1. rayon & acetate
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8/13/2019 1. Rayon & Acetate
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Conventional batch process for viscose rayon manufacture
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Cross-section of rayon fiber
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Properties of High Tenacity Rayon
Denier(De’)
Strength(dry, g/d)
Strength(wet, g/d)
Elongation(dry, %)
Elongation(wet, %)
Young’sModulus(kg/mm2)
Crystallinity(%)
HighTenacityRayon
1.5 4.0 2.9 22 28 800 29
RegularRayon 1.5 2.9 1.7 16 19 800 33
Cotton 1.5 4.6 4.5 5 7 850 61
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Properties of Modal
• Produced from beech wood (Lenzing, Austria)
• Higher tenacity, stronger and more stable than rayon and cotton
• Kind of HWM(High Wet Modulus), and different from general polynosic in terms of degree of
polymerization and crystallinity
• Overall physical properties
- wet modulus > 0.5, higher whiteness than cotton, gravity ~ 1.5, degree of polymerization ~ 400, high
wet modulus with small elongation rate (%)
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Modal vs. Polynosics
• Degree of polymerization
- Modal ~ 400, Polynosic > 500
• Production
- Modal: Viscose solution containing amine-based additives is extruded through zinc-concentrated
coagulation bath, typicall 40~50 m/min, using typical spinning machine for rayon fiber
- Polynosic: Viscose solution of high DP is spun into coagulation bath of low acidity at low temperature,
and then went to drawing process with higher draw ratio
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Spinning of Polynosics
A: viscose solution
B: spinneret
C: coagulation bath (1% H2SO4)
D: guiding roller
E: godet roller
F: guiding roller
G: take-up bobbin
H: side-view of E
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Spinning of Cuprammonium Rayon
A: spinning unit
B: guiding funnel
C: water inlet
D: steel rod
E: guiding roller
F: take-up bobbin
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Comparison: Viscose vs. Lyocell
Viscose Lyocell®
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Comparison: Viscose vs. Lyocell
• Problems in viscose process
- Environmentally unfriendly by-products (Sulfur Compounds, ammonia, Cu salts, Zn Salts), which
must be completely removed or chemically disposed of before discharged into the environment.
- Viscose not entirely satisfactory for making cotton like fabrics – poor mechanical properties, high
swelling and increase in wet elongation under low stress
• Advantages of NMMO Process
- Process utilizes materials that are environmentally clean and recycling of the solvent is an internal
part of the process.
- Apart from environmentally friendly the NMMO process for the production of cellulosic fibers is
potentially more cost effective and faster than the viscose process.
- Lyocell process take up to three hours to produce fibers compare to 40 hours in the case of viscose
process
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Overall Properties
• Structure and properties of Lyocell®
- since Lyocell is just dissolved cellulose in NMMO and not making any cellulose derivatives, it has a
different molecular structure than other regenerated cellulosic fibres.
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Diagram of Lyocell process
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Cellulose acetate process
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Position of –OHs during 1,4-addition of glucose
Cellulose from b-glucose Starch from a-glucose : amylose, amylopectin
• Amylose : linear polymer of glucose linked
mainly by α(1→4) bonds
• Amylopectin : highly branched polymer of glucose
having α(1→6) bonds