Stretch spinning

The second ceUulosic fiber process to be commercialized was invented by L. H. Despeissis (4) in 1890 and involved the direct dissolution of cotton fiber in ammoniacal copper oxide Uquor. This solvent had been developed by M. E. Schweizer in 1857 (5). The cuprammonium solution of ceUulose was spun into water, with dilute sulfuric acid being used to neutralize the ammonia and precipitate the ceUulose fibers. H. Pauly and co-workers (6) improved on the Despeissis patent, and a German company, Vereinigte Glanstoff Eabriken, was formed to exploit the technology. In 1901, Dr. Thiele at J. P. Bemberg developed an improved stretch-spinning system, the descendants of which survive today. 

The manufacture of cuprammonium rayon is based upon Schweitzer s discovery that cellulose is dissolved by a solution of copper hydroxide in ammonia. Attempts to utilize this discovery for the preparation of fibres were made by Depaissis, but Pauly, in 1897, was the first to work the process on a commercial scale. His venture did not survive and it was left in abeyance until Bemberg took it up again in 1919 and succeeded because he introduced the method of stretch spinning, based on earlier work by Thiele. 

Additives usually to porous moisture absorbent fiber Fluorine resin treatment Low comonomer, high orientation stretch-spinning process... 

The solution is spun by the stretch-spinning process, i.e., it is carried away from the spin cone by warm water and drawn or stretched. The fiber is then washed free from copper and ammonia residues by an acid bath (7%H2S0J. 

Stretch spinning n. A term used in the manufacture of rayon. Rayon filaments are stretched while moist and before final coagulation to decrease their diameter and increase their strength. 

FIGURE 4.4 Zero-temperature rate eonstant for Zeeman relaxation in collisions of rotation-ally ground-state NH( S) moleeules in the maximally stretched spin level with He atoms. Such field dependence is typical for Zeeman or Stark relaxation in ultracold collisions of atoms and molecules without hyperfine interaction. The variation of the relaxation rates with the field is stronger and extends to larger field values for systems with smaller reduced mass. (Adapted from Krems, R.V., Int. Rev. Phys. Chem., 24, 99, 2(X)5. With permission.)... 

H. Aizawa and F. Ishida (1962), Process and apparatus for stretch-spinning cuprammonium rayon. United States Patent 3049755. 

The quantum numbers tliat are appropriate to describe tire vibrational levels of a quasilinear complex such as Ar-HCl are tluis tire monomer vibrational quantum number v, an intennolecular stretching quantum number n and two quantum numbers j and K to describe tire hindered rotational motion. For more rigid complexes, it becomes appropriate to replace j and K witli nonnal-mode vibrational quantum numbers, tliough tliere is an awkw ard intennediate regime in which neitlier description is satisfactory see [3] for a discussion of tire transition between tire two cases. In addition, tliere is always a quantum number J for tire total angular momentum (excluding nuclear spin). The total parity (symmetry under space-fixed inversion of all coordinates) is also a conserved quantity tliat is spectroscopically important. 

One can note some interesting features from these trajectories. For example, the Mulliken population on the participating atoms in Figure 1 show that the departing deuterium canies a full electron. Also, the deuterium transferred to the NHj undergoes an initial substantial bond stretch with the up spin and down spin populations separating so that the system temporarily looks like a biradical before it settles into a normal closed-shell behavior. 

We now compare the results calculated for the fundamental frequency of the symmetric stretching mode with the only available experimental datum [78] of 326 cm . The theoretical result is seen to exceed experiment by only 8.3%. It should be recalled that the Li3 and Li3 tiimers have for lowest J the values 0 and respectively. Thus, the istopic species Li3 cannot contribute to the nuclear spin weight in Eq. (64), since the calculations for half-integer J should employ different nuclear spin weights. Note that atomic masses have been used... 

Carbon and Graphite Fibers. Carbon and graphite fibers (qv) are valued for their unique combination of extremely high modulus and very low specific gravity. Acrylic precursors are made by standard spinning conditions, except that increased stretch orientation is required to produce precursors with higher tenacity and modulus. The first commercially feasible process was developed at the Royal Aircraft Fstablishment (RAF) in collaboration with the acrylic fiber producer, Courtaulds (88). In the RAF process the acrylic precursor is converted to carbon fiber in a two-step process. The use of PAN as a carbon fiber precursor has been reviewed (89,90). 

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