Plastics and Elastomers

• Thermosetting and thermoplastics• Compounding of plastics• Application of plastics as engineering materials• Commercial plastics( PF, UF, polyurethanes)-

synthesis, properties and application• Speciality polymers: Conductive polymers, Self

healing plastics, Intelligent polymers. Applications of specialty polymers.

• Elastomers: Natural rubber, drawbacks of natural rubber, Vulcanization of rubber, applications of rubber

• Commercial elastomers (Buna-S, GR-S, Isocyanate rubber) - synthesis, properties and applications.

Plastics

• The term plastics or plastic material, in general, is given to “organic materials of high molecular weight, which can be moulded into any desired form, when subjected to heat and pressure in the presence of a catalyst”.

•Commercial plastics• ( PF, UF, polyurethanes)• - synthesis, properties and

application

PF• Phenol-Formaldehyde Resins

• Phenoplasts are the condensation polymerization products, a phenol with an aldehyde.

• The phenolic substance can be phenol or resorcinol and the aldehyde can be formaldehyde or furfural.

• There are three stages in the preparation of the thermosetting phenol- formaldehyde plastic

OH is Ortho, Paradirector

LOW MOL WT LINEAR MOLECULE

NOVOLAC

• The novolac is a linear polymer, thermosoftening and soluble in few aromatic solvents.

• It can be further polymerized to get thermosetting polymer (bakelite) or it can be used as such or as its solution

• Further heating of novolac above 150°C in the presence of hexamethylene tetramine, in a mould, produces highly crosslinked structure called as Bakelite, which is hard, rigid.

HIGHLY CROSSLINKED STRUCTURE[ BAKELITE]

HIGHLY CROSSLINKED STRUCTURE

HARD AND RIGID

BAKELITE

Properties of PF resins

Properties of PF resins

• i) Linear polymers (novolac, ) are thermosoftening

ii) Lower molecular linear polymers are easily soluble in many organic solvents.

iii) The crosslinked structure (bakelite) is very hard, strong, scratch resistant, brittle.

• iv) Bakelite is chemically resistant, fire resistant, heat resistant

v) Bakelite is good electrical insulator

vi) Bakelite has high abrasion resistance

Applications

Applications

• Applications

i) The liquid resins or solutions of linear polymers are used as adhesives, coating material in the form of varnishes, enamels.

Applications

• ii) The solution of linear polymer is used for impregnation of paper, cloth, wood to increase their strength. It is also used for plywood industry.

• iii) The linear polymers on further sulphonation or amination gives ion-exchange resins for water treatment.

Applications

• iv) Bakelite is used for electrical goods like switches, plugs, panels.

• v) Bakelite is used for making handles of cooker, Frypan, heaters etc.

• vi) Bakelite is used for high temperature service applications.

• vi) Bakelite is used for cabinets of radio, TV, telephone etc., for making laminates.

UF•UREA-Formaldehyde

Resins and plastics

• These are aminoplasts, prepared from organic amines and formaldehyde.

• Urea and formaldehyde react in basic medium to produce monomethylol and dimethylol ureas.

• These resins formed have tetrafunctionality and can produce crosslinked products on curing in mould.

UREA

• At the time of moulding, the methynol resins are compounded with filler like cellulose or wood flour, color and catalyst and all water is evaporated.

• Then the powdered mixture is cured in mould by application of heat and pressure.

• Properties

• It has • high tensile strength• high compressive strength• good electrical insulation• good resistance to heat, flame• high hardness, impact strength• resistance to water, high chemical resistance

except strong acids and alkalis.

Uses

• Liquid resins can be used for impregnation on paper for production of decorative laminates.

• The liquid resins can be converted to fine powder by drying and then used as adhesive for plywood industry.

Uses

• It is used for making laminates (sunmica), making various moulded articles like insulation goods, wall panels, control knobs, hardware appliances, plates, dishes, etc.

• The resin is water-white (Fevicol) and used as adhesive. It is also used in making varnishes.

• IMPORTANT THERMOPLASTIC RESINS

•Polyurethanes

• Carbamates are organic compounds derived from carbamic acid (NH2COOH).

• Carbamate esters are also called urethanes.

Chemical structure of carbamates

• A polyurethane (PUR and PU) is any polymer composed of a chain of organic units joined by carbamate (urethane) links.

