Topic 8 Natural Materials and Manufactured or Man Made Materials

8/12/2019 Topic 8 Natural Materials and Manufactured or Man Made Materials

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88 NaturalMaterials andManufacturedor Man-madeMaterials

By the end of this topic, you should be able to:

1. Define material;

2. Describe each type of materials;

3. Explain the properties of materials;

4. State the importance of materials;

5. Compare natural materials and manufactured materials;

6. Describe how to preserve our natural materials;

7. Describe composite materials; and

8. Discuss the materials in industry in the context of soap, natural andsynthetic rubber, natural and synthetic fibre and plastics.

LEARNING OUTCOMES

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TOPIC 8 NATURAL MATERIALS & MANUFACTURED OR MAN-MADE MATERIALS 71

INTRODUCTION

Materials are the things that you can observe all around you. From falling rain

to plants and human beings, from window curtains to floor mats and from

computers to printing materials, these are all materials. The air that you

breathe in and out is also a material.

Materials are very useful to human beings for their survival. They not only use

natural materials but also create new materials in order to fulfil their needs.

DEFINITION, PROPERTIES ANDIMPORTANCE OF MATERIALS

A cloud is seen as a bulk of moving object in the air. When it is very heavy, it

starts to drop tiny droplets of water. When the sun shines on the water

droplets, it turns to vapour. Have you ever thought of the processes that occur

in this event?

This event is just one in a thousand of events tha t involve materials. Materials

are the things all around you. Materials have mass and occupy space. Gases,

woods, plastics, foods, animals and water are all examples of materials.

According to the ancient Greek, there should be four things to make up a

substance. These four things are earth, fire, air and water. The Greeks believed

that these four things mix together in different amounts to make different

materials.

8.1.1 Definition of MaterialsWhat is material? Material is defined as follows.

8.1

Material is made up of thousands of small particles, not visible to the naked eye, called atoms. The composition of atoms in the material makes it different from one another.

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Based on these compositions of atom, material can be divided into three categories: element , compound and mixture .

(i) Element

An element is the simplest substance of a material. It cannot be broken

down or separated by chemical or physical methods into any simpler

components. An element is made up of only one type of atom. Some

elements have atoms of the same types, which are combined to form

molecules. There are 112 types of elements, in which 92 of these elements occur naturally in the earth and 20 are created by scientists.

Elements can be grouped into metals and non metals. Gold, zinc, iron,

aluminium, oxygen, carbon, hydrogen and nitrogen are examples of

elements.

Figure 8.1 shows the atom of an element with its nucleus at the centre

and electrons moving around the nucleus.

Figure 8.1: The atom of an element

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(b) Combined Elements

There are two types of combined elements compounds and mixtures.

(i) Compound

Two or more elements can be combined together chemically to form

a new material called a compound . A molecule is the smallest

particle in a compound. Water is an example of a compound. A

water molecule is made up of one oxygen atom and two hydrogen

atoms, which are combined chemically (see Figure 8.2).

Figure 8.2: Water molecule

Table 8.1 shows several types of compounds and its elements.

Oxygen atom

Hydrogenatoms

ACTIVITY 8.1

Look outside your laboratory. Identify the objects and list down the

objects. They are made of different types of materials. Most of the

materials are made from a combination of elements. Some are made

of only one type of element. Can you guess which objects are made of only one element? Can you name the element in each case? Write down your findings.

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ACTIVITY 8.2

Table 8.1: Several Types of Compounds

Compound Elements

Carbon dioxide One carbon atom, two oxygen atoms

Sodium chloride One sodium atom, one chloride atom

Benzene Six carbon atoms, six hydrogen atoms

Ammonia One nitrogen atom, three hydrogen atom

Water One oxygen atom, two hydrogen atoms

The components of a compound cannot be separated by physical methodssuch as crushing or by magnetic force. Components of a compound can beseparated by chemical methods. For example, pure water can be brokendown into its elements that are oxygen and hydrogen by using electrolysis.

Compounds can be prepared by a chemical reaction. Heat energy is releasedor absorbed when a compound is formed. This will form a new substancethat is different from its early substances. The characteristics of acombination of elements which are combined by specific ratios are differentfrom each of the origin element.

(ii) Mixtures

Material that is made up of a combination of two or more substances that are combined physically is called a mixture . This means that the

mixture can be separated by physical methods such as filtration,

evaporation, distillation, chromatography, extraction, precipitation,

magnetic forces, sieving and heating or evaporation processes. By

these separation methods, the chemical structure of the component is

not changed because the substance in a mixture does not unite.

