TXA205 Exam 2 Material - TXA205 Exam 2 Material Section...

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TXA205 Exam 2 Material Section II-5: Regenerated cellulosic fibers - Regenerated cellulosic fibers are produced from naturally occurring cellulose polymers . These cellulose polymers do not naturally occur as fibers; thus, processing is needed to convert them into fiber form. - Rayon - wet spinning - Lyocell - wet spinning - Cellulose acetate – dry spinning - Naturally occurring cellulose polymers - wood (major source; paper is cellulose) - Agriculture Residues - Cotton Linters - Recycled Cellulose - Cutting trees is not necessarily a bad thing: A healthy forest density is needed to - Prevent wildfire - Prevent infections and improve the growth of trees - Sustainable - Spinning process: - Preparing a viscous dope (melt or solution) - Forcing or extruding the dope through an opening in a spinneret to form a fiber - Solidifying the fiber by coagulation, evaporation, or cooling - Preparing the viscous dope: Melt or solution? - Some polymers can melt; they become liquids at a temperature higher than their melting points (Nylon, polyester, olefins, etc.) - Some polymers do not melt: At high temperatures, they decompose. However, they can be dissolved in some solvents, forming solutions. - If you put sugar in a frying pan, it becomes a liquid; this is called melting - if you put sugar in a glass of water, the sugar disappears and the water becomes sweet, this is called dissolving - Melt spinning: (best method) - nylon, olefin, polyester, saran - steps: 1. resin solids are melted in autoclave 2. fiber is spun into the air 3. fiber solidifies on cooling - least expenive - direct process - high spinning speeds - no solvent, washing, etc. required - fibers shaped like spinneret hole - Dry spinning: (good method) - acetate, acrylic, modacrylic, spandex (major method) - steps: 1. resin solids are dissolved by solvent 2. fiber is spun into warm air 3. fiber solidifies by evaporation of the solvent - direct process - solvent required - no washing, etc. required - Wet spinning: (worst method) - acrylic, rayon, spandex - steps: 1. raw material is dissolved by chemicals 2. fiber is spun into chemical bath 3. fiber solidifies when coagulated by bath - oldest process - most complex - weak fibers until dry - washing, bleaching, etc. required before use - Why don’t we use melt spinning?
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- Because currently, we have no other choices: Cellulose polymers do not melt ; they do not dissolve in ordinary solvents, either. - Rayon: - Wet spinning of rayon uses very toxic materials (carbon disulfite); 25% very toxic - Regular rayon - Length: Staple or filament - Diameter: Fine to coarse - Crimp: Can be controlled - Color: Can be controlled - cross section and surface contour of rayon: serrated, striated (some examples) - improved rayon: High wet modulus rayon has better quality and acceptable dimensional stability, which can be machine washed (regular rayon isn’t machine washable) - Chemical structures of viscose rayon: Chemical structures Regular rayon High wet modulus rayon Polymer Cellulose Cellulose Degree of polymerization
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This note was uploaded on 06/19/2008 for the course TXA 205 taught by Professor Craig during the Spring '07 term at University of Texas at Austin.

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TXA205 Exam 2 Material - TXA205 Exam 2 Material Section...

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