UNIT –II

THERMOSETS AND THERMOPLASTICS

Thermoplastics

Polymers soften or melt on heating are called

Thermoplastic Polymers

Characterized by liner chain molecules

Ex: Polyesterene , Polyethylene

Definition-Thermosetting Polymer A thermosetting polymer is a prepolymer in a

soft solid or viscous state that changes irreversibly into an infusible insoluble polymer network by curing.

Curing can be induced by action of heat or suitable radiation or both .

A cured thermosetting polymer is called Thermostat

DIFFERENCES Thermosets

Resin Cost is low

Exhibits moderate shrinkage

Exhibits good resistance to fluids and solvents

Interlaminar fracture toughness is low

Thermoplastics

Resin Cost is High

Shrinkage Is low

Poor resistance to fluids and solvents

Interlaminar fracture toughness is high

DIFFERENCES Thermosets

Long processing cycles

Poor Recycling capabilities

More difficult to repair ability

Good wetting and adhesion to reinforcement

Thermoplastics

Low processing cycle time

Recyclability and environmental protection

High reparability

Draping difficulties

THERMOSETS AND THERMOPLASTICS

THERMOPLASTICS 1.PHENOLI

CS & Cynate

Ester 2.Polyesters & Vinyl

esters

3.Polyimides

4.Epoxies 5.Bis

maleimide

1.Polypropylene

2.Nylon(Polyamide )

3.Poly ether Imide (PEI)

4.Poly-Ether

Sulphone (PES) 5.Poly Ether Ether

Ketone ( PEEK)

EPOXY RESIN

EPOXY

The term epoxy is a general description of a family of polymers which are based on molecules that contain epoxide groups

An epoxide is a cyclic ether with three ring atoms. This ring approximately defines an equilateral triangle, which makes it highly strained

An epoxide group is an oxirane structure, a three-member ring with one oxygen and two carbon atoms.

EPOXY

A polymer formed by reacting epoxide units is called a polyepoxide or an epoxy.

Epoxy is a copolymer; that is, it is formed from two different chemicals. These are referred to as the "resin" or "compound" and the "hardener" or "activator".

Epoxy, also known as PolyEpoxide, is a thermosetting polymer formed from reaction of an Epoxide "resin" with Polyamine "hardener".

.

EPOXY

Epoxies are polymerizable thermosetting resins containing one or more epoxide groups curable by reaction with amines, acids,amides, alcohols, phenols, acid anhydrides, or mercaptans.

The polymers are available in a variety of viscosities from liquid to solid.

EPOXY

The Common starting material : Diglycidyl Ether of Bisphenol A(DGEBA)

which contain two epoxide groups , one at each end of the molecule

EPOXY Most common epoxy resins are produced from

a reaction between Epichlorohydrin and Bisphenol-A

The hardener consists of polyamine monomers, for example Triethylene tetramine (TETA).

When these compounds are mixed, the amine groups react with the epoxide groups to form a covalent bond.

Each NH group can react with an epoxide group from distinct prepolymer molecules, so that the resulting polymer is heavily crosslinked, and is thus rigid and strong

Manufacturing of Epoxy Resin

Diluents – Reduce the viscosity

Flexibility agents – make epoxy flexible

Other agents – Protection against UV

Curing agents – organic amino compounds

(To obtain cross linking by introducing

chemicals that react with the epoxy and

hydroxyl groups between adjacent chains )

EPOXY Crosslinking :Stiffness, strengh increases but

toughness decreases

B-Stage: An epoxy before it is fully cross linked is said to be

in stage B

In stage B , epoxy has characteristic tackiness

The curing reaction can be lowered by lowering the reaction temperature

PROPERTIES OF EPOXY

Make an excellent matrix material because of their versatility,

• Good handling characteristics, • Low shrinkage, • Excellent adhesive properties, • Flame resistant, • Good chemical resistance, • Good mechanical properties including toughness, • Offer considerable variety for formulating Prepreg resins, • Hot molding (cold molding rarely), • High smoke emission, • Curing temperature is 120-175°C (250-3500F), and • No by-products formed during cure

EPOXY

Disadvantages : Brittleness and reduction in the properties in the

presence of moisture Slower processing time then polyester More expensive then polyesters

EPOXY –Applications Used in Aircraft Construction

Croyogenic applications

Epoxy-nylon, Epoxy-amide have good retention of both

tensile strength and elongation at cryogenic

temperatures and are usually the only materials that

will work well at these temperatures.

