quality (tenacity) are obtained by spinning at temperatures between and Ta, but as low as possible, The spun filament is solidified in a coagulating bath, preferably at temperatures below 5 °C. 

Fig. 5.23. During formation of the cocoon, the worm ejects the viscous content of the glands in the form of a filament which solidifies on contact with the air.

The filaments then descend through a cooling chamber which is enclosed 80 that they shall be protected against draughts. The newly solidified nylon is virtually free from moisture and there is a tendency for it to elongate slightly as it establishes equilibrium with the atmospheric humidity. If this... 

The polymer is heated until molten, forced through an appropriately sized aperture, and solidified as it is drawn into a fibre the commercial process produces multifilament fibres rather than single strands and cross-linking of the filaments adds strength to the final product. The composition of Nicalon fibres is not as simple as this description implies carbon and silica are present in addition to P-SiC. 

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