<<

Unit – 2

Polymers & Composites

Lesson plan:

1. – Introduction -a) Definition –, , degree of freedom, functionality, oligo polymer, High polymer, isotactic, atactic, syndiotactic, Homopolymers, Heteropolymers. b) Types of polymerization – Addition, condensation , co-polymerisation – comparison c)Mechanism of Free radical polymerization – 3 step process Step1-Initiation (Radical and Chain initiating species formation) Step2 -Propagation (Living polymer formation) Step3 -Termination (By coupling and disproportionation)

2. a) Classification – i)based on thermal property – Thermo / Thermoset plastics ii) Based on usage – Commodity and plastics b) Prepration, properties and applications of i) PVC ii) Teflon iii) Poly carbonate iv) Poly Urethane v)PET vi)

3. Rubber a) Raw rubber – Preparation - problems of raw rubber – Vulcanisation – Difference between raw and vulcanized rubber b)Synthetic rubber – Preparation, properties, uses of i) SBR ii) Butyl rubber

4. Composites a) Definition – properties - Types - Polymer matrix / Metal matrix / Ceramic matrix composties b) Fibre Reinforced Plastics (FRP) – Types of FRP - Applications of FRP TOPIC -1. POLYMERISATION:

1. Under the proper conditions of temperature, pressure and catalyst , the micro (Smaller) molecules are combining together to form a macro (big) molecule. This process is called Polymerisation. E.g n(CH2 = CH2 )  (CH2 - CH2 ) n

2. Micro molecules are called ‘Monomer’. Macro molecule is ‘Polymer’.

3. The number of present in a polymer is ‘ Degree of polymerisation’ (n). Degree of Polymerisation = Mol. Wt of polymer / Mol. Wt of monomer If n = low , Mol.Wt = 500 – 5000 Dalton units, it is Oligo polymer. If n = High, Mol.Wt = 10,000 – 2,00,000 Dalton units , it is High polymer.

4. If the polymer chain contains same type of monomer, it is “ Homo polymer”. e.g PVC structure : A – A – A- A- A-A -A If the polymer chain contains different type of monomer, it is “Hetero polymer”. e.g Nylon A-B- A-A-A-B-A

5.Number of Reactive sites present in a monomer is called ‘ Functionality’. e.g CH2 = CH2 , The double bond is acting as two reactive site, So, functionality is 2. CH2 – OH In glycerol three –OH groups present. So, functionality = 3 │ CH – OH │ CH2 – OH

If F = 2, they form linear chain structure. If F=3, they form branched structure. If F≥ 4, then they form complexed 3D structure.

6. Orientation of monomers in a polymer chain is called “Tacticity”. If the groups are in same orientation, it is isotactic. If they are random it is “atactic”. If they are arranged in alternative , it is syndiotactic.

A A A A A A B B A B A B A B A │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ M -M - M - M - M - M - M - M - M –M M - M - M – M - M │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ B B B B B B A A B A B A B A B

(Iso tactic) (Atactic) (syndiotactic) TYPES OF POLYMERISATION : 1. Addition 2. Condensation 3. Copolymerisation

No Addition Polymerisation Condensation Polymerisation 1 Eg. PVC Eg. Nylon 6,6 2 Otherwise known as “Chain growth Otherwise known as “Step wise Polymerisation”. Polymerisation”. 3 Monomers are adding together to form Monomers are condensed to form polymers. polymer. 4 No elimination of other molecules. Elimination of smaller molecules occur. 5 At least one multiple bond presence is Monomers must have two or more essential condition. functional groups. 6 Homo polymers are formed. Hetero polymers are formed. 7 are formed. Thermo set plastics are formed. 8 Molecular weight of the polymer is the Need not be so. integral multiple of monomers. 9 Monomers disappear slow and steadily. Monomers disappear at the initial stage of the reaction. 10 Longer processing time is needed. Longer time is essential. e.g Addition Polymerisation:

n(CH2 = CH2 )  -( CH2 - CH2 -)n Ethylene 

Condensation Polymerisation

n H2N - (CH2)6 – NH2 + n HOOC – (CH2)4 – COOH  Hexa methylene diamine Adipic acid [ - HN - (CH2)6 – NH - OC – (CH2)4 – CO - ]n Nylon 6,6

Co-Polymerisation

1. It is a special kind of polymerisation, otherwise known as “Joint polymerisation”. The product is known as ‘Co-polymers’. It is used to alter the hardness, strength, rigidity of the monomers.

e.g SBR synthesis CH2 = CH

n CH2 = CH - CH = CH2 + n O  ( 75% butadiene) (25% Styrene)

[ CH2 - CH = CH - CH2 - CH2 = CH -]n (Styrene – Butadiene RubberSBR) O

MECHANISM OF FREE RADICAL ADDITION POLYMERISATION : 3 steps in Free radical mechanism: 1. Initiation 2. Propagation 3. Termination