ACTIVITY 8.2

Have you ever burnt a magnesium ribbon? Magnesium andoxygen can be combined to make a compound. Hold a small pieceof magnesium ribbon by using a tong and move it slowly into aflame. Observe the appearance of magnesium and oxygen beforeand after it was burnt. Identify the end product of the experiment.

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There are two types of mixture homogenous and heterogeneous . A

homogenous mixture is formed when its substances are mixed

evenly and the identity of each substance cannot be identified easily.

A heterogeneous mixture is formed when its substance can be

identified easily. When sugar is put in a glass of hot drink, it

becomes a homogenous mixture. A mixture of sulphur with iron

fillings and air are examples of a heterogeneous mixture (see Table

8.2).

Table 8.2: Several Types of Mixtures

Mixture Components

Air Oxygen, nitrogen, hydrogen, carbon dioxide, inert

gases, microorganisms and water vapour

Soil Water, clay, loam, sand, humus, gravel

Sea water Sodium chloride, water, magnesium, plumbum,

oxygen

Chocolate

cake Flour, water, oil, egg, chocolate powder

Blood Blood cells, hormones, minerals, water, plasma,

oxygen

During the formation of a mixture, heat energy is not absorbed or

released. There is also no combination of elements in a specific ratio

and each component retains its original property. The components of

a mixture can be easily identified.

SELF-CHECK 8.1

1. What is a material?

2. Name a few examples of materials.

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(c) Making New Materials

Some materials around us are natural while others are man-made. Wool fromsheep and wood from trees are natural materials. All these materials are madefrom elements.

Scientists sometimes combine elements in new ways. This is a way to makeuseful man-made materials. Synthetic materials are an example of man-madematerials.

8.1.2 Properties of Materials

What are the physical properties of materials? Matter is the general word for

all materials. Therefore, specific matter such as wood, stone and paper are

called material. We know that materials can be divided into two types natural materials and synthetic materials . Natural materials are made from

organic material like paper or inorganic material like sand and lava. Humans

cannot create natural materials. However, scientists have managed to make synthetic materials. Plastics and ceramics are two types of synthetic materials.

Each material has its unique physical properties, which means different

materials have different properties. Some of the important physical properties

of materials are elasticity, shine, buoyancy, water absorbency, electrical

conductivity, heat conductivity and magnetism. Other physical properties of

materials are hardness, toughness and brittleness, strength, flexibility,

solubility and waterproof.

SELF-CHECK 8.2

State the types of combining elements.

ACTIVITY 8.3

Do you know how to separate gases in the air? What are theprocedures that should be taken to turn it into liquid? Discuss withyour coursemates.

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Scientists distinguish material properties according to their interesting

contextual factors. Among these properties are:

(a) Mechanical properties like elasticity;

(b) Thermodynamic properties like specific heat capacity and melting point;

(c) Electromagnetic properties like specific magnetic susceptibility and

specific electric conductivity;

(d) Chemical properties like the capacity for oxidation or the solubility in a

certain liquid;

(e) Biological or biochemical properties like LD50, antibiotic or anaesthetic

effect;

(f) Ecological properties like ozone depletion potential, greenhouse effect

factor; and

(g) Mixed material properties (two or more interesting factors are

combined) like photo chemical, thermo electrical, thermo electro

chemical.

Let us now take a look at the types of material properties.

(a) Elasticity

What is elasticity?

Materials that are able to return to their old shape when force is no

longer applied are called elastic materials. However, materials which

retain their new shapes when force is no longer applied are called plastic

materials or non elastic materials. Some materials such as rubber bands,

balloons and gloves are elastic materials but some materials such as

plastic, wood and belt are non elastic materials. To determine whether

materials are elastic or non elastic, you may need to carry out some

activity.

Elasticity is the ability of a material to return to its original shape and size after being bent, twisted, stretched and squeezed.

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(iii) Break

If enough force is applied to a material, it will become brittle and

eventually break or fracture.

Some materials that exhibit elastic behaviour are:

(i) Rubber: Large deformation if warm, then fracture or small

deformation and fracture if cold;

(ii) Metals: Small deformation, then permanently deform;

(iii) Ceramics: Small deformation, then fracture; (iv) Electronic materials: Small deformation, then fracture or deform;

(v) Glass: Small deformation, then fracture.

(vi) Human skin: Large deformations.

(vii) Polymers: Temperature dependent.

(viii) Liquids under uniform hydrostatic pressure.

(b) Shiny

When it comes to material properties, what does shiny mean?

