Saturday, June 4, 2011

REGENERATED CELLULOSE RAYONS

       The group includes viscose rayon cup rate rayon resin modified viscose types and magnified acetate rayon's  i e products which are substantially poly b glucose. They may be regarded chemically as swollen cellulose and their general reactions are similar to those of mercerised cotton though they are considerably more degraded. their shorter chain length causes them to have a considerably higher fluidity a greater susceptibility to chemical attack and a considerably greater swelling in water ( which results in a much greater extensibility when wet) than mercerised cotton . According to staudinger the mean chain length of cotton corresponds to 2,000 glucose units whereas the mean chain length of viscose probably contains not more than 300 to 450 units.
      Microscopically the main types of these rayon are fairly easily distinguished from each other . In addition to the normal forms there are products which have been de lustred by incorporation of pigments (titanium dioxide usually ) in the opining dope or by surface application of a pigment such as barium sulphate or by finely dispersed resins such as dimethyl urea or by substantive quaternary containing numerous air bubbles and one form which has a central canal . For examination of these types option solution of the main fibre by mounting in a medium of suitable ref active index is of great value.