Polymer Composites

Polymer composites definition

A composite is a material made from at least two or more materials with significantly different chemical and physical properties. When combined, they form another material that has properties different from the individual components.

Components are made of two parts: a fibre and a matrix. Fibres can be materials such as polyethylene, glass, carbon fibre, or Kevlar. At the same time, a matrix is what holds the fibres together.

The matrix is usually a thermoset such as an epoxy resin, polydicyclopentadiene, or polyimide. To make the material of the matrix stronger, the fibres are embedded into the matrix. This is one of the most common types of composite materials, called fibre-reinforced composites.

These days, polymer composites have found applications in various fields. They’re physical, chemical, and mechanical properties are what sets them apart from other metals.

• Good corrosion resistance.
• Lightweight
• Good abrasion resistance
• High strength along the direction of their reinforcements
• High stiffness
• faster assembly

• The individual characteristics of the fibre material
• The individual characteristics of the polymer matrix material.
• The ratio to which the fibre and the polymer matrix are combined (Also known as the fiber volume fraction)

Factors that decide the performance of polymer composites

And the geometry and the orientation of the fibre materials inside the polymer composite.

The performance of the polymer composites is usually called the mechanical properties of the composite materials. The mechanical properties are the most important physical and chemical properties.

Factors that influence the mechanical properties of composites:

The factors that influence the mechanical properties of the composites are given below:

• Size
• Type
• Concentration dispersion of reinforcing agent (filler)
• The interfacial tension between the matrix and filler

Polymer Composites are classified at two distinct levels:

The first level of classification: This is made according to the polymer matrix constituents. The major component classes under this type of classification include:

• Metal matrix composites (M.M.C.s)
• Organic matrix composites (O.M.C.’s)– Further divided into two classes of components: the polymer matrix composites (P.M.C.s) and the Carbon Matrix Compos, also known as the carbon-carbon composites.
• Ceramic matrix composites (C.M.C.s)

The second level of classification: This is made according to the reinforcement form. These are further divided into:

• Fibre-reinforced components are further divided into fibres containing continuous and discontinuous fibres.
• Laminar Composites.
• Particulate Composites.

Polymer composite materials

Metal matrix composites (M.M.C.s)

Applications of Metal matrix composites (M.M.C.’s)

The Aluminum-based matrix composites are widely seen in the aerospace and automotive industries. Fiber-based titanium composites are used in developing the structures of the aircraft. Titanium-based composites are used for manufacturing missile and aircraft structures, whose operating speeds are very high.
The main disadvantage of titanium-based composites is that they are highly reactive. Magnesium–matrix composites have lower thermal conductivity and are used actively in the space industry. Superalloys are commonly used for the manufacture of turbine blades as they operate at higher speeds and temperatures.

Polymer matrix composites (P.M.C.’s)

These polymer matrix composites are the most produced composite matrix materials. The fibers in Polymer Matrix Composites (P.M.C.’s) are embedded in the organic polymer matrix. This kind of polymer is used to enhance the properties of the materials.

These types of polymer composites are present in almost every aspect of life. Its applications range from gadget components to automotive accessories. The most common type of polymers that are used as composites is either elastomers, thermosetting polymers, or thermoplastic polymers. The many added advantages of the Polymer matrix composites (P.M.C.’s) include:

• Attractive optical properties
• Lesser specific weight
• High material stability against corrosion
• Economic mass production
• Ease of shaping
• Good electrical insulation
• Good thermal insulation

Properties of Polymer matrix composites (P.M.C.’s)

Properties of Polymer matrix composites (P.M.C.’s)

The two distinct types of categories include:

• Reinforced plastics: These P.M.C.’s have more strength as the embedded fibrous matter is added to plastics.
• Advanced Composites: These types of P.M.C.’s contain combinations of matrix and fibers. They facilitate more strength and stiffness. These composites contain continuous fibers such as aramid, graphite, organic fibers, and high-stiffness glass.

