Polymer Matrix Polymer Matrix Composites (PMC)Composites (PMC)

Reasons for the use of polymeric Reasons for the use of polymeric materials as matrices in materials as matrices in compositescomposites i. The mechanical properties of polymers i. The mechanical properties of polymers

are inadequate for structural purposes, are inadequate for structural purposes, hence benefits are gained by reinforcing the hence benefits are gained by reinforcing the polymerspolymers

Processing of PMCs need not involve high Processing of PMCs need not involve high pressure and high temperaturepressure and high temperature

The equipment required for PMCs are much The equipment required for PMCs are much simplersimpler

Disadvantages of PMCDisadvantages of PMC Low maximum working Low maximum working

temperaturetemperature High coefficient of thermal High coefficient of thermal

expansion- dimensional expansion- dimensional instabilityinstability

Sensitivity to radiation and Sensitivity to radiation and moisturemoisture

Classification of Polymer Classification of Polymer MatricesMatrices

1. Thermoset1. Thermoset 2. Thermoplastic- crystalline & 2. Thermoplastic- crystalline &

amorphousamorphous 3. Rubber3. Rubber

ThermosetThermoset Thermoset materials are usually liquid or Thermoset materials are usually liquid or malleablemalleable prior to curing, prior to curing,

and designed to be and designed to be moldedmolded into their final form into their final form has the property of undergoing a chemical reaction by the action has the property of undergoing a chemical reaction by the action

of heat, catalyst, ultraviolet light, etc., to become a relatively of heat, catalyst, ultraviolet light, etc., to become a relatively insoluble and infusible substance.insoluble and infusible substance.

They develop a well-bonded three-dimensional structure upon They develop a well-bonded three-dimensional structure upon curing. Once hardened or cross-linked, they will decompose curing. Once hardened or cross-linked, they will decompose rather than melt. rather than melt.

A thermoset material cannot be A thermoset material cannot be meltedmelted and re-shaped after it is and re-shaped after it is cured. cured.

Thermoset materials are generally stronger than Thermoset materials are generally stronger than thermoplasticthermoplastic materials due to this 3-D network of bonds, and are also better materials due to this 3-D network of bonds, and are also better suited to high-suited to high-temperaturetemperature applications up to the decomposition applications up to the decomposition temperature of the material. temperature of the material.

Some examples of Thermosets are:Some examples of Thermosets are: Polyester resinPolyester resin (used in glass-reinforced (used in glass-reinforced

plastics/fibreglass (plastics/fibreglass (GRPGRP)) )) Epoxy resinEpoxy resin (used as an adhesive and in (used as an adhesive and in

fibrefibre reinforced plastics reinforced plastics such as glass such as glass reinforced plastic and reinforced plastic and graphite-reinforced plasticgraphite-reinforced plastic) )

PolyimidesPolyimides used in printed circuit boards used in printed circuit boards and in body parts of modern airplanes and in body parts of modern airplanes

Vulcanized rubber Vulcanized rubber PhenolicPhenolic

PolyesterPolyester- polyester resins are generally copolymers of polyester resins are generally copolymers of

unsaturated polyesters with styrene unsaturated polyesters with styrene - Styrene is the crosslinking monomer and Styrene is the crosslinking monomer and

curing is effected by the use of an organic curing is effected by the use of an organic peroxide initiator which generates free radicals peroxide initiator which generates free radicals leading to the formation of 3-D networkleading to the formation of 3-D network

- Are relatively inexpensive and have low Are relatively inexpensive and have low viscosities, which is beneficial in many viscosities, which is beneficial in many fabrication processesfabrication processes

EpoxyEpoxy is a is a thermosettingthermosetting epoxide polymer that cures epoxide polymer that cures

(polymerizes and crosslinks) when mixed with (polymerizes and crosslinks) when mixed with a catalyzing agent or "hardener". a catalyzing agent or "hardener".

