Designer materials - PowerPoint PPT Presentation

What are designer materials?

Designer fibres are found in the fabrics of the clothing we wear to stay comfortable outdoors or when playing sports.

Lightweight waterproof clothing used to be made from nylon and PVC, but sweat often condensed inside the materials making them cold, wet and uncomfortable.

Today, special polymers are woven into fabrics to make them breathable, elastic or insulating.

The properties of many of these designer fibres were discovered by accident.

Insulating fabrics help to keep the body and extremities warm during cold weather.

Thinsulate™ is a synthetic insulating fabric made from thick polyester ‘staple’ fibres and very thin polypropylene fibres.

The lightweight polypropylene fibres in Thinsulate™are about 10 times thinner than those in other fabrics.

This means that more air can be trapped in the fabric, preventing the body's heat from escaping.

The first elastic fibres, known as elastane or ‘spandex’, were created from polyurethane in the 1940s by DuPont, and later became known as Lycra®.

When mixed with traditional or man-made fibres, elastic fibres allow clothes to stretch and recover their shape.

Unlike traditional rubber thread, Lycra® fibres are lightweight and resistant to damage from sunlight, sweat and detergents.

Lycra® fibres are made up of two distinct segments:

• A softsegment made from polyester.When Lycra® is stretched, the polyester segments expand up to six times their original length without being damaged. When released, the polyester segments contract, twisting and looping around themselves.

• A hardsegment made fromurethane. Urethane stretches very little but is rigid and gives Lycra®a high tensile strength (resistance to tearing).

Breathable fabrics are designed to keep the wearer warm and dry in extreme weather, but still allow sweat to escape.

GORE-TEX® is a breathable fabric made from a microporous membrane made from expanded polytetrafluoroethene (ePTFE).

The ePTFE is very fragile, so it is laminated between layers of nylon or polyester for added strength.

It is coated with a special covering to protect against oils, cosmetics and other substances that could cause damage.

Bullet-proof vests (or soft body armour) are made from tightly woven fibres and are much more flexible and comfortable than hard body armour.

Many bullet-proof vests are made from Kevlar® – a synthetic fibre called poly-paraphenylene terephthalamide.

Kevlar® is used as a protective material because it is:

• flexible and lightweight

• heat resistant

• five times stronger than steel (weight-for-weight)

In bullet-proof vest, several layers of Kevlar® fibres are tightly interlaced with each other and sandwiched between layers of plastic film.

These layers are then woven to an outer layer of normal ‘carrier’ fabric.

When a bullet or other object strikes the vest, it pushes backon the Kevlar® fibresat the point of impact.

As this happens, each fibre extends horizontally and vertically, distributing the impact over the whole fibre network.

Smart materials are plastic and metal items designed to instantly change their properties when triggered by a stimulus.

Common properties that can be significantly altered in smart materials include:

• size and shape

• state (solid, liquid, gas)

• viscosity

• conductivity

Different smart materials can respond to different stimuli, such as temperature, pressure, magnetism and voltage/current.

Shape memory polymers (SMPs) are rigid plastics that transform into other shapes when heated.

When SMPs are heated above their ‘transition’ temperature, they become very stretchy and flexible, allowing them to take on dramatically different shapes.

When the polymer is cooled it becomes fixed in this new shape and is very strong. When reheated it will automatically return to its original ‘memorized’ shape.

The ‘memory’ of an SMP comes from the mechanical energy stored when the polymer was first produced.

Because SMPs have such flexible properties they can be reshaped hundreds of times without degrading. Many SMPs are also biodegradable.

SMPs could be used in a range of products such as non-iron clothing (washing would trigger the fabric to de-crease) to biodegradable surgical stitches that gently tighten at body temperature, closing the wound.

Shape memory alloys (SMAs) are similar to shape memory polymers, in that they change shape when heated. The difference is that SMAs are made from metal.

SMAs work because their crystal structure changes at different temperatures.

One type of SMA is Nitinol, made from nickel and titanium. This is used to make flexible-framed spectacles, dental braces and medical equipment.

Other types of SMA change shape when exposed to strong magnetic fields or electric currents.

Thermocolour film is made from a thin layer of liquid crystals on a black background.

When heated, the structure of the liquid crystals changes, causing different wavelengths of light to be reflected and therefore changing the colour.

Thermocolour pigments can be contained in microcapsules bound to clothing fibres. When the clothing is heated, the structure of the pigment molecules alters, changing the colour of the clothing.

Polymorph is a biodegradable polymer that becomes soft and mouldable when heated to about 60°C, for example with hot water or a hair dryer.

