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PolymersChapter 1
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• What are the general structural and chemical characteristics of polymer molecules?
• What are some of the common polymeric materials, and how do they differ chemically?
• How is the crystalline state in polymers different from that in metals and ceramics ?
POLYMER STRUCTURES
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Polymer
Poly mer many repeat unit (building blocks)
C C C C C C
HHHHHH
HHHHHH
Polyethylene (PE)
ClCl Cl
C C C C C C
HHH
HHHHHH
Poly(vinyl chloride) (PVC)
HH
HHH H
Polypropylene (PP)
C C C C C C
CH3
HH
CH3CH3H
repeatunit
repeatunit
repeatunit
Carbon chain backbone
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Chemistry and Structure of Polyethylene
•Polyethylene is a long-chain hydrocarbon. •Top figure shows repeat unit and chain structures. •Other figure shows zigzag backbone structure.
Tetrahedral arrangement of C-H
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Ancient Polymers
• Naturally occurring polymers (those derived from plants and animals) have been used for centuries.– Wood – Rubber– Cotton – Wool– Leather – Silk
• Oldest known uses– Rubber balls used by Incas
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Cellulose
• Cellulose is a highly abundant organic compound. Extensive hydrogen bonding between the chains causes native celluose to be roughly 70% crystalline. It also raises the melting point (>280°C) to above its combustion temperature.
• Cellulose serves as the principal structural component of green plants and wood.
• Cotton is one of the purest forms of cellulose and has been cultivated since ancient times.
• Cotton also serves (along with treated wood pulp) as the source the industrial production of cellulose-derived materials which were the first "plastic" materials of commercial importance.
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Rubber
• A variety of plants produce a sap consisting of a colloidal dispersion of cis-polyisoprene. This milky fluid is especially abundant in the rubber tree (Hevea); it drips when the bark is wounded.
• After collection, the latex is coagulated to obtain the solid rubber. Natural rubber is thermoplastic, with a glass transition temperature of –70°C.
• Raw natural rubber tends to be sticky when warm and brittle when cold, so it was little more than a novelty material when first introduced in Europe around 1770.
• It did not become generally useful until the mid-nineteenth century when Charles Goodyear found that heating it with sulfur — a process he called vulcanization — could greatly improve its properties.
cis-polyisoprene
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The International Journal for the Science and Technology of Polymers
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Polymer for Medical Applications
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Biodegradable Polymers as Drug Carrier Systems
• Polyesters– Lactide/Glycolide Copolymers
• Have been used for the delivery of steriods, anticancer agent, antibiotics, etc.
• PLLA is found as an excellent biomaterials and safe for in vivo (Lactic acid contains an asymmetric α-carbon atom with three different isomers as D-, L- and DL-lactic acid)
• PLGA is most widely investigated biodegradable polymers for drug delivery.
• Lactide/glycolide copolymers have been subjected to extensive animal and human trials without any significant harmful side effects
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• Poly(amides)– Natural Polymers
• Remain attractive because they are natural products of living organism, readily available, relatively inexpensive, etc.
• Mostly focused on the use of proteins such as gelatin, collagen, and albumin
Biodegradable Polymers as Drug Carrier Systems
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• Polymer Processing– Drug-incorporated matrices can be
formulated either compression or injection molding
– Polymer & drug can be ground in a Micro Mill, sieve into particle size of 90-120 µm, then press into circular disc
– Alternatively drug can be mixed into molten polymer to form small chips, then it is fed into injection molder to mold into desired shape
Biodegradable Polymers as Drug Carrier Systems
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Commercial Suture materials
Braided Polyester Multifilament nylon
Polythetrafluoroethylene
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Polymers in Everyday Life
• Clothing• Oil recovery• Food and flavors• Agriculture • Packaging• Consumer items – clothing, toys, skin care• Automotive parts• Industrial (pipes, parts, additives, etc)• Electronics• Medicines (proteins, antibodies, coatings for
tablets, gel caps)• Just about everywhere!
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Compact Discs
• A compact disc (or CD) is an optical disc used for storing digital data. It was originally invented for digital audio in 1979.
• Compact discs are made from a 1.2 mm thick disc of plastic coated with a much thinner aluminum layer.
• Aluminum layer is protected by a film of lacquer, which can be printed with a label.
• Injection molding is used to manufacture compact discs.
Plastic
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Candidate 1- Polyethylene
• Produced from petroleum product (ethylene), most commonly used polymer in consumer applications.
• Provide toughness, rigidity and strength for blow molding applications, extruded products, films, and injection molded items.
• Excellent combination of stiffness and resistance to chemicals/liquids.
• Key applications– Containers- shampoo, detergent, milk, solvents and oils– Bays, garbage can liners– Toys, tote bins
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Candidate 2- Polystyrene
• First produced in 1938 by The Dow Chemical Company.
• Made from monomer styrene, another petroleum based product.
• Protects products against moisture, maintains strength and shape over long periods of time (sturdy).
• Key applications– Foam- egg cartons, insulation, packing materials, – Food trays, cups– Boxes for small objects, plastic utensils, cups– Large and portable appliances
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Candidate 3- Polycarbonate
• Polymers with carbonate functional groups in the backbone.
• Very durable, transparent material, high heat and scratch resistance, resistance to chemicals/liquids.
• Key applications– Bullet proof glass, safety wear (shields, glasses)– Automotive headlamp lenses– Bottles, high end tableware, computer housing– Medical equipment
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More About Polycarbonate
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The material of choice is…..
Rigid Strong Easy to fabricate Dimensional stability
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Thank you!