Step I - Initiation : 1a) Initiator  Radical 1b) Radical + Monomer  Chain Initiating Species (CIS) Step II - Propagation; CIS + n (monomer)  Living polymer Step III - Termination; 3a) By Coupling : Radical + Radical  Macromolecule ( Dead polymer) 3b) By disproportionation by Hydrogen transformation: Radical + Radical  Unsaturated polymer + Saturated polymer

EXPLANATION: 1. Initiation a) Initiator  Radical 1.The substance which undergoes homolytic cleavage to form radical is called ‘Initiator’. (e.g) acetyl peroxide initiator 2.The substance with single electron is called ‘ radical’. (e.g) acetyl peroxide radical 0 e.g Acetyl peroxide  Radicals ( at 80 C) CH3COO - CH3COO  2 CH3COO . b) Radical + Monomer  Chain Initiating Species (CIS) H H │ │

R. + CH2=C  R – CH2 - C. │ │ Cl Cl

2. Propagation: CIS + n (monomer)  Living polymer H H H H │ │ │ │

R – CH2 - C∙ + n ( CH2 = C )  R (-CH2 – C -)n-CH2 - C. │ │ │ │ Cl Cl Cl Cl

3. Termination a) Coupling Radical + Radical  Macromolecule ( Dead polymer)

H H H H │ │ │ │

R – CH2 - C∙ + R- CH2 – C.  R – CH2 – C – C – CH2 – R │ │ │ │ Cl Cl Cl Cl (Dead polymer) b) Disproportionation (by Hydrogen transformation) Radical + Radical  Unsaturated polymer + Saturated polymer H H H H │ │ │ │

R – CH2 - C∙ + R- CH2 – C.  R – CH = C + H– C – CH2 – R │ │ │ │ Cl Cl Cl Cl The products are known as dead polymers. TOPIC – 2 - PLASTICS Definition: Plastics are high polymers which can be moulded into any desired shape under proper conditions of temperature , pressure and catalyst. (e.g) PVC , PET

Advantages of plastics: Disadvantages of low quality plastics: 1. Insulator 1. very soft 2. Corrosion resistant 2. Embrittlement 3. Easy mouldability 3. Agening ( Low durability) 4. Used as shock absorbers 4. Cannot withstand high temperatures. 5. Has adhesive property 5. Creep (shape Deformation due to load) 6. Less weight 7. Chemical inertness 8. Available in various colours

CLASSIFICATION OF PLASTICS: a)Based on thermal properties - i) Thermo plastics ii)Thermo setting plastics b)Based on utility - i) ii) Engineering plastics

Differences between Thermoplastics and thermosetting plastics No THERMOPLASTICS THERMOSETTING 1 Eg. PVC , Polyethylene , Bakelite 2 Plastics which are melted at high They cannot be remoulded after their temperature, solidified at low first usage. temperature They can be remelted and remoulded into any desired shapes for any number of times. 3 Scarp can be used again. Scarp can not be used again. 4 Formed by addition polymerisation Formed by condensation polymerisation 5 They have linear structure They have complex 3D structure. M – M – M – M – M – M - M - M - M - M –M │ │ │ │ │ M -M - M - M - M │ │ │ │ │ M - M - M – M – M │ │ │ │ │ 6 The bond strength is low The bond strength is high 7 Molecular weight is low Molecular weight is high 8 Soluble in organic solvents. Insoluble in organic solvents. 9 Prepared by Prepared by compression moulding.

Differences between Commodity and Engineering plastics No COMMODITY PLASTICS 1 Eg. Low grade PVC ,, PVC, Teflon , , poly Polyethylene urethane, Nylon, PET 2 Used for domestic and general Used for special and engineering purposes. purposes 3 Easily affected by chemicals Not affected by most of the chemicals. 4 Thermal property is very poor. Thermal property is verygood. 5 They are not 100 % insulators. They are having high insulating properties. 6 They cannot withstand abrasion. They can withstand abrasion. 7 Mechanical strength is low. Mechanical strength is high. 8 Comparatively cheap. Comparatively costly. PROPERTIES AND USES OF ENGINEERING PLASTICS No Name Properties Uses 1 PVC 1.Colourless , odourless 1.Pipes powder. 2Electrical wire covering 2. Affected by Organic 3.Table cloth chlorinated acids. 4.Adhesives 3. It is degraded by high temperature and radiations. 2 TEFLON 1. Except Fluorine, it is 1. In chemical carrying chemically inert. pipes 2.Withstands up to 3500C 2.Gaskets in cookers 3. Electrical insulators. 3. Electrical switchboards. 3 POLY 1. Withstand very high 1. In sterilizable bottles. CARBONATE temperatures. 2. Film – Camera, 2. They are having high Photography films transparency. 3. Transparent bottles 4 POLY Used at Subzero (-ve) 1.Oceanography URETHANE temperatures. 2.In defense 3.High altitude mountains 5 PET 1.High stretch resistance 1. PET jars, bottles 2. High wrinkle resistance 2.Helmets 3. Unbreakable 3.Terylene fabrics 4. Acid proof 4.Textile , wool industry 6 POLY AMIDES 1.Flexibililty 1. Tooth brush bristles 2.Elasticity 2.Automobile gears 3.Elongatable property 3. 4. Nylon ropes