The polymorph can then be moulded into any shape required. As it cools, it sets hard and can be drilled, sawn and filed.

If the polymorph is heated again it will become semi-liquid and can be fully reshaped. Where might polymorph be useful?

Almost all products are packaged in some way for protection during transportation, handling or storage.

New types of ‘smart’ packaging are able to mechanically, chemically and electronically respond to their contents.

For example, a sensor fitted into fruit packaging detects chemicals released by the fruit as it ripens, and changes colour. This allows the customer to choose when to eat the fruit according to their preference.

Active packaging maintains the quality of products without the use of food additives. The packaging contains substances that absorb oxygen or moisture, or prevent the growth of microbes.

In normal (passive) packaging, oxygen molecules can pass through the wrapping, encouraging food spoilage and the growth of bacteria.

Sachets, bottle cap inserts and high-tech labels containing iron oxide or ascorbic acid bind to free oxygen molecules and trap them away from the package contents.

Nanotechnology is the science and technology of making items from nanoparticles.

Nanoparticles are single atoms or molecules that range from 1 to 100 nanometres (10-9m) in size. There are one billion nanometres in a metre.

Because nanoparticles are so small they have many surprising properties, making them potentially useful in a hundreds and thousands of applications.

Carbon nanotubes are a cylindrical arrangement of carbon molecules. They are hollow and align into ‘ropes’ held together by intermolecular forces.

Carbon nanotubes have many useful properties, including:

• very high tensile strength

• unique electrical properties, including superconductive at low temperatures

• good heat conductance

Multi-walled nanotubes exist, where several concentric tubes lie within in each other. The inner tubes can rotate and slide within the outer tube almost without friction.

structural

electrical

medical

How many different applications of carbon nanotubes can you think of?

A few examples include:

waterproof & tear-resistant fabrics

wires, circuits & motors

killing bacteria

strong, lightweight sports equipment

conductive films & displays

drug delivery systems

improving the strength of building materials

(electro)magnetic devices

regenerating damaged tissue

Because nanoparticles are so small, if they are free to move (rather than fixed to a surface), they could be absorbed by the skin and lungs, and enter the bloodstream and cells.

Although nanoparticles are routinely used in items such as sunscreens, cosmetics and toothpaste, little is known about the potential health and environmental risks.

A concern is that nanotubes might have similar effects as asbestos, which can causes respiratory diseases and cancer.

How have the media reported the risks and benefits of nanotechnology?

The glue on the back of Post-it® notes is contained within thousands of tiny spheres, each the same size as a paper fibre.

The glue was discovered accidentally in 1968 by Dr Spence Silver, a research scientist at 3M, while trying to develop super strong adhesives.

The glue in Post-it® notes is very adhesive but only a few spheres make contact with an object at any one time.

This means that Post-it® notes can be easily removed and reapplied many times.

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Teflon® was created by accident in 1938 when scientists at DuPont experimented with refrigeration gases.

The scientists produced a waxy resin – polytetrafluoroethene (PTFE) – that was inert to almost every chemical and stable over a wide temperature range.

PTFE is a chain of carbon atoms surrounded by fluorine atoms. The bonds between carbon and fluorine are very strong, and the fluorine ‘protects’ the carbon chain.

Teflon® is the slipperiest material in the world. In which products do you think it would be useful?

Hydrogels are a network of superabsorbentwater-soluble polymers that can be natural (e.g. made by seaweed) or synthetic. They are found in many products, such as:

• nappies and sanitary towels

• contact lenses

• water-release granules for plants

Hydrogels can be made into thin films, which make ideal wound dressings. They absorb liquid from the wound and swell, producing a soft, non-stick cushioning gel. Antiseptics can be added that are released directly into the wound.

Sunscreen contains active ingredients that prevent the skin from absorbing the Sun's dangerous ultraviolet (UV) rays and causing damage.

Inorganic ingredients like zinc oxide and titanium oxide act as physical barriers, reflecting the Sun’s UV rays.

Organic ingredients like oxybenzone act as chemical barriers, filtering the UV radiation and dissipating it as heat.

• GORE-TEX – A waterproof, windproof and breathable fabric containing a microporous membrane made of ePTFE.
• hydrogel – A network of polymers that can absorb large amounts of water.
• Kevlar – A soft body armour that contains lightweight fibres that are stronger than steel.
• Lycra – An elastic fibre made up of a polymer that has a hard, rigid segment, and a soft, stretchy segment.
• shape memory polymer – A polymer that changes shape when it is heated and then cooled. When reheated, it returns to its original shape.
• smart material – A material that can respond to changes in its environment.