polymer composite

POLYMER COMPOSITE

What is Composites? Combination of 2 or more materials Each of the materials must exist more than

5% Presence of interphase The properties shown by the composite

materials are differed from the initial materials

Can be produced by various processing techniques

Constituents of composite materials

1. Matrix phaseContinuous phase, the primary phase. It holds the dispersed phase and shares a load with it.

2. Dispersed (reinforcing) phaseThe second phase (or phases) is imbedded in the matrix in a continuous/discontinuous form. Dispersed phase is usually stronger than the matrix, therefore it is sometimes called reinforcing phase.

3. InterfaceZone across which matrix and reinforcing phases interact (chemical, physical,mechanical)

Matrix: Function

however the distribution of loads depends on the interfacial bondingshowever the distribution of loads depends on the interfacial bondings

Reinforcement: Function

Reinforcement can be in the form of: Continuous fiber

Organic fiber- i.e. Kevlar, polyethylene Inorganic fiber- i.e. glass, alumina, carbon Natural fiber- i.e. asbestos, jute, silk

Short fiber whiskers Particle Wire

Interface: Function

To transfer the stress from matrix to reinforcement

Sometimes surface treatment is carried out to achieve the required bonding to the matrix

a) Concentration (b) size (c) shape (d) distribution (e) orientation

Characteristics of dispersed phase that might influence the properties of composites

Characteristics of dispersed phase that might influence the properties of composites

Classification of compositesClassification of composites

Examples of composites

a) Particulate & randomb) Discontinuous fibers & unidirectionalc) Discontinuous fibers & randomd) Continuous fibers & unidirectional

Classification based on MatricesComposite materials

Matrices

Polymer Matrix Composites

(PMC)

Metal Matrix Composites

MMC)

Ceramic Matrix Composites

(CMC)

Thermoset Thermoplastic

Rubber

What is Hybrid composites?What are the advantages of hybrid composites?

Widely used- ease of processing & lightweight

Composite materials in the Boeing 757(courtesy of Boeing Commercial Airplane Group)

Properties of composites depend on Amount of phase- Amount/proportion (can be expressed in

weight fraction (Wf) or volume fraction (Vf))of phases strongly influence the properties of composite materials.

Xc = Xf Vf + Xm (1 - Vf ) - Rule of Mixture

Xc = Properties of composites

Xf = Properties of fiber

Xm= Properties of matrix

Voids

Free volume Gas emission leads to voids in the

final product In composites- Voids exist in the

matrix, interface and in between fiber & fiber

Voids create stress concentration points- influence the properties of the composites

Geometry of dispersed phase (particle size, distribution, orientation)

Shape of dispersed phase (particle- spherical or irregular, flaky, whiskers, etc)

Particle/fiber size ( fiber- short, long, continuous); particle (nano or micron size)

Orientation of fiber/particle (unidirection, bi-directions, many directions)- influence isotropic dan an-isotropic properties

Dictribution of dispersed phase (homogenus/uniform, inhomogenus)

Processing technique and parameters

Influence final product, selection of correct raw materials, void content, etc

Glass Fiber The types of glass used are as follows: E-Glass – the most popular and inexpensive glass fibers. The

designation letter “E” means “electrical” (E-Glass is excellent insulator). The composition of E-glass ranges from 52-56% SiO2, 12-16% A1203, 16-25% CaO, and 8-13% B203

S-Glass – stronger than E-Glass fibers (the letter “S” means strength). High-strength glass is generally known as S-type glass in the United States, R-glass in Europe and T-glass in Japan. S-Glass is used in military applications and in aerospace. S-Glass consists of silica (SiO2), magnesia (MgO), alumina (Al2O3).

C-Glass – corrosion and chemical resistant glass fibers. To protect against water erosion, a moisture-resistant coating such as a silane compound is coated onto the fibers during manufacturing. Adding resin during composite formation provides additional protection. C-Glass fibers are used for manufacturing storage tanks, pipes and other chemical resistant equipment.

Fiberglasses (Glass fibers reinforced polymer matrix composites) are characterized by the following properties:

High strength-to-weight ratio; High modulus of elasticity-to-weight ratio; Good corrosion resistance; Good insulating properties; Low thermal resistance (as compared to metals and

ceramics). Fiberglass materials are used for manufacturing:

boat hulls and marine structures, automobile and truck body panels, pressure vessels, aircraft wings and fuselage sections, housings for radar systems, swimming pools, welding helmets, roofs, pipes.