The detailed classification of polymer matrix composites is as follows:

• Glass Fiber Reinforced Plastic (GFRP) or FRP Composite:

When new fibers of glass are drawn, they are coated with a size. This is a thin layer that protects the glass fiber from undesirable environmental conditions and other damages. Before composite Fabrication, the size is removed and is replaced with a coupling agent that promotes the bond between the polymer matrix and the fiber.

The glass fiber reinforced plastic composite has high strength, but they are not used to construct airplanes or bridges because of their low rigidity and stiffness.

Applications of glass fiber reinforced plastic polymer composite

Glass Fiber reinforced Plastics – GFRP holds many applications, some of them include:

• Transportation industries
• Plastic pipes
• Storage container
• Automotive and marine bodies
• Industrial floorings

Carbon Fiber Reinforced Polymer composites

Advantages of using Carbon Fiber Reinforced Polymer Composites CFRP

• Among the other reinforcing fiber materials, Carbon fibers have the highest specific modulus and specific strength.
• At elevated temperatures, carbon fibers can retain their strength and modulus.
• Carbon fibers are not affected by acids, bases, moisture, etc., at higher temperatures.
• According to the applications of CFRP, the carbon fibers can be engineered.
• The manufacturing process of Carbon fibers are relatively cost-effective and inexpensive.
• Non-crystalline and graphite regions are represented by carbon fibers. The matrix materials include pitch, polyacrylonitrile (P.A.N.), and rayon.
• Usually, the carbon fibers are coated with an epoxy size, which improves the polymer matrix adhesion.

Applications of Carbon Fiber Reinforced Polymer CFRP

• Both military and commercial, helicopters (wing, body, etc.)
• Extensively used in sports, filament-wound rocket motor, recreational equipment (fishing rods, golf clubs).
• Cars (aircraft structural components and pressure vessels)

Aramid fiber reinforced polymer composites

The first organic fiber used as reinforcement in polymer composites was an aramid-fiber reinforced polymer. When compared to steel and glass fibers, aramid fibers have better mechanical properties and equal weight. This group of materials is known as the poly para phenylene terephthalamide.

Kevlar and Nomex are the most common aramid materials. Having high strength and moduli, these fibers are weak in compression. These fibers are susceptible to degradation by strong acid and bases and are stable at high temperatures (-200°C to 200°C).

Applications of Aramid fiber reinforced polymer composites – AFPC

• Automotive brake
• Missile cases,
• Bulletproof vests,
• Sporting goods, ropes, and clutch lining gaskets, etc.

Metal Matrix Composites

The matrix materials of M.M.C.’s are ductile metal.

The advantages of M.M.C.’s over P.M.C.’s include

• Higher operating temperature,
• Resistance to degradation by organic fluids.
• Non-flammability,

Ceramics Matrix Composites

If there is a slight increase in particle volume, producing compressive stresses near the tip’s surface. This stops the growth of the particle.

Reasons that cause is crack propagation n the ceramic whiskers:

• Deflecting crack tips.
• Energy absorbed from dull-out whiskers that are detached from the polymer matrix
• Forming bridges across crack forces.
• If there is redistribution of the stresses in the crack tips.

Applications of Ceramics Matrix Composites C.M.C.’s

Dome of the applications of CMC’s include the following:

• Aerospace sector
• Cutting tools
• Energy sector

Carbon Carbon Composites

In the Carbon-Carbon Composites (C.C.C), the carbon fiber is reinforced into the carbon fiber matrix. These composites are highly resistant to thermal shocks and have high tensile strength and moduli. The major drawback is that they are susceptible to oxidation at higher temperatures.

The processing techniques of such composites are complex, and hence the techniques for production are expensive. This is because carbon fibers are impregnated into the

polymer resin, and then to give it the final shape, we allow the resin to cure.

