Regenerated cellulosic fibers

Neha Singh, Assistant Professor, TD, NIFT, New Delhi

Regenerated cellulosic fibre

Viscose rayon Polynosic Modal Lyocel Cellulose acetate Cellulose triacetae

Viscose Rayon

The earliest processes for making rayon utilized natural materials that were fibrous in

nature , such as short cotton linters that could not be spun into yarns, or fibrous wood

pulp.

The pulp dissolved in chemicals that broke down the molecular structure of the fiber

somewhat , while still retaining a substantial quality of long chain molecules.

The solution was forced through a metal plate that had small holes in ti, exposed

either to heated air or to a chemical solution and then formed in to a long , hair like

filament

Properties Physical appearance

Colour- rayon fibers are normally white in color. But they can have color added to the solution from which the fibers is to be spun. This provides a permanently locked in color through a process known as solution dyeing.

Lustre- The lustre of rayon can be modified by the addition of titanium dioxide

Shape- man made fibers can be manufactured in any length and diameter.

Cross-section- irregular circle with serrated edges.

Longitudinal – longitudinal lines called striations

“Galaxy”- a Y–shaped viscose rayon fibre with highly absorbency and bulk

Viloft - a flat cross sectional viscose rayon fiber gives a unique soft handle and pleasing drape

Physical properties-

Strength- the strength of viscose rayon is low. The lower polymer chain length of viscose when compared with polymer length of cotton and linen is responsible for this lower strength of viscose.

Tenacity- when dry- 0.73 to 2.6, when wet 0.7 to 1.8 g/d

Density and specific gravity- 1.5-1.53

Crystallinity 35-40%

Elasticity and resilience- the elastic recovery of rayon is low, as is its resiliency . Untreated rayon tends to stretch and wrinkle badly.

Absorbency and moisture regain- the molecular structure of viscose is more amorphous that that of cotton or linen, making the viscose fibres more absorbent than natural cellulosic fibers viscous accepts dyes readily.

Dimensional stability- viscose rayon stretch and having low elastic recovery tends

to remain stretched.

Heat and electrical conductivity- The conductivity of both heat and electricity of

viscose rayon is satisfactory, so that the fiber is reasonably comfortable in hot

weather and does not build up static electricity.

Chemical Properties

Chemical reactivity- the amorphous molecular structure of viscose makes more

susceptible to action of alkalis and acids. Acids attack viscose more readily than

cotton or other cellulosic fibers.

Viscose is more susceptible to damage from alkalis as well.

Micro-organisms and insects- viscose is subjected to damage from mildew and rot

producing bacteria. Silver fish will attack the fiber.

Care in storage is necessary to prevent exposure of the fabric to conditions that

encourage mildew and silverfish.

Exposure to sunlight will deteriorate viscose rayon's more rapidly than cotton.

Cuprammonium Rayon

Properties- quite similar to those of viscose rayon. The fiber has a somewhat more

silk like appearance and feel and is after manufactured in fiber diameter.

Cross-section-round cross section and smooth longitudinal appearance

fibers can be made into very lightweight fabrics.

A good conductor of heat and fairly absorbent , it is especially suitable for use in

warm weather clothing.

Cellulose acetate and triacetate

In the 1920s experimentation with regeneration of cellulosic materials led to the

discovery of a by product called cellulose acetate.

Triacetate is another modification of cellulose fiber.

Appearance

Shape- in microscope appearance cellulose diacetate or triacetate are very similar.

Normally both fibers are clear and have irregular mutilobed shape in cross section

rather like popcorn.

Longitudinal- Broad striations

SEM mage of cellulose acetate cross-section

Polarized microscope image of cellulose acetate filament- striations on surface

Luster and color- if acetate and triacetate have not been treated to decrease luster,

both fibers will have a bright appearance and good luster.

Strength- both acetate and triacetate have very low strength. Both are weaker wet

than dry.

Crystallinity : 40%

Tenacity: 2.5 g/d

Elongation 16-18%

Moisture regain: 6.5 %

Density and specific gravity- lower than rayon or cotton at 1.32 and 1.3

Elasticity and resilience- acetate has poor elastic recovery and poor wrinkle

recovery.

Absorbency and moisture regain- 6.3 to 6.5 %

Dimensional stability- acetate fabrics may exhibit relaxation shrinkage on

laundering unless they are pretreated.

Heat and Electrical conductivity- neither heat nor electrical conductivity of acetate

and triacetate are as good as the conductivity of other cellulosic fibers.

Both fibers tend to build up static electricity charges, and neither acetate nor

triacetate is as cool to wear as cotton, linen or rayon.

Heat- thermoplastic fiber (they will soften and melt with the application of heat)

Effect of acid- resistant to cold, dilute acids, decomposed by strong acids, dissolves

in acetic acid

Effect of Alkali- good resistance to week alkali, saponified by strong alkali

Effect of bleaches- hydrogen peroxide or sodium perborate bleach recommended at

temperature below 90 degree F.

Effect of organic solvents- petroleum products safe for use. Dissolved by acetone.

Resistance to micro organisms and Insects- mildew will grow on acetate or

triacetate if the fabrics are incorrectly stored. The growth causes discoloration of the

fabric but no serious loss of strength.

Moth or carpets beetles do not attack either fiber.

Heavily starched or sized acetates are prone to attack from silver fish.

Environmental condition- extended exposure to sunlight will cause a loss of strength

and deterioration of acetate fabrics.

Cellulose acetate- properties

Microscopic appearance Crystallinity : 40% Tenacity: 2.5 g/d Elongation 16-18% Moisture regain: 6.5 % Thermal properties: Heat sensitive, softens at 175-1900C Chemical properties: More sensitive to acids than cotton

Effect of acids: Acids hydrolyze Effect of alkalis: Resistant to alkalies Effect of bleaches: Same as cotton fibres

Effect of sunlight:

Modal Comfort factors

- More stronger than viscose in wet and

dry state

- One problem is the almost perfectly

circular cross-sectional shape; this

makes leaner yarns than irregularly

shaped standard viscose rayon.

Care factors

- May be laundered or dry cleaned; easy to

iron

- But gradually fibrillate on wet processing

Cross-section of modal fibres

Lyocell Comfort factors- More absorbent than cotton

Care factors- May be laundered or dry

cleaned; easy to iron- But gradually fibrillate on

abrasion in wet state Produced by Acordis and

Lenzing AG. More costly than viscose rayon

Cross section of lyocell

Surface view of lyocell

Fibrillation of lyocell fibre

Regenerated protein fibre- soybean protein fibre

Soybean protein fibre (SPF) is produced from the residual cake

after oil is extracted from soybean seeds.

SPF fabrics have cashmere feel but is softer and smoother than

cashmere.

The moisture absorption is similar to that of cotton

It has silk like luster and elegant drape.

The elastic recovery rate is 55.4% where for other fibres it is 60-

70%.

Good colour fastness

Soybean seeds

Soybean fibre products