I would firstly like to thanks my principal ma’am, who proposed me to make a

project which can enhance our knowledge and help us to relate book’s

knowledge with real life.

I would like to thanks my subject teacher, who gave us marvelous project and

also her aid and succor made me capable to make this project.

I would also like to give regards to my parents and my friends whose endless

effort and help made me do my best.

Arunima Singh

XII A3

AIM- TO STUDY THE EFFECT OF ACIDS AND BASES ON THE

TENSILE STRENGTH OF FIBERS.

INTRODUCTION

Fiber is a fine thread like piece of silk, nylon, wool, cotton etc. These are classified

into 2 types on the basis of their origin-

1. Natural fibers such as silk, cotton, wool, jute etc.

2. Synthetic or manmade fibers such as nylon, terrene, rayon etc.

Natural fibers are further classified into 2 types depending upon their source

namely-

1. Vegetable fibers, e.g. cotton, jute

2. Animal fibers, e.g. wool and silk

These fibers differ in their chemical composition and properties for example-

vegetable fibers obtained from plants are cellulosic products of plant

biosynthesis. These are attacked by acids and not much by alkalis.

Animal fibers are proteins resulting from animal bio synthesis, for example silk

and wool are long polypeptide chains. Animal fibers are attacked by alkalis and

not by acid.

The quality of a fiber is fixed on the basis of its resistance towards alkalis, acids,

color fastness and durability of strength. A good fiber is said to be the one which

does not break while being woven and cloth made out of it should also not be

affected by air, water, acids and alkalis. That is it should have high strength.

“Tensile strength” means the extent to which a fiber can be stretched. In other

words it is the maximum force which a fiber can withstand.

That is, if two forces are being applied on a fiber, it will be stretched and if we go

on increasing the magnitude of either force, a stage will come, when thread will

break indicating that fiber can withstand certain force only or fibers can be

stretched only up to some limit. Thus, tensile strength of a fiber can be measured

in terms of the minimum force required to break it.

EXPERIMENT-1

Objective (1): To compare the tensile strength of given samples of nylon,

cotton and silk fibers.

Apparatus: Slotted weights, hanger or pan, hook, meter scale.

Materials: Nylon, cotton and silk and wool fibers.

Procedure:

1. Measure appropriate length of the given nylon thread.

2. Tie one end of it with a hook fixed vertically in a plane.

3. With the other end, tie a hanger or pan, i.e., a support on which weight can

be placed.

4. Hang the thread carefully. Now the thread will become straight, i.e. stretched.

5. Carefully, put a small weight on the hanger or pan and see for some time.

6. Go on increasing weights gradually on the support until the thread breaks.

The thread will break only, when it cannot be stretched more and the weights

placed on the support in that case will, therefore, represent the force which

the fiber an withstand.

So note the weights placed on the support and this minimum

weight to break the thread can be qualitatively said as the tensile strength of

the fiber.

7. Similarly, find out the tensile strength, i.e., minimum weight required to break

the thread of the fiber.

Observation-

S.NO. TYPE OF FIBER TENSILE STRENGHT i.e. MINIMUM WT.,

REQUIRED TO BREAK THE THREAD

1. NYLON 200g

2. COTTON 300g

3. SILK 200g

4. WOOL 250g

CONCLUSION- Tensile strength of given nylon, cotton, silk and wool fiber is in

the following order.

PRECAUTIONS-

1. Take fiber of almost equal length and same diameter, i.e. thickness.

2. Take dry fibers only.

3. Use same set of weights in every experiment.

4. Near the breaking point, add small weights (1-2g) to the weight hanger.

EXPERIMENT-2

Objective (1): To study the effect of acid and alkali on the tensile strength of

given cotton, nylon and wool fibers.

Theory: Strong acids or alkalis both weaken the fibers irrespective of

their origin. However, reaction of dilute solution of these is

different in case of different fibers.

Apparatus: Slotted weights, hanger or pan, hook, meter scale.

Chemicals: Dilute hydrochloric acid and sodium hydroxide solution.

Procedure:

1. Determine first the tensile strength i.e. minimum weights required to break

the given cotton, nylon and wool fibers.

2. Then soak a few fibers in acid and a few in an alkali solution baths for about

half an hour. That is, take same acid (dil. HCl) in a beaker and dip the fibers

into it for half an hour. Likewise dip the fibers in alkali taken into a beaker.