More expensive and more viscous than More expensive and more viscous than polyesterpolyester

Epoxies have a major advantage in that they Epoxies have a major advantage in that they are usually cured in two or more stages. This are usually cured in two or more stages. This allows preforms to be pre-impregnated with the allows preforms to be pre-impregnated with the epoxy in a partially cured stateepoxy in a partially cured state

The pre-preg may be stores, before moulded The pre-preg may be stores, before moulded into the final shape and then curedinto the final shape and then cured

- Generally start as linear low molecular weight Generally start as linear low molecular weight polymer, curing agents such as polyamides & polymer, curing agents such as polyamides & polyamines were used as curing agentspolyamines were used as curing agents

- The mechanical properties depend on the The mechanical properties depend on the particular resin system and the curing; particular resin system and the curing; generally epoxies are stiffer and stronger, but generally epoxies are stiffer and stronger, but brittle than polyesterbrittle than polyester

- Epoxies maintain their properties to higher Epoxies maintain their properties to higher temperature than polyestertemperature than polyester

PhenolicPhenolic Produced by reacting phenol and Produced by reacting phenol and

formaldehyde, characteristics of the resin formaldehyde, characteristics of the resin product depending on the proportions of the product depending on the proportions of the reactant and catalystreactant and catalyst

Good fire resistanceGood fire resistance An undesirable feature of phenolic resin- An undesirable feature of phenolic resin-

volatile by-product are evolved during curing; volatile by-product are evolved during curing; hence high pressures are often necessary in hence high pressures are often necessary in composite productioncomposite production

PolyimidesPolyimides

More expensive, less widely used than More expensive, less widely used than polyester and epoxies, but can withstand polyester and epoxies, but can withstand relatively high service temperaturerelatively high service temperature

The presence of ring structure, results in high The presence of ring structure, results in high stiffness, low CTE, and service temperature as stiffness, low CTE, and service temperature as high as 425C for several hourshigh as 425C for several hours

Like other thermoset, polyimides are brittleLike other thermoset, polyimides are brittle

where R′ and R″ are two carbon atoms of an aromatic ring.

ThermoplasticThermoplastic is a plastic that is a plastic that meltsmelts to a liquid when heated and to a liquid when heated and

freezes to a freezes to a brittlebrittle, very , very glassyglassy state when cooled state when cooled sufficiently. sufficiently.

Most thermoplastics are high Most thermoplastics are high molecular weightmolecular weight polymerspolymers whose whose chainschains associate through weak associate through weak van van derder Waals Waals forcesforces ( (polyethylenepolyethylene); stronger ); stronger dipole-dipoledipole-dipole interactions and interactions and hydrogen bondinghydrogen bonding ( (nylonnylon); or even ); or even stacking of stacking of aromaticaromatic rings ( rings (polystyrenepolystyrene). ).

The bondings are easily broken by the cobined action The bondings are easily broken by the cobined action of thermal activation and applied stress, that’s why of thermal activation and applied stress, that’s why thermoplastics flow at elevated temperaturethermoplastics flow at elevated temperature

unlike thermosetting polymers, thermoplastic can be unlike thermosetting polymers, thermoplastic can be remelted and remolded. remelted and remolded.

Thermoplastics can go through Thermoplastics can go through melting/freezing cycles repeatedly and the melting/freezing cycles repeatedly and the fact that they can be reshaped upon fact that they can be reshaped upon reheating gives them their name reheating gives them their name

Some thermoplastics normally do not Some thermoplastics normally do not crystallize: they are termed "amorphous" crystallize: they are termed "amorphous" plastics and are useful at temperatures plastics and are useful at temperatures below the below the TTg. They are frequently used in g. They are frequently used in applications where clarity is important. applications where clarity is important. Some typical examples of amorphous Some typical examples of amorphous thermoplastics are thermoplastics are PMMAPMMA, , PSPS and and PCPC..

Generally, amorphous thermoplastics are Generally, amorphous thermoplastics are less chemically resistantless chemically resistant

Depends on the structure of the Depends on the structure of the thermoplastics, some of the polymeric structure thermoplastics, some of the polymeric structure can be folded to form crystalline regions, will can be folded to form crystalline regions, will crystallize to a certain extent and are called crystallize to a certain extent and are called "semi-crystalline" for this reason. "semi-crystalline" for this reason.

