POLYMERS Chapter 2 1

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1 POLYMERS Chapter 2 1

(a natural polymer) for the ark gum based resins extracted from pine trees Dr.

2 Ancient Polymers Originally natural polymers were used: Wood Rubber Cotton Wool Leather Silk Oldest known use: Rubber balls used by Incas Noah used pitch (a natural polymer) for the ark gum based resins extracted from pine trees Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 2

3 Polymers What is a polymer? Poly many mer repeat unit C C C C C C repeat unit Polyethylene (PE) C C C C C C Cl repeat unit Cl Cl Polyvinyl chloride (PVC) repeat unit Polypropylene (PP) Adapted from Fig. 14.2, Callister 7e. C C C C C C C 3 C 3 C 3 Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

4 Polymer Composition Most polymers are hydrocarbons i.e., made up of and C Saturated hydrocarbons Each carbon singly bonded to four other atoms Example: Ethane, C 2 6 C C Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 4

5 Unsaturated ydrocarbons Double & triple bonds somewhat unstable Thus, can form new bonds Double bond found in ethylene or ethene - C 2 4 C C Triple bond found in acetylene or ethyne - C 2 2 C C Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 5

6 Structures of Polymers about hydrocarbons Why? Most polymers are hydrocarbon (e.g. C, ) based Bonding is highly covalent in hydrocarbons Carbon has four electrons that can participate in bonding, hydrogen has only one Saturated versus unsaturated C C C Ethylene C Acetylene Unsaturated C C Ethane Saturated Unsaturated species contain carbon-carbon double/triple bonds Possible to substitute another atom on the carbon Saturated carbons have four atoms attached Cannot substitute another atom on the carbon Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

7 Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 7

10 NOTE: See Table 15.3 for commercially important polymers including trade names

13 Polymer Molecules Molecules are gigantic Macromolecules Repeat units Monomer Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

14 Polymer chemistry Polymers are chain molecules. They are built up from simple units called monomers. E.g. polyethylene is built from ethylene units: which are assembled into long chains: Polyethylene or polythene (IUPAC name poly(ethene)) is a thermoplastic commodity heavily used in consumer products (notably the plastic shopping bag). Over 60 million tons of the material are produced worldwide every year. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

15 Molecular Structures for Polymers Covalent chain configurations and strength: secondary bonding Linear Branched Cross-Linked Network Direction of increasing strength Adapted from Fig. 4.7, Callister & Rethwisch 3e. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 15

16 Linear polymers polymers in which the monomers units are connected end-to-end along the whole length of the chain These types of polymers are often quite flexible Van der waal s forces and -bonding are the two main types of interactions between chains Some examples polyethylene, teflon, PVC, polypropylene Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

17 secondary bonding Linear Branched Cross-Linked Network In cross-linked polymers, adjacent linear chains are joined to one another at various positions by covalent bonding of atoms. Examples are the rubber elastic materials. Small molecules that form 3 or more active covalent bonds create structures called network polymers. Examples are the epoxies and polyurethanes. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 17

Polymer Crystallinity Ex: polyethylene unit cell Adapted from Fig. 14.10, Callister 7e.

18 Polymer Crystallinity Ex: polyethylene unit cell Adapted from Fig , Callister 7e. Crystals must contain the polymer chains in some way Chain folded structure Adapted from Fig , Callister 7e.

Polymer Crystallinity Polymers rarely exhibit 100% crystalline Too difficult to get all those chains aligned crystalline region % Crystallinity: how much is crystalline.

19 Polymer Crystallinity Polymers rarely exhibit 100% crystalline Too difficult to get all those chains aligned crystalline region % Crystallinity: how much is crystalline. amorphous region Adapted from Fig , Callister 6e. (Fig is from.w. ayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)

20 Mechanical Properties i.e. stress-strain behavior of polymers brittle polymer σ FS of polymer ca. 10% that of metals elastic modulus less than metal plastic elastomer Strains deformations > 1000% possible (for metals, maximum strain ca. 100% or less) Adapted from Fig. 15.1, Callister 7e.