Glass Fiber

Carbon Fiber The types of carbon fibers are as follows:

UHM (ultra high modulus). Modulus of elasticity > 65400 ksi (450GPa).

HM (high modulus). Modulus of elasticity is in the range 51000-65400 ksi (350-450GPa).

IM (intermediate modulus). Modulus of elasticity is in the range 29000-51000 ksi (200-350GPa).

HT (high tensile, low modulus). Tensile strength > 436 ksi (3 GPa), modulus of elasticity < 14500 ksi (100 GPa).

SHT (super high tensile). Tensile strength > 650 ksi (4.5GPa).

Carbon Fiber Reinforced Polymers (CFRP) are characterized by the following properties:

Light weight; High strength-to-weight ratio; Very High modulus elasticity-to-weight ratio; High Fatigue strength; Good corrosion resistance; Very low coefficient of thermal expansion; Low impact resistance; High electric conductivity; High cost. Carbon Fiber Reinforced Polymers (CFRP) are used for

manufacturing: automotive marine and aerospace parts, sport goods (golf clubs, skis, tennis racquets, fishing rods), bicycle frames.

Carbon Fiber

Kevlar Fiber Kevlar is the trade name (registered by DuPont Co.)

of aramid (poly-para-phenylene terephthalamide) fibers.

Kevlar fibers were originally developed as a replacement of steel in automotive tires.

Kevlar filaments are produced by extrusion of the precursor through a spinnert. Extrusion imparts anisotropy (increased strength in the lengthwise direction) to the filaments.

Kevlar may protect carbon fibers and improve their properties: hybrid fabric (Kevlar + Carbon fibers) combines very high tensile strength with high impact and abrasion resistance.

Kevlar fibers possess the following properties: High tensile strength (five times stronger per

weight unite than steel); High modulus of elasticity; Very low elongation up to breaking point; Low weight; High chemical inertness; Very low coefficient of thermal expansion; High Fracture Toughness (impact resistance); High cut resistance; Textile processibility; Flame resistance. The disadvantages of Kevlar are: ability to absorb

moisture, difficulties in cutting, low compressive strength.

Kevlar Fiber

There are several modifications of Kevlar, developed for various applications:

Kevlar 29 – high strength (520000 psi/3600 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used for manufacturing bullet-proof vests, composite armor reinforcement, helmets, ropes, cables, asbestos replacing parts.

Kevlar 49 – high modulus (19000 ksi/131 GPa), high strength (550000 psi/3800 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used in aerospace, automotive and marine applications.

Kevlar 149 – ultra high modulus (27000 ksi/186 GPa), high strength (490000 psi/3400 MPa), low density (92 lb/ft³/1470 kg/m³) highly crystalline fibers used as reinforcing dispersed phase for composite aircraft components.

Kevlar Fiber (poly-paraphenylene

terephthalamide)

Reasons for the use of polymeric materials as matrices in composites

i. The mechanical properties of polymers are inadequate for structural purposes, hence benefits are gained by reinforcing the polymers

Processing of PMCs need not involve high pressure and high temperature

The equipment required for PMCs are much simpler

Disadvantages of PMC Low maximum working

temperature High coefficient of thermal

expansion- dimensional instability

Sensitivity to radiation and moisture

Classification of Polymer Matrices1. Thermoset2. Thermoplastic- crystalline &

amorphous3. Rubber

Thermoset Thermoset materials are usually liquid or malleable prior to curing,

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

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

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

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

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

Thermoplastic is a plastic that melts to a liquid when heated and

freezes to a brittle, very glassy state when cooled sufficiently.

Most thermoplastics are high molecular weight polymers whose chains associate through weak van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene).

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

unlike thermosetting polymers, thermoplastic can be remelted and remolded.

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

Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC.

Generally, amorphous thermoplastics are less chemically resistant

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

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

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

Why HDPE exhibits higher cystallinity than LDPE?

Comparison of typical ranges of property values for thermoset and thermoplastics

Properties t/set t/plastic Young’s Modulus (GPa)1.3-6.0 1.0-4.8 Tensile strength(MPa) 20-180 40-190 Max service temp.(ºC) 50-450 25-230 Fracture toughness,KIc 0.5-1.0 1.5-6.0

(MPa1/2)

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

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

Rubber

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

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

materials The term elastomer is often used interchangeably with

the term rubber Natural rubber is obtained from latex from Hevea

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

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

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

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

POLYMER Applicatios

Most of polymers need to add with specific ingredients to obtain desirable properties.