Shine is important in making jewellery and accessories. In relation to this

shiny property of materials, some materials allow light to pass through

them but some do not. Materials such as glass and plastic allow light to

pass through them. On the other hand, materials such as wood and

metal do not allow light to pass through them. According to the ability

of materials to allow light to pass through them, materials can also be

SELF-CHECK 8.3

1. State the importance of physical properties of materials.

2. Give an example of a material for each physical property.

Some materials are shiny and some are not. Shiny materials can reflect the light such as some types of metals and glasses.

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(c) Buoyancy

How do we define buoyancy? Let us take a look at the following

definition.

Why do some things float? Dense objects sink and light objects float.

Therefore, buoyancy is also related to density. Density is mass per unit of

volume.

Floating is related to the volume of liquid displaced by an object. The liquid is

pushed aside when an object is placed in it. Therefore, our body displaces the

water. When an object floats in water, only a part of it displaces the water.

The other part of the object remains above the water. The objects float after a

definite amount of water is displaced. According to Archimedes, the ancient

Greek physicist, when the mass of the displaced liquid is equal to the mass of

the objects, the objects will float. Plastic, wood and rubber are examples of

floating materials. Figure 8.5 shows floating materials and liquids of different

densities.

Figure 8.5: Floating materials and liquids of different densities

Buoyancy is the ability of materials to float in liquid.

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(d) Water Absorbency

Materials which can absorb water are known as absorbent materials and

materials which cannot absorb water are known as non absorbent

materials. The materials that are able to absorb water become completely

wet. Examples of absorbent materials are wood, paper and cotton cloth.

Raincoats, umbrellas, plastic and hats are examples of non absorbent

materials.

(e) Electrical Conductivity

A material that allows electricity to pass through it is a material that conducts electricity . Almost all types of metal such as zinc, copper, brass

and gold are materials that conduct electricity. Non metals such as glass,

wood, plastic, cotton wool and leather are materials that do not conduct

electricity. Electrical conductivity is a measure of the ease with which an

electrical current can move in a material. It may be inferred by looking at

their resistivity, which refers to its ability to resist the passage of an

electrical current. Figure 8.6 shows the test of electrical conduction.

ACTIVITY 8.4

ACTIVITY 8.4

Your friends child is asking you about absorbent materials. How doyou explain to your friends child to test absorbent and non-absorbentmaterials? Discuss in pairs.

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Figure 8.6: Test of electrical conduction

Table 8.3 summarises the electrical resistivity of some common materials.

Table 8.3: Electrical Resistivity of Some Common Materials

Materials Electrical Resistivity (10 8 ohms/m)

Copper 1.67

Aluminium 2.65

Iron 9.71

Steel 12.0

Pyrex glass 105

Concrete 0.1

Nylon 1016

Rubber

Softwood

ACTIVITY 8.5

How do you test for electrical conduction? Arrange equipment to findout which materials are electrical conductors and which are electricalinsulators. Figure 8.6 will help you do the test. Place the material between the battery and the bulb to be tested. See what happens to thelightbulb. Test several types of samples such as pencil, flower, soil,water and spoon.

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(f) Heat Conductivity

What is heat conductivity?

Metals can conduct heat while non metals cannot conduct heat. Each

material conducts heat in its own special way. A good conductor would

be used in radiators whereas a poor conductor would be used to insulate extreme heat.

Scientists have a way of measuring the value of how well heat is

conducted. If the value of a material is larger, it is a better heat conductor

compared to materials with small values. Table 8.4 shows the values of

heat conduction of some materials. A piece of copper with a heat

conduction value of about 8000 is a better heat conductor than foamed

plastic with a heat conduction value of about 1 because copper ranks

higher than plastic.

Table 8.4: Values of Heat Conduction of Some Materials

Materials Values of Heat Conduction (Relative)

Copper 8000

Aluminium 4000

Brass 2500

Steel 1100

Pyrex glass 24

Concrete 2

Solid plastic 6

Rubber 2

Foamed Plastic 1

A material that allows heat to pass through it easily is a material that conducts heat .

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Materials may have tensile strength and compressive

strength. Tensile strength means resistance to stretching

such as squeezing and pulling on the rope. It depends on

its cross sectional area. Compressive strength means

resistance to pressure, meaning it is hard to break by

crushing.

Flexibility The material, which is easy to bend without breaking, has

both tensile strength and compressive strength.

Solubility The solubility is the concentration of solute in a saturated solution. It is stated as the mass in grams of the solute that

will saturate 100 grams of solvent at a certain temperature.

Waterproof Resistance to liquids. Repels water.

