Submitted by,

Menon Lakshmi Suresh

Roll No : 11

CPBST

Introduction Manufacturing How silicone materials work Properties Applications

Silicones are a family of materials that include siloxanes & silanes.

Silicones derive ultimately from silicon, as contained in sand & other minerals. It is thesecond most common element in the Earth’s crust.

Silicones are sophisticated products that are extremely versatile & can be manufactured in more than 2,000 different forms, within the general categories of silanes, fluids, elastomers & resins.

Silicones have important chemical & physical

qualities derived from their molecular

structure.

Depending on requirement these include

longevity, thermo stability, chemical,

electrical & ultraviolet resistance, enduring

elasticity, tensile strength ,inertness

& microbial resistance.

They can be formulated either to resist or

absorb water. They are much valued

for their purity, especially for

advanced electrical devices,&

for their cleanliness

Silicones are durable, reliable & often

employed to enhance or to confer specific

performance properties.

They promote sustainable development by

making other materials last longer-reducing

society’s consumption of basic raw

materials to ensure their availability for

future generations.

Silicones, or polysiloxanes, are inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl, ethyl, and phenyl.

These materials consist of an inorganic silicon-oxygen backbone (...-Si-O-Si-O-Si-O-...) with organic side groups attached to the silicon atoms, which are four-coordinate.

Silicon does not exist on its own in nature. Most of it is bound with oxygen in materials like sand and quartzite and granite rock.

The silicon-oxygen bond in quartz is so stable it can only be broken by white heat!

Silicon producers reduce high-grade quartz sand to elemental silicon via a carbo-thermic smelting process:

SiO2 + 2C Si + 2COSand(silica ) carbon Silicon carbon monoxide

This reaction occurs in an electric furnace at <1,400°C (<2,600°F).

The carbon monoxide gas (g) leaves the furnace so the silicon cannot react with the carbon to form silicon dioxide.

The molten elemental silicon, which is about

99 percent pure, is then cooled and broken

into lumps.

When used in silicone production, the silicon

is ground into a fine powder to increase the

surface area available for reactions

Silicones Value Chain Silicones are a vital ingredient in a large &

diverse number of final applications.

Silicones may be supplied directly to

producers of final products but more often

they pass through several stages of what is

known as the ‘value chain’.

This means that their routes to end markets

may be complex, involving several

interdependent stages.

The diagram below shows the way the value chain works. This is a

highly simplified representation of a system which, in real life, is

sophisticated, complex & covers many more products than the examples

shown.

Raw

materialsSilicone producers

Transform

silicon

metal

made from

sand into

basic

silicones

Basic

silicones

Formulators

Silicone fluid

Silicone elastomer

Silicone resin

Silicon metal

Convert basic

silicones into

products

Silicones’ chemical structure allows them to be produced in a number of variations.

By using siloxane units with different valences, products can be made with oily, polymeric, resinous or cross linked properties.

At the same time, the organic groups bound to the silicon pave the way for a diverse range of modifications.

It is this variability that makes possible the impressive variety of silicone products: greases, release agents, antifoam agents, paint additives, paper coatings, hydrophobizing agents, high or room-temperature vulcanizing silicone rubbers, and many, many more.

Silicone is usually tetravalent but can assume hexavalantcharacteristics

Silicon is more electropositive than carbon and hence silicon-carbon bonds are polar

Moulded silicones are characterised by the following points :

Good dimensional stability at high temperature

Good electrical and dielectric properties over wide frequent & temperature ranges

Low water absorption

Good flow properties

Long curing time in comparison with other moulding compounds

Limited shelf life

Average level of mechanical properties

High cost

Resistance to Chemicals : Dilute mineral acid & alkaline solutions, sea water, methanol, glycol & formic acid

but not resistant to aromatic hydrocarbons, numerous solvents & concentrated acids & alkalis

Weathering resistance : The weathering resistance of silicone resin mouldings is same as other thermo set compounds such as epoxy, phenol formaldehyde & unsaturated polyester-styrene mouldings

Flammability : Silicone exhibits a higher temperature than other plastics. It burns so long as an ignition source is present, developing a characteristic silica smoke.

Toxicological Assessment: Silicone resins not usually used for utensils which come in contacts with food, although the silicones are basically physiological inert

Compounded rubbers are suitable for normal

processing techniques employed in rubber

technology

e.g Extrusion, calendaring and compression

moulding

Availability Silicone polymers are available in various

forms such as oils, resins ,pastes and

elastomeric moulding compounds.

Silicones work two ways – mechanically and

chemically – to improve performance and

enable innovation.

Their flexible backbone and unique surface

activity, silicones can do many things very

well.

Common types of silicone products adhere,

manage foam, add gloss and shine, lubricate,

release, soften and condition, emulsify, and

waterproof substrates.

Silicone fluids principally consist of chains of

alternating silicon and oxygen atoms with the

free valences of the silicon occupied with

organic radicals (“R,” usually methyl groups,

though in special cases they may also be phenyl,

vinyl or amino groups).

