Polymers PDF

POLYMER SUMMARY POLYMER MOLECULES - Polymers in which the repeated (mer) Definition: A polymer is a large units are connected end-to-end molecule composed of repeating along the whole length of the chain structu...

POLYMER SUMMARY POLYMER MOLECULES - Polymers in which the repeated (mer) Definition: A polymer is a large units are connected end-to-end molecule composed of repeating along the whole length of the chain structural units called monomers. These types of polymers are often flexible These monomers are linked by some examples – polyethylene, covalent bonds to form Teflon, PVC, polypropylene. macromolecular structures. 2. Branched polymers POLY means (MANY) - Molecules having branch points that MER means (REPEAT UNIT) connect 3 or more segments. Composition: Most polymers are - This leads to inability of chains to hydrocarbons, primarily composed of pack very closely together. hydrogen and carbon, are the - This branches are usually result of building blocks of polymers. side-reactions during polymerization Types: Polymers can be classified - of the main chain. into different structural types such as linear, branched, crosslinked, and 3. Crosslinked polymers network polymers. - Adjacent chains attached via covalent bonds MOLECULAR WEIGHT AND STRUCTURE - Carried out during polymerization or Molecular Weight: The size of a by a non-reversible reaction after polymer is determined by its synthesis (referred to as crosslinking) molecular weight, which ranges from - Materials often behave very thousands to millions of atomic mass differently from linear polymers units. It is often expressed as an - Many “rubbery” polymers are average because polymer chains crosslinked to modify their vary in length. mechanical properties; in that case it Degree of Polymerization (DP): is often called vulcanization Refers to the number of monomer - Generally, amorphous polymers are units in a polymer chain. weak, and cross-linking adds Molecular Structure: Polymer Strength: Vulcanized rubber is physical properties depend on their polyisoprene with sulfur cross-links. molecular structure. The structure of 4. Network polymers a polymer refers to the arrangement - polymers that are “trifunctional” of its atoms. Polymers can be instead of bifunctional amorphous (randomly arranged) or - There are three points on the mer crystalline (highly ordered), impacting that can react their rigidity, transparency, and - This leads to three-dimensional thermal properties. connectivity of the polymer Molecular Shape: Polymers can backbone have linear, branched, or cross-linked structures. The shape affects the Highly crosslinked polymers can also physical properties of the polymer, be classified as network polymers including its density, crystallinity, and Examples: epoxies, phenol- how it responds to stress. formaldehyde polymers. Four Main Structure: Average Molecular Weight: Since 1. Linear polymers polymer chains vary in length, molecular weights are given as averages. Some chains are longer  and heavier, others are shorter and hoses, and gaskets. They are valued lighter. for their flexibility, durability, and Dispersity (Ð): The spread of resistance to wear. molecular weights is characterized by FORMING TECHNIQUES OF dispersity, which shows how much ELASTOMERS variation exists between the lengths of the chains. In older texts, dispersity 1. Extrusion is also known as the polydispersity Process: Elastomer material is forced index (PDI). through a die to create long continuous Molecular Shape (or shapes like tubes, rods, and profiles. Conformation) – chain bending and Applications: Seals, gaskets, and hoses twisting are possible by rotation of 2. Injection Molding carbon atoms around their chain Process: Elastomer is heated until it bonds. becomes fluid and then injected into a C-C bonds are typically 109° (tetrahedral, mold where it cools and solidifies. sp³ carbon). Applications: Complex shapes like automotive parts, medical devices, and Polymer Microstructure consumer goods Covalent chain configurations and 3. Compression Molding strength: The spatial arrangement of atoms Process: Pre-measured elastomer is within a polymer chain is called configuration. placed into a heated mold cavity, This includes features like cis-trans compressed, and then cured. isomerism and tacticity, which influence the Applications: Large, simple shapes like polymer's physical properties. mats, seals, and gaskets Polymer