8.1.3 Importance of Materials

Materials play a pivotal role in our life, particularly in the areas of living

environment, health, communication, consumer goods and transport. Pressing

environmental concerns force us to use materials more efficiently. It will help

in

the

long

run

if

we

develop

new

energy

generation

technologies,

more

energy efficient devices, and easily recyclable, less toxic materials. As far as

consumer goods are concerned, we need to emphasise not only on the

material products but also on the way they are handled such as packaging,

faster production and higher quality goods.

In health, materials are important to help us overcome disease and provide

worldwide medical care. In transport, we need durable, high performance

materials that make travelling faster, safer and more comfortable. In

ACTIVITY 8.6

Go on the Internet and find out more on materials and their uses

based

on

their

properties.

Discuss

your

findings

with

youcoursemates.

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communication, the development of new electronic inventions is very

important and requires optical and magnetic materials. Without development

of materials in all areas, we may face many difficulties.

(a) Importance of Physical Properties of Materials

Knowledge about the properties of materials is very important, especially

in choosing suitable materials to make various objects. Sometimes these

objects need more than one type of physical property. For thousands of

years, people only used natural properties of natural materials. However, scientists have now developed many new materials, influencing its

properties in the process.

(b) Use of Properties of Materials in Everyday Life

Humans have exploited physical properties of materials for their own use

in everyday life. We use materials that conduct electricity to produce

conductors and insulators. We use materials that allow light to pass

through them to produce transparent, translucent and opaque objects.

Table 8.6 shows other uses of properties of materials in producing some everyday objects.

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Table 8.6: Other Uses of Properties of Materials in Producing Some Everyday Objects

Property Materials Uses

Strength

Metals

Structural components

E.g., rolled steel joints

Malleability Water pipes

Thermal

conductivity Radiators, saucepans, ovens

Electrical

conductivity Electrical cables

Hardness Drill bits, hammerheads

Strength

Ceramics

Brick, concrete

Heat resistance Ovenware

Abrasion

resistance Crockery

Thermal

insulation Glass Loft, cavity wall insulation

Transparency Windows

Flexibility

Plastics

Moulded items

Electrical

insulation Sheathing of electrical cables

Thermal

insulation Saucepan handles

Lightness and

strength

Construction, window frames

Lightness and

strength Wood Construction, doors, window

frames,

furniture

Flexibility,

insulation Fabrics

Curtains, clothing, furnishing

Adapted from: Farrow, S. (1996). The really useful science book: A

framework of knowledge for primary teachers. London: Falmer Press.

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NATURAL MATERIALS

All living things and non living things are sources of materials. Materials that

are originated from nature such as living organisms, plants and animals are

classified as biotic or biological derived natural material. Materials originated

from soil, petroleum or metals are classified as abiotic or non biological

natural materials. We need these materials to support our daily needs.

Natural materials are made naturally after a long period of time. For example,

a rubber tree may take many years to become mature and ready for cutting down to make furniture, papers and insulators. Chemistry has enabled us to

synthesise new materials, which have desired properties, thus making them

even better than natural materials in a shorter period of time.

(a) Identifying Natural Materials

Materials that are classified as natural materials originated from soil,

rocks, water, plants, animals or minerals. Air is a mixture of gases, which

make up the earths atmosphere and has an abundance of components.

Parts of their uses can be seen in Table 8.7.

Table 8.7: Gases and Their Uses

Gas % Present in Air

Uses

Nitrogen 78.0 Nitrates in soil, use in ammonia production.

Oxygen 21.0 Respiration, oxidation, medical application

Carbon dioxide 0.04 Photosynthesis, dry ice

Neon Trace Lighting

Argon Trace Domestic light bulb

Helium Trace Airships

Krypton Trace High temperature light bulb

Xenon Trace High temperature light bulb

8.2

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Water is a colourless, odourless liquid, which is originally derived from the earths atmosphere. It is recycled from the atmosphere to the crust of the earth. It is important because it supports life on the planet, as almost all the significant reactions at cellular level depend on the aqueous solutions.

Wood, metal, leather, cotton, rubber and silk are materials that are made

of natural materials. These materials are considered valuable in their

relatively unmodified (natural) form.

(b) Objects from Natural Materials Materials from natural materials vary in their use. Table 8.8 shows

natural materials and their uses.

Table 8.8: Natural Materials and Their Uses

Natural Material Uses

Rubber Latex

Wood Timber

Paraffin wax and stearic acid Candles

Carbon black and water or oil Ink

Vegetable fibre Wood pulp

Vegetable waxes, oil and sap Carnauba wax, linseed oil

Animal fibre Wool, alpaca

Animal product Leather , tallow, lard

(c) Source of Raw Materials

Raw materials are materials that are extracted from the earth. Processed raw materials are called semi finished materials. When it is transferred

into a new cycle of production, the end product is ready for use.