Silicone fluids are transparent, tasteless and

odourless liquids with no known harmful effects.

Their viscosities lie between 0.65 and 1,000,000

mm2/s depending on the type. They have

excellent thermal resistance from -60 to +300°C.

Silicone fluids are also characterized by very

low volatility, excellent shearing resistance,

low surface tension and very good water

repellence

Another important feature, of course, is

their remarkable electrical properties over a

wide temperature range.

Silicone fluids are ideal for use as hydraulic or transformer oils, damping liquids, diffusion pump fluids, thermally resistant lubricants, dielectrics, defoamers and release agents for photocopiers and laser printers.

Used for hydrophobic treatment of glass and mineral wool.

Special silicone fluids can be processed into impregnating agents for textiles and leathers.

They are also used in very small amounts as paint additives. Other important applications are to be found in cosmetics, pharmaceuticals and medicine.

How silicone release agents work

One of the key properties of silicone is its

low surface tension – in particular, its low

critical surface tension of wetting (or low

surface energy). This combines with the low

cohesive strength conferred by its methyl

groups to give silicone excellent release

characteristics.

Unlike more rigid carbon-carbon backbones,

silicone polymers can easily expose their

low-interacting/surface-active methyl groups

to provide low adhesion, or easy release.

Silicone benefits for release

Excellent spreading on many different

substrates, including metal mould surfaces

Thermal stability

Formulations with the ability to cure to form

thin films that do not transfer or interfere

with the bulk properties of the substrate

Lower surface tension than typical acrylic

and SBR adhesives, facilitating release in

pressure-sensitive label applications

Typical silicone release agent applications

Release liners for pressure-sensitive adhesive

labels

Rubber tire release

Metal mould release

Food release

Silicone resins are prepared batchwise by

hydrolysis of a blend of cholorosilanes.

Highly branched polymer structures, they are

networks of irregular, mainly tri- or

tetrafunctional structural units. Because they

can be combined with many organic

polymers, it is possible to tailor the

numerous properties of silicone resins

e.g. their curing behaviour, flexibility,

adhesion properties or weathering resistance.

The outstanding heat resistance of silicone

resins is particularly striking.

They can sustain high temperatures of 200 to

250 °C in continuous service, and even up to

600 °C for brief periods.

Their dielectric behaviour is ideal.

Moreover, silicone resins’ excellent oxidation

resistance and superb mechanical properties

make them particularly durable and

economic materials.

Silicone resins as pure products, solvent-based and solvent-free systems, emulsions, but also powders.

With their excellent thermal resistance, silicone resins are first class binders for all heat-resistant coatings.

Silicone resins with reactive groups are principally used for modifying alkyd, epoxy and acrylic coatings. Such modified coatings offer excellent weathering resistance and elasticity (e.g. for coil coating).

In the plastics industry, silicone resins are also used as heat-resistant moulding compounds and release coatings.

Silicone resins’ excellent heat resistance and

outstanding range of properties are also very

much in demand for electrical applications,

such as binders for fiberglass laminates and

cements for incandescent lamp base.

In addition, they are useful as water

repellents in masonry protection or as

binders in silicone resin facade paints.

Silicone rubber compounds consist of long-

chain polysiloxanes and various fillers, such

as pyrogenic silica. They can be cured to

form silicone elastomers.

They are classified according to the curing

method, the viscosity of the base polymer,

and whether they cure at high or room

temperature.

• heat stability 180 °C , 300 °C peak temperature)

• down to -50 °C, special grades -110 °C

• color

• flame retardance

• low compression set

• sun, weathering, UV resistance

Only contain : siloxanes, silica, cross linker/catalyst

• No organic stabilizers, organic impurities, preservatives, animal-derived products

and genetically-modified organisms

• No plasticizers or softeners like phthalates

medical and pharmaceutical articles

Silicone Elastomer

Room temperature curing

One componentRTV-1

moisture curing

Tin-catalyzed

High temperature

curing

Solid Silicone RubberHCR

Peroxide curing Platinum curing

Liquid Silicone RubberLSR

Two componentsRTV-2

Platinum curingAddition curing

Platinum-catalyzed

Condens. curing

Tin-catalyzed

SILICONE ELASTOMERS –

CLASSIFICATION BY CHEMISTRY

High-Consistency Silicone Rubber (HCR) Solid silicone rubbers are cured at elevated temperature, either by means of organic peroxides or platinum catalysts.

The cured rubber is compounded with reinforcing fillers to give it its mechanical strength.

No known physical or physiological harmful effects, and excellent aging resistance.

Applications in the automotive industry, in the electrical transmission and distribution sector, electrical applications, food and personal hygiene, machinery and plant construction and in the construction industry.

High-temperature-vulcanizing rubbers also include liquid silicone rubbers. Their consistency and curing mechanism give them outstanding processing advantages.

