Materials Chemistry - Polymers PDF

Unit 2 Materials Chemistry Polymers 1. Introduction to polymer The word polymer is derived from two Greek words, poly and meros, where poly means many and meros means parts. Polymers are giant molecules formed by the combination of several simple molecules having two or more binding sites...

Unit 2 Materials Chemistry Polymers 1. Introduction to polymer The word polymer is derived from two Greek words, poly and meros, where poly means many and meros means parts. Polymers are giant molecules formed by the combination of several simple molecules having two or more binding sites linked through covalent bonding. H H H H Polymerisation n C C C C H H n H H Ethene Polythene The simple molecules which are repeating units of the polymer are called monomers. Eg: Polythene is formed by the combination of several ethene (ethylene) molecules. Degree of polymerization (DP): Degree of polymerization is the number which expresses the total number of repeating units (n) in the polymer chain. Polymers with large number of repeating units are called high polymers and those with lower number of repeating units are called oligomers. DP is used to determine the molecular weight of the polymer by multiplying the number of repeating units (n) with the molecular weight of repeated unit. Functionality: The total number of functional groups, bonding sites or reactive sites present in the monomer is called the functionality of the monomer. The reactive functional groups can be –OH, -COOH, -NH2, -SH , –NCO etc. Eg: In CH3CH2OH one reactive - OH group is present, hence functionality is one ( monofunctional) HO- CH2 -CH2 – OH has two – OH groups hence bifunctional HOOC CH2 CH (COOH) CH2 COOH has three -COOH groups, hence trifunctional The presence of double or triple bonds in the molecule imparts polyfunctionality to the molecules. Eg: Ethylene - due to the presence of a double bond, it can take on two atoms of hydrogen or halogens. Depending upon the functionality of the monomers used linear, branched or three dimensional cross-linked polymers are formed. 2. Classification of polymers based on molecular structure Polymers can have different molecular structures, which significantly influence their physical properties and behavior. The three main types of polymer structures are linear, branched, and network (or cross-linked) structures. 2.1. Linear polymers: Linear polymers consist of long, unbranched chains of monomers linked together in a straight line. The monomers are connected by covalent bonds, forming a continuous backbone. Examples of linear polymers include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyesters like polyethylene terephthalate (PET).Linear polymers tend to have high strength and stiffness due to the ability of the chains to align and crystallize. They also exhibit good resistance to solvents and chemicals, as well as relatively high melting and glass transition temperatures.If ‘M’ represents a monomer, the typical structure of a linear polymer is represented as: –M–M–M–M–M–M– 2.2. Branched polymers: Branched polymers have a main linear backbone with additional side chains or branches attached to it. The branches can be short or long, and they can be evenly distributed or randomly placed along the main chain. Examples of branched polymers include low-density polyethylene (LDPE), polyisobutylene, and certain types of polypropylene. Branched polymers generally have lower densities and lower crystallinity compared to their linear counterparts. They exhibit improved flow properties, making them easier to process and mold. Additionally, branched polymers tend to have better impact resistance and flexibility due to the disruption of chain packing caused by the branches. The typical structure of a branched-chain polymer may be represented as: 2.3. Network (cross-linked) polymers: Network or cross-linked polymers are formed when linear or branched polymer chains are chemically connected at various points along their lengths, creating a three- dimensional network structure. The connections between the chains are typically covalent bonds, but they can also involve ionic or hydrogen bonding. Cross-linked polymers are highly resistant to solvents, heat, and chemicals due to their rigid network structure. They exhibit high strength, toughness, and dimensional stability, but they are also relatively inflexible and insoluble. Examples of cross-linked polymers include vulcanized rubber, thermoset resins like epoxy and polyurethane, and certain types of hydrogels. The typical structure of a cross-linked polymer is represented as:  The degree of cross-linking plays a crucial role in determining the properties of network polymers. Highly cross-linked polymers are more rigid and brittle, while those with lower degrees of cross-linking exhibit greater flexibility and elasticity. The molecular structure of polymers significantly affects their properties and applications. Linear polymers are used in packaging, textiles, and engineering plastics, while branched polymers find applications in film manufacturing and packaging. Cross-linked polymers are employed in various applications, such as tires, coatings, adhesives, and advanced composite materials. Structure and properties of polymers The structure of a polymer has profound influence on some of the properties of polymers. The properties such as crystallinity, tensile strength, elasticity, resistance to chemicals and plasticity depend mostly on the polymer structure and are discussed below. Strength: This property is discussed based on forces of attraction and slipping power. Based on forces of attraction: Strength of the polymer is mainly determined by the magnitude and distribution of attraction forces between the polymer chains. These attractive forces are of two different types viz., primary or covalent bond and secondary or intermolecular forces. In case of straight chain and branched chain polymers, the individual chains are held together by weak intermolecular force of attraction. But in these