Santa Rosa Junior College Spring 2009 Engr 45 – Materials Science POLYMERS By: Tesfaberhan Habtemariam, Omid Borjian and Elena Foster Spring 2009
Table of contents • What is a polymer • How are polymers created in lab? (Video) • What types of Polymers are there? • What is the chemical structure? • How are polymers used? • What are the physical and chemical properties of polymers • Nanopolymers • Shape Memory Polymers (SMPs) • Light emitting polymers (OLED/PLED/LEP)
What is a polymer? • A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds
Different types of Polymers - Polyethylene • Most common and important polymer; bags, insulation for wires, squeeze bottles High density Low density
Different types of Polymers - Polypropylene • Max T: 275°F/135°C • Min T: 32°F 0°C • Melting P: 338°F 170°C • Tensile Strength: 4,500 psi • Hardness: R95 • UV Resistance: Poor • Excellent resistance to dilute and concentrated Acids, Alcohols, Bases and Mineral Oils • Good resistance to Aldehydes, Esters, Aliphatic Hydrocarbons, Ketones and Vegetable Oils • Limited resistance (for short term use only) to Aromatic and Halogenated Hydrocarbons and Oxidizing Agents Fibers, indoor-outdoor carpets, bottles
Different types of Polymers - Polystyrene • Styrofoam, inexpensive household goods, inexpensive molded objects Properties of EPS Molded Packaging
Different types of Polymers –Polyvinyl chloride (PVC) • Synthetic leather, clear bottles, floor covering, water pipes • Max T: 158°F 70°C • Min T: -13°F -25°C • Melting P: 176°F 80°C • Tensile Strength: 6,500 psi • Hardness: R105 • UV Resistance: Good
Nonstick surfaces, chemically resistant films Different types of Polymers – Polytetrafluoroethylene (Teflon) • Max T: 572°F 300°C • Min T: 392°F -200°C • Melting P: 626°F 330°C • Tensile Strength: 6,240 psi • Hardness: R58 • UV Resistance: Excellent
Different types of Polymers – Poly(methylmethacrylate)(Lucite, Plexiglas) • Unbreakable “glass,” latex paints • Clear, colorless polymer used extensively for optical applications
Different types of Polymers – Polyacrylonitrile (Orlon, Acrilan, Creslan) • Fiber used in sweaters, blankets and carpets • most commonly used in fiber form. Since it softens only slightly below its thermal degradation temperature, it must be processed by wet or dry spinning rather than melt spinning.
Different types of Polymers – Poly(vinyl acetate)(PVA) • Adhesive, latex paints, chewing gum, textile coatings primarily used in adhesives, both emulsion and hot-melt types. It is also used in water based emulsion paints.
Different types of Polymers – Natural Rubber • Polymer cross-linked with sulfur (vulcanization)
Different types of Polymers – Polychloroprene (neoprene rubber) • Cross-linked with ZnO; resistant to oil and gasoline • Resists degradation from sun, ozone and weather • Performs well in contact with oils and many chemicals • Remains useful over a wide temperature range • Displays outstanding physical toughness • Resists burning better than exclusively hydrocarbon rubbers • Outstanding resistance to damage caused by flexing and twisting
Different types of Polymers – Styrene butadiene rubber (SBR) • Styrene butadiene rubber (SBR) is the largest volume synthetic rubber. With over 70% of SBR being consumed in the manufacture of tires • Elongation (%) 150 • Melting point oC 120 • Specific gravity 1.04 • Tensile strength (Psi) 400
Nanopolymers • Polymer nanocomposites (PNC) is a polymer or copolymer having dispersed in its nanoparticles. These may be of different shape (e.g., platelets, fibers, spheroids), but at least one dimension must be in the range of 1 to 50 nm. • PNC's belong to the category of multi-phase systems (MPS, viz. blends, composites, and foams) that consume nearly 95% of plastics production. These systems require controlled mixing/compounding, stabilization of the achieved dispersion. • increase in surface are-to-volume ratio, which increases as the particles get smaller, leads to an increasing dominance of the behavior of atoms on the surface area of particle over that of those interior of the particle. Because of the higher surface area of the nano-particles the interaction with the other particles within the mixture is more and this increases the strength, heat resistance etc. • Silicon nanospheres, fullerens (buckyballs), carbon nanotubes (buckytubes), graphene, etc
Some areas of nanopolymer research and use • Materials that don’t normally stick together can be bonded by using a one-nanometer-high layer of self-assembling polymer chains. The nanoglue consists of chains of carbon and hydrogen atoms customized with appropriate molecules at the ends. This one has chains with sulfur at one end, to join copper components with other materials on computer chips (can be customized) . This glue is 10 times thinner than current chips’ glue. • Electro-Spinning is a process that utilizes high electrical voltage to produce polymer fibers from polymer solutions or melts. It produces ultra-fine fibers, with huge surface-to –volume ratio, which have great application potentials in many fields such as protective clothing, air filtration, sensors, drug delivery system, sensors.