The earth is the main source of raw materials. Biotic materials and non biotic materials are the types of sou rces of raw materials. Wood, straw,

humus, spider silk, and bone are examples of biotic materials. Biotic

materials are usually biodegradable, renewable and processing has

minimal impact on the environment. Somehow, in certain cases,

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processing produces carbon emission. Polylactic acid, cornstarch and

bioplastic are examples of non biodegradable biotic materials. Non biotic materials are materials that do not originate from plants and

animals. Water, soil, coal, crude oil, natural gas, rocks and air are

examples of non biotic raw materials.

Another example is cotton. Cotton is produced from a matured flower of

a cotton tree. It is harvested by plucking from a matured cotton tree

flower. The fluffy white material is then brought to the factory and

processed to produce cotton thread.

MANUFACTURED MATERIALS

Manufactured materials are made from a mixture of natural materials

through chemical processes. These materials are also called man made

materials . These materials are processed in factories with a combination of a

few different types of materials or from one type of natural material.

(a) Identifying Manufactured Materials

Basic manufacturing processes frequently used in the production of manufactured materials are relatively simple, often involving

irreversible chemical reactions. These reactions are important in order to

provide further raw materials for more complicated secondary

processes.

The physical process of raw materials would include the refining of

metals from ores, the firing of ceramic from clays and the making of

glass from sand and minerals.

SELF-CHECK 8.3

1. What is a natural material?

2. State some objects that are made from natural materials.

3. Give as many examples as you can of raw materials that can be foundin your surroundings.

8.3

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The sawing of timber, the production of paper from wood pulp and the

production of latex from rubber are examples of basic manufacturing

processes that involve biological raw materials. Secondary industries

involve the production of plastics (including synthetic fibres such as

nylon and terylene) from crude oil derivatives, detergents, paint and

perfume from coal, and others.

Manufactured materials usually have better properties compared to the

natural materials from which they come from. They are usually designed

for specific needs, like tyres are made of latex and sulphur. Metals, glass, ceramics, plastics (including rubber), paper and fabrics are examples of

manufactured materials.

(b) Objects from Manufactured Materials

Table 8.9 lists a few examples of objects from manufactured materials

and their uses. You can list your own examples that are used in our daily

life.

Table 8.9: Objects from Manufactured Materials

Manufactured Material

Synthetic Polymer

Uses

Synthetic

rubber

Styrene butadiene rubber (SBR)

Tyres, shoe soles

Neoprene rubber Water pipes, hand gloves

Butyl rubber Tyres, shoe soles, hoses

Metals Stainless steel Cooking utensil,

Bronze Medals,

Duralumin Cooking utensil

ACTIVITY 8.7

Search the Internet for manufactured materials. Find out theproperties of manufactured materials.

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PRESERVATION OF NATURAL

MATERIALS

About a century ago, almost the entire country was covered with forests. Wild

cutting of forests during the early settlement caused vast areas of bared land.

This phenomenon of cutting down plants for timber and development

continues today.

Preservation refers to the effort to maintain natural resources in their original state or in good condition. Generally, preservation is related to conservation.

Conservation refers to the sustainable use and management of natural

materials to prevent loss, wastage or damage.

The importance of preservation is to ensure a continuous supply of natural

resources, reduce environmental pollution, maintain balance in nature,

prevent extinction of living organisms, prevent loss of habitats and keep the

environment clean and conducive for healthy living.

Preservation should be practised. Some of the actions that should be taken to preserve natural materials are:

(a) Preventing Forest Fires

Forest fires are wildly destructive. Plants and wildlife are killed. Forest

fires are caused by lightning (natural cause) and peoples carelessness

(accidental cause).

(b) Improvement Cutting

Unwanted trees in a forest are removed from the stand. Crooked, aged

and diseased trees as well as trees of less desirable species are cut. In this way, space is provided for the growth of healthy, more valuable trees.

This practice increases lumber yield and improves its quality.

(c) Enforcement of Laws and Regulation

This action is taken to protect endangered species and to prevent them

from becoming extinct. Examples of protected endangered species are

the Malayan tiger, Sumatran rhinoceros, leatherback turtle, orang utan

(see Figure 8.7) and deer.

8.4

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cellulose fibres in a lignin matrix (see Figure 8.8). Seashells and limestone are

both made of calcium carbonate, but seashells are much harder because they

are composites of crystalline calcium carbonate with embedded polypeptide

fibres.

