siurvey of industrial chemestry - chapter 17

8/17/2019 Siurvey of Industrial Chemestry - chapter 17

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Chapter 17

Fibers

1.

HISTORY, ECONO M ICS,

AND

TYPES

OF

FIBERS

Fibers have been used for thousands of years to make various textiles.

For centuries certain natural products have been known to make excellent

fibers.

Probably

the first

synthetic

fiber

experiment came with

the

work

of

Christian Schonbein,

who

made cellulose trinitrate

in 1846. After

breaking

a

flask of

nitric

and

sulfuric acids,

he

wiped

up the

mess with

a

cotton apron

and

hung

it in

front

of the

stove

to

dry. Cellulose trinitrate

was

developed

by

Hilaire

de

Chardonnet

as a

substitute

for

silk

in

1891,

but it was

very

flammable and was soon nicknam ed mother-in-law silk," being an

appropriate gift

for

only disliked persons. W hen rayon came along

in

1892,

Chardonnet silk" was soon forgotten. Then the entirely synthetic fibers

came, with the pioneering work of W. Carothers at Du Pont synthesizing the

nylons in 1929-30. Com mercialization occurred in 1938. Polyesters were

made by

Whinfield

and

Dixon

in the

U.K.

in

1941. They were

commercialized in 1950.

It is important to understand the different types of fibers. Classes are best

differentiated

based

on

both

the

origin

of the fiber and its

structure.

The

structure

and

chemistry

of

many

of

these polymers

was

discussed earlier

in

Chapter

14.

Table

17.1

contains

a

list

of the

three important types

of

fibers—natural, cellulosic,

and noncellulosic—as

well

as a

list

of

specific

polymers

as

examples

of

each type.

The

ones marked with

an

asterisk

are

the most important.



Table 17.1 Types of fibers

Natural

From plant sources—all

are

c ellulose polymers

a. *

Co tton

(from

the cotton plant)

b. Flax (from

blueflowers)—used

to m ake linen

c. Jute (from

an

East

Indian plant)—used

fo r

burlap

and

twine

2. From animal sources—all are proteins

a.

Silk (from the silkworm)—mostly glycine and alanine

b.

*Wool (from sheep)—complex m ixture

of

amino acids

c.

Mohair

(from

the Angora

goat)

3.

From inorgan ic sources

a.

Asbestos—mostly calcium and magnesium silicates

b. Glass—silicon

dioxide

Cellulosic

These

fibers are

also called semisynthetic since

the

natural cellulose

is

modified

in

some way chemically.

1.

*Rayon (regenerated cellulose)

2. *C ellulo se acetate

3. Ce llulose triacetate

Noncel lu los i c

These are entirely synthetic, made from polym erization of small mo lecules.

1.

*N ylons 6 and 6,6

2.

*Polyester— poly(ethylene terephthalate)

mostly

3. *Polyolefms— polypropylene mostly

4. Acrylic—polyacrylonitrile

5. Polyurethane

Referring back to Fig. 16.1, we see that the value of U.S. shipments for

cellulosic and

noncellulosic

fibers,

though quite small compared

to

plastics,

is still a big industry. W hile Plastics M aterials and Resins (NA ICS 3 25211 )

in 1998

was

$44.9 billion, N oncellulosic Fibers (NA ICS 325222)

was

$10.5

billion and Cellulosic Fibers (NAICS 325221) was $1.5 billion. These tw o

fibers together have a $12.0 billion value, which is 3% of Chemical

Manufacturing.

W e must also remember that many of these fibers are sold

outside the chemical industry, such as in Textile Mill Products, Apparel, and

Furniture,

all

large segments

of the

economy.

The

importance

of

fibers

is

obvious.

In

1920

U.S. per

capita

use was

30 Ib/yr, whereas

in

1990

it was 66

Ib/yr. From 1920 to 1970 the most important fiber by far was

cotton.



Year

Figure 17.1 U.S. production of fibers. Source: Chemical and Engineering News,

Chemical and

Economics

Handbook,

and the

U.S. Department

of

Agriculture/Foreign

Agriculture Service)

However, synthetic fibers (cellulosic and noncellulosic) increased much

m ore rapidly in importance, w ith cellulosics boom ing between W orld W ars I

and

II and noncellulosics dominating after World War II, w hi le all that time

cotton showed only a steady pace in com parison. The m ore recent

competition between the various fibers in the United States is given in Fig.

