Polymer Composites

Polymer Composites

Above image credit: https://www.pslc.ws/macrog/kidsmac/composit.htm

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 fiber and a matrix. Fibers can be materials such as polyethylene, glass, carbon fiber, 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 a 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.

Properties of Polymer Composites

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

Factors that decide the performance of polymer composites

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

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

Classification of Polymer Composites

Polymer composites examples

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:

  • Fiber-reinforced components, which are further divided into fibers containing continuous and discontinuous fibers.
  • Laminar Composites.
  • Particulate Composites.

Polymer composite materials

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

Metal matrix composites (M.M.C.’s) are some materials (such as alloys, metallic, and intermetallic compounds) incorporated with reinforcing phases such as whiskers, particulates, or continuous fibers.

According to the matrix material, they are classified into the following metal matrix configurations:

  • Aluminum-based composites; Aluminum is either used as a cast alloy, or it is used as a wrought alloy (such as AlMgSi, AlZnMgCu, AlCu, AlMg, AlCuSiMn, AlSiCuMg)
  • Super alloy-based composites
  • Titanium-based composites
  • Magnesium-based composites
  • Copper-based composites
Polymer composites Classification of Metal Matrix Composite

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)

The overall properties of a P.M.C. are affected by its constituents; these are:

  • Matrix: This polymer is in the continuous phase. This is the weak link in the structure of the P.M.C.
  • Reinforcement: This part can either be carbon fiber, quartz, basalt, or glass. This is the main load-bearing element, and it is in the discontinuous phase.
  • Interphase: This part is where the load transmission takes place between the matrix phases and the reinforcement.
  • Apart from these factors, the properties of the P.M.C. are affected by the nature of the interphase, the reinforcement geometry, and the constituents’ relative proportions.

    The Polymer Matrix Composites (P.M.C.’s) are classified into different categories based on their stiffness and strength level.

Polymer matrix composites
Image credit: https://coventivecomposites.com/explainers/types-of-polymer-matrix/

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:

The Glass Fiber Reinforced polymer composite is produced in the largest quantities. GFRP composite or FRP composite consists of glass fibers in the polymer matrix. The diameter of the glass fiber ranges between 3-20mm. glass is widely used as reinforcement due to the following reasons:

  • You can draw glass easily into fibers from its molten state.
  • It is readily available
  • Glass is economical to fabricate
  • One can use many composite manufacturing techniques.
  • The composites produced from glass have high tensile strength.
  • When the glass fibers are combined with the polymer matrix, they possess chemical inertness. This composite is very useful in corrosive environments.
Glass fiber reinforced plastics polymer composite
Image credit: https://www.researchgate.net/figure/Glass-fiber-reinforced-plastic-GFRP-composite-beam_fig1_276042216

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

In Carbon Fiber Reinforced Polymer CFRP composites, the carbon fibers provide stiffness and strength to the polymer composites, whereas the polymer matrix holds the fibers together to provide some toughness.

Carbon fiber reinforced polymer composites
Image credit: https://link.springer.com/chapter/10.1007/978-3-030-39062-4_20

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

Ceramics Matrix Composites C.M.C.’s, the fibers, whiskers, or particulates of the ceramic’s internal toughness are embedded together into the ceramic polymer matrix. This technique increases the toughness of the polymer composite. The Ceramics Matrix Composites C.M.C.’s are fabricated by liquid phase sintering, hot pressing, and hot isotactic techniques.

The interaction between the advanced cracks formed and the dispersed phase particles improves the fracture toughness properties.

Transformation toughening is a technique in which partially stabilized zirconia is dispersed into the matrix material to retain the metastable tetragonal phase at ambient conditions.

The stress causes the particles to transform the monoclinic phase.

Ceramics Matrix Composites
Image credit: https://www.google.com/url?sa=i&url=https%3A%2F%2Flink.springer.com%2Fchapter%2F10.1007%2F978-981-10-2134-3_16&psig=AOvVaw076tYVcu3IGmbAJY2YYADG&ust=1611769225269000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCKiK-bKSuu4CFQAAAAAdAAAAABAD

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.

  • Properties of the Matrix

The properties of the polymer will determine the application of the matrix.

The main added advantages include:

  • Low specific gravity
  • Easy processability,
  • Good chemical resistance, and
  • Low cost.