polymers, strength increases with increase in chain length (increase in molecular weight) i.e., attains mechanical strength if the chain length is greater than 150 – 200 carbon atoms in the chain. Less than these numbers, the polymers will be soft and gummy, but brittle at low temperature. Intermolecular forces can be increased by introducing polar groups like carbonyl & hydroxyl. In cross-linked polymers, monomeric units are held together only by means of covalent forces. Hence possess greater strength than straight and branched chain. Based on slipping power: Slipping power is defined as movement of molecules one over the other. Eg: polyethylene molecule is simple and uniform, hence movement of molecule one over other is possible, i.e., slipping power is high. Hence it has lesser strength. But in case of polyvinyl chloride (PVC), bulky chlorine atoms are present along the chain length hence, movement is restricted, i.e., slipping power is less. Hence it has higher strength compared to polyethylene. But in case of cross-linked polymer, movement is totally restricted because of the presence of covalent bond. Hence these products are strong, rigid and tough. Plastic deformation: When a polymer is subjected to some stress in the form of heat or pressure or both, permanent deformation in shape takes place, which is known as plastic deformation. This property actually helps in moulding of plastics. Slippage is more in case of linear molecules than branched and cross-linked, because of the presence of weak intermolecular forces and hence they show greatest degree of plastic deformation. At high pressure and temperature the vander Waal‘s forces acting between molecules become more and more weak. No slippage occurs in case of cross-linked polymers, because only strong covalent bonds are present throughout the entire structure. However, when considerable external force or temperature exceeding the stability of material is applied, it will result in total destruction. Crystallinity: Based on the relative arrangement of polymer chains with respect to each other, polymer can exhibit amorphous and crystalline nature. An amorphous state is characterized by completely random arrangement of molecules and crystalline form by regular arrangement of molecules. The crystallization tendency of a polymer depends on the ease with which the chains can be aligned in an orderly arrangement. Crystalline regions of a polymer are formed when the individual chains are linear (without branching), contain no bulky substituents and are closely arranged parallel to each other. The chains of polymer may be held together by vander Waal‘s forces, hydrogen bonding or polar interactions. A polymer with high degree of crystallinity will have high tensile strength, impact and wear resistance, high density and high fusion temperature. Polymers with a long repeating unit or with low degree of symmetry do not crystallize easily, hence forms amorphous structure e.g., polystyrene. Crystallization imparts denser packing of molecules due to increase of intermolecular forces of attraction. Such type of polymers will have sharp softening point, greater strength and rigidity. e.g PVC, Polypropylene. Polymers are in general, amorphous with some degree of crystallinity. Chemical Resistance: Chemical resistance of polymer depends upon the chemical nature of monomers and their molecular arrangement. A polymer is more soluble in structurally similar solvent. For example, polymers containing polar groups like – OH, - COOH, usually dissolve in polar solvents like water, alcohol etc but are chemically resistant to non-polar solvents. Similarly non-polar compounds like hydrocarbons dissolve only in non-polar solvents like benzene & toluene. As a general rule, the tendency of solubility in a particular solvent decreases with increase in molecular weight of the polymer- (i) high molecular weight polymer on dissolving yield solutions of high viscosities (ii) crystalline polymers exhibit higher resistance than less crystalline polymers of similar chemical character (iii) greater the degree of crystallinity, lesser is its solubility. Today several drugs and essential oils are stored in plastic bottles for long shelf life. If they disintegrate or change in their chemical composition they may render the drug ineffective or may cause it to react adversely when used, leading to specific disorder. Therefore, chemical resistance of plastic bottles is important to prevent drug polymer interactions. Elasticity: Elastic nature in polymers results due to the uncoiling and recoiling of the molecular chains on the application of force. In an upstretched elastomer we can observe a peculiar configuration of irregularly coiled and entangled snarls in a random fashion, indicating the amorphous state. In a stretched state snarls disentangle and straighten out in a proper chain orientation, indicating the crystalline state. The crystallinity in a stretched rubber band can be observed from its opaqueness and warmth it produces when touched by lips. The main criteria for a polymer to show elastic nature is that , the individual chains should not break even after prolonged stretching. This can be done by introducing suitable crosslinking in the chains, by allowing nonpolar groups or side groups in the repeating unit. Glass transition temperature Tg Amorphous polymers do not have sharp melting points. They possess softening point. At low temperature, polymers exist as glassy substances. Since the molecular chains cannot move at all easily in this state, the solid tends to shatter, if it is hit. If the solid polymer is heated, eventually it softens and becomes flexible. This softness and flexibility is obtained at the glass transition temperature. After this temperature, crystalline and amorphous thermoplastic polymers behave differently. Heating has little effect on thermosetting polymers and at a high temperature, they are destroyed. So the glass transition temperature can be defined as the temperature below which an amorphous polymer is