Applications of Carbon-Carbon Composites:

• Furnace fixturing
• Heat shields
• Load plates
• Heating elements
• X-ray targets.

Hybrid Composites

These contain glass fibers and carbon fibers. These types of composites are good for sports and orthopaedic components.

• Super hybrid
• Interplay hybrid
• Intraply hybrid
• Interplay – Intraply – a combination of both
• Super hybrid

Applications of hybrid composites

• CFRP and aluminum honeycomb– Antenna dishes
• CFRP & G.R.P.- device shaft of automobile, leaf, and springs.
• CFRP & GRP– Helicopter rotors.
• CFRP/GRP/Wood hybrid– golf club racquets, Artificial limb, external bearing.

Structure Composites:

• Sandwich Panels

The sandwich panels consist of 2 sheets that are separated by less dense material. This has lower strength and stiffness. The core is foamed or made of honeycomb materials.

Applications

• Roofs
• Floors,
• Walls of buildings,
• Aircraft wings.
• Laminated Composite

These composites are made of many laminae. The Lamina is thin, about 0.1mm to 1mm.

Examples:

• Plywood
• Sheet molding compounds
• Tufnol
• Metal to metal laminate
• M.C.
• Linoleum

Factors Affecting Properties of P.M.C.’s

Interfacial Adhesion

The composite material’s behavior is based on the individual elements’ combined behavior: the polymer matrix, the fiber/interface, and the reinforcing element. The interfacial adhesion must be strong so that the mechanical properties of the composite materials are strong. The matrix molecules determine the extent of interfacial adhesion.

Shape and Orientation of Dispersed Phase Inclusions

The particles are mainly used to improve the properties of the isotropic materials and have no preferred directions. The shapes of the reinforced particles can be cubic, regular or irregular, or spherical. The particulate reinforcements have directions that are almost equal in every direction.

Thermoplastic polymers

Thermoplastic polymers contain branched or linear molecules that have weak intermolecular and strong intramolecular bonds. The application of heat and pressure can reshape these polymers. These can either be semi-crystalline or amorphous in structure.

The plastic materials can be melted or softened by heating, and they get set again when cooled is called Thermoplastics.

Types of thermoplastics:

• Polyamide (nylon)
• PTFE
• LDPE
• HDPE
• Polystyrene
• PMMA
• PVC
• Polypropylene

Uses: Thermoplastic Polymers

Thermoplastic Properties and applications

• Polypropylene– String, rope, medical and laboratory equipment, and kitchen utensils.
• Polystyrene (P.S.)- Rigid packaging.
• Low-density Polythene (LDPE)- plastic bags, packaging, Toys, and film wrap.
• High-density Polythene (HDPE)- Plastic bottles and casing for household goods.
• PTFE, Teflon- Machine components, gears, non-stick cooking utensils, and gaskets.
• Polyvinyl Chloride (P.V.C.)- Flooring, pipes, cabinets, toys, and general household and industrial fittings.
• Polyamide (nylon)- bearings, gear components, Curtain rails, power tool casings, and clothes.
• Polymethyl Methacrylate (PMMA, acrylic) – Windows, bathroom sinks, signage, aircraft fuselage, and bathtubs.

Properties of Thermoplastic polymers

Examples:

Polyether ether ketone, Polysulfone, Nylons, Polyacetals, Polyamide-imides, Polycarbonate, Polyphenylene sulfide, Polyetherimide, Polyethylene, Polypropylene, Polystyrene.

Thermosetting polymers
A Thermosetting polymer is also known as a thermoset. It is a polymer that has heavily branched molecules that have a cross-linked structure.

The Thermosetting polymers are in their viscous state or soft solid state. These polymers undergo extensive cross-linking, which results in becoming insoluble products that are irreversibly hard.

Properties of Thermosetting Polymers

One of the most important properties of thermosetting polymers or plastics is that they become hard in their molding process. After the polymers are solidified, they cannot become softened in any other circumstances.

