1. rayon & acetate

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.



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

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1. rayon & acetate

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