21 Tensile Response: Elastomer Case σ(mpa) x brittle failure plastic failure x elastomer ε x final: chains are straight, still cross-linked Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along elastomer curve (green) adapted from Fig , Callister 7e. (Fig is from Z.D. Jastrzebski, The Nature and Properties of Engineering Materials, 3rd ed., John Wiley and Sons, 1987.) initial: amorphous chains are kinked, cross-linked. Deformation is reversible! Compare to responses of other polymers: -- brittle response (aligned, crosslinked & networked polymer) -- plastic response (semi-crystalline polymers)

22 Polymer Structure 22

23 Processing of Plastics The response of a polymer to mechanical forces at elevated temperature is related to its dominant molecular structure. One classification of polymers is according to its behavior and rising temperature. Thermoplastics and Thermosets are the 2 categories. Thermoplastic A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. can be reversibly cooled & reheated, i.e. recycled ex: polyethylene, polypropylene, polystyrene, etc. Thermoset large crosslinking hard and brittle Once hardened a thermoset resin cannot be reheated and melted to be shaped differently ex: urethane, epoxy

24 Thermoset data

25 Polymer Processing 1. Injection Molding 2. Extrusion 3. Thermo-Forming 4. Blow Molding (injection blow molding with preforms or extrusion blow molding with parison) 5. Rotational Molding (combination of 3 and 4) Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 25

26 Processing Plastics - Molding Injection molding (most common 60-70%) thermoplastic Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

28 Injection Molding Steps for Injection Molding Clamping Injection Cooling Mold-opening Ejection Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 28

29 Injection molding 29

Extrusion produces items such as pipe/tubing, weather stripping, fencing, deck railings, window frames,

30 Processing Plastics Extrusion Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weather stripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation. Adapted from Fig , Callister 7e. (Fig is from Encyclopædia Britannica, 1997.)

31 Injection molding Software Simulation software for optimizing plastic injection molding designs, reducing cycle time and improving product appearance. Ex: CoreTech System Co., Ltd. (Moldex3D) was founded in 1995, it has provided the professional plastic injection molding simulation solution Moldex series for the plastic injection molding industry, and the current product Moldex3D is marketed worldwide. --- Project 31

32 Injection molding Simulation 32

33 Polymer Types: Elastomers Elastomers rubber Crosslinked materials Natural rubber Synthetic rubber and thermoplastic elastomers SBR- styrene-butadiene rubber styrene butadiene Silicone rubber

34 Advanced Polymers A number of new polymers having unique and desirable combinations of properties have been developed over the past several years. This include: A niche in new technologies and/or A satisfactorily replaced other materials Some of these include: Ultrahigh molecular weight polyethylene (UMWPE) Liquid crystal polymers (LCPs) Shape memory polymers Nanotechnology

35 Ultrahigh molecular weight polyethylene (UMWPE) Ultrahigh molecular weight polyethylene (UMWPE) is a linear polyethylene that has an extremely high molecular weight. Also known as high-modulus polyethylene, (MPE), or high-performance polyethylene (PPE), it has extremely long chains. Its typical Mw is approximately 4 x 10 6 g/mol greater than that of high density polyethylene. This results in a very tough material, with the highest impact strength of any thermoplastic presently made. UMWPE in fibre form has trade name spectra UMWPE Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

36 Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 36

37 Some of the extraordinary characteristics of this material are as follows: An extremely high impact resistance. Outstanding resistance to wear and abrasion. A very low coefficient of friction. A self-lubricating and nonstick surface. Very good chemical resistance. Excellent low-temperature properties. Outstanding sound damping and energy absorption characteristics. Electrically insulating and excellent dielectric properties. Nontoxic Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 37

38 This unusual combination of properties leads to numerous and diverse applications for this material, including: bullet-proof vests, composite military helmets, fishing line, ski bottom surfaces, golf ball cores, bowling alley and ice skating rink surfaces, biomedical blood filters, bulk material handling equipment (for coal, grain, cement, gravel, etc.), bushings, pump impellers, and valve gaskets Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 38