Bridge Structures :

Epoxy reinforced concrete Carbon reinforced Epoxy Structures Glass reinforced Epoxy Structures

POLYESTER MATRICES

POLYESTER (Thermosetting) Polyester is a category of polymers which

contain the ester functional group in their main chain.

The term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET)

Esters are chemical compounds consisting of a carbonyl adjacent to an ether linkage

POLYESTER A condensation reaction between the

GLYCOL ( Ethylene, Propylene, diethylene glycol)

+ Unsaturated Dibasic Acid

= Linear Polyester

POLYESTER

PET(polyethylene terephthalate) is made from

Ethylene Glycol and Terephthalic Acid by

splitting out water molecules (-H from alcohol

and -OH from acid.

The units are joined to make the ester group.

POLYESTER

A simple representation is -[A-B-A-B-A-B]-.

POLYESTER

Polyester- Properties

Hard strong and extremely tough

High abrasion resistance

Low coefficient of friction

Good chemical resistance

Good surface appearance

Electrical properties are stable upto the rated

temperature limits

Polyester-Advantages

The relatively easy accessible raw materials.

The very well understood and described simple

chemical process of polyester synthesis.

The low toxicity level of all raw materials and

side products during polyester production and

processing

Polyester-Advantages

The possibility to produce PET in a closed loop

at low emissions to the environment

The outstanding mechanical and chemical

properties of polyester

The recyclability

The wide variety of intermediate and final

products made of polyester.

POLYESTER- Drawbacks Higher volumetric shrinkage

Surface defects

POLYESTER – APPLICATIONS

It can also be made into textile fibers known as Dacron

and accounts for 50% of all fibers used to make clothing.

Blended with cotton, made into no-iron clothes.

Industrial polyester fibers, yarns and ropes are used in

tyre reinforcements, fabrics for conveyor belts, safety

belts, coated fabrics and plastic reinforcements

Polyesters are also used to make bottles, films,

tarpaulin, canoes, liquid crystal displays, holograms,

filters, dielectric film for capacitors, film insulation for

wire and insulating tapes

NYLON MATRICES

Nylon Matrices Nylon is a generic designation for a family of

synthetic polymers known generically as polyamides

Nylon is a thermoplastic, silky material, first used commercially in a nylon-bristled toothbrush.

Nylon is made of repeating units linked by amide bonds and is frequently referred to as polyamide (PA)

NYLON Chemically, nylon is formed by chains of amide

molecules. The chains are arranged parallel to each other, attached by hydrogen bonds.

To make nylon's fibers strong, a polymerizing process must occur that allows the molecules to combine without retaining any water. In effect the process of making nylon is a condensation reaction.

Nylon 6,6

NYLON –CHEMISTRY

A molecule of water is given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers

Nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amides are formed at both ends of each monomer in a process analogous to polypeptide biopolymers

NYLON - Characteristics

Variation of luster: nylon has the ability to be very lustrous, semilustrous or dull. Durability: its high tenacity fibers are used for seatbelts, tire cords, ballistic

cloth and other uses. High elongation Excellent abrasion resistance Highly resilient (nylon fabrics are heat-set) Paved the way for easy-care garments High resistance to insects, fungi, animals, as well as molds, mildew, rot and

many chemicals Used in carpets and nylon stockings Melts instead of burning Used in many military applications Good specific strength Transparent to infrared light (−12dB)[3]

NYLON –PROPERTIES Excellent material for machining Tough, strong, and impact resistant material Very low coefficient of friction Abrasion resistant. Excellent resistance (no attack) to Oils, Bases

and THF Good resistance (no attack) to Solvents,

Formaldehyde and Alcohols Limited resistance to Dilute Acids Poor resistance (not recommended for use

with) Phenols, Alkalis, Iodine and Acids

NYLON – APPLICATIONS Nylon is commonly used in the production of

tire cords, rope, belts, filter cloths, sports equipment and bristles.