The thermosetting polymers, after they are molded, acquire a three-dimensional shape and have a cross-linked structure. The covalent bonds that the structure produces acquire the polymer to retain its strength and structure even if it is very high. Thermoset resins are insoluble.

Thermosetting Process

The processing of the Thermoset usually occurs in three stages.

Stage One- The first stage of the thermosetting process is known as the resole stage. In this stage, the resin is in an insoluble state and a fusible condition.

Stage Two- The thermoset resins in the second stage are partly soluble. In this stage, they tend to show similar characteristics to a thermoplastic where the changes are reversible.

The temporary state of a thermoset lasts for only a couple of minutes in its molten form. When the thermosets are in their molten state, they start forming cross-links as soon as there is more temperature increase.

Stage Three- this is when the cross-linking reaction occurs in the polymers. In this stage, the final structure of the thermoset polymers is created. This stage is similar to the molding stage, where the polymers are under controlled temperature and pressure.

The end product of the network structure consists of many cross-linked polymer chains. Once this polymer is formed, it cannot be thermally deformed under any circumstances.

The different kinds of thermosetting polymers

• Epoxy resin
• Urea-formaldehyde
• Melamine formaldehyde
• Polyester resin
• Phenol formaldehyde resin
• Polyurethane

Uses: Thermosetting Polymers

• Alkyl (polyester)

Industrial equipment housings, coatings, tool housings, brackets, automotive body panels, and fender/wing walls.

• Epoxy

Encapsulating for electrical components, laminates, coatings, casting compounds, and adhesives.

• Phenolic

Knobs and electrical motor components, relays, laminates, adhesives, handles (pans and cooking pots), electrical switch housings.

• Polyurethane

Automotive body panels, foams, adhesives, and coatings, sealants.

• Urea and Melamine Formaldehyde

Handles appliance components, adhesives, receptacles, closures, knobs, Electrical breakers, coatings, and laminates.

• Melamine formaldehyde

Electrical insulation, work surface laminates, and tableware.

Examples

Silicone, and polyimides, Polyesters, Phenolics, Ureas, Melamines, and Epoxies.

Difference between polymer and composite

Polymers- Is a long or larger molecule consisting of a network or chain of repeating units. Polymers are formed by chemically bonding together many monomers that are identical or similar small molecules. A polymer is formed by the joining of many small monomer molecules by a process called polymerization.

Composites– Made up of multiple compounds, components, or complexes.

Polymer composites applications – used in construction

There are several polymers used in civil engineering infrastructure. such as-

• R.P. (Reinforced plastics)
• GFRP(Glass fiber reinforced plastics)
• A.C.M. (Advanced composites material)
• F.R.P. (Fiber reinforced polymers

Rubber-Composites

Reinforced rubber products use the rubber matrix and combine another reinforcing material. This is done to achieve the desired flexibility and strength ratios.

The reinforcing material is usually a kind of fiber. This fiber is used to provide stiffness and strength. The rubber matrix has low stiffness and strength, and it is used to make the air-fluid tight and support its reinforcing materials to maintain the positions.

The positions are of great importance because they directly impact the mechanical properties of the composites.

Fiber reinforced components

These are fiber reinforced composite materials made of a polymer matrix reinforced with fibers.

The composer F.R.P. is used to strengthen the slabs, columns, and other beams. Even if the components’ structures are damaged due to the loading conditions, it is possible to increase their strengths.

The first human-made fiber-reinforced component was a raincoat. Charles Macintosh, a Scottish man, came up with this idea in the nineteenth century. He remembered that cotton is a form of a natural polymer called Cellulose.

This fiber that is embedded into the matrix is used to make the material stronger. The reason why fiber-reinforced composites are used is that their properties make them strong and lightweight. These composites are stronger than steel but weigh much lesser. This is why these composites are often used in automobiles as they make it fuel-efficient, and lesser pollution is emitted.