Liquid silicone rubbers are characterized by a low viscosity compared to solid silicone rubbers and other elastomers. Liquid silicone rubbers are free-flowing, pumpable two-component compounds that are supplied ready to process..

Used in the automotive industry, transmission and distribution, electrical, food and personal care, through the machinery, plant engineering and construction sectors to medical applications.

advantages

- short cycle time

- fully automated injection molding process

- molds with up to 128 cavities

- complex part geometries possible

- 2-compentent injection molding possible

HCRLSR

advantages

- better mechanical properties,

- various processing techniques

- compression molding

- extrusion

- calendering

Two-Component Silicone Rubber (RTV-2)

RTV-2 silicone rubbers are two-component

pourable, spreadable or kneadable compositions

that vulcanize when the curing agent component

is added and form highly elastic silicone rubber.

They are cured at room temperature (RTV =

room-temperature vulcanizing).

There are two ways of vulcanizing them:

condensation curing is performed with an

organotin catalyst, generating alcohol as

byproduct. On the other hand, uses a platinum

catalyst and does not produce byproducts.

RTV-2 silicone rubber products allows cured

rubbers to be produced with extremely

versatile, highly specialized properties.

Therefore, they offer solutions to problems

in diverse industrial sectors, including

moldmaking, electronics and

optoelectronics, household appliances,

machinery and industrial plant engineering,

medical applications.

One-Component Silicone Rubber (RTV-1)

RTV-1 silicone rubbers are one-component systems.

They consist of polydimethylsiloxane, curing agent, fillers and additives. After application, they are cross-linked by contact with atmospheric moisture releasing by-products in the process.

Crosslinking starts with the formation of a skin on the surface of the applied silicone rubber and gradually works its way into the compound.

RTV-1 silicone rubbers solve numerous problems in sealing bonding and coating. Their outstanding weathering and aging resistance is the result of their special chemical properties

Silicones can take many forms – from liquids to solids –that allow engineers, scientists, inventors and companies to use them as a vital component in thousands of consumer and industrial applications.

Whether as fluids, rubber, gels, resins or mixtures, it is their versatility that makes silicones a key ingredient in products that make our lives better every day.

From baking moulds and cars to computers and precision engineered spacecraft, silicones can be found in a myriad of applications.

Put simply, silicones make things work better.

SILICONES &

CONSTRUCTION

Silicone materials have revolutionized

construction since they were first introduced on

the market in the 1960s.

Silicones bond with most materials, from concrete, glass, granite and marble to aluminium, steel and plastics.

They are extremely durable and can resist decay caused to other materials by rough weather conditions, moisture or sunlight.

Silicone sealants can prevent humidity and hot or cold air from coming through joints and cracks, thereby making buildings more energy efficient. Their flexibility can also reduce damage from small to medium-scale earthquakes.

These unique properties silicones are essential not only in residential and office buildings, but also in bridges, oil rigs, industrial plants and pipelines

As modern means of transport become faster, more reliable and more efficient, demands on materials to perform become tougher. As such, smaller parts must resist exposure to extreme heat, moisture, salt and fuels. Most materials deteriorate in these conditions, but not silicones.

Silicones retain their properties and – most important –ensure that cars, ships, airplanes and trains operate safely for the long haul.

SILICONES &

TRANSPORT

Cars and vans

Silicones are used in almost all aspects of car

assembly, from the tires to the engine, windows

and sun-roof.

They insulate electronic parts, reduce tire rolling

resistance, bond lightweight materials together,

and seal windows and doors.

The same can be said about silicones’ uses in

airplanes, trains, and even space vessels.

Ships and boats

Silicone-based paints and coatings are safer alternatives

to traditional marine coatings and paints.

By applying these silicone products to hulls of ships and

boats, the build-up of dirt and film is dramatically

reduced, thereby improving fuel efficiency enormously.

For large cargo ships, this improvement is particularly

important because ships’ fuel consumption is quite

significant. This fact makes the benefit of silicones in

this application all the more impressive – fuel savings

outweigh CO2 emissions from production of the silicone

product 182 times!

Reducing the environmental impact

Silicones make an impressive contribution to

minimising fuel consumption of cars and ships, thus

reducing significantly the CO2 footprint of the

transport sector.

SILICONES &

HEALTH

When it comes to health care, we want the best for ourselves and our families.

We want the reassurance that the tools used by health care professionals are

safe, clean and dependable. Health care professionals want that too and more.

Silicones are well tolerated by the human skin and body.

They can facilitate healing, improve the appearance of existing scars, and reduce discomfort. This makes silicones an integral part of innovative medical treatments and care.

Medical applications and infant care products with silicone can satisfy the highest quality standards demanded by health care professionals and their patients.

Resistant to bacteria, silicones are easy to sterilize and are excellent for sensitive applications, such as respiratory tubing and topical medications.

Silicones do not react with other materials and do

not irritate the body.

They are also hypoallergenic so can be used safely

for skin contact use as well as intravenously. Of

course silicones used in medical applications are

subject to thorough testing and regulations to

ensure their safety