• urethane groups — NH-(C=O)-O-

Synthesis of polyurethanes

• Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer (with at least two isocyanate functional groups) with another monomer (with at least two hydroxyl or alcohol groups) in the presence of a catalyst.

PolyurethanesMonomer (with at least two isocyanate functional groups)

Monomer (with at least two hydroxyl or alcohol groups)

Polyurethane synthesis, wherein the urethane groups — NH-(C=O)-O- link the molecular units.

General equation Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics.

A urethane linkage is produced by reacting an isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH.

APPLICATIONS of Polyurethanes :

Polyurethanes are applied to the manufacture of • flexible, high-resilience foam seating• rigid foam insulation panels• microcellular foam seals and gaskets• durable elastomeric wheels and tires• automotive suspension bushings• electrical potting compounds• high performance adhesives• surface coatings and surface sealants• synthetic fibers (e.g. Spandex); carpet underlay; and hard-

plastic parts (i.e. for electronic instruments).

Properties of Polyurethanes :

• (I) Polyurethanes are less stable than polyamides (nylons) at elevated temperature.

• (ii) They are characterized by excellent resistance to abrasion and solvents.

Uses of Polyurethanes :

• Polyurethanes are used as coatings, films, foams, adhesives and elastomers.

• Resilient polyurethane fibres (spandex) are used for foundation garments and swim-suits.

• They also find use as a leather substitute (corfoam).

• They are used to cast to produce gaskets, and seals.

Polyurethanes- synthesis of Perlon-U

APPLICATIONS OF PLASTICS AS

ENGINEERING MATERIALS

• Engineering plastics or performance plastics are a group of materials obtained from high polymer resins, which possess :

• (i) plasticity at some stage of their processing • (ii) high load—bearing characteristics • (iii) high mechanical strength

Engineering plastics or performance plastics

• (iv) high dielectric constants • (v) readily mouldable characteristics into

complicated shapes• (vi) rigidity • (vii) high abrasion resistance

Engineering plastics or performance plastics

• (viii) dimensional stability • (ix) fairly good thermal stability• (x) light weight • (xi) high performance properties, which permit

them to be used in the sante manner as metals, allots and ceramics.

Engineering plastics

• Not only engineering plastics can replace metals, but they can also be used along with metals.

• The economy and ease of fibrication have now made them engineering materials of construction. They meet the crucial needs of the day with greater efficiency, and reduction in both cost and weight.

Engineering plastics

They are finding applications in demanding areas like • Automobiles• Defence• electrical and electronics• Telecommunications• Textiles• satellite robots• Mountaineering• computer components, etc., where so far only metals

or ceramics have been found suitable.

Engineering plastics

• Some of the engineering plastics with special characteristics and uses are given below

• (1) Polyamides or nylons (like nylon-6 and nylon-11, kevlars)

Engineering plastics

• (1) Polyamides or nylons (like nylon-6 and nylon-11, kevlars) are

• easily mouldable• tough, strong• abrasion resistant• good chemical resistant• and of low coefficient of friction.

Engineering plastics

• Aromatic polyamides (kevlars) are high temperature resistant.

-----applications in gears, automobile tyres, watch straps, unlubricated hearings, electrical mountings, high tensile ropes, etc

Engineering plastics

• (2) Polycarbonates (like lexan, merlan)

Engineering plastics

• (2) Polycarbonates (like lexan, merlan) possess high impact and tensile strengths over a wide range of temperature, good dimensional stability, stiffness, transparency, etc.

Engineering plastics

• They are used for making electrical insulators, housings for apparatus, industrial plugs, sockets, switches, crash helmets, cooking utensil covers, hair-drier bodies, sterilizable transparent containers, camera and binocular bodies, solar collectors, telephone booths, lenses, photographic films, etc.

Engineering plastics

• (3) Polyurethanes (like perlon-U)

Engineering plastics

• (3) Polyurethanes (like perlon-U) possess • Excellent flexibility• Toughness, even at subzero temperature, • Excellent resistance to abrasion and solvents.

Engineering plastics

• They are used in defence, oceanographic research, mountaineering, plastic foam (e.g., coirfoam, thermocole), etc.

Engineering plastics

• (4) Solid silicones:• Solid silicones possess good electrical

insulating properties and outstanding heat-resistance, chemical inertness, good water-repellency, resistance to weathering effects, etc.