PREPARATION OF SOME IMPORTANT ENGINEERING PLASTICS

1. PVC – POLY

Step 1 – is treated with at 60-800C in presence of some metallic chloride catalyst. It forms Vinyl chloride.

0 CH≡CH + HCl MCl / 60-80 C CH2 = CH │ Cl (Acetylene) (Vinyl chloride)

Step 2 – Vinyl chloride, in presence of Hydrogen peroxide undergoes polymerisation to form Poly vinyl Chloride.

CH2 = CH H2O2 CH2 CH │ │ Cl Polymerisation Cl n

Vinyl Chloride PVC

2. TEFLON (Poly Tetra Flouro Ethylene –PTFE)

Step – 1 When Chloro Diflouro methane is heated, it forms Tetra flouro ethylene is formed. 2CHClF2 heating CF2 = CF2 (Chloro difluro methane) (Tetra flouro ethylene)

Step 2 - Tetra flouro ethylene , in presence of Benzoyl peroxide (Be2O2) , polymerized to form PTFE. n (CF2 = CF2 ) Be2O2 CF2 - CF2 n polymerisation (Tetra flouro ethylene) (Teflon – PTFE)

3. POLY CARBONATE ( Lexan / Merlan)

O _O CH3 l C = O + OH - O __C __ O __OH _ O l O CH3

4.POLY URETHANE ( Perlon – u)

O O ║ ║

C = N – (CH2)6 – N = C + HO – (CH2)4 – OH  (Hexa methylene di iso cyanate) (Butane diol)

O O ║ ║ (-C – NH – (CH2)6 – NH – C – O – (CH2)4 – O- )n (poly urethane)

5. POLY ETHYLENE TERYPTHALATE (PET)

O HO – (CH2)2 - OH + HOOC - - COOH 

Ethylene glycol Terypthalic acid

(-O – (CH2)2 – O – C - O - C - )n + 2 H2O ║ ║ O O (PET)

6. ( NYLON -6) (nylon 6)

Condensation Polymerisation

n H2N - (CH2)6 – NH2 + n HOOC – (CH2)4 – COOH 

Hexa methylene diamine Adipic acid

[ - HN - (CH2)6 – NH - OC – (CH2)4 – CO - ]n Nylon 6,6 TOPIC – 3 - RUBBERS

Rubber is a high polymer with basic qualities of elasticity and non-crystallinity. They are known as elastic + polymer = elastomers.

Types – i) Raw (natural) rubber ii) Synthetic rubber

Natural rubber preparation:

1. When we cut the bark of rubber tree, latex milk is coming out. It is collected in containers. 2. Latex contain major portion of water (70%) and 30% rubber as isoprene C5H8 units. 3. To get colloidal rubber, as coagulant, we are adding acetic acid. 4. The colloidal rubber is dried in air or passing smoke. The previous one is called ‘dried rubber’ and another one is ‘smoked rubber’. 5. Then it is made as sheets using rollers.

Vulcanisation: To remove the defects of rubber, we are adding sulphur to rubber and heating at 100 – 1400C under high pressure. This process is called Vulcanisation. The defect of rubber is mainly due to the non-cross linked isoprene structure of rubber. But, the added sulphur attacks the double bond of isoprene units and converts the non-cross linked structure into a cross linked structure. So, the defects of natural rubber are removed. If 3 -5 % sulphur is added, it is soft rubber. They are used in tyres. If more than 30% Sulphur is added, it is called ‘hard’ or ‘ebonite rubber’. They are used in acid battery cases.