17.1.

N ylon was originally the most im portant synthetic (195 0-197 1) but

polyester now leads the market (197 -present). For a few years (1970-1980)

acrylics were third in production, but since 1980 polyolefms have been

rapidly increasing. Po lyolefm s are now second o nly to polyester in synthetic

fiber prod uction. Cotton, being an agricultural crop, certainly dem onstrates

its

variable production w ith factors such as weather and the econom y. It is

an

up-and-do wn industry m uch m ore so than the synthetics.

The student should also review Chap ter 1, Table

1.16,

where the top

polym er production is given numerically. Overall a 1.8% per year growth

was recorded for 1990-2000 in synthetic fibers. A net decrease in the

cellulosics

of 3.6% per year shows their dim inishing importance. A crylics

also decreased 3.9% ann ually in this period. The rising star is po lyole fm s,

which

increased 5.8% per year in the past decade.

otton

Polyester

Polyolefms

Nylon

crylics

i

o

o

o

u

n

d

s



U.S. price trends show that cotton and polyester are the most popular for

good

reason: they

are the

cheapest. N ylon

and

acrylic have

had

price

increases

over the last few years, part of which may be due to improvements

and

safeguards needed to manufacture their precursors acrylonitrile,

butadiene, and

benzene, which

are on

carcinogen lists.

2. PROPERTIES

OF

FIBERS

It

is important to understand some common terms used in this industry

before

studying

fiber

properties

or

individual fibers.

The term fiber

refers

to

a one-dimensional structure, something that is very long and thin, with a

length at least 100 x its diameter. Fibers can be either staple fibers or

monofilaments.

Staple fibers are bundles of parallel short fibers.

Monofilaments are extruded long lengths of synthetic fibers. Monofilaments

can be used as sing le, large diameter fibers (such as in fishing line) or can be

bundled

and

twisted

and

used

in

applications similar

to

staple fibers.

Fabrics are

two-dimensional materials made from

fibers.

Their primary

purpose is to

cover things

and

they

are

commonly used

in

clothes,

carpets,

curtains,

and upholstery. The motive for covering may be aesthetic, therm al,

or acoustic. Fabrics are made out of yarns or twisted bundles of fibers. The

spinning

of

yarns can occur in two ways: staple

fibers

can be twisted into a

thread

( spun yarn )

or

monofilaments

can be

twisted into

a

similar usable

thread

( filament yarn" or continuous filament yarn"). A ll these definitions

are important in order to understand the conversation of the fiber industry.

The tensile properties of fibers are not usually expressed in terms of

tensile

strength (lb/in

2

or kg/cm

2

). The strength of a fiber is more

often

denoted

by

tenacity.

Tenacity (or

breaking tenacity)

is the

breaking strength

of a fiber or yarn in force per unit denier (Ib/denier or

g/denier).

A denier is

the weight in grams of 9,000 m of fiber at 7O

0

F and 65% relative humidity.

A denier

defines the

linear density

of a fiber

since

it

depends

on the

density

and the diameter of a fiber. To give you an idea of common values of

deniers for fibers, most commercially useful fibers are

1-15

den ier, yarns are

15-1600 den ier, and monofilament (when used singly) can be anywhere from

15 denier on up. Table 17.2 lists common values of tenacity for various

fibers and

compares these values

to

tensile strength. Tenacities

can be

converted into tensile strength

in

pounds

per

inch square

by the

following

formula:

tensile strength (lb/in

2

)

=

tenacity

(g/denier) x

density (g/cm

2

)

x 12,791

Note that tenacity values fo r m ost fibers range from

1-8

g/denier.