Disadvantages

  • Low strength
  • Low modulus, and
  • Low operating temperature
Varieties of polymers for composites
Image Credits: https://www.adhesiveandglue.com/thermoplastic.html
  • 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.

This Wickwire Run Bridge was in critical condition and had to be replaced. In July 1997, a new bridge was constructed using F.R.P. The composite deck modules 500 supported by wide flange steel beams.

Advantages of using F.R.P. for civil infrastructure/construction applications

  • The use of F.R.P. in civil infrastructure increases the structure of service life.
  • The use of F.R.P. resulted in the faster construction of the bridges reducing traffic delays.
  • The added benefit of using F.R.P. in bridges is that You can optimize the product and system design for specific loads.
  • Working as a waterproofing material.
Wickwire Run Bridge
Image credit: https://cee.statler.wvu.edu/files/d/497e4726-93e8-4e92-8493-2beff19d5ac0/frp-bridges-in-wv-2-2-17.pdf.

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

  • Injection molding
  • 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)

Animal and Mineral Fibers

 

Mineral Fibers are those fibers that are extracted from minerals. These are either naturally occurring fibers or changed fibers.

 

Animal fibers contain a large number of proteins. Such as mohair, downy, cases, silk, alpaca. The animal strands are the animal’s hair, such as horsehair, alpaca hair, Sheep’s downy, goat hair, and so on.

Banana plant is a large herb that has leaves and emerges from stems. The height of the banana plant varies between 10-50 feet. Each plant is surrounded by at least 8-12 large leaves. The fibers are the waste end product of banana cultivation. So, without any additional costs, these fibers are sent for industrial purposes.

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.

Natural banana fibre
Image credit: https://www.indiamart.com/proddetail/natural-banana-fibre-18384698033.html

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:

  • Resin-60%
  • Hardener -10%
  • Filler- 30%

Properties of Banana Fibers:

  • Lignin- 15.00%
  • Residual Gum- 41.90%
  • Moisture Regain- 13.00%
  • Elongation- 6.54
  • Tenacity- 29.98 g/denier
  • Total Cellulose- 81.80%
  • Alco-ben Extractives- 1.70%
  • Alpha Cellulose- 61.50%
  • Fineness- 17.15

How does the fiber parameters affect tensile strength?

The mechanical behavior of the banana fiber is based on the epoxy composites. This depends on the fiber’s parameters.

The banana fiber’s tensile strength increases with an increase in fiber loading and length.

How does the fiber parameters affect the flexural strength?

When the fiber length increases, the flexural strength also increases up to 10mm, decreasing.

The fiber loading increases the fabricated composite’s strength by 15%, and then it decreases.

The maximum flexural strength is observed when the fiber length is 10mm, and then the fiber loading is 15%.

How do the fiber parameters affect the impact strength?

It is observed that the impact energy increases with an increase in fiber energy and also fiber length.

The maximum impact energy is absorbed by 15mm of the fiber material and 20% of the fiber content.

How do the fiber parameters affect the hardness?

The value of hardness increases with an increase in fiber length. The maximum fiber length is 10mm.

With an increase in fiber length, the fiber hardness value also increases up to 15%, decreasing.

Uses

  • Floor topping of houses
  • Construction industries
  • Automobile industries
  • Banana fiber composite wall
  • Window application
  • Production of paper
  • Currency
  • Teabags

Wood polymer composites

Wood Polymer Composites are composite materials made of thermoplastics, wood, fiber/wood flour such as P.V.C., P.P., PE, etc.

Chemical additives are added to the composite structure. They provide the integration of wood flour (powder) and polymer in an optimal processing condition.

It is estimated, in 2020, the Wood polymer composites market was USD 5.85 billion growing at a CAGR of 12.4%

History

In 1960, Covema in Milan was founded by the Terragni brothers, first invented and patented using W.P.C.’s.

Under Coleman, the W.P.C. was called by its trade name, Plastic-Wood. After a few years, A company named Icma San Giorgio was the first to add wood flour or wood fiber to the thermoplastics.

Uses of  Wood polymer composites

In North America, Wood polymer composites are widespread in the outdoor deck floors. These are also used for timbers, park benches, railings, landscaping, windows, fences, indoor furniture, and door frames.

Manufacturers claim that the wood composites are eco-friendly and they require less maintenance.