Additives were used: To improved or modify the mechanical, chemical, and physical

properties To prevent degradation (both during fabrication and in service) To reduce materials costs To improve the processability

Each of the additives in formulation has specific functions either during processing or end products applications

Typical additives include filler materials, Plasticizer stabilizers, colorants flame retardants.

IntroductionIntroduction

Fillers normally add in polymeric materials for economical or technical

Filler materials are most often added to polymers to improve tensile and compression strengths, abrasion resistance, toughness, dimensional and thermal stability and other properties.

Materials used as particulate fillers include wood flour (finely powdered sawdust), silica flour and sand, glass, clay, talc, limestone, and even some synthetic polymers.

Particle sizes range all the way from 10 nm to macroscopic dimensions

Because these inexpensive materials replace some volume of the more expensive polymer, the cost of the final product is reduced.

FillersFillers

Can be in liquid, half solid or solid form.

It must be compatible with the polymeric materials and other compounding ingredients incompatibility will results in poor processing properties.

Plasticizer were used for:

1. ‘extender’ (large amount >20 pphr) to make the end products cheaper

2. Processing aid (small amount 2-5 pphr) to make the processing easier

3. Modifier to modifies some polymeric properties.

PlasticizersPlasticizers

The aid of additives called plasticizers can :

improved the flexibility, ductility, and toughness

produces reductions in hardness and stiffness

lowers the glass transition temperature at ambient conditions the polymers may be used in applications requiring some degree of flexibility and ductility.

These applications include thin sheets or films, tubing, raincoats, and curtains.

Some polymeric materials under normal environmental conditions are subject rapid deterioration in mechanical properties.

Most often this deterioration is a result of exposure to light in particular ultraviolet radiation and oxidation

Ultraviolet radiation causes a severance of some of the covalent bonds along the

molecular chain also result in some crosslinking.

Oxidation deterioration is a consequence of the chemical interaction between oxygen atoms and the polymer molecules.

Additives that counteract these deteriorative processes are called stabilizers.

StabilizersStabilizers

Colorants impart a specific color to a polymer

They may be added in the form of:

dyes The molecules in a dye actually dissolve and become part

of the molecular structure of the polymer.

pigments. Pigments are filler materials that do not dissolve but

remain as a separate phase;

have a small particle size, are transparent, and have a refractive index near to that of the parent polymer.

Others may impart opacity as well as color to the polymer.

ColorantsColorants

The flammability of polymeric materials is a major concern, especially in the manufacture of textiles and children's toys.

Most polymers are flammable in their pure form exceptions include those containing significant contents of chlorine and/or fluorine such as polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE).

The flammability resistance of the remaining combustible polymers enhanced by additives called flame retardants.

These retardants may function by

interfering with the combustion process through the gas phase, or

by initiating a chemical reaction that causes a cooling of the combustion region and a termination of burning.

Flame retardantsFlame retardants

Special purpose additivesSpecial purpose additives

Additives Function

Blowing agents Gas generating chemicals that are necessary for manufacturing sponge or micro porous products

Odorants Strongly scented substances added in small amounts that are capable of imparting a pleasant scent

Antistatic agents Added to reduce the accumulated of dust or dirt on surface and also to minimize possibility of sparking resulting from the discharge of accumulated static electricity

Retarders Substances that used to reduce the tendency of rubber mix to scorch avoid premature vulcanization during processing

Antioxidants Protects products from oxidation of heat

Antiflex cracking Agents that retard cracking caused by cyclic deformations

What is the function of additives in polymeric materials?

Discuss the used of fillers as one of polymer compounding ingredients.

Example of the exams questionExample of the exams question

EBB 220/3MISCELLANEOUS

APPLICATIONS

DR AZURA A.RASHIDRoom 2.19

School of Materials And Mineral Resources Engineering,

Universiti Sains Malaysia, 14300 Nibong Tebal, P. Pinang Malaysia

Coating are frequently applied to the surface of materials to serve one or more of the following function:

1. to protect the item from the environment that may produce corrosive or deteriorative reactions;

2. to improve the item's appearance

3. to provide electrical insulation.

