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CHAPTER 6-MANUFACTURED CELLULOSIC FIBERS - In 1664, English scientist Robert Hooke first to suggest that ppl ought to be able to produce fibrous materials that had same qualities as natural fibers - Nitrocellulose, first rayon fiber, obtained as early as 1832—found by attempting to imitate silkworm in extruding material that would harden in fiber form - Production of cellulosics declined rapidly: 21% 6% RAYON - First regenerated fiber - “artificial silk” - Rayon adopted in 1924 - “manufactured fiber composed of regenerated cellulose, as well as manufactured fibers com regenerated cellulose in which substituent have replaced not more than 15% of the hydroge hydroxyl groups”—FTC - Major fiber groups: Viscose rayon, cuprammonium rayon, & high-wet-modulus (HWM) rayon - Viscose rayon acct. for largest amt of rayon manufactured VISCOSE RAYON - Raw Materials o Wood pulp major source of cellulose used to produce o Cotton fibers, especially short cotton linters, also used o Most of timber used comes from eucalyptus, beech, or pine trees raised in nurseries o Chips of trees treated to remove lignin (binding agents) and to remove as much of resin o Dissolving pulp— more than 95% cellulose; purer grade than wood pulp used for making paper - Manufacture o Steeping or Slurring Quantity measured carefully by weight; placed in soaking press, or slurry press Remains immersed in solution of sodium hydroxide (caustic soda) for about an hr. Action of sodium hydroxide swells structure and separates polymer chains- much like mercerization Excess solution pressed out of pulp material; leaving slurry consisting of alkali cellulose o Aging Alkali cellulose shredded into small, fluffy particles— white crumbs
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These aged under carefully controlled conditions for several days Cellulose chains broken into shorter polymers that can be dissolved more easily o Xanthation Carbon disulfide added to white crumbs; produces sodium cellulose xanthate and changes color to bright orange-yellow Lg. xanthate groups push polymers farther apart Cellulose xanthate then soluble in sodium hydroxide o Dissolving and ripening Orange-yellow crumbs placed in dissolving tanks of dilute sodium hydroxide and aged Resulting solution is thick and viscous— viscose Solution now gold w/ consistency similar to that of honey o Filtration Viscose filtered to remove any insoluble particles At this pt., delustering agents or pigments for coloring may be added o Extrusion Forcing of viscous liquid through spinneret Solution is wet spun into dilute sulfuric acid bath Acid hydrolyzes xanthate—reversing xanthate formation and regenerating cellulose in form of long continuous filaments Filaments then wash to remove chemicals or impurities o **because of environ. Problems, viscose rayon no longer manufactured in US** - High-wet-modulus Rayon o Physical structure more like cotton o In process of manufacturing, alkali cellulose not aged after steeping step, cellulose xanthate dissolved
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