F.R.P. in Civil Infrastructure

F.R.P. is most popular in rehabilitation. This is the renewal of the construction of the buildings, pipelines, bridges, and other infrastructures.

The process of rehabilitation includes repairing damaged and deteriorated civil infrastructure.

Use of FRP in bridge rehabilitation

There are many parts of the bridge where FRP.’s are used:

• In bridge deck
• In stringer
• In abutment panel
• In retaining structure, parapets
• Steel girder

Use of F.R.P. in bridge deck and stringer

The F.R.P.’s are used to increase the service life of the bridge decks. Because of their lightweight, this reduces the construction of the time of the bridge deck.

Use of FRP in the abutment panel

The FRP composite panels provide a strong, durable, and lightweight structure. This structure will not rust like steel, rot like Wood, or spall like concrete.

Due to the corrosion-resistant and fatigue properties, the abutment panels have a long service life and a reduced maintenance cost.

Use of F.R.P. in the retaining structure

The high-temperature resistance, lightweight insulation, high strength and corrosion-resistance properties of F.R.P.’s are used in the retaining wall structure.

Use of FRP in the Parapets

The Parapet is strengthened with the help of Fibre Reinforced Polymer (F.R.P.). The F.R.P. is a cost-effective alternative to strengthen the parapets.

Use of FRP in the Parapets

Carbon fiber reinforced polymers (CFRP) are used for the effective strengthening of the steel girder bridges. The C.R.P. improvises the live load carrying capacity of the steel bridges.

Practical Applications of F.R.P. Bridges

There are many countries adopting FRP for the construction of bridges and their rehabilitation processes. Some of them are given below:

• Joffer bridge (Ontario, Canada)
• Wickwire run bridge(West Virginia, U.S.A.)
• Morristown( Vermont, U.S.A.)
• Tampico( Veracruz, Mexico)
• Peldar( Envigado, Colombia)

The Joffer bridge in Canada

For the rehabilitation of the Joffer Bridge in Canada, different F.R.P.’s are used to strengthen the sidewalk, the concrete deck slab, and the traffic barrier.

Additionally, fiber petro strain sensors are installed in the steel girders and the F.R.P. grid. This helps develop an understanding of traffic loading and environmental conditions.

Disadvantages

Greater initial expense
Many engineers and constructors are not familiar with F.R.P.
There is an increment of deflections due to the low modulus of elasticity,
The F.R.P.’s lack the required load-bearing capacity to handle the wall structures and the high-performance deck.
To build a bridge faster with low maintenance, one may use FRP’s.

FRP in the Automotive industry

31% of FRP is used in the automotive industry.

History

• After World War-2, Stout Engineering Laboratories replaced the aluminum framework with an eight-piece fiberglass body in a Minivan. The minivan was the first vehicle that used an air suspension.
• The first vehicle to use carbon composite materials for its body was Mclaren F1 MP4/1. It was built by McLaren using Carbon-Fibre-Composites supplied by Hercules Aerospace (the U.S.A.

Other vehicles include Stout 46, Ford Thunderbird – 1954, Chevrolet Corvette fiberglass body – 1953.

Why use composite parts in the automotive industry?

• The composite parts make the vehicle lighter. They are used in sports cars because of their fuel economy and low center of gravity.
• They have high strength to weight ratios.
• The carbon fibers make the vehicles more economical in electric cars because the lithium-ion batteries are otherwise expensive.
• The carbon-fiber body makes the vehicle have a better driving experience.

