Polymers PDF

INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES POLYMERS The word polymer is derived from the Greek word poly meaning 'many' and meros meaning 'parts'. Polymers are macromolecules, whose structure consists of large number of simple repeating units....

INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES POLYMERS The word polymer is derived from the Greek word poly meaning 'many' and meros meaning 'parts'. Polymers are macromolecules, whose structure consists of large number of simple repeating units. The repeating unit is generally obtained from low molecular weight simple compound known as monomers. The process of conversion of Monomer into Polymer is known as Polymerization. Classification of Polymers Polymers have been classified on different basis as follows: (A). Classification on the basis of Origin/Source On this basis, polymers have been broadly classified into two types: 1. Natural Polymers They occur naturally and are found in plants and animals. Examples: Proteins, Nucleic acids, Starch, Cellulose and Natural rubber 2. Synthetic Polymers These are man-made polymers. Plastic is the most common and widely used synthetic polymer. E.g., Nylons, Polythene, PVC, Synthetic rubbers, etc. (B). Classification on the basis of Structure On this basis, polymers have been broadly classified into three types: 1. Linear Polymers Polymers comprising of long and straight chains are called as linear or straight chain polymers. e.g., High density polyethene (HDPE) 2. Branched-chain Polymers Polymers comprising of linear chains with branches are called as branched chain polymers. e.g., Low-density polyethene (LDPE). 3. Cross-linked Polymers Polymers in which various individual chains are connected together by covalent bonds (cross links) are called as cross-linked polymers. These polymers are formed from bi-functional and tri- functional monomers and the additional functionality produces the cross links. E.g., Bakelite and Melamine.  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES (C). Classification on the basis of nature of Monomers On this basis, polymers have been broadly classified into two types: Homo-polymers Polymers which are comprising of only one type of monomers are called as homo-polymers. e.g., Polyethene, PVC, Nylon-6, etc. This can be represented as: Co-polymers Polymers which are comprising of more than one (generally two) types of monomers are called as homo-polymers. e.g., Nylon-6'6, Terylene, SBR, etc. Co-polymers have further been classified into four types on the basis of relative arrangement of the monomer units with respect to each other. These are: Alternate Co-polymers: Polymers comprising of alternating A and B units. The order is regularly followed throughout the chain. This can be represented as: Block Co-polymers: Polymers comprising of regular alternating blocks of A and B units. The order is regularly followed throughout the chain. This can be represented as: Graft Co-polymers: Polymers in which the main chain is comprising of one type o monomers and the other monomer forms the branches. Therefore, for being a graft co-polymer, the polymer must be branched. This can be represented as: Random Co-polymers: Polymers in which no regular order of arrangement is followed by the monomer units. This can be represented as: (D). Classification on the basis of Inter-molecular Forces (ultimate form) On this basis, polymers have been broadly classified into four types: Elastomers Polymers in which intermolecular forces are very weak (van der Waals forces) are called as elastomers. These are rubber-like solids weak interaction forces are present. e.g., Rubber. Fibres Polymers in which intermolecular (inter-chain) forces are very strong (Hydrogen bond or dipole- dipole interaction) are called as Fibres. These are strong, tough, with high tensile strength. e.g., Nylons, Terrylene, etc. (E) Classification on the basis of Temperature Thermo-plastics Polymers in which intermolecular (inter-chain) forces are intermediate are called as thermo-  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES plastics. These polymers on heating become soft and on cooling again become hard and retain their original shape. In this case, the intermolecular forces, on heating, get weaken and the polymer becomes soft and vise-versa. Therefore, these polymers are recyclable, i.e., they can be moulded and re-moulded again and again. e.g., Polyethene, Polyvinyl chloride, Polystyrene, etc. Thermo-sets Polymers in which there is extensive cross linking, are called as thermo-settings. These polymers on heating become soft and on cooling again become hard but do not retain their original shape. In this case, the cross links get broken and rearranged on heating. It is purely a chemical change and chemical changes are generally irreversible. Therefore, these polymers are not recyclable, i.e., once moulded, they cannot be moulded again. These polymers greatly improve the material’s mechanical properties. e.g., Bakelite, Epoxy resins, etc. Difference between thermosets and thermoplast (F) On this basis Synthesis, polymers have been broadly classified into two types: Addition Polymers Polymers which are formed by addition reaction are called as addition polymers. e.g., Poly ethene, Teflon, Polyvinyl chloride, etc. For addition polymerization to take place, the monomer must be unsaturated. Addition polymerization is a chain reaction, which once initiated, propagates itself till the chain is not terminated. It involves three steps: Chain initiation, Chain propagation and Chain termination.  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Polyethene Polyethene is a homo-polymer and its monomer unit is ethene (ethylene). It is the most common and with simplest structure among all plastics. The reaction for preparation of polyethene can be shown as: Polyethene is broadly of two types: i). Low Density Polyethene (LDPE) ii). High Density Polyethene (HDPE) Low Density Polyethene (LDPE): As the name itself indicates, it is a polymer of very low density. It is prepared via free radical mechanism at a temperature of 80 to 350oC under high pressure (1000 to 3000 atm) in presence of Benzoyl peroxide as initiator, wherein extensive branch formation takes place and the density of the resultant polymer is very low in the range of 0.910– 0.940 g/cm3. Properties: It is a waxy translucent material, exhibits high impact strength, low brittleness temperature, film transparency and outstanding electrical insulating properties. It is chemically inert and has good resistance to acids and alkalis. However, it swells in and is permeable to oils. It melts in temperature range of 107-120oC. Its Tg (Glass Transition) value is -120oC. It is flexible over a wide temperature range. Applications: It is used in making packaging materials for food, garments, etc. It is used in production of squeeze bottles, coatings, wrappings, etc. It is also used in cable and wire insulations. High Density Polyethene (HDPE): It is a linear polymer with little or no branching. It is prepared via ionic mechanisms at a low temperature of 60 to 70oC and very low pressure (6 to 7 atm), wherein little or no branch formation takes place and the density of the resultant polymer is high in the range of 0.945–0.965 g/cm3. However, HDPE is also prepared by coordination polymerization using Ziegler-Natta catalyst (Triethyl aluminium and Titanium tetrachloride). Properties: It is opaque and has less impact strength, but, better barrier properties than LDPE. It has better chemical resistance than LDPE. It melts in temperature range of 130-138oC. Its Tg (Glass Transition) value is -20oC. It is exhibiting better stiffness, toughness, good tensile strength and heat resistance. Applications: It is used in manufacture of dust bins, cans, buckets, fuel tanks, etc. It is used for making corrugated pipes. It is also used in cable and wire insulations. Condensation Polymerization Polymers which are formed by condensation reaction are called as condensation polymers. e.g., Nylon-6'6, Nylon-6, Dacron, Bakelite, etc. This type of polymerization is called as condensation polymerization. Example of condensation polymerization is preparation of Nylon 6,6 and reaction are as follow:  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Difference between addition and condensation polymerization Commercially Available Fibers (Polyamides/polyesters) Polymers in which monomer units are linked together by amide bonds. For polyamide formation, the monomers should be dicarboxylic acids and diamines are used. Polyamides belong to the fibres as per the classification on the basis of intermolecular forces. Q. Define Fibers. Write Preparation, properties and uses of Nylol nylol6,6, teyelene Ans: When a polymer is drawn into filament like material, whose length is at least times its diameter with high aspect ratio Polyamides are the polymers obtained by condensation polymerization of acids (bifunctional) and amines (bifunctional). They contain the amide linkage. eg: - nylons POLYESTERS are the polymers, obtained by the condensation of acid (bifunctional) and alcohol (bifuctional), and have ester linkage. Eg. PET INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Commercially available thermoplastics and thermosets  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Commercially available thermoset polymer Or Discuss the synthesis uses and application of Bakelite/ phenol-formaldehyde resins/ phenolic resin Bakelite is a polymer made up of the monomers, phenol and formaldehyde. This phenol- formaldehyde resin is a thermosetting polymer. Properties Bakelite can be easily generated, and the mouldings of Bakelite are corrosion and thermal-resistant. It would be resistive to current flow because of its low conductivity to electricity. Due to its low electrical properties and high heat resistance, Bakelite has also been used primarily in the production of mechanical and electrical components for electrical devices. Bakelite contains phenolic components in the structure. For this, it is widely used in bindings. Bakelite is moulded at a very rapid rate and enables the production of extremely smooth mould. When heated, it melts and solidifies. Then It becomes hard and can be moulded into desired shapes.  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Uses To offer adequate security, it is used in parts that do not use radios or other electronic parts, such as plugs, buttons, hoods, wire cables, brakes, and so on and due to its shaping capacity, it is frequently used in everyday culture. Due to its strong tensile strength and thermosetting nature, Bakelite may maintain its shape even after extensive production. It has the ability to mould itself in various shapes, making this substance too much useful in modern society. It is extensively used in making the parts of washing machines, cooking utensils, watches, toys, and many more. ELASTOMERS It can stretch at least twice of their original length under the action of force and recover its dimension after removal of applied force. Elastomers have long linear coiled chains, amorphous structure and a few widely separated Cross links. The Polymeric chains are held together by weakest intermolecular forces. When such polymers are subjected to external force the coils open up partially and get aligned in the direction of elongation. The aligned chains have a natural tendency to revert back in their original state as soon as external force is removed. Examples 1) Natural rubber 2) Synthetic rubber. Natural Rubber It is obtained from tree Hevea brazilensis. The rubber is obtained from latex collected from the cuts made in the bark of the tree. Chemically natural rubber is cis poly isoprene. Draw backs of natural rubber: It is weak due to its low tensile strength. (200 Kg/cm2) It becomes soft in summer and the brittle in winter. It has large water absorption capacity. It swells in organic solvents and gradually disintegrates. It has less durability due to oxidation in air. It is attacked by oxidizing agents like cone. H2SO4 and conc. HNO3. To improve these drawbacks vulcanization of rubber is done. Vulcanization: -It was discovered by Charles Goodyear in 1839. Raw rubber is heated with Sulphur to 100 to 140°C. Chemically Sulphur add to the double bonds of different polymeric chain providing cross linking between them and hence it stiffens the raw rubber. The strength of Vulcanized rubber depends upon the amount of Sulphur used. Greater is Sulphur, greater is cross linking between the rubber so more is hardness.  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Advantages of Vulcanized rubber Good tensile strength. Can bear load up to 2000Kg I cm2 Greater working temp range (-40° C to 100° C) Good oxidation resistance. Low water absorption capacity. Good resistance to organic solvent. INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Polymer blend A Polymer blend is any physical mixture of two or more different polymers that are not linked by covalent bond. A polymer blend or polymer mixture is a class of materials analogous to metal alloys, in which at least two polymers are blended together to create a new material with different physical properties. Classification of Polymer Blends Polymer blends are classified in two ways- 1. On the basis of preparation methods- Mechanical blends, Solution-cast blends, Latex Blends and Inter-penetrating polymer Networks (IPN) or Chemical Blends. 2. On the basis of compatibility -can be broadly divided into two categories: Immiscible polymer blends (heterogeneous polymer blends): They are usually opaque and exhibit separate glass transition temperature characteristic of each component. e.g, Polystyrene and Polybutadiene blend (HIPs). Miscible polymer blends (homogeneous polymer blend): They are usually clear and exhibit a single glass transition temperature between those of the individual components. Polyethylene terephthalate and polybutyleneterephthalate. Preparation of Polymer blends Amorphous and semicrystalline polymers are mixed at temperatures above Tg or Tm respectively. This mixing leads to formation of Mechanical blends. Polymers are dissolved in a common solvent and then solvent is removed to give Solution-cast blends. Fine dispersions of polymers in water are mixed and the mixture is coagulated to give Latex Blends. Cross-linked polymer is swollen with different monomer, then monomer is polymerized and cross-linked. This method results in formation of Inter-penetrating polymer Networks (IPN) or Chemical Blends. Advantages Providing material with full set of desired properties at low price. Offering the means for industrial/ municipal plastic waste recycling. Blending also benefits the manufacturer by offering scrap-reduction and product uniformity. Applications ABS plastics made by blending Acrylonitrile-styrene copolymer with styrene - butadiene rubber is used in automobile industry for making door covers, panels. Electroplated ABS- used as name plates, reflectors. Nylon-6 and polycarbonate blend-sport equipment and transport container. Polymer Composites Any multiphase material which consists of two or more physically and chemically distinct phases with an interface separating them. Matrix phase The primary phase, having a continuous character, is called matrix. Matrix is usually more ductile and less hard phase. It holds the dispersed phase and shares a load with it.  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Dispersed (reinforcing) phase: The second phase is embedded in the matrix in a discontinuous form. This secondary phase is called dispersed phase. Dispersed phase is usually stronger than the matrix, therefore it is called reinforcing phase. Classification of composites Advantages  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES CONDUCTING POLYMERS Conducting polymers are organic polymers that conduct electricity. Until 1970, all organic polymers were used in electrical, electronic and other applications as insulators, taking advantage of their excellent insulation properties. Thus, organic polymers having electrical conductance of the order of conductors are now called as conducting polymers. Conducting polymers have been classified into two types: Extrinsically Conducting Polymers They are prepared by mixing conducting fillers like metal fibres, metal oxides or carbon black with insulating polymers. These are also called as conductive element filled polymers. Here, insulating polymer forms the continuous phase and added fillers form the conducting network. A minimum concentration of conducting filler has to be added so that the polymer starts conducting. The conductivity in this type of polymer is not due to the matrix polymer but due to conducting fillers which are added. Intrinsically Conducting Polymers In this type of polymer, conductivity is due to the organic polymers themselves. They conduct electricity when doped with oxidizing or reducing agents or protonic acids. The factor responsible for conductance in these polymers is conjugated electrons. Organic polymers with highly de-localized π-electrons having electrical conductance of the order of conductors are called as inherently or intrinsically conducting polymers or synthetic metals. Some important intrinsically conducting polymers are:  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Applications of Conducting Polymers In antistatic materials and as electrode materials in rechargeable batteries. In light emitting diodes and display devices. As conductive track on printed circuit boards (Polyaniline). As resisters for lethography (emeraldine base). In information storage devices. As humidity sensors, gas sensors, radiation sensors. In electro-chromic display windows. In fuel cells as electro-catalytic materials. As membrane for gas separation. INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES  INDERPRASTHA ENGINEERING COLLEGE, GHAZIABAD DEPARTMENT OF APPLIED SCIENCES Ill) LIQUID CRYSTAL POLYMER liquid-crystal polymer is a polymer in which the various mesogen molecules link to form long polymeric chains. Most commercial LCPs incorporate p-hydroxybenzoic acid as one of the monomers that build molecular chains through various condensation methods. Monomer additives such as bisphenol are then introduced into the to lower processing temperatures and allow for easier manufacturing. In addition to these monomers, fillers can be added to the material to further enhance its properties. These fillers can include graphite, fiberglass, or carbon. Liquid crystal polymer is one specific type of the broad class of polymers that are known as thermoplastics. Three of the most common forms of liquid crystal polymers include semi- aromatic copolyesters, copolyamides, and polyester-co-amides. Advantages Very low melt viscosity - long flow paths with very small wall thicknesses can be achieved Very low water absorption Self-reinforcing Inherent flame retardancy High heat resistance and continuous service temperature Very good chemical resistance Excellent insulating properties (but low creep resistance) Applications Electrical connectors: They function to eliminate static build-ups and discharges that would otherwise create noise interference in electrical signals. Vascular catheter reinforcement braiding: Vascular catheters with LCP plastic braiding can be important for patients undergoing MRI scans. Surgical instruments: CPs are ideal for this because they can withstand the radiation without breaking down during sterilization. Cookware coatings -. LCPs can withstand temperatures up to 280°C and the coating is not harmed by dishwasher machines. Disadvantages High cost: Anisotropic properties: Properties may vary depending on the direction of the applied load as polymer chains tend to align longitudinally in the direction of extrusion during processing.