Unit – 2 Polymers & Composites Lesson plan: 1. Polymers – Introduction -a) Definition –monomer, polymer, 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. Plastics a) Classification – i)based on thermal property – Thermo / Thermoset plastics ii) Based on usage – Commodity and Engineering plastics b) Prepration, properties and applications of i) PVC ii) Teflon iii) Poly carbonate iv) Poly Urethane v)PET vi) Nylon 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 monomers 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, Ethylene 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 fashion, 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 Thermoplastics 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 Polyethylene 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) Commodity plastics ii) Engineering plastics Differences between Thermoplastics and thermosetting plastics No THERMOPLASTICS THERMOSETTING PLASTIC 1 Eg. PVC , Polyethylene Polyester, 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 Injection moulding Prepared by compression moulding. Differences between Commodity and Engineering plastics No COMMODITY PLASTICS ENGINEERING PLASTIC 1 Eg. Low grade PVC ,polystyrene, PVC, Teflon , Polycarbonate, 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 industry – 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.Textile industry 4. Nylon ropes PREPARATION OF SOME IMPORTANT ENGINEERING PLASTICS 1. PVC – POLY VINYL CHLORIDE Step 1 – Acetylene is treated with Hydrochloric acid 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