Isoprene C5H8  Poly isoprene

CH3 CH3 CH3 │ │ │

CH2 = C – CH = CH2  –CH2 – C= CH–CH2 –CH2 – C = CH – CH2 –

–CH2 – C= CH–CH2 –CH2 – C = CH – CH2 – │ │ CH3 CH3 ( Rubber defects due to non-cross linked structure)

Adding sulphur during vulcanization alters the structure as follows: CH3 CH3 │ │ –CH2 – C– CH–CH2 –CH2 – C – CH – CH2 – │ │ │ │ S S S S │ │ │ │ –CH2 – C– CH–CH2 –CH2 – C – CH – CH2 – │ │ CH3 CH3 Differences between raw and vulcanized rubber

No Raw rubber Vulcanised rubber 1 Soft and sticky during summer Not Soft and sticky during summer 2 Hard and brittle during winter Not Hard and brittle during winter 3 Swells in oil Does not Swell in oil 4 Absorbs high amount of water Does not Absorb high amount of water 5 Affected by organic and inorganic Not Affected by organic and inorganic acids acids 6 Easily undergoes oxidation Does not easily undergo oxidation 7 Poor life time High life time 8 Tensile strength is low (200 kg/cm2) Tensile strength is high (2000 kg/cm2) 9 Used between 10 – 60 0C Used between - 40 to 100 0C 10 E.g) Raw rubber E.g) SBR , Butyl rubber

SOME IMPORTANT SYNTHETIC RUBBER

1.SBR – Styrene Butadiene Rubber – Buna -S CH2 = CH

n CH2 = CH - CH = CH2 + n O  ( 75% butadiene) (25% Styrene)

[ CH2 - CH = CH - CH2 - CH2 = CH -]n (Styrene – Butadiene RubberSBR) properties: O 1. For vulcanization, it needs little amount of sulphur but more amount of accelerators. 2. High tensile strength. 3. Not Soft and sticky during summer 4. Not Hard and brittle during winter 5. Not affected by organic and inorganic acids.

Uses: Tyres – Belts – Gaskets – Shoes – Tank linings

2. BUTYL RUBBER – (GR-I) rubber CH3 │

n [ H2C = C (CH3)2 ] + n [CH2 = C – CH = CH2]  CH3 │ [ H2C – C (CH3)2 - CH2 – C = CH –CH2] n

Properties: 1. Low permeability to air 2. High tensile strength. 3. Not Soft and sticky during summer 4. Not Hard and brittle during winter 5. Not affected by organic and inorganic acids.

Uses: Inner tubes of automobile tyres - Belts – Gaskets – Shoes – Tank linings TOPIC 4 – COMPOSITES AND FIBRE REINFORCED PLASTICS (FRP)

COMPOSITES

# Composites are the special kind of material system consist of two distinct phases – matrix and dispersed phase. # Matrix phase is the external continuous body constituent. (e.g) Ceramics, Polymer, metals # Dispersed Phase is the internal structural constituent. (e.g) Fibre, Flakes, particulates

Need / Advantages / Properties of composites:

1. They are inert towards chemicals. 2. Corrosion resistance 3. Improved mechanical strength. 4. Improved creep resistance. 5. High insulation property. 6. Variable dielectric constant. 7. Withstand very high temperature. 8. High dimension stability.

Types of composites (Based on Matrix) 1. Polymer matrix composite 2.Metal matrix composite 3. Ceramic matrix composite

POLYMER MATRIX COMPOSITE ( FIBRE REINFORCED PLASTICS –FRP)

Synthesis: 1. Polymer plastic resin is taken as matrix phase. (e.g.) Polyester resin, Epoxy resin (For High mechanical strength) Silicone resin, Phenolic resin (For good electrical and thermal properties)

2. Fibre is taken as Dispersed Phase. (e.g.) Alumina – for dimension stability Boron - For stiffness Glass - For corrosion resistance Carbon – For bio compatibility Graphite – For Lubrication

3. Matrix Phase + Dispersed Phase are suitably mixed, and cured under proper heat and pressure. This results in FRP.

Various types of FRP

Polyester – Glass FRP Polyester – Boron FRP Polyester – Carbon FRP Epoxy – Glass FRP Epoxy – Boron FRP Epoxy – Alumina FRP Silicone – Alumina / Silicone – Boron / Silicone – Glass FRP …..etc. APPLICATIONS OF FRP: 1. Medical field 2. Aero planes 3. Air crafts 4. Automobiles 5. Sports 6. Industries 7. Submarines 8. Pollution control

1. Medical field: - For hip joints and fracture curing plate treatment, steel may have some side effects due to non-bio compatibility. But Carbon FRP plates are highly bio compatible and they are used as plates.

2. Aeroplane: - In Aero planes vertical and horizontal wings, Boron FRP are used due to their very low mass / volume ratio. It is 30% lighter than steel.

3. Air crafts: - In aircraft wings, high resistant blocks, nose cones of missiles, Carbon or graphite FRP are used.

4. Automobiles -Due to high mechanical strength, they are used in automobile parts.

5. Sports - Due to high water resistivity, graphite, silicone FRPs are used in sports mats and artificial sports lawns.

6. Industries - As they are not affected by chemicals, they are used in chemical industries as reservoirs.

7. Submarines - Due to high water resistivity and strength, Glass FRP and silicone FRP are used in submarines.

8. Pollution control - As they are easily bio degradable, their pollution problem is minimum.