Figure 8.8: The combination of cellulose fibres and lignin make the cell wa ll

strong

The composite industry was launched in the early 1960s with the development

of fibreglass or glass reinforced plastic. It is made by embedding short fibres of glass in a matrix of plastic. The glass fibres give the plastic extra strength so

that it does not break when it is bent or moulded into shape. The finished

product has the lightness of plastic as well as the strength and flexibility of the

glass fibres. They have found in many marine, housing, construction, sports

and industrial applications. Figure 8.9 shows the use of glass reinforced

plastic in making the body of the boat.

Figure 8.9: The glass reinforced plastic used to make boats

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Another composite material which is usually used for the construction of large

structures like high rise buildings, bridges and oil platforms are reinforced

concrete (see Figure 8.10). Concrete is a composite material that consists of a

mixture of stones, chips and sand bound together by cement. It is strong but

brittle and weak in tensile strength. To overcome this weakness, the concrete

can be reinforced with steel wire netting or steel rod, which results to a very

tough material with high tensile strength. Reinforced concrete is relatively

cheap and can be moulded into any shape.

Figure 8.10: The reinforced concrete with steel wire netting and steel rods

The strongest new composite are the advanced composites, in which fibres are

aligned or interwoven before being set within the resin. Advanced composites

have extraordinary strength in the direction of the aligned fibres and are

relatively weak in the perpendicular direction. Weakness in one direction can be overcome by laminating layers together at different angles, as in plywood,

a familiar composite. Strength in all directions can be achieved by weaving the

fibres into a three dimensional network. Besides strength, advanced

composites are also known for their lightness, which make them ideal for car

parts, sporting goods and artificial limbs. Advanced composites tend to be

expensive, however because much of their production is still done by hand.

Aeroplane parts, and even whole aeroplane, are now being fabricated out of

lightweight advanced composites in order to save fuel. In 1986, the first plane

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built with all advanced composites material is Voyager, which can fly

around the world without refuelling (see Figure 8.11).

Figure 8.11: The all advanced composite Voyager aeroplane

MATERIALS IN INDUSTRY

Let us now learn on the materials in industry.

8.6.1 Soap

Millions of tonnes of soaps are manufactured worldwide every year (see

Figure 8.12). Soap is manufactured by heating natural fats and oils of either

plants or animals with a strong alkali. These fats and oils, called triglycerides,

are complicated ester molecules. Pioneers prepared their soap by boiling

animal fat with an alkaline solution obtained from the ashes of hardwood. The

resulting lye soap could be salted out by adding sodium choride, because

soap is less soluble in a salt solution than in water.

8.6

ACTIVITY 8.10

1. What is a composite and what are some examples found in nature other than given in the text?

2. Where are you most likely to find composites in the marketplace today?

3. Why are composites an ideal material for aircraft?

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Figure 8.12: Soap is manufactured by heating natural fats and oil with a strong

alkali

Nowadays, fat is boiled with aqueous sodium hydroxide to form soap. The

esters are broken down in the presence of water hydrolysed. This type of

reaction is called saponification . The equation given below is that for the

saponification of glyceryl stearate (a fat) (see Figure 8.13).

Figure 8.13: Saponification reaction

glyceryl stearate + sodium hydroxide sodium stearate + glycerol

(soap)

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The cleaning properties of the soap depend on its structure and bonding.

Sodium stearate consists of a long hydrocarbon chain which is hydrophobic

(water hating) attached to an ionic head which is hydrophilic (water loving)

(see Figure 8.14).

Figure 8.14: Simplified diagram of a soap molecule

Covalent compounds are generally insoluble in water but they are more

soluble in organic solvents. Ionic compounds are generally water soluble but

tend to be insoluble in organic solvents. When soap is put into water which

has a greasy dish (or a greasy cloth) in it, the hydrophobic hydrocarbon chain

on each soap molecule become attracted to the grease and become embedded

in it (Figure 8.15).

Figure 8.15: How soaps work

withagitation

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Figure 8.17: Polyisoprene (natural rubber)

Natural rubber commonly has highly elasticity but is unstable to heat and oxidation. When it is warmed above 50C, it softens and becomes sticky and will decompose if

we heat it to a temperature above 200C. The presence of double bonds in the polymer chain makes it susceptible to oxidation and breaks up the polymer chains.

Vulcanisation is a manufacturing process discovered by Charles Goodyear in 1939 to convert natural rubber into a tough useful product. In this process, about 1% to 3% by weight of sulphur is added to raw rubber and the mixture is carefully heated. Sulphur atoms form cross links between adjacent chains of rubber polymer at the carboncarbon double bonds (see Figure 8.18).