brittle, hard and glassy and above the temperature it becomes flexible, soft and rubbery. Glassy state rubber state (Hard brittle plastic) (soft flexible) In the glassy state of the polymer, there is neither molecular motion nor segmental motion. When all chain motions are not possible, the rigid solid results. On heating beyond Tg segmental motion becomes possible but molecular mobility is disallowed. Hence flexible, Factors affecting glass transition Temperature Glass transition temperature of a polymer depends on parameters such as chain geometry, chain flexibility, molecular aggregates, hydrogen bond between polymer chains, presence of plasticizers and presence of substrates in the polymer chains. A polymer having regular chain geometry show high glass transition temperature, the bulky groups on chain increases the Tg of the polymer. E.g., polyethylene has Tg -110 oC. The Tg is quite low because there are no strong intermolecular forces and no bulky side groups are present, the side chain is only hydrogen atom. But nylon 6 has Tg 50 oC because of the presence of large number of polar groups in the molecule leading to strong intermolecular hydrogen bonding. The Tg of a polymer is influenced by its molecular weight. However, it is not significantly affected if molecular weight is around 20000. With increase in molecular mass, the temperature (Tg ) will be higher. In crystalline polymers the polymer chains are arranged in a regular parallel fashion. Each chain is bound to the other by strong forces like H-bonding. Hence crystalline polymers have higher Tg than amorphous polymers. The added plasticizers reduce the Tg of the polymer by reducing the cohesive forces of attraction between the polymers. e.g., dibutyl phthalate, diacetyl phthalate etc., The glass transition temperature is an important parameter of polymeric material. This helps in choosing the right processing temperature. It is a measure of flexibility of a polymer and also gives the idea of the thermal expansion, heat capacity, electrical and mechanical properties of the polymer. Molecular weight of polymers A polymer comprises of molecules of different molecular weights and hence, its molecular weight is expressed in terms of an ‘average’ value. The molecular weight of a polymer can be expressed by the two most and experimentally verifiable methods of averaging – (i) Number – average molecular weight and (ii) weight – average molecular weight Number – average molecular weight: Number average molecular mass of a polymer can be defined as the total mass of all the molecules in a polymer sample divided by the total number of molecules present. ∑ 𝑛𝑖 M𝑖 𝑀𝑛 = ∑ 𝑛𝑖 Weight – average molecular weight: The sum of the fractional masses that each molecule contributes to the average according to the ratio of its mass to that of the whole sample. The formula to determine 'weight average molecular weight' of polymers is, ∑ 𝑛𝑖 M𝑖 2 𝑀𝑤 = ∑ 𝑛𝑖𝑀𝑖 1) A polymer sample contains 1, 2, 3 & 4 molecules having molecular weight 105 , 2X 105 , 3X105 and 4X 105 respectively. Calculate the number average & weight average molecular weight of the polymer. 1(1𝑋105 )+2(2𝑋105 )+3(3𝑋105 )+4(4𝑋105 ) Mn= 1+2+3+4  = 3.0 X105 Mw = 1(1 X105)2 + 2(2 X105)2 + 3(3 X105)2+ 4(4 X105)2 1(1 X105) + 2(2 X105) + 3(3 X105) + 4(4 X105) = 3.3 X105 2) Calculate the number average & weight average molecular weight of a polymer sample in which 30 % molecules have molecular mass of 20000, 40 % have molecular mass of 30000 & rest 30 % have molecular mass of 60000. Mn = 30 X 20000 + 40 X30000 + 30 X 60000 30 + 40+30 = 36000 MW = 30 X (20000) 2+ 40 X (30000) 2+ 30 X (60000)2 30 X 20000 + 40 X30000 + 30 X 60000 = 43,333 3) Polymers molecule with different degree of polymerization such as 500, 750, 950 and 1500 are mixed in molecule ratio1:2:3:4 in a sample of high polymer of ethylene. ( Mole. Mass= 28). Calculate number average and weight average mol.mass. Mn = 1(28 X 500) + 2(28 X 750) + 3(28 X 950) + 4(28 X 1500) 1+2 +3 +4 = 30380 Mw= 1(28 X 500)2 + 2(28 X 750) 2 + 3(28 X 950) 2 + 4(28 X 1500)2 1(28 X 500) + 2(28 X 750) + 3(28 X 950) + 4(28 X 1500) = 33761 3) A polymer sample contains:  Polymer of 400 500 600 800 1000 DP Percentage 10 15 35 15 25 Calculate the average degree of polymerization. Solution: DP = 10X400+15X500+35X600+15X800+25X1000 10+15+35+15+25 = 695 Determination of Molecular weight of polymers by viscometry Viscometry: The molecular weight obtained by this technique is the viscosity average molecular weight, Mv. The viscosity of a polymer solution is considerable high as compared to that of pure solvent. The relationship between the viscosity of a polymer solution and molecular weight is given by Mark-Houwink equation- [η] = KMa Where [η] is the intrinsic viscosity, M- molecular weight and a and K are constant for a particular polymer/solvent/temperature system. Values of K and a are available for may known polymers. A plot of log [η] against log M gives a straight line. From the graph, the value of K and a can be determined from their ordinate intercept and slope of the line.. [η] = KMa log [η] = log K + a logM Engineering Polymers Introduction to Engineering polymers An introduction to engineering polymers provides a foundational understanding of these advanced materials, their properties, and their diverse applications across various industries. Engineering polymers, also referred to as high-performance polymers, represent a specialized class of materials designed to meet stringent performance requirements in demanding applications. Definition and Significance of Engineering Polymers: Polymer engineering comprises the engineering discipline, focusing on the design, analysis, and modification of the polymer materials. It encompasses various facets of the petrochemical industry, including polymerization processes, polymer structure and characterization, polymer properties, compounding, and processing techniques, as well as the study of major polymers, their structure-property relationships, and diverse applications. Key attributes of engineering polymers include: Mechanical Properties: Engineering polymers often exhibit high strength, stiffness, toughness, and impact resistance, making them suitable for structural applications where mechanical performance is crucial. Ex: ultra-high molecular weight polyethylene (PE)- have better tensile strength than steel, Fibers (KevlarTM , carbon fiber and nylon) Thermal Stability: These polymers maintain their properties over a wide range of temperatures, including both high and low extremes. They can withstand prolonged exposure to elevated temperatures without significant degradation. Ex: polybenzoxazoles (PSPBOs), poly phenyls Chemical Resistance: Engineering polymers are resistant to a wide range of chemicals, solvents, and environmental conditions, making them ideal for applications where exposure to harsh substances is common.  