Crystal (Crystal form by folding 4. Transfer Molding polymer chains) Process: Similar to compression Crystallinity: Some polymers can form molding, but the elastomer is preheated crystalline regions where chains are tightly in a chamber and then transferred into packed in an ordered arrangement. This the mold. increases strength and rigidity. Applications: More intricate parts than Amorphous Regions: In other regions, compression molding, such as electrical polymer chains are randomly arranged, components and seals leading to amorphous structures with lower 5. Calendering strength and higher flexibility. Process: Elastomer is passed through a Crystallinity and Properties: The degree of series of rollers to produce thin sheets or crystallinity influences a polymer's melting coatings. point, stiffness, and transparency. Applications: Conveyor belts, flooring, and coated fabrics ELASTOMERS OR RUBBERS 6. Blow Molding Definition : Elastomers are one of Process: Elastomer is extruded into a polymer types that exhibit rubber-like tube, inflated into a mold, and then elasticity and flexibility. They can cooled. undergo large deformations and Applications: Hollow products like bottles recover their original shape after the and containers deformation force is removed. 7. Rotational Molding Rubber is a well-known example of Process: Elastomer is placed in a mold an elastomer. that is rotated around two perpendicular Examples: Natural rubber, synthetic axes, distributing the material evenly. rubber, and thermoplastic elastomers Applications: Large, hollow items like like SBR (styrene-butadiene rubber). tanks and containers Elastomers are used in tires, seals, 8. Thermoforming  Process: Elastomer sheets are heated lamellae, which compose larger spheroidal until pliable, then formed over a mold and structures named spherulites. cooled. Processing Techniques: Various Applications: Packaging, trays, and techniques such as extrusion, panels injection molding, and compression 9. 3D Printing molding are used to form polymers Process: Layer-by-layer deposition of into specific shapes. elastomer material to create complex Applications: Polymers are used in shapes. a wide range of industries, including Applications: Prototyping, custom parts, packaging, construction, and medical and intricate designs devices. CHARACTERISTICS, APPLICATIONS, PLASTICS AND PROCESSING OF POLYMERS These are synthetic polymers that can be Mechanical Properties: Stress- molded and shaped into various forms. They strain behavior varies among are typically derived from petrochemicals polymers, exhibiting brittle, plastic, or and can be further classified into elastomeric responses. thermoplastics and thermosetting plastics. Three types of stress-strain behavior of Types: Plastics are classified into two polymers. main categories: Strains - Deformations > 1000% possible(for o Thermoplastics: Can be metals, maximum strain ca. 10% or less) remelted and reshaped, e.g., 1. Brittle polyethylene, PVC. 2. Plastic o Thermosets: Undergo a 3. Elastomer permanent chemical change when molded and cannot be Polymer Fracture remelted, e.g., epoxies, Crazing ~ Griffith cracks in metals phenolics. - spherulites plastically deform to fibrillar Applications: Plastics are widely used in structure industries such as packaging (e.g., - microvoids and fibrillar bridges form polyethylene), automotive (e.g., polypropylene), electronics (e.g., PVC), and Factors that affect the mechanical construction (e.g., polycarbonate). properties of polymer Viscoelastic Deformation - It is a Forming Techniques: The most common condition for intermediate forming techniques for plastics include: temperatures where the polymer is a Injection Molding: Molten plastic is rubbery solid that exhibits the injected into a mold, where it cools and combined mechanical characteristics solidifies. of glass and viscous liquid. Extrusion: Plastic is melted and forced Time Dependent Deformation - through a die to create long shapes like This behavior is primarily pipes or sheets. characterized by viscoelasticity, Blow Molding: Used to form hollow which means polymers exhibit both plastic objects like bottles by inflating viscous (fluid-like) and elastic (solid- molten plastic inside a mold. like) properties when deformed. Thermoforming: A plastic sheet is Crystallization heated until pliable, then shaped into a Crystallization of polymers is a process mold. associated with partial