The most common production process for Wood polymer composites is the injection molding procedure. The polyethylene-based Wood polymer composites is the most common type of W.P.C. used in the industry. Additives such as blowing agents, lubricants, U.V. stabilizers, colorants, and foaming agents help the Wood polymer composites end product.

Advantages of using Wood polymer composites

  • Polymer composites (P.C.) are corrosion-resistant; they do not decay or rot.
  • They have good work abilities, and they can be reshaped using conventional wooding tools.
  • P.C.’s are considered a sustainable material because using recycled plastics; You can use them and the wood industry’s waste products.
  • Wood can be molded into its desired shape.
  • These materials do not need painting.

Disadvantages of wood polymer composites

  • Wood is susceptible to a fungal attack.
  • They have temperature-dependent behavior.
  • Lower strength
  • Vulnerable to U.V. radiation

Bio-Composites

A bio composite is formed by a resin (matrix) and a reinforcement of natural fibers. The resin matrix is formed by polymers derived from non-renewable and renewable resources.

The bio composites are divided into two categories, namely the non-wood fibers and wood fibers. Cellulose and Lignin are present in all of them. In addition to this, the principal components of biocomposites are fibers. The fibers are derived from biological origins.

For example, the fibers from crops are derived from (Hemp, cotton, or flax), regenerated cellulose fiber (rayon/viscose), crop processing byproducts, recycled Wood, wastepaper.

Carbon nanotube-polymer composites

Nanocomposites can be broadly classified into three-dimensions, i.e., one, two, and three-dimensional amorphous materials. These nanocomposites have different components that are blended at the nanometer’s scale. Nanocomposites differ in chemical and physical properties. It encompasses gels, copolymers, colloids, and porous media. The nanocomposite optical, catalytic, mechanical, and electrical properties differ from materials’ individual properties.

Nanocomposites are also found naturally, for example, in abalone shells and inside the structure of the bone.

The difference between conventional composite materials and nanocomposites is that they have a high surface to volume ratio of the high aspect ratio or the reinforcing phase. These are the properties that enhance the electrical and thermal conductivity of the nanocomposites. These properties enhance the optical properties of heat resistance or mechanical resistance, such as stiffness, strength, and resistance to wear and tear.

Polymer Nanocomposites

Polymer nanocomposites (P.N.C.) comprises a copolymer or a polymer with nanoparticles or nanofillers in the polymer matrix.

The shape of the nanofillers vary. These may be spheroids, fibers, or platelets. These dimensions must be under 50nm.

The change in the particles’ size from micro to nano causes changes in the materials’ properties. One of the most significant changes to be noticed is the increase in the surface area to volume ratio with the particle’s decreasing size.

This increases the atom’s dominant behavior.

Polymer carbon nanotube composites

There are two types of Polymer carbon nanotube composites

  1. Single-walled Polymer carbon nanotube composites – these consist of a single graphene sheet. The sheet is wrapped into cylindrically shaped tubes. The diameter of the tube ranges between 0.7mm to 2nm and have lengths of micrometers.
  2. Multi-walled Polymer carbon nanotube composites (MWCNTs)- Multi-walled Polymer carbon nanotube composites are concentric groups of SWCNTsthat have comparatively larger diameters. The unique individual properties of the Polymer carbon nanotube composites make them the best reinforcing agents in numerous applications.

Polymer carbon nanotube composites properties

  • Carbon nanotubes have a very high tensile strength
  • Carbon nanotubes are highly flexible; you can bend them highly without facing any damages.
  • Carbon nanotubes aspect ratio
  • Carbon nanotubes are very elastic- they possess 18% elongation to failure
  • Carbon nanotubes have a high thermal conductivity
  • Carbon nanotubes have high electrical conductivity
  • Carbon nanotubes have a low thermal expansion coefficient
  • Carbon nanotubes are good electron field emitters

Methods for Fabrication of polymer carbon nanotubes composites

 

One can use several methods to fabricate the C.N.T./polymer composites. These can either be thermosetting or thermoplastic matrices. They mainly include the following:

 

1) Solution mixing

2) Sol-Gel Method

3) In situ polymerization

4) Electrospinning

5) Chemical functionalization of carbon nanotubes

6)  Melt blending

Sol gel process diagram

Sol gel process diagram
Image credit: https://www.researchgate.net/figure/Steps-of-the-sol-gel-process-of-materials-and-examples-of-the-microstructure-of-final_fig1_260301110

The Sol-gel synthesis method produces nanocrystalline elements, alloys, and composite powders. This is the most cost-effective way to create such nanocrystalline materials. In the Sol-Gel process, the Sol is formed, followed by the gel’s formation. The Sol- is the suspension of the colloidal solid particles in the liquid phase. The sol gel is the network that is interconnected and is formed between the phases.