It is particularly useful when machined into bearings, gears, rollers and thread guides.

Solid nylon is used for mechanical parts such as machine screws, gears and other low- to medium-stress components previously cast in metal.

NYLON – APPLICATIONS Engineering-grade nylon is processed by

extrusion, casting, and injection molding.

Solid nylon is used in hair combs.

Type 6,6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of molded nylon

POLYPROPYLENE

Polypropylene Polypropylene is a plastic polymer, of the

chemical designation C3H6.

Polypropylene- Isotactic

Most commercial polypropylene is isotactic

and has an intermediate level of crystallinity

between that of low-density polyethylene

(LDPE) and high- density polyethylene (HDPE)

Polypropylene-Types 1. Homopolymer 2. Copolymer 3.Block Copolymer

PP is also used for plastics reinforced constructions. For this typical application, it is possible to

use two different types of polypropylene. PP sk is the traditional type polyether-backed but as

standard product, it exist also PP copolymer polypropylene-backed: PP-DWU-SK: Homopolymer, permanent-heat resistant,

grey, polyester-backed PP-C-PK: Copolymer, permanent-heat resistant, grey,

polypropylene- backed

Those PP-C-PK sheets have a lot of advantage: Allows excellent three-dimensional thermoforming It is not necessary to finish the fabric at welding zones Better adhesive properties than PP polyester backing

sheets

PP-EL is an electrically conductive homopolymer polypropylene. This material is treated with

electrically conductive particles which discharge the static. PP-EL has high surface resistivity and

is ideal for use in potentially explosive atmospheres. PP-EL-S (special type) includes a flame-retardant

additive

Polypropylene-Manufacturing

It is manufactured from the propylene gas in the presence of catalyst such as titanium chloride

Melt processing of polypropylene can be achieved by extrusion and moulding

Common extrusion methods A) Injection mouldingB) Blow moulding C) Injection stretch moulding

Polypropylene-properties Semi-rigid Translucent Good chemical resistance Tough Good fatigue resistance Integral hinge property Good heat resistance

Polypropylene-Applications Since polypropylene is resistant to fatigue,

most plastic living hinges, such as those on flip-top bottles, are made from this material

Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap

Polypropylene-Applications Polypropylene is used in the manufacturing

piping systems; both ones concerned with high-purity and ones designed for strength and rigidity.

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave

Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles

Polypropylene – Applications Food containers made from it will not melt in

the dishwasher, and do not melt during industrial hot filling processes.

For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminum foil (both heat-resistant materials)

Car batteries, wastebaskets, pharmacy prescription bottles, cooler containers, dishes are often made of polypropylene

Polypropylene Polypropylene, highly colorfast, is widely used in

manufacturing carpets, rugs and mats to be used at home.[17]

Polypropylene is widely used in ropes, distinctive because they are light enough to float in water

Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables for LSZH cable in low-ventilation environments, primarily tunnels. This is because it emits less smoke and no toxic halogens, which may lead to production of acid in high-temperature conditions.

Polypropylene-Polyester

For equal mass and construction, polypropylene rope is similar in strength to polyester rope.

Polypropylene costs less than most other synthetic fibers.

Polypropylene- Applications Used for plastic moldings, wherein it is injected

into a mold while molten, forming complex shapes at relatively low cost and high volume; examples include bottle tops, bottles, and fittings.

It can also be produced in sheet form, widely used for the production of stationery folders, packaging, and storage boxes.

The wide color range, durability, low cost, and resistance to dirt make it ideal as a protective cover for papers and other materials.

Polypropylene Polypropylene is a major polymer used in

nonwovens, with over 50% usedfor diapers or sanitary products where it is treated to absorb water (hydrophilic) rather than naturally repelling water (hydrophobic).

polypropylene yarn is the lightest fibre of all synthetic and natural fibers. Final users gain more comfort because the garments are lighter.