Ta ble 17.2 Ph ysic al

Properties of

Typical Fibers

Polymer

Cellulose

Cotton

Rayon

High-tenacity

rayon

Cellulose

diacetate

Cellulose

triacetate

Proteins

Silk

Wool

Nylon 6,6

Polyester

Polyacrylonitrile

(acrylic)

Polyurethane (Spandex)

Polypropylene (polyolefm)

Asbestos

Glass

Tenacity

(g/denier)

2.1-6.3

1.5-2.4

3.0-5.0

1.1-1.4

1.2-1.4

2.8-5.2

1.0-1.7

4.5-6.0

4.4-5.0

2.3-2.6

0.7

7.0

1.3

7.7

Tensile Elongation

Strength

(%)

(kg/cm

2

)

3000-9000

2000-3000

5000-6000

1000-1500

1000-1500

3000-6000

1000-2000

4000-6000

5000-6000

2000-3000

630

5600

2100

2100

3-10

15-30

9-20

25-45

25-40

13-31

20-50

26

19-23

20-28

575

25

25

3

Source:

Seymour/Carraher

In

general, you should recall

that

the tensile strength and modulus of

fibers

must be much higher than that fo r plastics and their elongation must

be m uch lower. Synthetic fibers are usually stretched and oriented

uniaxially to increase their degree of parallel chains and increase their

strength and modulus.

What makes a polym er a good fiber? This is not an easy question to

answer. If one fact can be singled out as be ing important, it would be that all

fibrous polymers must have strong intermolecular forces of one type or

another. Usu ally this means hydrogen bonding or dipole-dipole interactions,

shown

on the

following page

for

various types

of fibers.

Besides the high tenacity, a number of other properties are considered

necessary for most fiber applications. A lthough no one polymer is superior

in all of these categories, the list in Table 17.3 represents ideals for polymers

being screened as fibers.



Table 17.3 Ideal Properties of Polymers for Fiber App lications

1. High tensile strength, tenacity, and modulus

2. Low elongation

3. Proper

T

g

and

T

m

.

A low

T

8

aids

in

easy orientation

of the fiber. The

T

m

should

be

above 20O

0

C

to

accept ironing

(as a

textile)

but

below 3 0O

0

C

to be

spinnable.

4.

Stable

to

chemicals, sunlight,

and

heat

5. Nonflammable

6.

Dyeable

7.

Resilient (elastic) with

a

high

flex

life

(flexible lifetime)

8. No static electrical build-up

9.

Hydrophilic (adsorbs water

and

sweat easily)

10. Warm

or

cool

to the

touch

as

desired

11. Good "drape" (flexible

on the

body)

and

"hand" (feel

on the

body)

12.

No

shrinking

or

creasing except where intentional

13. Resistance

to

wear after repeated washing

and

ironing

hydrogen bonding:

dipole-dipole:

cellulosics proteins,

nylons

polyesters acrylics

3.

IMPORTANT

FIBER S

A

study of the fiber industry is not complete without some knowledge of

the

characteristics

of

individual

fibers.

Since each

is so

different

it is

difficult

to

generalize

or

com pare directly. This section presents

a

summary

of each important fiber, including pertinent information on their

manufacture, properties, uses, and current economics in a brief, informal and

concise manner.



(a pure form of cellulose)

1.

Fewer processing steps, cheaper than wool

2. Good hand

3.

W ears hard and long

4. Easily dyed

via

free hydroxy groups

5. A bsorbs water but dries easily. If preshrunk, it is stable to washing

and ironing more than other fibers.

6. Hydrophilic—cool and comfortable. Comfort never matched by

synthetics. Used especially

in

towels

and

drying cloths.

7. Disadvantages: creases easily, requiring frequent ironing;

agricultural variables in growing the plant; brown lung disease in

workers

in

mills;

waste

about

10% in

harvest; variable strength;

unpredictable

price

3.1.2 Wool

(protein, mostly keratin, a complex mixture of amino acids)

1. Processing requ ires 20 stages, therefore very expensive

2. Good resilience (elasticity) because orientation changes

a-keratin

(helical protein) into p-keratin (zigzag). Example: woolen carpet

recovers even after years of heavy

furniture.

3. Good warmth

due to

natural crimp (many folds

and

waves) which

retains air, therefore a good insulator

4. Hydrophilic—absorbs perspiration away from body and is

comfortable, not sweaty

5.

Dyed easily since

it has

acidic

and

basic groups

in the

am ino acid

6.