• They are used mostly in high voltage insulators, high thermally stable mouldings and high temperature insulating foams

Engineering plastics

• (5) Polyacetals

Engineering plastics

• (5) Polyacetals possess low coefficent of friction, stiffness, resistance to creep, excellent fatigue endurance, etc.

• They find use in gears, links in chains, bearings, pump impellers, conveyor belts, etc.

• (6) Teflon

• (6) Teflon possesses • Extreme toughness• Excellent chemical resistance• Very low coefficient of friction• Extremely good mechanical properties• Very good electrical insulator, etc.

• Used as electrical insulating material in motors, cables, transformers, electrical fittings

• for making non-lubricating bearings, chemical-carrying pipes, tubings, etc.

Elastomers( Rubbers)

• Elastomers: Natural rubber, drawbacks of natural rubber, Vulcanization of rubber, applications of rubber• Commercial elastomers (Buna-S,

GR-S, Isocyanate rubber) - synthesis, properties and applications.

• The elasticity character in the rubbers is due to the fact that its polymer molecules in the unstressed condition are coiled or spring like. Hence on stretching, it elongates and on compression its size shortens.

• Rubbers are of two types: (1) Natural (2) Synthetic.

• Both the types of rubbers can be vulcanised for removing drawbacks.

•Natural Rubber • Natural rubber is made from latex obtained

from a rubber tree Hevea barsilensis. • These trees are found in tropical countries like

Brazil, Malaysia, Indonesia, South American countries, India, Thailand, etc.

• The latex is a milky-white emulsion of

immiscible liquids, water and isoprene. This emulsion is stabilised by natural protenious stabilizers present in it.

• The latex contains about 30% of isoprene. • Latex is obtained by making small cut in the

bark of the rubber tree. Such tapping of latex from the cuts is done at the intervals of six months.

• The latex exuded from the cut is collected and sent for processing or treatment.

Natural rubber

• 1,2-disubstituted alkenes are described as:cis- if the two alkyl groups, R-, are on the same side of the C=C

• trans- if the two alkyl groups, R-, are on the opposite side of the C=C.

• These terms are used as prefixes.

•cis-trans-

• The cis-polymer contains unsaturation. • The polymer obtained has cis-structure

(similar groups lying to same side of C = C).

• Therefore, the cis-polyisoprene molecules are in coiled or spring form and the material shows elastic character.

• The molecular weight of polymer is 1,00,000 to 5,00,000.

• It may be noted that the —CH3 groups are oriented outwards from the coiled structure.

• The distance between the two successive —CH3 groups is found to be 8.1 A°, meaning the rubber molecules are coiled.

The cis-polyisoprene molecules are in coiled or spring form

•Properties and Drawbacks of Natural Rubber

• (1) Natural rubber becomes brittle below 10°C and too soft after 50°C.

• Hence it is useful only in limited temperature range.

• (2) Natural rubber has C=C unsaturations throughout its structure. Therefore, it is easily attacked by various chemicals including air, ozone, etc.

• (3) Natural rubber has very low tensile strength 20 kg/cm2.

• (4) It is excessively elastic. • (5) Natural rubber undergoes deformation if

stretched as there is very weak force of attraction between the neighbouring coiled molecules.

• (6) It has property to absorb water. (7) It is weak. (8) It swells in many organic solvents. (9) It has excessive tack property (tack is the property of rubbers due to which two pieces of rubbers form one-piece on pressing). (10) It has very poor abrasion resistance.

• Because the natural rubber does not have useful properties, generally it is not used as such, but used after vulcanization.

Vulcanisation of Rubbers

• • To remove the drawbacks in the natural rubber (or to improve properties of synthetic rubbers), we carry out the process of vulcanisation.

• • Vulcanisation is the process of crosslinking the rubber by use of sulphur, quinone, selenium, etc. as vulcanising agent at 110-140° C, to make mechanically strong and chemically resistant rubber.

•Process of vulcanisation

Process

• The rubber is cut into small pieces or ground to fine powder.

• Suitable amount of a vulcanising agent (antioxidant, colouring agent, filler, etc. optional) is added in it.

• The mixture is heated at 110°C to 140°C for sufficient time and kept stirring during heating. Then the vulcanised mass is cooled.

• The amount of vulcanising agent used for vulcanisation decides the stiffness of rubber produced e.g. sulphur can be added upto 5% for soft rubber and upto 30% for hard rubber.