The Sol-Gel method is used to deposit the nanocomposite films. In this process, component materials such as metallic nanoparticles for metals, metal alkoxides and metal chlorides precursors for metal oxides, stabilizers, tetraethoxysilane for silica matrix, were prepared first.

The Sol material first undergoes hydrolysis, and then it undergoes polycondensation to form a gel-like network. The formation of the nanocomposite films from the sol-gel precursor involves a spin coating or a dip coating of the compounds. The growth of the crystallites follows the removal of water and the organics.

 

The requisites for obtaining a good quality in the sol-gel process

  • Phase transitions
  • Time
  • Drying
  • Concentration of Catalyzer
  • Concentration of Reagent
  • Variation of PH Temperature

Advantages of Sol-Gel Processes

 

  • Can get new composites of glass
  • With the help of the Sol Gel Process, we are able to get uniform & small sized powder
  • New microstructure and composition
  • The sol gel process is easier to be conducted for the coating of the films
  • Sol-Gel Processes can get objects or films with special porosity

In situ polymerization

Derived from the Latin phrase meaning, ‘In position.’ The in-situ technique involves a chemical reaction that results in a thermodynamically stable reinforcing phase and a matrix.

Process

In the In Situ Polymerization phase, the nanoparticles are first dispersed in a liquid monomer or a relatively lower molecular weight precursor and as well as in their solutions. When the homogeneous mixture is formed, the initiator is added, and then the mixture is exposed to the sunlight, heat, etc.

The polymerization performed in position or situ results in the formation of the nanocomposites. The polymers are synthesized; these are called the thermoset. The polymerization is processed within a mold’s cavity or in some other in situ situation. The thermosets usually do not reshape because of their covalent cross-links.

The thermosets can therefore be reused as a filler. Nylon-6 was the first nanocomposite to be developed as a product of the in-situ polymerization. Bismaleimide, Epoxy, phenolic, and cyanate polymers as thermosets are applied to manufacture nanocomposites.

To promote the cross-linking process, the use of a hardener or catalyst is needed. Epoxies, such cross-linkers as anhydrides, Lewis acids, and amines, are applied.

Advantages of the In-situ polymerization process

 

  • Thermodynamic compatibility
  • Free of contamination
  • Dispersion bond
  • Stronger matrix

Electrospinning nanofibers

The electrospinning method is used for drawing very small and fine nanoscale fibers from a liquid.

This technique is used for producing polymer fibers of diameters ranging from 2nm to several micrometers in size. This is done by using polymer solutions of both synthetic and natural polymers.

Electrospinning nanofibers shares the characteristics of the conventional solution dry spinning of fibers. For this reason, the electrospinning method is suitable for the production of fibers of very large and complex materials. Electrospinning gained much popularity due to its versatility and constant ability to produce fibers in the submicron ranges. This is otherwise very difficult to achieve using the stand technologies if the fiber-spinning.

Electrospinning nanofibers
Image credits: https://www.researchgate.net/figure/Schematic-view-of-electrospinning-process_fig9_305662363

Spun Nanofibers Also Offer Several Advantages Such As the following:

  • Tunable porosity
  • The electrospinning methodology can control the nanofiber composition. With this, we can achieve the desired results from its properties and functionality.
  • An extremely high surface-to-volume ratio
  • Malleability to strengthen to a wide variety of sizes and shapes

Polymers that are used in this process:

Electrospun nanofibers have been reported from various natural polymers, synthetic polymers, or a blend of both, including polysaccharides, nucleic acids, and even proteins.

Typical natural polymers include gelatin, casein, silk protein, chitin, cellulose acetate, collagen, chitosan, fibrinogen, etc. Better clinical functionality is promised by scaffolds fabricated from natural polymers.