Ex: low density polyethylene (LDPE), Polytetrafluoroethylene (PFTE). Electrical Properties: Conducting polymers possess the ability to conduct electricity, which arises from the presence of delocalized π-electrons along the polymer backbone or within conjugated segments. Many engineering polymers possess excellent electrical insulation properties, making them suitable for electronic and electrical components where insulation and reliability are paramount. Ex: conducting polymers like polyaniline (PANI), Polypyrrole (PPy) Insulating polymers: silicone, Ethylene Propylene Diene Monomer (EPDM) Dimensional Stability: These materials exhibit minimal dimensional changes under varying environmental conditions, ensuring precision and consistency in critical applications. i.e., they have ability to maintain their size even in changing environmental conditions. A dimensionally stable shows low water absorption and thermal expansion. Ex: Polyether ether ketone (PEEK), Polyethylene terephthalate (PET), polyvinylidene difluoride (PVDF) o Flame Retardancy: Some engineering polymers are formulated to meet stringent fire safety standards, making them suitable for applications where flame resistance is essential. They are made by incorporation of aromatic rings or heterocycles. They are also called as fire safe polymers, and find applications in construction of small, enclosed space like in air plane cabins, skyscrapers etc. Ex: Polyimides, polybenzoxazoles (PBOs), polybenzimidazoles, and polybenzthiazoles (PBTs) High-performance polymeric materials represent a specialized class of polymers engineered to exhibit exceptional properties and performance characteristics, surpassing those of conventional plastics. They have crucial role to play in various industries such as medical, aerospace, automotive, electronics, and other industrial sectors because of their superior properties and performance. Polyamides Polyamides, commonly known as nylon, are a versatile class of engineering polymers with a wide range of applications across various industries. Polyamides are prepared by the melt polycondensation between di-carboxylic acid and diamines. Synthesis of Polyamides is shown in Fig. 1. H Polyamides are synthetic polymers characterized by the presence of repeating amide (–CONH) linkages along the polymer chain. These amide groups contribute to the material's strength, toughness, and chemical resistance. The aliphatic polyamides are generally known as nylons. Types of Polyamides: There are several types of polyamides, each with unique properties and applications and are usually indicated by numbering system. The no. gives the carbon atom present in the monomer molecules. Some common examples include: Nylon 6 (polycaprolactam) Nylon 6,6 (polyhexamethylene adipamide) Nylon 11 (polyamide 11) Nylon 12 (polyamide 12) Commercially, Nylon 6,6 and nylon 6,10 are extremely important. Nylon 6,6 Preparation: The synthesis of Nylon 6,6 is shown in Fig. 2. Nylon 6,6 is prepared by the polycondensation of adipic acid and hexamethylenediamine at high temperatures, forming a polymer with the elimination of water. Fig.2. Synthesis scheme for Nylon 6,6 Applications of Nylon 6,6: Nylon 6,6 is used as plastic as well as fiber. It has a good tensile strength, abrasion resistance and toughness up to 150 ֯C. Also, it resists many solvents. However, formic acid, cresols and phenols dissolve this polymer. It is used in the production of tyre cords, monofilaments, and ropes. Used in the manufacturing of textile fibers. Being a tough plastic, it is a good substitute for metals in gears and bearings. Used to manufacture articles like brushes. Polyesters: Polyester is a category of polymers that primarily include polyethylene terephthalate (PET). It is widely used in textiles, packaging, and many other applications due to its strength, durability, and resistance to shrinking and stretching. However, traditional polyester is derived from petrochemical sources and is not biodegradable, contributing to plastic pollution and environmental degradation. Types of Polyesters: The specific arrangement of the atoms in a polyester molecule can affect its properties. For example, the strength and stiffness of a polyester fiber can be controlled by varying the length of the chains and the degree of crystallinity. Polyesters are a category of polymers that contain the ester functional group in their main chain. They are widely used in a variety of applications due to their versatile properties. Some common types of polyesters are: 1. Polyethylene Terephthalate (PET): It is Strong, lightweight, transparent, and resistant to impact and moisture. They are used in Bottles, food packaging, fibers for clothing (such as Dacron), and films. 2. Polycarbonate (PC) (often classified with polyesters): They are high impact resistance, transparency, and heat resistance polymers. They are employed in Eyewear lenses, optical disks (CDs, DVDs), and bulletproof glass. 3. Polytrimethylene Terephthalate (PTT): They have good elasticity, stain resistance, and softness. They are used in Carpets, textiles, and apparel. 