topic 8 natural materials and manufactured or man made materials
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TT oopp iicc
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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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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