3. After half an hour, remove the fibers from the both i.e., beakers. Wash them

thoroughly with water and keep in sun or oven maintained at 400C. For drying.

4. Determine the minimum weight required to break the dry fiber exactly in a

manner described in above experiment.

5. Compare the different value so obtained and conclude.

Observation-

Strength of the Alkali = 5.5m

Length of the fiber = 32cm

MINIMUM WEIGHT REQUIRED TO BREAK THE FIBER

FIBER Before soaking After soaking in

alkali (NaOH sol.)

After soaking in acid

(dil HCl)

Cotton 200g 200g 100g

Nylon 250g 200g 200g

Wool 250g 150g 250g

Silk 300g 200g 300g

CONCLUSION-

1. Acid and alkali affect the tensile strength of fibers.

2. Tensile strength of cotton fibers is decreased by acid and not bay alkali.

3. Nylon fiber strength almost remains same even after soaking in acid or alkali.

4. Alkali decreases the tensile strength of wool fiber but if almost remains same

in dil. Acid.

PRECAUTIONS-

1. Take fiber of almost equal length and same diameter, i.e. thickness.

2. Take dry fibers only.

3. Use same set of weights in every experiment.

4. Near the breaking point, add small weights (1-2g) to the weight hanger.

FIBERS

Fiber, also spelled fiber, is a class of, materials that are continuous filaments or

are in discrete elongated pieces, similar to lengths of thread. They are very

important in the biology of both plants and animals for holding tissues together.

Human uses for fibers are diverse. They can be spun into filaments, strings or

rope, used as component of composite materials, or matted into sheets to make

products such as paper or felt. Fibers are often used in the manufacture of other

materials. Synthetic fibers can be produced very cheaply and in large amount

compared to natural fibers, but natural fibers enjoy some benefits such as

comfort, over their man-made counterparts.

TYPES OF FIBERS-

1. Textile- A unit in which many

complicated textile structures are built

up is said to be textile fiber. It is the

basic constituent (basic raw material)

required for textile industry.

2. Natural Fibers- Natural fibers include those produced by plants, animals

and geological processes. They are

biodegradable over time. They can

be classified according to their

origin.

(i) Vegetable fibers are

generally based on

arrangements of cellulose,

often with lignin: example

include cotton, hemp, jute,

flax, ramie and sisal. Plant fibers are employed in the manufacture of

paper and textile and dietary fibers is an important component of

human nutrition.

(ii) Wood fiber, distinguished from vegetable fibers, is from tree sources.

Forms include ground wood, thermo mechanical pulp (TMP) and

bleached or unbleached draft

or sulfite pulps.

(iii) Animal fibers consist largely of

particular proteins. Instances

are spider silk, sinew, catgut,

wool and hair such as

cashmere, mohair and angora,

fur such as sheepskin, rabbit, mink, fox, beaver etc.

3. Man Made Fibers- Synthetic or man-made fibers generally come from

synthetic materials such as petrochemical. But some types of synthetic

fibers are manufactured from natural cellulose, including rayon; modal and

the more recently developed Lyocell. Cellulose- based fibers are of two

types, regenerated or pure cellulose such as from the cupro-ammonium

process and modified cellulose such as the

cellulose acetates.

(a) Cellulose fibers- Cellulose fibers are

subset of man-made fibers, regenerated

from natural cellulose comes from

various sources. Modal is made from

beech trees, bamboo; seacell is made

from seawood etc.

(b) Mineral Fibers- (i) Fiberglass, made from specific glass, and

optical fibers, made from purified natural

quartz are also man-made fibers that come

from natural raw materials.

(ii) Metallic fibers can be drawn from ductile

metals such as copper, gold or silver and

extruded or deposited from more brittle

ones, such as nickel, aluminum or iron.

(iii) Carbon fibers are often based on carbonized polymers, but the end

product is pure carbon.

(c) Polymer Fibers- Polymer fibers are a subset of man-made fibers,

which are based on synthetic chemicals (often from petrochemical

sources) rather than arising from natural materials by a purely

physical process.

(d) Microfibers- Microfibers in textile

refer to sub-denier fiber. Denier and

detex are two measurement of yield

based on weight and length.

Laboratory Manual –XI

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This is to clarify that Arunima Singh is a bonafide

student of class 12th Rani Laxmi Bai Memorial Senior Secondary

School. C-Block, Indira Nagar, Lucknow. In a session of 2010-

2011.

Principal Signature Subject Teacher Signature