CoatingCoating

Many of the ingredients in coating materials are polymers with majority are organic in origin

These organic coatings fall into several different classifications:

paint, varnish, enamel, lacquer, and shellac :

An adhesive substance used to join together the surfaces of two solid material (termed "adherends") to produce a joint with a high shear strength

Adhesives may come from either natural or synthetic sources.

Some modern adhesives are extremely strong, and becoming increasingly important in modern construction and industry

The bond forces between the adhesive and adherend surfaces are electrostatic similar to the secondary bonding forces between the molecular chains in thermoplastic polymers

A strong joint may be produced if the adhesive layer is thin and continuous.

If a good joint is formed, the adherend material may fracture or rupture before the adhesive.

AdhesivesAdhesives

Polymeric materials that fall within the classifications of thermoplastics, them setting resins, elastomeric compounds, and natural adhesives (animal glue, cast starch, and resin) may serve adhesive functions.

Polymer adhesives may be used to join a large variety of material combinations: metal-metal, metal-plastic, metal-ceramic, and so on.

The primary drawback is the service temperature limitation.

Organic polymers maintain their mechanical integrity only at relatively low temperatures, and strength decreases rapidly with increasing temperature.

Natural adhesives Adhesives based on vegetable (natural resin), food (animal hide and

skin), and mineral sources (inorganic materials).

Synthetic adhesives Adhesives based on elastomers, thermoplastic, and thermosetting

adhesives.

Drying adhesives These adhesives are a mixture of ingredients polymer dissolved in a

solvent e.g. glues and rubber cements As the solvent evaporates the adhesive hardens and they will adhere

to different materials to greater or lesser degrees. These adhesives are typically weak and are used for household

applications. Some intended for small children are now made non-toxic.

Hot adhesives (thermoplastic adhesives) Also known as "hot melt" adhesives they are applied hot and simply allowed to harden as they cool. These adhesives have become popular for crafts because of their ease

of use and the wide range of common materials to which they can adhere.

Some categories of adhesivesSome categories of adhesives

Adhesives may fail in one of two ways:

1. Adhesive failure is the failure of the adhesive to stick or bond with the material to be adhered (also known as the substrate or adherend).

2. Cohesive failure is structural failure of the adhesive. Adhesive remains on both substrate surfaces, but the two items separate.

Two substrates can also separate through structural failure of one of the substrates

this is not a failure of the adhesive. In this case the adhesive remains intact and is still bonded to one substrate and the remnants of the other.

For example, when one removes a price label, adhesive usually remains on the label

and the surface this is cohesive failure. If, however, a layer of paper remains stuck to the surface the

adhesive has not failed.

when someone tries to pull apart oreo cookies with the filling all on one side. The goal is an adhesive failure, rather than a cohesive failure.

Adhesives failureAdhesives failure

Polymeric materials have found widespread use the form of thin films.

Films having thicknesses between 0.001-0.0005 in (0.025 -0.125 mm)

Used extensively as bags for packaging food products and other merchandise, as textile products, and a host of other uses.

Important characteristics of the materials produced and used as films include:

Low density, high degree of flexibility, high tensile and tear strengths, resistance attack by moisture and other chemicals, low permeability to some gases, especially water vapor.

FilmsFilms

Some of the polymers that meet these criteria and are manufactured in film form are:

polyethylene, polypropylene, cellophane, and cellulose etate.

There are several forming methods:

simply extruded through a thin die slit followed by a rolling operation that serves to reduce thickness and improve strength.

Blown moulding continuous tubing is extruded through an annular die; and

maintaining a controlled positive gas pressure inside the tube,

wall thickness may be continuously reduced( to produce a thin cylindrical film, which may be cut and laid flat.

Some of the newer films produce using co extrusion that is, multi layers of more than one polymer type are extruded simultaneously.

Very porous plastic materials produced in a process called foaming

Both thermoplastic and thermosetting materials may be foamed by including in the batch a blowing agent upon heating decomposes with the liberation of a

gas.

gas bubbles are generated throughout the now-fluid mass remain as pores up cooling and give rise to a sponge-like structure.

The same effect is produced bubbling an inert gas through a material while it is in a molten state.

FoamsFoams

Some of commonly foamed polymers are :

polyurethane, rubber, polystyrene, and polyvinyl chloride.

Foams are commonly used as:

cushions in automobiles and furniture in packaging and thermal insulation.

Discuss two of the various applications of polymeric materials.

What are the polymer characteristic to produced a film?

Example of the exams questionExample of the exams question