AMINA.P.E

2nd M Sc BPS

CBPST, KOCHI

Introduction to composites: Definition:A composite material can be defined as a

macroscopic combination of two or more distinct material having arecogenisable interphase between them.

It consist of a continuous phase & discontinuous phase.

continuous phase is called matrix & discontinuous phase is

called reinforcement, which is stronger than the

continuous phase

Category of fibers &matrix for composites: Fibers:

Natural fibers

Synthetic organic fibers

Aramid fiber

Polyethylene fiber

Synthetic inorganic fibers

Glass fibers

Alumina fibers

Boron fibers

Carbon fibers

Si C fibers

Whiskers(SiC is available in the form of whiskers, i.e., small

single crystals):A few tens of microns in length and less than

one micro in diameter.

Matrix:

Polymer (polymeric composites)

Metals (metal matrix composites)

Ceramic (ceramic matrix composites)

Carbon (carbon/carbon composites)

Nanocomposites:

Polymer nanocomposites are also called polymer nanostructured materials.

They are materials of which composition includes at least one constituent with dimensions less than 100 nm.

Their feature is that the nanoscale constituents can drastically improve and/or modify properties and functionality of the macroscopic material.

A challenge in developing the nanocomposites is to make exceptional properties (mechanical, optical, etc.) of the nanomaterials obvious at the micro- and macroscale levels of the hosting bulk materials.

Nanoparticle classification:

Isodimensional or zero-dimensional; the same size in all directions; aspect ratio is close to unity (L/D ~1). examples: spherical silica, metallic nanoparticles, carbon black, fullerenes.

Fibrillar; examples: carbon nanotubes and cellulose nanofibrils. Layered; examples: clay mineral and synthetic.

The most common nanofillers used (inorganic): Clays, Carbon nanotubes, Carbon black, Fumed silica, Cellulose-based fibrils as organic nanofiller.

Basic preparation methods:

Solution dispersion,

Melt dispersion,

Sol–gel processing,

In situ polymerization,

Self-assembly (layer-by-layer technique).

What is In Situ?

In situ is a Latin phrase which translates literally

to 'In position'.

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What is In –situ technique?

Involve a chemical reaction resulting in the formation

of a very fine and thermodynamically stable

reinforcing phase within a matrix.

In -situ polymerization process:

Nanoparticles are dispersed in a liquid monomer or relatively low-molecular-weight precursor as well as in their solution.

When a homogeneous mixture is formed, initiator is added and it is exposed to appropriate source of heat, light, etc.

The polymerization performed in situ results in the nanocomposite.

Polymers thus synthesized are called thermoset.

Polymerization can be processed either within a mould cavity or in some other in situ situation.

Thermosets are usually covalently cross-linked that does not allow them to reshape. They can be reused by granulating and using as a filler.

Nylon-6 was first used to develop nanocomposites by in situ polymerziation of caprolactam monomer.

Epoxy, phenolic, bismaleimide and cyanate polymers as thermosets are applied to manufacture nanocomposites.

To promote the crosslinking process, the curing of these polymeric material usually needs the use of a hardener or catalyst.

In a case, for example, epoxies, such cross-linkers as amines, anhydrides, and Lewis acids are applied.

The disadvantage of use of curing agents is that they modify the physical properties and influence the functionality of nanocomposites.

Advantages :• There is thermodynamic compatibility at the matrix-

reinforcement interface.

• Also, the reinforcement surfaces are likely to be free of

contamination~ Therefore, stronger matrix dispersion bond

can be achieved.

• Important for the preparation of insoluble and thermally

unstable polymer composites, which cannot be processed by

solution or melt processing.

• For preparation of polymer composites with high nanotube

loading, in-situ provides very good miscibility with almost any

types of polymers.

In -situ polymer processing:• In-situ polymerization methods used to fabricate CNT-

PMMA composites by incorporating CNTs during the course of polymerization of MMA.

• Basic starting materials:1. Nanotubes

2. MMA monomer

• Method: In-situ free radical polymerization method involves polymerization of monomer using a radical initiator such as 2.2´-azobisisobutyronitrile (AIBN).

• CNTs are dispersed through ultrasonication in the prepolymer.

Adding CNT at prepolymer provides good dispersion in the low viscosity of the prepolymer.

As the polymerization progresses, the viscosity of the solution increases and the polymer grows and wraps around the dispersed CNTs.

Benefits:

a) Higher interfacial strengths as CNTs interact with the growing polymer, thus forming stronger CNT-polymer bonds via non-covalent or covalent interactions.

b) Composites with enhanced mechanical, electrical and tribological were obtained.

Ingot Metallurgy

(Synthesis of composites)

Al (99.9%) +

Ti (99.7%)

Graphite powder

(40-50 μm)

Heated

1100 °C – 1200°C

1h

1300 °C – 1400°C

10 minutes

Mixture direct chill

cast into ingot bars

Melt in

graphite-lined

induction

furnace with

argon gas flow.

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Example of ingot metallurgy:

PRECIPITATION

PMMA/GO COMPOSITE:

• The method for achieving controlled dispersion of grapheneoxide(GO) , in PMMA via the precipitation polymerisation process in a water/methanol mixture.

• GO act as surfactant and adsorbs on the interface between polymerised PMMA particles and solvent mixture.

• SEM confirmed that the precipitate consist of particles surrounded by the GO sheets. Compression molding of the precipitate yields a polymer nano composite with GO organized into a regularly spaced 3D network which percolates at 0.2 wt % GO.

DIAGRAM