alignment of their molecular chains. These chains fold FIBERS together, and form ordered regions called  Definition: Fibers are filamentous - Needle Punching: Mechanical bonding materials with high surface area-to- where needles are used to entangle volume ratios, used in textiles and fibers, creating a fabric without weaving or composites. knitting. Key Characteristics of Fibers 1. HIGH SURFACE AREA TO VOLUME RATIO: This makes fibers extremely strong 4. Weaving and Knitting and capable of withstanding significant - Weaving: Involves interlacing two sets of stress. yarns at right angles to form a fabric. This 2. FLEXIBILITY and FINENESS: These method provides high strength and properties allow fibers to be woven or matted stability. into various forms, such as fabrics, - Knitting: Uses a series of interconnected composites, and non-woven materials. loops to create a fabric. Knitted fabrics are 3. VERSATILITY: Fibers are used in known for their stretchability and comfort. numerous applications, including textiles, 5. Bonding Techniques biomedical materials, advanced engineering - Thermal Bonding: Uses heat to bond composites, geotextiles, and protective fibers together, often used in nonwoven clothing fabric production. - Chemical Bonding: Involves using Forming Techniques adhesives or chemical binders to bond 1. Spinning Techniques fibers. - Melt Spinning: This involves melting the - Mechanical Bonding: Includes methods polymer and extruding it through a spinneret like needle punching and to form fibers. The fibers are then cooled and hydroentangling, where fibers are solidified. This method is commonly used for physically entangled. synthetic fibers like polyester and nylon. - Solution Spinning: This includes both wet Types: Natural fibers (cotton, wool) and and dry spinning. In wet spinning, the synthetic fibers (nylon, polyester). polymer solution is extruded into a Applications: Textiles, biomedical coagulation bath where it solidifies. In dry materials, and high-performance spinning, the solvent evaporates as the fiber composites. Fibers are used in clothing is extruded into a warm air chamber. (e.g., polyester), industrial materials - Gel Spinning: A variant of solution spinning, (e.g., nylon ropes), and composites (e.g., where the polymer is in a gel state, allowing fiberglass). They are lightweight, durable, for the production of high-strength fibers. and can be woven or knitted. 2. Texturing and Crimping - These processes modify the surface texture FAILURE AND DEGRADATION OF and structure of synthetic fibers to mimic the POLYMERS properties of natural fibers. Texturing can Types of Failure: involve mechanical, thermal, or chemical Elastic Deformation: Polymers can methods to create crimped, bulked, or looped experience elastic deformation when fibers. subjected to stress, but if the stress exceeds 3. Nonwoven Fabric Formation the material's elastic limit, it can lead to - Spunbond: This method involves extruding permanent deformation or failure. the polymer to form continuous filaments, Creep: Creep is the time-dependent plastic which are then laid down in a web and deformation of materials under constant bonded together. stress. It is the slow, permanent deformation - Meltblown: Similar to spunbond, but the of a polymer under constant stress over time. fibers are much finer and are bonded by Over long periods, especially at high entangling during the extrusion process. temperatures, polymers can slowly deform, leading to creep rupture. Fracture: Fracture occurs when a polymer breaks due to stress This can happen suddenly (brittle fracture) or after significant deformation (ductile fracture). Factors like temperature, strain rate, and the presence of flaws can influence the fracture behavior. Corrosion: Corrosion in polymers involves chemical reactions that degrade the material. This can happen through chemical attack or solvation, where the polymer absorbs a corrosive agent, leading to softening, swelling, and eventual failure. PRESENTATION OF POLYMER PRODUCTS MANUFACTURING Examples of Polymer Products: o Nylon Rope: Strong and lightweight, formed by extrusion and spinning. o PVC Pipes: Rigid and corrosion-resistant, produced via extrusion. o Teflon (PTFE): Heat- resistant and non-stick, formed by molding and sintering. o Rubber Gloves: Durable and flexible, manufactured through dipping or molding. o Plastic Bottles: Lightweight and shatterproof, created using blow molding.