The replaceable body parts in the vehicles

• Outer frame/body
• Shocks, steering tie rods, even gears
• Chassis – monocoque cars

Fabrication methods used

• Prepreg molding
• VARTM, SQVARTM
• Compression molding
• Fitting pre-made carbon/glass fiber panels

Materials used

• Prepregs
• Glass fiber
• Carbon
• Epoxy resin
• Graphite reinforced polymers Sandwich structure
• Honeycomb and closed-cell cores fiber

Adaptations for the automotive processing

• Woven fabrics are used in the automotive industry to decrease the unidirectional nature.
• The adhesives used are- M.M.A. based, Epoxy/polyester, and polyurethane.
• Epoxy resins are used because their cute time is of 3-4 minutes.
• The low viscosity resins benefit the vacuum molding and the injection molding.

Natural Fiber Composites

The natural fibers are biodegradable, renewable, and non-abrasive. These possess a good calorific value, are inexpensive, and possess good mechanical properties.

The natural fibers are environmentally friendly, and that is why they are used extensively in the market.

Natural Composites exist in both plants and animals. A popular example is Wood. Made of cellulose fibers (polymer) and held together by a weaker substance named Lignin. These two substances form a strong bond. Cellulose is also found in cotton, but due to the absence of Lignin, it is much weaker.

The bones inside your body are also natural composites. It is made of a hard and brittle material named hydroxyapatite and flexible material called collagen. The collagen is found in other parts of your body too much as your fingernails and your hair. But without hydroxyapatite, they are not strong enough.

Early Composites

Composites have been a part of human life for over a thousand years. One such example of an early composite is mud bricks.

Early mankind have noticed that you can dry mud out easily, and one can give it shape to building material. It does not break if one tries to squash it ( because it has high compressive strength), but if one tries to bend it (due to its low tensile strength), it breaks easily. In contrast, straw can be stretched easily. Therefore by mixing both of these materials, early men made mud bricks resistant to squeezing and tearing.

Concrete is another example. Concrete is a mixture of sand, stone, and cement. This gives it good compressive strength. You can increase concrete’s tensile strength by adding wires or rods. The concrete that contains such materials is known as reinforced concrete.

Based on their origin, Natural composites are categorized into the following:

• Mineral Fibers
• Plant Fibers
• Animal Fibers

Plant Fibers

Plant fibers mainly consist of Cellulose. Examples- Flax, Sisal, Hemp, Ramie, Jute, Bamboo, Cotton, and Coir.

These cellulose fibers find many applications:

• Skin fibers (Received from the skin of the stems)
• Leaf fibers (Agave and sisal)
• Stalk fibers (Rice, bamboos, wheat)
• Fruit fibers (Banana and coconut)
• Silk fibers (Kapok and cotton)

Bananas produce textiles fibers. They grow easily in young shoots and are usually found in hot climatic regions.

All the banana plants have large fibers. This plant is a good source for the textile industry, especially in countries like Nepal and Japan

Properties of Banana Fiber

• It has smaller elongation.
• It is lightweight.
• It is a highly strong fiber
• The banana fiber is similar to bamboo fiber, but its spinnability and fineness is much better
• Depending upon the spinning and extraction process, the banana fibers have a shiny appearance.
• It absorbs moisture and releases it fast
• The chemical composition of banana fibers is Lignin, hemicellulose, cellulose.
• It is biodegradable
• It is an eco-friendly fiber
• You can spin it through bast fiber spinning, ring spinning, open-end spinning, and semi-worsted spinning.

Required materials for preparation

• Banana fiber
• Releasing agent
• Resin (Polyester)
• Hardener (methyl ethyl ketone peroxide)
• Filler (silicon powder)

Method of Preparation

Steps involved

The banana fiber is removed from the banana plant. The extracted fibers are dried out in the sun and then in the oven. This is used to remove the water content from the fiber. The fiber is mixed with the matrix mixture by simple stirring, and the mixture is poured slowly into molds of different sizes.

The releasing agent is used on the mold sheet and used to remove the composite from the mold easily. After pouring into the mold cavity, it is heated to 30 degrees. It is heated for 24 hours. A load is put on the mold constantly. After the curing is done, the specimen is taken out from the mold.

Composition of the materials in the banana composite: