Polymers - Chemistry for Engineer's Topic 2 PDF

Polymers Chemistry for Engineers Topic 2  Learning objectives 1 2 3 Students should Understand the Understand the learn the importance polymer characterization and of polymers processing and testing of polymers to stru...

Polymers Chemistry for Engineers Topic 2  Learning objectives 1 2 3 Students should Understand the Understand the learn the importance polymer characterization and of polymers processing and testing of polymers to structures and manufacturing assess their properties, properties. techniques. as well as their mechanical properties.  Polymers Polymers are the high molecular weight compounds obtained by repeated union of simple molecules. (Monomers). Ex: Starch, Polyvinyl chloride, Polyethylene, Nylon 6, 6 and etc.  History The word ‘ Polymer’ is coined from two Greek words: poly means many and mer means unit or part. The term polymer is defined as very large molecules having high molecular mass. These are also referred to as macromolecules, which are formed by joining of repeating structural units on a large scale.  Note Polymer is used as a synonym for plastic All plastic are polymers, but not all polymers are plastics  Key Notes Mer - the repeating unit in a polymer chain Monomer - A single mer unit (n=1) Polymer - Many mer-units along a chain (n=10^3 or more) Degree of Polymerization -The average number of mer-units in a chain. Atomic Number and Mass Number Atomic Number - number of protons in particular atom in an elements. Mass Number - the total number of protons and neutrons (together known as nucleons) in an atomic nucleus carbon atom made up almost of polymers 12 C14 Atomic number of Carbon = 6 C6 6 Mass Number = A 12 C6 (Protons + Neutrons) Atomic Number = Z (Protons ) Atomic Number and Mass Number Example: An isotope of cobalt (Co, Z = 27) is used in radiation therapy for cancer. This isotopes has 33 neutrons in its nucleus. What is its nuclear symbol? Mass Number (Protons + Neutrons) A XZ Atomic Number (Protons ) Atomic Number and Mass Number Try this: One of the most harmful components of nuclear waste 90 is a radioactive isotope of strontium. Sr : it can be deposited in your 38 bones, where it replaces calcium. How many protons are in the nucleus of Strontium? How many neutrons? Mass Number (Protons + Neutrons) A XZ Atomic Number (Protons ) Atomic Number and Mass Number Atomic Mass Unit (amu): -24 1 amu = 1.6605x10 g Isotopes - Atoms with the same number of protons but different numbers of neutrons are called isotopes. There are stable isotopes, which do not emit radiation, and there are unstable isotopes, which do emit radiation. The latter are called radioisotopes.  Atomic Number and Mass Number Try on your paper: The Chlorine precent in PVC has two isotopes. Cl35 with a mass amu of 34.97 amu makes up 75.77% of teh natural chlorine found. The other isotopes is Cl37, whose mass is 36.95 amu. What is the atomic weight of Chlorine?  Ions An ion is an atom or group of atoms that has an electric charge. Ions with a positive charge are called cations. Ions with a negative charge are called anions. Monotomic ions - derive from single atom (anions ending with “ide”, while cations ending “ion”. Polyatomic ions - When group of atoms carry a charge.  Types of Polymer Natural Polymer Commodity plastics Homopolymer PE = Polyethylene Copolymer PS = Polystyrene PP = Polypropylene Thermoplastics PVC=Poly(vinyl chloride) Long chain polymers PET= Poly(ethylene terephthalate)  Types of Polymer Specialty or Engineering Plastics Teflon (PTFE) = Poly(tetrafluoroethylene) PC = Polycarbonate (Lexan) Polyesters and Polyamides (Nylon) Monomers The repeating structural units are derived from some simple and reactive molecules Polymerization Monomers are linked to each other by covalent bonds. This process of formation of polymers from respective monomers  Monomers Polymers The transformation of ethylene to polyethylene and interaction of hexamethylene diamine and adipic acid leading to the formation of Nylon 6,6 are examples of two different types of polymerization reactions.  Monomers Monomer is a simple repetitive unit which when joined together in large numbers which give rise to a polymer. These are the building blocks of Polymer Ex: Vinyl chloride, ethene, propylene etc. Degree of polemerization The number of repeating units (n) (monomers) in the chain so formed is called the Degree of polymerization (DP=n). Molar mass of Polymer (M) Degree of Polymerization = Molar mass of manomer (m) Degree of polemerization How to calculate the degree of polymerization? Step 1: Write the chemical formula of the polymer. For example, let us consider tetrafluoroethylene. Its chemical formula is written as -(CF2-CF2)n Step 2: Determine the atomic mass. In the case of tetrafluoroethylene, the atomic mass of carbon is 12 and the atomic mass of fluorine is 19. Degree of polemerization How to calculate the degree of polymerization? Step 3: Evaluate the molecular weight. Multiply the atomic mass of carbon element by the number of carbon atoms in the monomer Multiply the atomic mass of fluorine element by the number of fluorine atoms in the monomer Add the products C ((2) x 12) + F ((19) x 4) = 100 Degree of polemerization How to calculate the degree of polymerization? Step 4: Divide. Divide the molecular mass of the polymer by the molecular weight of the monomer. For example, if the molecular mass of tetrafluoroethylene is 120,000 120, 000 DP = 100 DP = 1, 200 Degree of polemerization Polymers with a high degree of polymerization are called High polymers and those with low degree of polymerization are called Oligopolymers. By knowing the value of DP, the molecular weight of the polymer can be calculated. [Molecular weight of the polymer] = DP x Molecular wt of each monomer. DP is represented as ‘n’.  (CH2-CH2 ) n Polyethylene Calculate the molecular weight of the polyethylene polymer given DP is 100. [Molecular weight of the polyethylene= DP x Molecular wt of Polyethylene Atomic mass: Carbon-12, Hydrogen-1 [Molecular weight of the polythene = 100 x 28 = 2800 What is the degree of polymerization of polyethylene (PE) with molecular weight of 56,000?  Functionality The functionality of a monomer is the number of sites it has for bonding to other monomers under the given conditions of the polymerization reaction. Thus, a bifunctional monomer, i.e., monomer with functionality two, can link to two other molecules under suitable conditions. A polyfunctional monomer is one that can react with more than two molecules under the conditions of the polymerization reactions The number of bonding sites (or) reactive sites or functional groups present in the molecule. The double bond in vinyl monomers (CH2 = CHX) can be considered as a site for two free valencies. When the double bond is broken, two single bonds become available for combination. A). When the functionality of monomer is two bifunctional linear (or) straight chain polymer is formed. Ex: (a)vinyl monomers (b)adipic acid (c)hexamethylene diamine Example for polymer: HDPE (high density polyethylene) B.)When the functionality of monomer is three (tri- functional), three-dimensional net work polymer is formed. Ex: phenol, glycerol Examples for polymers : Urea formaldehyde, phenol formaldehyde. C.) When a trifunctional monomer is mixed in small amounts with a bifunctional monomer, a branched chain polymer is formed. Ex: LDPE (LOW density polyethene) When the functionality of monomer is three (tri- functional), three-dimensional net work polymer is formed. Ex: phenol, glycerol Examples for polymers : Urea formaldehyde, phenol formaldehyde. Nomenclature of Polymers a) Homo Polymers : Graft copolymers: Polymers made up of with If main chain consists of one same type of monomers are monomer and branched chain called homo polymers consists of another monomers eg: Poly ethylene, PVC are called Graft copolymers b) Hetero polymers : Polymers made up of with different type of monomers are called hetero polymers eg: buna-s rubber Nomenclature of Polymers c) Homo chain Polymers : d) Hetero chain polymers: If the main chain consists of If the main chain consists of only one type of atoms called different type of atoms called Homo chain Hetero chain Polymers Polymers eg: polyethylene. eg: Polyester, Nylon-6. Nomenclature of Polymers Copolymers Homopolymer from a single monomer, copolymer from two (or more) monomers chain copolymerization (different monomers incorporated during the growth of the polymer chain) can lead to: alternating copolymer – ABABABABABABABABABABABA block copolymer - AAAAAAAABBBBBBBBBBBBAAA random copolymer - BAABBAABABBABABBBAABBAB graft copolymer - branches of a different polymer are attached to a polymer chain AAAAAAAAAAAAAAAAAAAAAAAAABBBBBBBBBBBBBBBBBBB (generate reactive site on existing polymer chain, grow new chain)  a). Isotactic – If all the Tacticity functional groups are arranged on the same side of main chain is The difference in called isotactic configuration due to the orientation of different functional groups with b).Syndiotactic - If all the functional groups are arranged respect to the main chain in the alternative fashion of is called tacticity. It has main chain is called Syndiotactic three types; Tacticity c). Atactic - If all the functional groups are arranged in random of main chain is called atactic  Based on Source Natural Polymers: These polymers are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber. Semi-synthetic Polymers: Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this sub category. Synthetic Polymers: A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna - S) are examples of man-made polymers. Classification of Polymers Based on Backbone of Polymer Chain Organic and Inorganic Polymers: A polymer whose backbone chain is essentially made of carbon atoms is termed as organic polymer. The atoms attached to the side valencies of the backbone carbon atoms are, however, usually those of hydrogen, oxygen, nitrogen, etc. The majority of synthetic polymers are organic. On the other hand, generally chain backbone contains no carbon atom is called inorganic polymers. Glass and silicone rubber are examples of it. Organic and Inorganic Chemistry Organic compounds are derived from or produced by living organisms and have carbon-hydrogen covalent bonds. Inorganic compounds are derived from nonliving components, and generally have ionic bonds, lack carbon-hydrogen bonds, and rarely, if ever, contain any carbon atoms. Organic and Inorganic Chemistry Example. Poly(methyl methacrylate is widely known as plexi glass. The structure formula of manomer. methyl methacrylate is shown below, write the corresponding line structure for methyl methacrylate: Organic and Inorganic Chemistry Try this: The structural formula for styrene, which is the monomer for common plastic polystyrene, is shown below. Covert this to a line of drawing.  Based on Structure Linear Polymers: These polymers consist of long and straight chains. The examples are high density polyethylene (HDPE), PVC, etc. Branched Polymers: These polymers contain linear chains having some branches, e.g., low density polyethylene (LDPE).  Based on Structure Cross-linked Polymers: These are usually formed from bi- functional and tri- functional monomers and contain strong covalent bonds between various linear polymer chains, e.g. vulcanized rubber, ureaformaldehyde resins, etc. Cross linked polymers are hard and do not melt, soften or dissolve in most cases.  Based on Composition Homopolymer: A polymer resulting from the polymerization of a single monomer; a polymer consisting substantially of a single type of repeating unit. Copolymer: When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer.  Based on Composition 1.) In an alternating copolymer, the two monomers are arranged in an alternating fashion 2.)In a random copolymer the two monomers may follow in any order. In a block copolymer all of one type of monomers are grouped together , and all of the other are grouped together 3.) In graft copolymer, a block copolymer can be thought of as two homopolymers joined together at the ends: branched copolymers with one kind of monomers in their main chain and another kind of monomers in their side chains.  Based on Composition Alternating Random Block Graft  Based on Composition Copolymerization: A heteropolymer or copolymer is a polymer derived from two (or more) monomeric species, as opposed to a homopolymer where only one monomer is used. Alternating Copolymerization refers to methods used to chemically Random synthesize a copolymer. Commercially relevant copolymers Block ABS plastic Styrene-butadiene Styrene-butadiene Styrene-acrylonitrile rubber (SBR) Glass (SBG) Resins  Based on Mode of Polymerisation Same kind of manomers are stright forwardly added. It is rapid chain reaction having chemically activated mers Each reaction sets up the condition for another process. Initiation Propagation Termination (Birth) (Growth) (Death) Types of Polymerization There are four types of polymerisation reactions; (a) Addition or chain growth polymerisation (b) Coordination polymerisation (c) Condensation or step growth polymerisation and (d) Copolymerization Based on Mode of Polymerisation Polymers can also be classified on the basis of mode of polymerisation into two sub groups; (a) Addition Polymers and (b) Condensation Polymers. a. Addition Polymers: The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds, e.g., the formation of polyethylene from ethyne and polypropane from propane Based on Mode of Polymerisation a. Addition Polymers: However, the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymer, e.g., polythene. Based on Mode of Polymerisation a. Addition Polymers: The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc. (a) Chain-Reaction (Addition) Polymerization  Based on Mode of Polymerisation b. Condensation Polymers: The condensation polymers are formed by repeated condensation reaction between two different bi- functional or tri- functional monomeric units. In these polymerisation reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. take place. The examples ar terylene (dacron), nylon 6, 6, nylon 6, etc. For e.g., nylon 6, 6 is formed by the condensation of hexamethylene diamine with adipic acid. Based on Mode of Polymerisation b. Condensation Polymers: It is also possible, with three functional groups (or two different monomers at least one of which is trifunctional), to have long linkage sequences in two (or three) dimensions and such polymers are distinguished as cross linked polymers. Based on Molecular Forces Elastomers: These are rubber – like solids with elastic properties. In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. Based on Molecular Forces Fibers: Fibres are the thread forming solids which possess high tensile strength and high modulus. These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding. These strong forces also lead to close packing of chains and thus impart crystalline nature. Examples are polyamides (nylon 6,6), polyesters (terylene), etc. Based on Molecular Forces Liquid Resins: Polymers used as adhesives, potting compound sealants, etc. in a liquid form are described liquid resins. Examples are epoxy adhesives and polysulphide sealants. Based on Molecular Forces Plastics: A polymer is shaped into hard and tough utility particles by the application of heat and pressure; it is used as a ‘plastic’. Typical examples are polystyrene, PVC and polymethyl methacrylate.  Based on Molecular Forces Plastics: (a) Thermoplastic and (b) thermosetting plastic. Thermoplastic Polymers: Some polymers soften on heating and can be converted into any shape that they can retain on cooling. The process of heating, reshaping and retaining the same on cooling can be repeated several times. Such polymers, that soften on heating and stiffen on cooling, are termed ‘thermoplastics’. These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres. Polyethylene, PVC, nylon and sealing wax are examples of thermoplastic polymers. Based on Molecular Forces Plastics: (a) Thermoplastic and (b) thermosetting plastic.  Based on Molecular Forces Thermosetting Polymers: Some polymers, on the other hand, undergo some chemical change on heating and convert themselves into an infusible mass. They are like the yolk of egg, which on heating sets into a mass, and, once set, cannot be reshaped. Such polymers, that become infusible and insoluble mass on heating, are called ‘thermosetting” polymers. These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea- formaldelyde resins, etc. Based on Molecular Forces Characteristics of Polymer Low density Poor tensile strength Low coefficient of Low mechanical properties friction Poor temperature resistance Good corrosion Can be produced resistance transparent or different Good mould ability colour  Polymer Processing Powder, melt, dispersion, solution ( ) Extrusion, calendering, coating Thermoforming Moulding: compression, transfer, injection Machining, decoration, assembly  Steps of Polymer Processing The first step consists of mixing additives into the polymer to achieve the required modification to the properties of the raw polymer. The second stage is to create the desired shape. Inherent in the forming stage is the requirement to set or maintain that shape.  Steps of Polymer Processing Forming can be conveniently divided into two- dimensional forming, where products have a relatively simple geometry, and also three- dimensional forming with complex geometry  Steps of Polymer Processing A crucial feature of most polymer processes is the preparation of the polymeric material in a appropriately softened state to suit the forming stage. Usually the softened state is achieved by heating the polymer.facture of a particular product may require more than one forming process.  Steps of Polymer Processing Setting the shape is achieved by either cooling or carrying out a chemical process (crosslinking) to achieve the necessary dimensional stability. Common Polymer Processing 1. Heat Transfer Polymeric materials are characterised by high specific heat and also low thermal conductivity. Therefore, this makes them unsuitable for heating by conduction in thick sections. Consequently, the best form of feed is as finely divided granules or powders. Common Polymer Processing 2. Flow and Deformation (Rheology) In the melt state thermoplastics show varying resistance (viscosity) to applied flow stress. -Viscosity (resistance to flow) : decreases with increasing temperature increases with increasing pressure decreases with increasing shear strain rate (shear thinning, pseudoplastic) Common Polymer Processing 2. Flow and Deformation (Rheology) Increases with increasing molecular size (MW) decreases with increasing lubricant content increases with increasing filler content Polymer dispersions (latex, plastisols) can exhibit both shear thinning (pseudolplasticity) and shear thickening (dilatancy). Common Polymer Processing 3. Extrusion Extrusion is a process in which polymeric materials, in the form of powder, granules, trip or melt, are converted into products of controlled cross- section in a continuous fashion. Common Polymer Processing 4. Injection Moulding For thermoplastics the dominant process for producing complex shapes is injection moulding in which the polymer melt is produced efficiently in one part of the machine. Common Polymer Processing The injection moulding process can be conveniently divided into four phases. Transformation of thermoplastic powder or 1 Plasticisation granules into a homogeneous melt state Transfer of melt from the plasticisation unit to all 2 Injection parts of the mould cavity Cooling of the melt in the mould cavity to below its 3 Setting heat distortion temperature Opening of the mould and also removal of the 4 Ejection finished moulding Common Polymer Processing The injection moulding process can be conveniently divided into four phases. Transformation of thermoplastic powder or 1 Plasticisation granules into a homogeneous melt state Transfer of melt from the plasticisation unit to all 2 Injection parts of the mould cavity Cooling of the melt in the mould cavity to below its 3 Setting heat distortion temperature Opening of the mould and also removal of the 4 Ejection finished moulding  Materials Most thermoplastics can be blow moulded. However, for best results there are special grades that have the desired level of hot strength; too low will result in parison sag; too high will require higher inflation pressures. The most popular materials for blow moulding are, polyethylene, polypropylene, polystyrene, PVC-u, polycarbonate and also polyethyleneterephthalate (PET).  Application of Polymers In the bottle and container market polyethylene and polypropylene are used for their chemical resistance, low cost and flexibility in containers for detergents, bleach, polishes, inks and also cosmetics. Polystyrene has been used in yoghurt pots, cosmetics packaging and also medical packaging.  Application of Polymers Transparent rigid PVC bottles was originally used for water, fruit juice, wine, vegetable oils, shampoo and disinfectant but this market has been mostly taken over by PET. With its excellent impact resistance, polycarbonate (PC) has been used for large water bottles.  Application of Polymers Polyethylene terephthalate (PET) provides high clarity, high strength, lightweight bottles for many of the above products. The excellent barrier properties make PET particularly suited to packaging of carbonated drinks (Coke, lemonade, beer).  Application of Polymers Medicine: Many biomaterials especially heart valve replacement and blood vessels are made up of polymers like dacron, teflon Consumer Science: Plastic containers of all shapes and sizes are light weight and economically less expensive than more traditional containers  Application of Polymers Industry: Automobile parts, pipes, tanks, packing material, adhesives are all polymer application used in industrial market Sports: Playground equipment, golf clubs, swimming pools and protective helmets are produced from polymers. Polymer Analysis Techniques Chromatographic polymer characterization -Chromatography, an analytical technique used to separate mixtures into individual components, is one of the most useful tools for polymer characterisation. Polymer Analysis Techniques Thermal polymer characterization Differential Scanning Calorimetry (DSC) is one of the most common and measures how much heat is needed to increase the temperature of a polymer sample. Data helps manufacturers and product developers determine key thermal transition temperatures. These include glass transition temperature (Tg), melting temperature (Tm) and crystallisation temperature (Tc). Polymer Analysis Techniques Thermal polymer characterization Thermogravimetric Analysis (TGA) is another widely used thermal analysis technique. It works by measuring weight changes when the polymer is exposed to different temperatures. Increases or decreases in weight can be used to predict how a polymer will behave when exposed to harsh environments. Polymer Analysis Techniques Spectroscopic polymer characterisation The cutting-edge spectroscopy techniques being used for polymer analysis. Near-Infrared (NIR) spectroscopy and NIR imaging for polymer characterisation. The technique analyses electromagnetic spectra in the NIR region and is used extensively across a wide range of industries, including engineering and industrial manufacturing. Polymer Analysis Techniques Microscopic polymer characterisation The Used to reveal surface structures and patterns, microscopic polymer characterisation is a powerful tool used to analyse polymer materials. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) have replaced traditional optical microscopes. Both are classed as electron microscopy techniques and allow analysts to generate high-resolution images of polymer samples. Polymer Analysis Techniques Rheometric polymer characterisation Polymers have a higher molecular weight than other materials, which means they can exhibit unusual deformation behaviours. It’s this characteristic that makes many polymers elastic and viscous. Rheometric polymer characterisation allows researchers to analyse the viscoelastic properties of polymers, optimise manufacturing formulas and improve product performance. Polymer Analysis Techniques Mechanical polymer characterisation Strength, elasticity, viscoelasticity and anisotropy are some of the most important properties used to characterise polymers. These are known as mechanical properties and are influenced by interactions between individual polymer chains. Mechanical properties are also impacted by the ability of chains to stretch and realign when exposed to force. Thank you!