Some areas of nanopolymer research and use • Adding nanoparticulates to a polymer matrix can enhance its performance, often in very dramatic degree, by simply capitalizing on the nature and properties of the nanoscale filler ( nanofilled polymer composites ). For example, reinforcing a polymer matrix by much stiffer nanoparticles of ceramics, clays, or carbon nanotubes; also to add new properties like fire resistance or accelerated biodegradability. • Bio-hybrid polymer nanofibers : Many technical applications of biological objects like proteins, viruses or bacteria such as chromatography, optical information technology, sensorics, catalysis and drug delivery require their immobilization. Carbon nanotubes, gold particles and synthetic polymers are used for this purpose. This immobilization has been achieved predominantly by adsorption or by chemical binding and to a lesser extent by incorporating these objects as guests in host matrices
Some areas of nanopolymer research and use Self-Assembling Polymer Nanostructures • Formed by dissolving a coil-like polymer such as polystyrene in a fast-evaporating solvent such as benzene; placed on a glass slide, air is directed across it as the solvent evaporates. The temperature drops, producing a three-dimensional pattern of closely packed water droplets preserved in the polymer film. The water then evaporates layer by layer, leaving an interconnected network of ‘perfect’ air bubbles. • Application: in optics, using structures with pore dimensions comparable to the wavelength of visible light. That makes them of interest as potential photonic band gap materials, optical waveguides, beam-steering systems -- and even arrays of dye lasers. Photonic band gap (PBG) materials are a new class of dielectrics which are the photonic analogues of semiconductors (used for optical switches). (like single crystal colloidal silica in a silicon wafer; all-optical information processing) Image shows air bubbles in self- assembled polymer structure.
Shape Memory Polymers (SMPs) • are polymeric smart materials which have the ability to return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus • Two properties: • strain recovery rate (Rr) • strain fixity rate (Rf). The strain recovery rate describes the ability of the material to memorize its permanent shape, while the strain fixity rate describes the ability of switching segments to fix the mechanical deformation. • Triggers • Temperature • pH • Light • Magnetic or electric field
Shape Memory Polymers (SMPs) • where N is the cycle number, Em is the maximum strain imposed on the material, and Ep (N) and Ep (N-1) are the strains of the sample in to successive cycles in the stress-free state before yield stress is applied.
Light Emitting Polymers • also called organic light emitting diode (OLED) • an LED whose emissiveelectroluminescent layer is composed of a film of organic compounds. The layer contains a polymer that allows organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors. • or involves an electroluminescentconductive polymer that emits light when connected to an external voltage source; used as a thin film for full-spectrum color displays
Light Emitting Polymers • Advantages: • low energy requirements; flexibility • can be printed onto any suitable substrate using an inkjet printer • greater range of colors, gamut, brightness, contrast and viewing angle than LCDs • pixel colors appear correct and unshifted, even as the viewing angle approaches 90 degrees from normal • LCDs use a backlight and cannot show true black, while an off OLED element produces no light and consumes no power • OLEDs also have a faster response time than standard LCD screens. Whereas the fastest LCD displays currently have a 2ms response time (manufacturer's quote), an OLED can have less than 0.01ms response time. • Disadvantages: • limited lifetime of the organic materials (5 years at 8 hours a day) • To increase lifetime: a metal membrane helps deliver light from polymers in the substrate throughout the glass surface more efficiently than current OLEDs. The result is the same picture quality with half the brightness and a doubling of the screen's expected life (exceeding the lifetime of LCDs) • Water will damage or destroy the OLED; Therefore, improved sealing processes are important for practical manufacturing and may limit the longevity of more flexible displays.
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