Applications of Electrospun fibers

  • Drug delivery
  • Protective Clothing
  • Biomedical
  • Wound healing
  • Enzyme Immobilization
  • Filtration
  • Affinity Membrane
  • Scaffolds in the tissue engineering

Characterization of the Electrospun Nanofibers

The electrospun fibers are categorized into three distinct categories, those are:

  • Geometrical characterizations
  • Chemical characterizations

Mechanical characterizations

Challenges in Fabrication faced by Carbon Nanotube Polymer Matrix Composites

Carbon Nanotubes (C.N.T.’s) are the best reinforcing agents for high strength polymers. This is due to their high mechanical, magnetic, and electrical properties. The C.N.T. from stabilized bundles due to Van der Waals interactions. This makes them difficult to disperse. Tools are required for assessing the dispersion, controls, and alignments of the C.N.T.’s. 

Carbon Nanotubes Applications

 

  • Carbon Nanotubes conductive properties
  • Carbon Nanotubes conductive adhesive
  • Carbon Nanotubes fibers and fabrics
  • Carbon Nanotubes biomedical applications
  • Carbon Nanotubes thermal conductivity
  • Carbon Nanotubes energy storage
  • Carbon Nanotubes Air & Water Filtration
  • Carbon Nanotubes catalyst supports
  • Carbon Nanotubes thermal materials
  • Molecular electronics based on Carbon Nanotubes
  • Carbon Nanotubes structural applications
  • Carbon Nanotubes field emission
  • Other Carbon Nanotubes applications

Other potential applications of Carbon Nanotubes include nanoporous filters, catalyst supports, solar collection, and other coatings. It plays a role in air and water filtration, ceramic applications, structural composites, etc.

Synthesis of Carbon Nanotubes

The Arc Discharge Method

 

  • To synthesize the C.N.T.’s in small quantities, the first successful method used was the Arc Discharge method.
  • Graphite rods of Anodes and Cathodes made of 6mm and 9mm, respectively, are placed in an inert environment.
  • Once paced, a string current is passed between these two terminals. This generates a plasma that evaporates the carbon atoms in the graphite. This allows the nanotube to grow from the surface of the terminals.
  • A catalyst is then inducted into the graphite terminal.
  • The MWNTs can be formed without a catalyst, whereas SWNTs are only formed after inducing a metal catalyst such as cobalt or iron.

Laser Ablation technique

 

You first developed the Laser Ablation technique in 1995. This principle is similar to the Arc Discharge method.

In this method, using a graphite target, the carbon is evaporated from high temperatures using a laser beam. In this technique, a graphite target ranging from 1.25 cm is placed in a quartz tube in a furnace at 1200 degrees. This tube is filled with argon at a pressure of 500 Torr. The nanotubes are mixed with amorphous carbon and cooled at the end of the chamber.

Both of these methods are for scaleup. The solid graphite should be evaporated at 3000C. Extensive purification methods are required to remove the fullerenes and the carbon in the process.

Chemical Vapor Deposition (CVD)

For the mass production of carbon nanotubes, CVD has the highest potential. This can produce a bulk amount of Carbon Nanotubes at low temperatures.

Polymer processing methods

For the thermosetting matrix composites, the following are used for polymer processing:

  • Hand layup and spray-up techniques.
  • Resin transfer molding.
  • Pultrusion
  • Autoclave molding.
  • Filament winding.

For the Thermoplastic matrix composites, the following are used for polymer processing:

  • Diaphragm forming.
  • Injection molding.
  • Thermoplastic tape laying
  • Film stacking.

The Hand Layup Techniques

In the hand layup technique process, a gel coat is applied to the open mold. On the open mold, a fiberglass reinforcement is used. By pouring and brushing techniques, a base resin is applied with the help of catalysts. To obtain the desired amount of thickness that is required, one layer is stacked upon another layer.

The most popular open molding process in the industry is the hand layup molding process. Although this is a slow and manual process that involves labor work, this technique is quite famous.

This technique involves the following operations:

  • An anti-adhesive agent coats the mold. This prevents the molded part from sticking to the surface of the mold.
  • The prime surface is formed by applying a coating of gel. After this, a fine layer of the fiber reinforcing tissue is applied.
  • In the form of rovings chopping strands, and woven fabric, layers of the liquid matrix resin are applied. The mixture of the resin is applied either by a brush or a roll.
  • The parts are cured at room temperatures and are eliminated from the surface of the bold.

The disadvantages of the hand layup process include the low densification of the composites and the reinforcing phase’s low concentration.