4. Polycyclohexylenedimethylene Terephthalate (PCT): They are High temperature and chemical resistance polymers. They exhibit high-performance engineering plastics, especially in the electronics industry. 5. Polyester Polyols: They find application in the production of polyurethane foams and elastomers. They are used in Flexible foams for cushions, rigid foams for insulation, and elastomers for adhesives and coatings. Polyethylene terephalate (PET) The most common type of polyester is polyethylene terephthalate (PET), which is used in a variety of applications, including clothing, food packaging, and plastic bottles. PET is made from the reaction of ethylene glycol and terephthalic acid. Synthesis: Polyethylene terephthalate (PET) is typically prepared through a polycondensation reaction between terephthalic acid and ethylene glycol. Here are the steps involved in its preparation. Fig 3. Synthesis of PET (terylene or dacron) Structure: Polyethylene Terephthalate Fig. 4. Terephthalate group and ethylene group of PET with ether linkage Each type of polyester has unique properties that make it suitable for specific applications, ranging from everyday consumer products to specialized industrial components. Epoxies : They are a class of reactive prepolymers and polymers which contain epoxide groups. They are known for their excellent mechanical properties, strong adhesion, and resistance to chemical and environmental degradation. Here are some key types of epoxies and their applications: Structure: Epoxy resins are formed from a long-chain molecular structure similar to vinyl ester with reactive sites at either end. In the epoxy resin, however, epoxy groups instead of the ester groups form these reactive sites. The absence of ester groups means that the epoxy resin has particularly good water resistance. Fig: Synthesis of Epoxy resin from Bisphenol A and Epichlorohydrin Types of Epoxies 1. Bisphenol A Epoxy Resins Properties: High mechanical strength, good thermal and chemical resistance, and excellent adhesion. Uses: Coatings, adhesives, electrical and electronic components, composites, and laminates. 2. Bisphenol F Epoxy Resins Properties: Lower viscosity compared to bisphenol A epoxies, good chemical resistance, and improved performance at higher temperatures. Uses: Adhesives, coatings, and applications requiring higher chemical resistance. 3. Novolac Epoxy Resins Properties: Superior chemical resistance, high temperature performance, and excellent mechanical properties. Uses: Chemical-resistant coatings, high-performance composites, and applications requiring high thermal stability. 4. Cycloaliphatic Epoxy Resins Properties: High dielectric strength, good weather ability, and improved resistance to yellowing. Uses: Electrical insulation, outdoor coatings, and high-voltage applications. 5. Glycidylamine Epoxy Resins Properties: High glass transition temperature (Tg), excellent mechanical properties, and good chemical resistance. Uses: High-performance composites, structural adhesives, and aerospace applications. General Properties of Epoxies:  o High bonding strength to a variety of substrates including metals, ceramics, glass, and plastics o Excellent protective properties, resistance to corrosion, chemicals, and abrasion o High strength-to-weight ratio, durability, and resistance to environmental factors. o Excellent insulation properties, thermal stability, and protection against moisture and contaminants o Clear, glossy finish, and ability to embed object Biodegradable Polymers Biodegradable polymers are a class of polymers that can be broken down by microorganisms, such as bacteria, fungi, and algae, into harmless byproducts like water, carbon dioxide, and methane, under aerobic or anaerobic conditions. This makes them a more environmentally friendly alternative to traditional plastics, which can take hundreds or even thousands of years to decompose and contribute significantly to plastic pollution. Biobased Biodegradable Polymers: derived from renewable resources such as plants, animals, or microorganisms. Eg. Polylactic acid (PLA), polyhydroxyalkanoates (PHA). Synthetic Biodegradable Polymers: created through chemical synthesis but designed to degrade under specific environmental conditions. Eg. polycaprolactone (PCL) and polybutylene succinate (PBS) Advantages of Biodegradable Polymers: Reduce accumulation of plastic waste in landfills, oceans, and other ecosystems. Production of biodegradable polymers often requires less energy and generates fewer greenhouse gas emissions compared to traditional plastics. Many biodegradable polymers are made from renewable resources, decreasing reliance on finite fossil fuels. Unlike traditional plastics that take centuries to break down, biodegradable polymers decompose much quicker. Some biodegradable polymers can be composted, potentially returning nutrients to the soil. Applications of Biodegradable Polymers: Biodegradable polymers find applications across various industries due to their versatility and environmentally friendly nature. Some of the key applications include: Packaging: an eco-friendly alternative to traditional plastic packaging and can be composted or recycled after use. Agriculture: improve soil health, conserve water, and reduce plastic waste in agricultural settings. Medical Devices: offer biocompatibility, controlled degradation, and the ability to be absorbed by the body over time. Textiles: production of sustainable fabrics, fibers, and clothing, offer properties such as breathability, moisture-wicking, and biodegradability. Food Service Products: disposable cutlery, plates, cups, and food packaging, offer an eco-friendly alternative to single-use plastics and can be composted after use. Personal Care Products: cosmetics, toiletries, and hygiene products, offer biocompatibility and gentle formulations compared to conventional ingredients. 