Disadvantages: expensive; retains water

by

hydrogen bonding with

washing, causing shrinkage; many people allergic

to

protein

3 1 Natural

3.1.1 Cotton



3.2

Cellulosic

3.2.1 Rayon

(regenerated cellulose from wood pulp, especially higher molecular

weight

"alpha"

fraction not

soluble

in

18%

caustic)

1.

Manufacture

a. Steeping 1 hr in 18% caustic gives "soda"

cellulose,

(C

6

H

10

Os)

n

+ NaOH

^ [(C

6

H

10

Os)

2

-NaOH]

n

where some

C—OH are

converted into

C— OTsIa

+

b. Reaction with CS

2

,

about

1

xanthate

for

each

tw o

glucose units, soluble

in 6%

NaOH

for

sp inning, called

"viscose rayon"

c.

Ripening—slow

hydrolysis

viscose —different molecular weight than starting cellulose,

has some xanthate groups

d.

Spinning—ZnSO

4

, H

2

SO

4

bath.

H

2

SO

4

neutralizes N aOH of viscose solution. ZnSO

4

gives

interm ediate w hich decomposes mo re slowly.



2. Properties

Dyeable

(free

hydroxy groups), hydrophilic (comfortable), stable,

low

price,

poor wash

and

wear characteristics

3. Uses

Apparel, 31%; home furnishings (curtains, draperies, upholstery,

mattress ticking), 24%; nonwovens (medical and surgical, wipes

and towels, fabric softeners), 33%; miscellaneous, 12%.

4.

Economics

Peak production in 1950s, 1960s. Declined by 5.6%/yr in 1970-

1980,

4.9% /yr

in

1980-1990,

and

3.6%/yr

in

1990-2000.

3.2.2 Acetate

1. Manufacture

a.

Esterification

b.

Ripening with M g(OA c)

2

, H

2

O

.

Mg(OAc)

2

cellulose sulfoacetate

——

>

[C

6

H

7

O

2

(OH)O^

5

(AcO)

2

Os]

n

+

MgSO

4

Usually

the primary carbon has the OH, secondary carbons the

OA c. Ce llulose triacetate

has

three

OA c

groups.



2. Properties

Lower tenacity than any other

fiber

because the bulky OAc group

keeps molecules far apart

Free OH more easily dyed and more hydrop hilic than triacetate

Random acetate groups make

it

less crystalline than triacetate.

So

triacetate

is

better

for ironing. But triacetate gives

stiffer

fabrics

with

inferior drape

and

hand.

Both are softer than rayon but not so strong, have poor crease

resistance,

and are not

colorfast.

3. Uses

Cigarette filters, 61%; yarn (especially

for

apparel, curtains,

draperies, bedspreads, quilt covers), 39%.

4. Economics

Down 4.5%/yr from 1970-1980, 4.2%/yr from 1980-90, and 3.6%/yr

from 1990-2000

3 3 Noncellulosic

3.3.1 Nylon 6 and 6,6

nylon

6

nylon

6,6

1.

Manufacture

Nylon 6,6

developed

by W. H.

Carothers

of Du

Pont

in

1930s.

Adipic acid, HMDA, 280-30O

0

C, 2-3 hr, vacuum. Trace of

acetic acid terminates chains with acid groups and controls

molecular w eight.

Nylon 6 developed by Paul Schlak in Germany in 1940.

Caprolactam plus heat plus water as a catalyst.

Fibers are melt spun (no solvent) while still above T

m

(=

265-27O

0

C

for nylon 6,6 and 215-22O

0

C fo r nylon 6). Extruded through a

spinerette.

Fibers oriented

by

stretching

to 4 x

original length

by

cold drawing

(two pulleys at different speeds) or by spin drawing as it is being

cooled

2.

Properties

Strongest and hardest wearing of all fibers



Figure

17.2

Pilling chambers to test, by

rapid

rotation, the tendency of a

fabric

to

form

pills as in repeated washings and use. (Courtesy of Du Pont)

Heat stable

Dyeable

Disadvantages: hydrophobic

("cold and

clammy"), degraded

by

UV, yellows with

age,

poor hand, tends

to "pill"

(gentle rubb ing

forms

small nodules

or

pills, where surface fibers

are

raised,

see

Fig.