Hand lay up process
Image credit: https://www.eppcomposites.com/hand-layup-process.html

Advantages of the Hand Layup method

The hand layup method is one of the most prevailing methods used in the industry to produce polymer composites. This method has many advantages; some of them have been listed down below:

  • Custom shape.
  • The hand layup method is widely used.
  • This method costs low tooling.
  • Heavier and complex items can be produced using this method.

Disadvantages of the Hand Layup method

The disadvantages of the hand-layup process include the following:

  • The hand layup method requires intensive labor.
  • Styrene emission.
  • Low-volume process.
  • Quality control is entirely dependent on the skill of laborers.

Hand Layup products

Aircraft skins, diesel truck cabs, boats, car bodies, hardshell truck bed covers, interiors, portable toilets, and picnic tables.

Spray lay up Process

During the spray lay-up process, chopped reinforcing fibers and the liquid resin matrices are sprayed on the mold’s surface. These fibers are chopped to 25-50 millimeters in length and then sprayed by an air jet simultaneously with a resin spray. This is sprayed at a predefined ratio between the matrix phase and the reinforcing.

This Spray Up method allows a uniform coating and faster formation. As the method cannot use continuous reinforcing fibers, the material’s mechanical properties are quite moderate. The roving is chopped into a spray gun. If automated with robots, this technique can produce higher results. The labor costs are much lower.

In this method, the resins and the fibers are sprayed continuously into the mold.

Spray lay up process
Image credit: https://netcomposites.com/guide/manufacturing/spray-lay-up/

Applications

  • small boats, caravan bodies, Bathtubs, truck fairings, etc.
  • Hand and Spray Layup
  • In both these layers, the deposits are densified with the help of rollers.
  • For this, accelerators and catalysts are used.

Why is a catalyst used?

The catalyst is used to initiate the curing process by adding the gel or resin coat.

Why is an accelerator used?

An accelerator is used to accelerate the action of the catalyst in a resin mix. The curing procedure is carried out either at moderately higher temperatures in an oven or at room temperatures.

Advantages of Hand Layup and Sprayup Methods

 

  • Tooling costs in these two methods are low.
  • Semiskilled workers are easily trained for these methods.
  • The methods are designed Flexible.
  • Structural changes and Molded-in inserts are possible.
  • Sandwich constructions is possible in both methods.
  • Complex items and large items can be produced.
  • Least equipment purchase is necessary.
  • The cost and the startup lead time are minimal.

Disadvantages of the Hand Layup and Sprayup techniques

 

  • Both the methods are Labor Intensive.
  • The Handup and Sprayup methods create low volume.
  • These have higher curing times.
  • Production uniformity is difficult in both the Hand Layup and Sprayup processes.
  • The waste factor is high in both processes.

Prepreg Process

Continuous fiber reinforcement in the industry is known as the prepreg method. In this method, a polymer resin is partially cured with a polymer resin. This is delivered to the manufacturer in the form of tape. The manufacturer then molds and cures the product fully without adding any resins.

For such reasons, the prepreg process is mostly used for structural applications. The manufacturing of the prepreg process begins by collimating continuous fiber tows. The tows are pressed within the sheets and carrier paper using heated rollers.

The paper sheet that is released is used to provide a solution for its impregnation of the fibers and is coated with a small quantity of resins. The final product consists of aligned and continuous fibers that are embedded in a partially cured resin.

The prepreg material is packaged by winding it into the core of cardboard. The thickness of the tape ranges between 0.08 and 0.25 mm, and the width is between 25 and 1525 mm.

The resin material lies between 35 and 45 vol%. The prepreg material is stored at 32 degrees Fahrenheit because, at room temperature, the matrix undergoes curling. You must reduce the time the prepreg is used at room temperature. The lifetime of the prepreg is about 6 months.

The common reinforcement materials are aramid fibers and carbon, glass fibers. The resins utilized are both thermoplastic and thermosetting. The fabrication process begins with the layup. To attain the desired level of thickness, the layers are stacked on top of one another. This layup can either be automated or by hand.

Applications of Prepreg

  • Pressure vessels,
  • Commercial products
  • Sporting goods,
  • Aerospace
  • Racing

Filament Winding

The filament winding involves the reinforcing materials to be wounded into a rotating mandrel. This rotation is done in layers at different layers. The wet filament winding process occurs when the liquid thermosetting resin is applied before the winding. If the resin material is sprayed into the mandrel with the wound filament, this process is called the dry filament winding. Autoclave curing may be used.