Typical semi-crystalline thermoplastics are PE, Typical semi-crystalline thermoplastics are PE, PP, PBT and PET. PP, PBT and PET.

Semi-crystalline thermoplastics are more Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque. light, the thermoplastic is hazy or opaque.

Why HDPE exhibits higher cystallinity than Why HDPE exhibits higher cystallinity than LDPE?LDPE?

Polyetheretherketone (PEEK) is a Polyetheretherketone (PEEK) is a semicrystalline polymer having 20-40% semicrystalline polymer having 20-40% crystallinity.crystallinity.

It has a rigid backbones, which gives It has a rigid backbones, which gives high Tg and Tm (Tg= 143C and Tm= high Tg and Tm (Tg= 143C and Tm= 343C). Can be employed at temperature 343C). Can be employed at temperature as high as 230C)as high as 230C)

It is possible to blend two or more It is possible to blend two or more polymers to obtain a multi-phase product polymers to obtain a multi-phase product with enhances propertieswith enhances properties

Comparison of typical ranges of Comparison of typical ranges of property values for thermoset and property values for thermoset and thermoplasticsthermoplastics

PropertiesProperties t/sett/set t/plastict/plastic Young’s Modulus (GPa)1.3-6.0Young’s Modulus (GPa)1.3-6.0 1.0-4.81.0-4.8 Tensile strength(MPa)Tensile strength(MPa) 20-18020-180 40-19040-190 Max service temp.(ºC)Max service temp.(ºC) 50-45050-450 25-23025-230 Fracture toughness,KFracture toughness,KIcIc 0.5-1.00.5-1.0 1.5-6.01.5-6.0

(MPa(MPa1/21/2))

Thermoplastics are Thermoplastics are expected to receive expected to receive attention compared to attention compared to thermoset due to:thermoset due to:

Ease of processing Ease of processing Can be recycledCan be recycled No specific storageNo specific storage Good fracture modulusGood fracture modulus

RubberRubber

Common characteristics;Common characteristics; Large elastic elongation (i.e. 200%)Large elastic elongation (i.e. 200%) Can be stretched and then immediately return to Can be stretched and then immediately return to

their original length when the load was releasedtheir original length when the load was released Elastomers are sometimes called rubber or rubbery Elastomers are sometimes called rubber or rubbery

materialsmaterials The term The term elastomerelastomer is often used interchangeably with is often used interchangeably with

the term rubber the term rubber Natural rubber is obtained from latex from Natural rubber is obtained from latex from Hevea Hevea

BrasiliensisBrasiliensis tree which consists of 98% poliisoprena tree which consists of 98% poliisoprena Synthetic rubber is commonly produced from Synthetic rubber is commonly produced from

butadienebutadiene, spt , spt styrene-butadienestyrene-butadiene (SBR) dan (SBR) dan nitrile-nitrile-butadienebutadiene (NBR) (NBR)

To achieve properties suitable for To achieve properties suitable for structural purposed, most rubbers structural purposed, most rubbers have to be vulcanized; the long have to be vulcanized; the long chain rubber have to be crosslinkedchain rubber have to be crosslinked

The crosslinking agent in The crosslinking agent in vulcanization is commonly sulphur, vulcanization is commonly sulphur, and the stiffness and strength and the stiffness and strength increases with the number of increases with the number of crosslinkscrosslinks

PREPREGPREPREG

It is short form for pre-impregnation It is short form for pre-impregnation materialmaterial

It is a semifinished product It is a semifinished product It will be used in next processing It will be used in next processing

technique to obtain a finish producttechnique to obtain a finish product It can be produced from thermoset It can be produced from thermoset

or thermoplastic matrix or thermoplastic matrix

Thermoplastic prepregs are Thermoplastic prepregs are getting attention due to:getting attention due to:

Easy storage Easy storage High toughnessHigh toughness Fast & easy processingFast & easy processing Can be recycledCan be recycled