• Greater the percentage of vulcanising agent used, greater is the stiffness, chemical, abrasion and heat resistance developed, but elasticity decreased

• Sulphur is most common vulcanising agent used but other such agents are

• Diazoaminobenzene• Quinine• Benzoyl peroxide• Sulphur monochloride (S2C12)• Selenium• Tellurium• ZnO• MgO• Mercuric oxide, etc.

• Before vulcanisation, the intermolecular force of attraction between the coiled molecules, is very weak. The spring like molecules are loose and can slide over each other easily. Therefore unvulcanised rubber is mechanically weak.

• But on vulcanisation, the neighbouring spring molecules are crosslinked or tied to each other by the vulcanising agent, at the C = C portions.

• The presence of C = C is in large number throughout the rubber molecule, makes it reactive to acids, alkalis, oxidising agents, air, ozone, etc.

• But after vulcanisation, this unsaturation gets removed to large extent and the vulcanised rubber becomes chemically resistant material.

• All the drawbacks or limitations in natural rubber thus are removed by vulcanisation.

•Applications of Rubbers

• Rubber is used in the manufacture of following types of goods:

1. Tyres: The manufacture of tyres is the leading application of rubber.

•2. V-belts and conveyor belts: V-belts for transmission of power and conveyor belts for conveying many types of goods such as grain. Sand, coal, ice, ore etc. are manufactured out rubber.

• 3. Rubber lined tanks : Rubber lined tanks are used in chemical engineering plants to resist the corrosive action of chemical processed. The best metals for lining with rubber are steel and aluminium.

•4. Gaskets: Rubber is used for the manufacture of gaskets for sealing many types of materials such as refrigerator cabinet door seals, cooker autoclaves.

• 5. Mountings : Mountings are sections of rubber sandwiched between two metal plants. Mountings reduce or isolate machine vibrations, prolong the life and improve the quietness of the equipment.

•6. Hoses: All types of hoses are manufactured from rubber.

• 7. Electhrical industries : Due to remarkable resistance to electricity, hard rubber is largely used in electrical industry as insulating coating for wires and cables used for electrical power transmission. It is also used in switch board panels, plugs, sockets, telephone receivers, battery cases and electrical gloves.

• Commercial elastomers • (Buna-S, GR-S, Isocyanate

rubber) - synthesis, properties and applications.

• Most of the synthesis rubbers are the copolymers of butadiene or substituted butadiene.

• However, the synthetic rubbers of thiocol, isocynate, silicone etc. types also can be prepared.

• Synthetic rubbers in general are much superior in properties as compared to natural rubber, synthetic rubbers containing C = C in the polymer chain, can be easily vulcanized.

• Buna-S • GR-S• SBR

Styrene - butadiene rubber (SBR) is the copolymer made by using 75% butadiene and 25% styrene by weight.

Properties

•(1) Tensile strength of SBR is low but it can be increased to 250kg/cm2 by addition of carbon black filler during compounding. (2) It has high resistance to heat and ageing. (3) It has high abrasion resistance. (4) It possesses high load bearing capacity.

• (5) It is attacked by even traces of ozone if present in air. (6) Its disadvantage is that it is attacked or spoiled by oils and solvents, due to swelling. (7) Its strength can be increased by Vulcanising. (8) It can be reinforced with nylon cords, nylon net, steel wires.

• Uses • SBR is the most widely used rubber. • It is used in making tyres of Vehicles / motors.

• ISOCYANATE RUBBER

Polyurethane rubber (or isocyanate rubber) is produced by reacting

polyalcohols with di-isocyanates, e.g.,

Properties :

• Polyurethanes are highly resistant to oxidation, because of their saturated character.

• They also show good resistance to many organic solvents, but are attacked by acids and alkalis, especially concentrated and hot.

• The polyurethane foams are light, tought and resistant to heat, abrasion, chemicals and weathering.

• Uses : For surface coatings and manufacture of foams and spandex fibres.

Speciality polymers:

• Conductive polymers• Self healing plastics• Intelligent polymers• Applications of specialty polymers.

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Conducting polymers

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Conjugated system

• In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds

• The conductivity further can be increased by p-doping or n-doping.

• p-doping is carried out with oxidising agents and the n-doping is carried out by reducing agents.

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• A P-type doping (P for Positive) is obtained by adding a certain type of atoms in order to increase the number of free charge carriers (in this case positive).