Figure 8.18: Vulcanised rubber showing disulfide cross links

Synthetic rubber is any type of artificial elastomer mainly synthesised from

petroleum by products. An elastomer is a material with the mechanical (or

material) property that it can undergo much more elastic deformation under

stress than most materials and still return to its previous size without

permanent deformation. Synthetic rubber, like natural rubber, has uses in the

automotive industry for door and window profiles, hoses (see Figure 8.19),

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belts, matting, flooring and dampeners (antivibration mounts). Table 8.10

shows the differences between synthetic rubber and natural rubber.

Table 8.10: Comparison of Properties between Manufactured Materials

(Synthetic Rubber) and Natural Materials (Natural Rubber)

Synthetic Rubber Properties Natural Rubber

Synthetic Type of polymer Natural

Able to withstand

high temperature High temperature effect

Decomposes and

become liquid Very permeable to

gas and water Permeability to gas and

water Not permeable to gas

and water

Does not react to

acid and alkali

Ability to withstand

actions of acid and

alkali

React to acid and

alkali

Low ability Ability to absorb

pressure, vibration and

sound High ability

Can be vulcanised Vulcanisation Easily vulcanised

Figure 8.19: Product from synthetic rubber

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8.6.3 Natural and Synthetic Fibres

Natural fibres can be defined as substances produced by plants and animals

that can be spun into filament, thread or rope and in a next step be woven,

knitted, matted or bound. The oldest fibres used by mankind are cotton

(5,000BC) and silk (2,700BC), but even jute and coir have been culti vated since

antiquity. The main reasons for the popularity of biocomposites or natural

fibre composites are the availability and consistent quality of a wide range of

fibres, and their environmental friendliness. Moreover, new production

processes, such as injected moulded components, make it possible to use these materials for industrial products.

Additional key advantages of natural fibres are their high strength and

stiffness per weight along with benefits such as acoustic isolation, safety

management, rapid production and potentially low cost. The most viable

structural fibres typically derive from specifically grown textile plants and

fruit trees. There are two categories of natural fibres, vegetable fibres and animal fibres . Vegetable fibres are subdivided into bast fibres (flax, hemp, jute

and kenaf) leaf fibres (sisal, pineapples and henequen), grass fibres (bamboo

and miscanthus), straw fibres (corn and wheat), seed fibres (cotton and capok), wood fibres (pinewood) and fruit fibres (coconut), whereas animal

fibres are silk, avian, hair and wool (see Figure 8.20). Figure 8.21 shows kenaf

plants which is from the bast fibres category.

Figure 8.20: Two categories of natural fibres

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Figure 8.21: Kenaf plants is a source of natural fibre

Synthetic fibres are made from synthesised polymers or small molecules. The

compounds that are used to make these fibres come from raw materials such

as petroleum based chemicals or petrochemicals. These materials are

polymerise into a long, linear chemical that bond two adjacent carbon atoms.

Different chemical compounds will be used to produce different types of fibres. Although there are several different synthetic fibres, they generally

have the same common properties. Synthetic fibres are commonly very heatsensitive, resistant to most chemicals, insect, fungi and rot. It has low moisture

absorbency, flame resistant, low melting temperature. Synthetic fibres are also

very easy to wash and maintain and the main thing is that it is often less

expensive than natural fibres.

The first synthetic fibre known as nylon was discovered in 1931. Its novel use

as a ma terial for womens stocking overshadowed more practical uses, such as

a replacement for the silk in parachutes and other military uses. Other common synthetic fibres are modacrylic, olefin, acrylic, polyester and carbon

fibre. Specialty synthetic fibres include vinyon, saran, spandex, vinolon,

aramids, modal, sulfar, orlon, zylon, vecran, derclon and rayon. Figure 8.22

shows two examples of synthetic fibres.

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\

Figure 8.22: Nylon and polyester

8.6.4 Plastics

With a record

of

wartime

successes,

plastics

were

readily

embraced

in

the

post war years. In the 1950s, Dacron polyester was introduced as a substitute

for wool. The 1950s was also the decade during which the entrepreneur Earl

Tupper created a line of polyethylene food containers known as Tupperware

(see Figure 8.23).