3D Printing: filaments in 3D printing, offer versatility, printability, and environmentally friendly properties for additive manufacturing processes. Poly(lactic acid) (PLA) is a biodegradable and bioactive thermoplastic derived from renewable resources such as corn starch, sugarcane, or cassava roots, reducing dependence on fossil fuels. Advantages Renewable Resources: Made from renewable biomass, reducing reliance on fossil fuels. Mechanical Properties: High tensile strength, good rigidity, and crack resistance. Biodegradability: decomposes into lactic acid, a naturally occurring substance, under composting conditions, reducing environmental pollution. Low Toxicity: Safe for food contact and medical applications. Good Printability: Excellent material for 3D printing due to ease of use and low warping. Disadvantages Low Thermal Resistance Brittle and less impact-resistant compared to some traditional plastics.  Degradation Conditions: Requires industrial composting facilities to be biodegradable effectively, which may not be available everywhere. Uses Production of biodegradable plastic films, containers, cups, and utensils. Popular material for 3D printing due to its ease of use, low printing temperature, and minimal warping. for sutures, stents, and drug delivery systems due to its biocompatibility and biodegradability. PLA fibers are used in clothing, upholstery, and non-woven fabrics. used in mulch films and other agricultural applications. Polyhydroxyalkanoates (PHAs) are a class of biodegradable and biocompatible polymers produced by various microorganisms as intracellular carbon and energy storage compounds. PHAs are gaining significant attention for their potential to address environmental and sustainability challenges associated with traditional petroleum-based plastics. Advantages: Biodegradability: broken down by microorganisms in natural environments such as soil, marine environments, and composting facilities. This reduces the accumulation of plastic waste in landfills and oceans. Renewable Resources: produced from renewable resources, including agricultural waste, plant oils, and sugars, thus reducing reliance on fossil fuels and contributing to a circular economy. Reduced Carbon Footprint: Production of PHAs results in lower greenhouse gas emissions compared to conventional plastics, contributing to climate change mitigation efforts. Thermal Stability: exhibit good thermal stability, making them suitable for a wide range of applications, including those that require heat resistance. Uses: Biocompatibility: non-toxic and biocompatible, making them ideal for medical applications. Packaging: production of biodegradable packaging materials, helping to reduce plastic pollution.  Agriculture: in agricultural films, controlled-release fertilizer coatings, and biodegradable plant pots, promoting sustainable agricultural practices. Consumer Goods: disposable items, textiles, and personal care products. Conducting polymers Introduction: Conductive polymers are organic polymers that conduct electricity. Such compounds may be true metallic conductors or semiconductors. It is generally accepted that metals conduct electricity well and that organic compounds are insulating, but this class of materials combines the properties of both. The biggest advantage of conductive polymers is their processability. Conductive polymers are also plastics (which are organic polymers) and therefore can combine the mechanical properties (flexibility, toughness, malleability, elasticity, etc.) of plastics with high electrical conductivities. Their properties can be fine-tuned using the methods of organic synthesis. Classification of conducting polymers based on nature of conductivity: 1. Intrinsically conducting polymers or conjugated 𝝅 −electron conducting polymers It is a polymer whose backbones or associated groups consist of delocalized electron pair or residual charge.Such polymers essentially contain conjugated 𝜋-electrons backbone, which is responsible for electrical charge. In an electric field, conjugated 𝜋-electrons of the polymers get excited, thereby can be transported through the solid polymeric material. Overlapping of orbitals ( of conjugated pi-electrons) over the entire backbone results in the formation of valence bands as well as conduction bands, which extend over the entire polymer molecule. Presence of conjugated 𝜋 -electron in a polymer increases its conductivity to a larger extent. Examples: Polyacetylene , Polyaniline, Polypyrrole, Polythiophene 2. Extrinsically conducting polymers : The polymers whose conductivity is due to the presence of externally added ingredient in them. (a)Conducting polymer composites: The polymers mixed with conductive fillers like carbon black,graphite ot metal particles. (b)Doped conducting polymers: It is obtained by exposing a polymer to a charged transfer agent in either gas phase or in solution. Intrinsically conducting polymers possess low conductivity ( 10-10 Ω -1cm -1), but these possess low ionization potential  and high electron affinities, so these can be easily oxidized or reduced. Consequently, the conductivity of ICP can be increased by creating either positive or negative charges on the polymer backbone by oxidation or reduction. This technique, called doping ( an analog with semiconductor), is two types: i) P-doping: It involves treating an intrinsically conducting polymer with a Lewis acid, thereby oxidation process takes place and positive charges on the polymer backbone are created. Some of the common P-dopant used are I2, Br2, AsF5, PF6, naphthylamine, etc. used for example NH NH N =N Emeroldine base ( a polyaniline) HCl (Lewis acid) Conductivity Oxidation Cl Cl + NH NH N N+ ----- H H Emerolidine hydrochloride ( a salt known as synthetic metal) Conductivity (i) N-doping: It involves treating an intrinsically conducting polymer with a lewis base thereby reduction process takes place and negative charges on the polymer backbone are created. Some of the common N-dopant used are Li, Na, Ca, tetrabutyl ammonium, FeCl3, For example: Reduction _ ---- HC CH CH CH ---- +B ---- HC CH CH CH ---- Polyacetylene (Lewis base) + B _ Reduction ---- HC CH CH CH ---- + C10H7NH2 ---- HC CH CH CH ---- + C10H8 Polyacetylene Naphthylamine + Naphthalene NH (Lewis base) Applications: - Conducting polymers are finding increased use because they are light weight, easy to process and have good mechanical properties. Some of the important applications of conducting polymers are i) In rechargeable light weight batteries based on perchlorate doped polyacetylene- lithium system. These are about 10 times lighter than conventional lead storage batteries. Such batteries are sufficiently flexible to fir a variety of designed configuration. ii) ii) In optically display devices based on polythioplene. When the structure is electrically biased ( 1 to 3V), the optical density of the film changes. i.e., its colour changes. Such electrochromic system produce coloured displays with faster switching time and better viewing than conventional liquid crystal display devices (LED). iii) wiring in aircrafts and aerospace components. iv) telecommunication systems v) antistatic coatings for clothing. vi) electromagnetic screening materials. vii) electronic devices such as transistors and diodes. viii) solar cells, drug delivery system for human body, etc. ix) photo voltaic devices, e.g., Al /polymer / Au photovoltaic cells. x) non-linear optical materials. xi) molecular wires and molecular switches. Smart polymers: Smart polymers, also known as stimuli-responsive or intelligent polymers, are materials that can undergo reversible changes in their physical or chemical properties in response to external stimuli such as temperature, pH, light, electric field, or solvent composition. These materials have attracted significant attention due to their potential applications in various fields including drug delivery, tissue engineering, sensors, actuators, and controlled release systems. The responsiveness of smart polymers allows for precise control over their behavior, making them highly versatile and promising for innovative technological advancements. Temperature responsive polymers Thermosensitive polymers are a class of intelligent materials capable of adjusting their properties in response to temperature variations. They achieve this by leveraging the controlled and easily measurable stimulus of temperature, which triggers the expansion or contraction of their polymer chains. This transformative process leads to transitions between solution and phase states. The crucial factor in this transition lies in the equilibrium between the hydrophilic (water-attracting) and hydrophobic (water-repelling) segments along the polymer chain, coupled with the overall energy dynamics of the system. These polymers exhibit distinct temperature thresholds known as the upper critical solution temperature (UCST) and lower critical solution temperature (LCST). In the case of LCST polymers, they dissolve readily at lower temperatures but become insoluble as the temperature rises. Conversely, UCST polymers dissolve at higher temperatures yet lose solubility at lower temperatures. Examples LCST: Poly (vinyl amide), poly (N-substituted acrylamide), poly (N vinylcaprolactam), cellulose, chitosan, xyloglucan and PLGA–PEG– PLGA triblock copolymers UCST: poly (2-dimethyl) methacryloxyethyl-ammonium propanesulfonate Electro-responsive polymers: Electro-responsive or electroactive polymers (EAPs) represent a specialized category within smart polymers capable of dynamically adjusting their physicochemical characteristics upon exposure to electric signals. Through the conversion of electrical energy into mechanical energy, they exhibit reversible changes in shape, including swelling, shrinking, or bending. These alterations depend on various parameters of the electric current, such as its magnitude, duration, and frequency. The application of electric current disrupts the hydrogen bonds between polymer chains and induces changes in the pH level, contributing to the polymers' responsiveness. Prominent examples of electroresponsive polymers encompass polythiophene (PT) and polypyrrole (PPY), distinguished for their conductive properties. Photo-responsive polymers: Light-responsive polymers offer significant advantages across a range of applications, delivering swift and precise responses under specific conditions. Upon exposure to light, these polymers undergo a phase transition, rendering them highly sensitive to light stimuli. Leveraging light as a trigger provides several benefits, including instantaneous application and high precision. Moreover, the tunability of light wavelength enables precise control, while the utilization of fiber optic cables extends this control to long-distance applications. Photo- responsive polymers exhibit distinct changes in their behavior when exposed to light, regulating various molecular properties such as conformation, polarity, amphiphilicity, charge, optical chirality, conjugation, and more. Examples: Polymers containing chromophores may become active in photo-responsive systems. pH-responsive polymers: pH-responsive polymers undergo structural and property changes, including alterations in surface behavior, solubility, and chain conformation, in response to shifts in environmental pH levels. These polymers feature acidic or basic groups, which render them sensitive to pH stimuli. They respond to pH changes by either accepting or releasing protons. Polyelectrolytes, characterized by numerous ionizable groups, are particularly responsive to pH variations. The fluctuation in pH triggers ionic interactions that lead to the expansion or collapse of polymer chains in aqueous solutions. This behavior stems from electrostatic repulsion between the resulting charges. Common examples of pH-responsive materials include polyacids and polybases. Ion-responsive polymers: Ion-responsive polymers have the potential to pave the way for the development of new materials and devices with adjustable behaviours that can react to changes in their environment. Poly (acrylic acid) (PAA) is an example of an ion-responsive polymer. As a polyelectrolyte, PAA exhibits the ability to swell and deswell in response to changes in ionic strength. Under low pH conditions, PAA becomes protonated and