Cooling fiber orientation

Analogous results have been found for stress relaxation. In fibers, orientation increases the stress relaxation modulus compared to the unoriented polymer (69,247,248,250). Orientation also appears in some cases to decrease the rate, as well as the absolute value, at which the stress relaxes, especially at long times. However, in other cases, the stress relaxes more rapidly in the direction parallel to the chain orientation despite the increase in modulus (247.248,250). It appears that orientation can in some cases increase the ease with which one chain can slip by another. This could result from elimination of some chain entanglements or from more than normal free volume due to the quench-cooling of oriented polymers. 

Fibers oriented by stretching to 4 x original length by cold drawing (two pulleys at different speeds) or by spin drawing as it is being cooled... 

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. 

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

At lower temperatures (180-200°C) the material was processed without melting the LCP and a real composite structure with solid LCP fibers in the PP matrix was formed. When processing was done above the Tm of the LCP (280°C), all the material was molten during processing and a compositelike blend morphology was created in situ during cooling of the oriented melt phase. 

Fibers are thin threads produced by extruding a molten polymer through small holes in a die, or spinneret. The fibers are then cooled and drawn out, which orients the crystallite regions along the axis of the fiber and adds considerable tensile strength (Figure 31.3). Nylon, Dacron, and polyethylene all have the semicrystalline structure necessary for drawing into oriented fibers. 

The next stop is to cool the nylon below its Tg without removing the stress, retaining its molecular orientation. The nylon becomes rigid with a much higher elastic modulus in the tension direction [15,000 to 20,000 MPa (2 to 3 x 106 psi)]. This is nearly ten times the elastic modulus of the unoriented nylon-66 plastic. The stress for any elastic extension must work against the rigid backbone of the nylon molecule and not simply unkink molecules. This procedure has been commonly used in the commercial production of man-made fibers since the 1930s via DuPont. 

We use the spinning process to make polymer fibers and filaments that can be converted into fabrics and cordage. During fiber spinning, molten polymer is pumped through holes in a plate to form a multiplicity of strands that are rapidly stretched and cooled. The finished product comprising oriented fibers is either wound up on spools or converted directly into a non-woven fabric. 

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