17.2)

3. Uses

Carpets and rugs, 74%; industrial and other (tire cord and

fabric,

rope and cord, belting and hose, sewing thread), 16%; apparel

(especially hosiery, anklets,

and

socks), 10%

4. Economics

Production increased

5.7%/yr

from 1970-1980, only 1.2%/yr from

1980-1990, and decreased 0.2%/yr

from

1990-2000.

The carpet and rug market has increased dramatically in recent

years.

Nylon 6,6 is two

thirds

of the

U.S. market, nylon

6 one

third.



3.3.2 Polyester, Poly ethylene terephthalate),

PET

1. Manufacture

Developed by Whinfield and Dixon in the U.K . Originally mad e by

transesterification of DMT and

ethylene glycol

in a

1:2.4 ratio,

distillation of the methanol, then polymerization at

200-29O

0

C

in

vacuo with SbOa as catalyst.

In

early

1960s

pure

TA

began

to be

used with

excess

ethylene glycol

at

25O

0

C,

60 psi to

form

an oligomer with n = 1-6, followed by

polymerization

as in the DMT

method.

N ow

both methods

are

used.

M elt spin like nylon, T

m

= 250-265

0

C

Orientation above T

g

o f

8O

0

C

to 300-400%

2.

Properties

Stable in repeated laundering

Complete wrinkle resistance

Blends com patibly with other fibers, especially cotton

Can vary from low tenacity, high elongation to high tenacity, low

elongation by orientation

Disadvantages: stiff

fibers

(aromatic rings), poor drape except with

cotton blends, hydrophobic, pilling, static charge

buildup,

absorbs oils

and

greases easily (stains)

3. Uses

Clothing

(suits, pants, shirts,

and

dresses either nonblended

or

blended with other fibers such as cotton), 50%; home

furnishings (carpets, pillows, bedspreads, hose, sewing thread,

draperies, sheets, pillowcases), 20%; industrial (tire cords),

30%

4.

Economics

Production increased

10.5%/yr from

1970-1980, decreased 2.2%/yr

from

1980-1990,

and

increased 1.9%/yr from 1990-2000.

3.3.3 Polyolefin



Figure

17.3 Spinning of fibers for use in carpets. (Courtesy of Du Pont)

1. Manufacture

Mostly isotactic polypropylene homopolymer,

but

some copolymer

with polyethylene,

and

some HDPE

A

high molecular weight

is needed, 170,000-300,000, for

good

mechanical strength because of weak intermolecular forces,

only

van der Waals.

Fiber

produced by melt spinning

2. Properties

Low

density (0.91),

the

lowest

of all

commercial

fibers,

meaning

lightness and high cover

Outstanding chem ical resistance, serving industrial filtration

High abrasion resistance for floor covering, upholstery, and hosiery

Insensitive to water, giving dimensional stability and

fabric dryness

in

contact with the skin

Resistance to mildew, microorganisms, and insects

Good insulator and electrical properties

Lowest thermal conductivity of commercial

fibers,

giving high

thermal insulation

in

textiles

No

skin irritation

or

sensitization, non-toxic



Disadvantages: not easily dyeable, low resistance to oxidation—but

additives help, easily soiled, poor

fo r

ironing, poor

for dry

cleaning

3. Uses

Industrial, including rope, twine, conveyor belts, carpet backing,

tarpaulin, awnings, cable, bristles; home textile applications,

including floor covering, upholstery fabric, wall covering,

blankets; apparel, especially sportswear and hosiery

4. Economics

Growth rate large, 11%/yr from 1970-1980, 9%/yr from 1980-1990,

and 5.8%/yr from 1990-2000

Surpassed acrylics

in

1980, nylon

in

1998,

and is

catching

up to

polyester

Suggested

eadings

Kent,

Riegel s Handbook of Industrial

Chemistry, pp. 735-799.

Wittcoff and Reuben, Industrial Organic Chemicals in Perspective. Part

Two:

Technology,

Formulation,

and

Use,

pp.

104-125.

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