ACTIVITY 8.11

1. Compare and contrast natural fibres and synthetic fibres.

2. Find out the uses of all common natural and synthetic fibregiven in the text

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Figure 8.23: Tupperware, polyethylene food container

A plastic material is any material of a wide range of synthetic or semisynthetic organic solids that are mouldable. Plastics are typically organic

polymers of high molecular mass, but they often contain other substances

known as additives. They are usually synthetic, most commonly derived from

petrochemicals, but many are partially natural. The amount of additives range

from zero

percentage

for

polymers

used

to

wrap

foods

to

more

than

50%

for

certain electronic applications. Example of additive is fillers which function to

improve performance and/or reduce production costs. Stabilising additives

include fire retardants to lower the flammability of the material.

Plastics are usually classified by their chemic al structure of the polymers

backbone and side chains. Some important groups of these classifications are

the acrylics, polyesters, silicones, polyurethanes and halogenated plastics.

Other type of classification is based on the chemical reaction toward heat.

Examples are thermoplastics and thermosetting polymers. Thermoplastics are

the plastics

that

do

not

undergo

chemical

change

in

their

composition

when

heated and can be moulded again and again. This type of plastics includes

polyethylene, polypropylene, polystyrene and polyvinylchloride.

Thermosetting polymers can melt and take shape once. After they have

solidified, they stay solid because in the thermosetting process, a chemical

reaction occurs that is irreversible. An example is the vulcanised rubber.

Other classifications are based on qualities that are relevant for manufacturing

and also on the physical properties.

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By the 1960s, a decade of environmental awakening, many people began to

recognise the negative attribution of plastics. Being cheap, disposable, and

non biodegradable, plastic readily accumulated as litter and as landfill. With

petroleum so readily available and inexpensive, however, and with a growing

population of plastic dependent baby boomers, little stood in the way of an

ever expanding array of plastic consumer products. By 1977, environmental

concerns started to grow, and in 1980s plastics recycling programmes began to

appear. Researches to produce biodegradable plastics have been done

progressively. An example is the use of starch powder mixed with plastics as a

filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically

engineered bacteria that synthesise a completely biodegradable plastic.

Physical properties of materials include elasticity, shininess, buoyancy, water absorbency, electrical conductivity and heat conductivity.

Other physical properties of materials include hardness, toughness and brittleness, strength, flexibility and solubility.

Elasticity is the ability of a material to return to its original shape and size after being bent, twisted, stretched and squeezed. Materials that are able to return to their old shape when force is no longer applied are called elastic materials.

Some materials are shiny and some are not.

Materials can also be divided into three types according to its ability to allow light to pass through it. These are transparent materials, translucent materials and opaque materials.

Buoyancy is the ability of materials to float in liquid.

SELF CHECK 8.6

Search from the Internet or other resource on research/products of

biodegradable plastics that has been done in Malaysia.

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Materials which can absorb water are known as absorbent materials and materials which cannot absorb water are known as non absorbent materials.

A material that allows electricity to pass through it is a material that conducts electricity.

A material that allows heat to pass through it easily is a material that conducts heat.

Magnetism is the property of materials to attract iron, for example, iron oxide, cobalt, nickel and certain types of alloy.

Knowledge about the properties of materials is very important, especially in choosing suitable materials to make various objects.

The properties of materials have many useful applications in our daily life.

Materials are made of thousands of small particles called atoms.

Materials can be divided into three categories according to their

components of atom: element, compound and mixture.

Materials can be classified into two types according to their use: natural

materials and man made materials or manufactured materials.

Natural materials originate from soil, rocks, water, plant, animal or

minerals.

Manufactured materials are made from a mixture of natural materials

through chemical processes.

Manufactured materials are designed according to the needs of the market.

Preservation refers to the effort to maintain natural resources in their

original state or in good condition. Conservation refers to the sustainable use and management of natural

materials to prevent loss, wastage or damage.

Composite materials are the materials which combine the properties of

two substances in order to get the exact properties required for a particular

job.

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Saponification is the process of making soap by heating natural fats and oil

with a strong alkali.

Polymerisation is the process of isoprene units join together to form

poly(isoprene) or natural rubber.

Synthetic rubber is any type of artificial elastomer mainly synthesised

from petroleum by products with better quality than natural rubber.

Natural fibres is substances produced by plants and animals that can be

spun into filament, thread or rope and in a next step be woven, knitted,

matted or bound, while synthetic fibre are made from synthesised

polymers or small molecules.

A plastic material is any of a wide range of synthetic or semi synthetic

organic solids that are mouldable. All plastics are polymers but not all

polymers are plastics.

Abiotic

Biotic

Component

Composite materials

Conservation

Element

Fibre Manufactured material

Material

Mixture

Natural material

Plastics

Preservation

Raw material

Rubber

Soap Synthetic

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Documents

Topic 8 Natural Materials and Manufactured or Man Made Materials