39 Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 39

The AC socket are made from Cobalt-chrome metal alloy or ceramic, AC cup

40 It is commonly used for the construction of articular portions of implants used for hip and knee replacements. The AC socket are made from Cobalt-chrome metal alloy or ceramic, AC cup made from polyethylene Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering

Liquid crystal polymers (LCPs) The liquid crystal polymers (LCPs) are a group of chemically complex and structurally distinct materials that have unique properties and are utilized in diverse

41 Liquid crystal polymers (LCPs) The liquid crystal polymers (LCPs) are a group of chemically complex and structurally distinct materials that have unique properties and are utilized in diverse applications. Liquid crystal materials generally have several common characteristics. Among these are a rod-like molecular structure, rigidness of the long axis, and strong dipoles and/or easily polarizable substituents. In the solid state, molecules are highly ordered and have little translational freedom. The characteristic orientational order of the liquid crystal state is between the traditional solid and liquid phases and this is the origin of the term mesogenic state, used synonymously with liquid crystal state. Liquidcrystal polymers are present in melted/liquid or solid form. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 41

42 The following may be said about their processing and fabrication characteristics: All conventional processing techniques available for thermoplastic materials may be used. Low melt viscosity, which permits molding of thin sections and/or complex shapes. Low heats of fusion; this results in rapid melting and subsequent cooling, which shortens molding cycle times. Anisotropic finished-part properties; molecular orientation effects are produced from melt flow during molding. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 42

43 By incorporating an infrared-sensitive dye in the mixture, polymer films that undergo reversible shape deformations on heating are formed. Illustration representation of preparation of a side chain LCP via hydrosilylation reaction between a linear siloxane polymer (green), mesogen (blue) and cross-linker (orange). Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 43

44 Applications The most common application of liquid crystal technology is liquid crystal displays (LCDs.) This field has grown into a multi-billion dollar industry, and many significant scientific and engineering discoveries have been made. Liquid-crystal polymers: Exotic actuators Kevlar (solid) Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 44

45 Shape memory polymers Introduced to United States in 1984 after its original introduction in Japan. Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus (trigger), such as temperature change. SMPs can retain two or sometimes three shapes, and the transition between those is induced by temperature. Light weight Potentially biodegradable for surgical procedures. Cheaper to manufacture than Shape memory Alloys. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 45

46 Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 46

47 SMP: Linear block copolymers Representative shape-memory polymers in this category are polyurethanes, polyurethanes with ionic or mesogenic components. Other block copolymers also show the shape-memory effect, such as, block copolymer of polyethylene terephthalate (PET) and polyethyleneoxide (PEO), block copolymers containing polystyrene and poly(1,4- butadiene), and an ABA triblock copolymer made from poly(2-methyl-2-oxazoline) and polytetrahydrofuran. The PEO-PET block copolymers can be crosslinked by using maleic anhydride, glycerin or dimethyl 5- isopthalates as a crosslinking agent. Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 47

48 Applications Self Deployment Mechanisms Eyeglass Frames Automatic auto body repairs. Biodegradable biomedical stents. Artificial muscles Aeronautical Morphing Wings

49 Shape memory Polymers Dr. Anwar Abu-Zarifa. Islamic University Gaza. Department of Industrial Engineering 49

Chapter 14 Polymers CHAPTER 7 POLYMERIC MATERIALS. Ancient Polymer History. Rubber balls used by Incas Noah used pitch (a natural polymer) for the ark

Chapter 14 Polymers CHAPTER 7 POLYMERIC MATERIALS. Ancient Polymer History. Rubber balls used by Incas Noah used pitch (a natural polymer) for the ark Chapter 14 Polymers What is a polymer? Polymers are organic materials made of very large molecules containing hundreds of thousands of unit molecules called mers linked in a chain-like structure (repeated