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• N-type doping is a type where the dopant atoms are capable of providing extra conduction electrons to the host material (e.g. phosphorus in silicon).

• This creates an excess of negative (n-type) electron charge carriers.

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Oxidation with Halogen( P doping)

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• iodine I [Kr]4d105s2 5p5

• Electron Configuration of sodium:1s2 2s2p6 3s1

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• The common p-type doping agents are I2, Br2, AsF5 and

• The n-type doping agents are Na, K, sodium naphthalide

• Generally the doping of the conductive polymer is done by immersing the polymer film in solution of dopant.

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• There are a few other conductive polymers synthesized (which also need doping); some are given below;

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The conductivities of such doped polymers is from 100 to 105 mhocm.

All above given examples are the intrinsically conducting polymers.Eg…………………………………………….

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Extrinsically conducting.

• A common plastic compounded with carbon black, metal powder, conducts much lesser and such conducting polymers are known as extrinsically conducting.

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Conduction mechanism

• The conduction mechanism of the doped polymers occurs by mechanisms like

• positive holes• negative ions• ionic conduction• band-type conduction• excitonic conduction.

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•Applications of Conducting Polymers

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• 1) Rechargeable batteries : high charge carrier concentrations, batteries of small size, long lasting

• 2) As antistatic material : To avoid static electricity in plastic carpets in offices, theatres, doped polyaniline can be used as antistatic material.

• 3) Optical filters : Radiations from computer screens, other electrical devices can be absorbed by conductive polymers by coating on casing.

• 4) Sensors: The conductive polymers have chemical properties suitable to use them as sensors for pH, O2, NO2, SO2, NH3, glucose, reducing and oxidizing chemicals, for the study of their even very low concentrations.

• 5) In electronics They are used for photodiodes, light emitting wall-papers, light emitting diodes (LED) and data storage.

6) Photovoltaic cells : The conductive polymers can be used in construction of photovoltaic cells.

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Self healing plastics

• Self-healing materials are a class of smart materials that have the structurally incorporated ability to repair damage caused by mechanical usage over time

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Liquid-based healing agents

• An epoxy system containing microcapsules. • These microcapsules were filled with a

(liquid) monomer. • the monomer fill the crack of wounds.

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Solid-state healing agents

• Supramolecular polymers are materials formed by reversibly connected non-covalent bonds (i.e. hydrogen bond), which will disassociate at elevated temperatures.

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• Supramolecule is thus a single molecule but can perform functions like large complex compound.

• Supramolecule chemistry is the chemistry beyond the molecule, whose goals is to gain control over the intermolecular forces of attraction.

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Mechanism

• Healing of these supramolecullary based materials is accomplished by heating them and allowing the non-covalent bonds to break.

• Upon cooling new bonds will be formed and the material will potentially heal any damage.

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• Intelligent polymers

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• One can define "intelligent" polymers as those polymers that respond with large property changes to small physical or chemical stimuli.

• These are defined as polymers that undergo reversible large, physical or chemical changes in response to small external changes in the environmental conditions, such as temperature, pH, light, magnetic or electric field, ionic factors, biological molecules, etc.

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• Smart polymers have very promising applications in the biomedical field as

• delivery systems of therapeutic agents, • tissue engineering scaffolds• cell culture supports• bioseparation devices• sensors or actuators systems

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• pH-sensitive polymers: General considerations

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• pH-sensitive polymers are polyelectrolytes that bear in their structure weak acidic or basic groups that either accept or release protons in response to changes in environmental pH.

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• A few examples of cationic polyelectrolytes are

• poly( N,N -diakyl aminoethyl methacrylates) (Figure 4 and Fig 2),

• poly(lysine) (PL)• poly(ethylenimine) (PEI)• and • chitosan.

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Examples of pH sensitive polymers

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Examples of pH sensitive polymers

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• Temperature responsive polymers

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• Polymers sensitive to temperature changes • This type of systems exhibit a critical solution

temperature(CST) (typically in water) at which the phase of polymer and solution is changed in accordance with their composition.

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• example is poly( N -isopropylacrylamide) (PNIPAAm) that presents a LCST at 32ºC in water solution

• Below that temperature the polymer is soluble as the hydrophilic interactions, due to hydrogen bonding, are predominant, whereas a phase separation occurs above the LCST (cloud point) due to predomination of hydrophobic interactions

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Examples of temperature sensitive polymers

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Thanks

• Thanks