hydrophobic, causing the polymer chains to collapse and reduce swelling. Conversely, under high pH conditions, PAA becomes deprotonated and hydrophilic, causing the polymer chains to expand and increase swelling. Glucose and enzyme responsive polymers: They are sensitive to sugar and react differently depending on how much glucose there is. Engineered with glucose-responsive moieties like boronic acid or phenylboronic acid, these polymers form reversible bonds glucose molecules through covalent or non-  covalent interactions. These binding triggers various physical or chemical changes in the polymer, including swelling or contraction, release of encapsulated drugs, or modulation of fluorescence or conductivity. Enzyme-responsive polymeric systems can be created by using polymers that can be degraded by enzymes or by modifying polymers with groups that can react with specific enzymes. Both synthetic polymers (e.g., PNIPAAm, PEG, and PLL) and natural polymers (e.g., dextran, polypeptides, and gelatin) have been employed to make enzyme-responsive systems. A polymer that can react to an enzyme has either a part that looks like what the enzyme usually acts on or a part that can change how the polymer interacts with other molecules, causing it to change its shape or behavior. Applications: (1) Smart polymeric carriers can deliver drugs in response to a stimulus. (2) Smart polymers can be engineered to detect and respond to specific biomolecules, such as disease markers or drugs. (3) In addition to this, various types of smart polymers can be utilized across different fields Such as sensors, medical devices, fabrics, share memory materials. FILTRATION MEMBRANES The non-biodegradable polymers contribute to the accumulation of plastic waste in landfills, oceans, and other natural environments, posing threats to wildlife, ecosystems, and human health. Hence, Sustainable biodegradable or recyclable polymers offer solutions to mitigate plastic pollution and promote responsible waste management practices. Hence, filtration membranes are important to overcome this problem. Polymers are sometimes preferred for membrane filtration because they are more flexible, eas ier to handle, and less expensive than inorganic membranes fabricated from oxides, metalss and ceramics. A membrane is a semi-permeable thin layer of material capable of separating contaminants due to their physical/chemical characteristics. It is a thin layer of material that will only allow certain compounds to pass through it. Usually, the membrane filtration method separates components that are dissolved or suspended particles in a liquid. Membrane filtration is a physical procedure for particle separation of particles using semi-permeable membranes. Membrane filtration is a rapidly expanding field in water treatment. Many different types of filters are available in a wide range of pore sizes and configurations. In addition, there are numerous possible applications for membrane filtration ranging from removing relatively large particulate material to removing dissolved compounds. Types of filtration membranes (a)Microfiltration: Microfiltration membranes have the most open pore sizes of all polymeric membranes. With a pore size range of 0.1 to 10μm, microfiltration membranes are capable of separating large suspended solids such as colloids, particulates, fat, and bacteria, while allowing sugars, proteins, salts, and low molecular weight molecules to pass through the membrane. The PVDF microfiltration membrane filters are manufactured to sustain excellent chemical and heat resistance. They are available in both spiral-wound and flat sheet configurations, to provide more flexibility for customization around specific process applications. (b)Ultrafiltration membranes: These membranes have pore sizes of 0.01 to 0.1µm, between that of nanofiltration and microfiltration. which contributes to the production of high-quality water. Ultrafiltration membranes are capable of separating larger materials such as colloids, particulates, fats, bacteria, and proteins while allowing sugars and other low molecular weight molecules to pass through the membrane. Example: Polyethersulfone (PES) (c)Nanofiltration Nanofiltration is a separation process characterized by organic, thin-film composite membranes with a pore size range of 0.1 to 10nm. Unlike reverse osmosis (RO) membranes, which reject all solutes, NF membranes can operate at lower pressures and offer selective solute rejection based on both size and charge. Nanofiltration membranes allow water and some salts to pass through the membrane while retaining multivalent ions, low molecular weight molecules, sugars, proteins, and other organic compounds. The nanofiltration technique lies between ultrafiltration and reverse osmosis techniques, and it is considered a low-cost process and is capable of removing pesticides, organic matter, desalination of sea water, oil process and pollutants from industrial wastewater. (d) Reverse osmosis Reverse osmosis is a membrane treatment process primarily used to separate dissolved solutes from water. Reverse osmosis is most commonly known for its use in drinking water purification, particularly for removing salt and other effluent materials from water molecules. In this process, due to the presence of a membrane, large molecules of the solute are not able to cross through it and they remain on the pressurized side. The pure solvent, on the other hand, is allowed to pass through the membrane. When this happens the molecules of the solute start becoming concentrated on one side while the other side of the membrane becomes dilute. Furthermore, the levels of solutions also change to some degree. In essence, reverse osmosis takes place when the solvent passes through the membrane against the concentration gradient. It moves from a higher concentration to a lower concentration. Generally, RO membranes are in the form of flat sheets and hollow fine fibers. The semi- permeable membranes used for the RO process are typically made of a thin polyamide layer (