Polymers (part I)

Polymer: “a substance consisting of molecules characterized by the repetition (neglecting ends, branch junctions and other minor irregularities) of one or more types of monomeric units.” ASTM

FIGURE 6-10 Various polymer structures. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Categorizing Polymers Natural / Synthetic Organic / Inorganic Thermoplastic / Thermoset Linear / Cross-linking General Purpose / Engineering Floating / Sinking Toxic / Non-toxic Chemical Makeup Etc.

FIGURE 6-2 Industrial polymers. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Plastic “a material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight, is solid in its finished state, and, at some stage in its manufacture or processing into finished articles, can be shaped by flow.” ASTM A synthetic polymer

Plastics are: “any one of a large and varied group of materials consisting wholly or in part of combinations of carbon with oxygen, hydrogen, nitrogen, and other organic or inorganic elements which while solid in its finished state, at some stage in manufacture is made liquid, and thus capable of being formed into various shapes, most usually through the application, either singly or together, of heat and pressure.” Society of Plastics Industry. (p.341)

Figure C-4 Color Polymer Stuff: products made of various plastics and elastomers demonstrate the wide ranges of colors, forms, and properties possible with synthetic polymers. Note the white and blue and white and black toothbrushes in the middle with flexible heads, contoured shape, and soft rubber dots and strips for gripping. What types of plastics and elastomers are shown here? James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-60 SPI’s voluntary plastic container coding system FIGURE 6-60 SPI’s voluntary plastic container coding system. (Dow Chemical) James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-22 Plastic food containers—(a) tough and lightweight properties of plastics make them very competitive with glass and steel. The barrier plastic ketchup bottle on the left, made of layered composite plastics [see detail in b], weights 80% less than the glass catsup bottle on the right. The plastic container is less likely to break than the glass bottle and saves transportation costs. Why would one company choose glass and the other company plastic? James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-22 (b) Five layers of barrier plastic container. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Resin Solid or semisolid uncompounded ingredients or monomers that are mixed by not yet polymerized (“Resin” is sometimes used in the trade to refer to bulk polymer materials, such as polyethylene pellets for injection molding.)

Monomer “a low-molecular-weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.” ASTM

Homopolymers Have repeating units of a single mer E.g., polyethylene, polystyrene

FIGURE 6-3 Types of polymers: (a) Simple polymer. (b) Homopolymers. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Copolymers “contain two different types of monomers.” E.g., “polyvinyl chloride mixed with vinyl acetate to produce polyvinyl acetate.”

Terpolymers “contain three types of monomers” E.g., acrylonitrile butadiene styrene (ABS)

Isomers “variations in the molecular structure of the same compositions.”

FIGURE 6-3 Types of polymers: (c) Copolymers. (d) Isomers. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Polymerization “a chemical reaction in which the molecules of monomers are linked together to form polymers.” ASTM Types: Addition Condensation

Addition Polymerization Or “Chain Reaction” polymerization “By the use of heat and pressure in an autoclave ore reactor, double bonds of unsaturated monomers break loose and then link up into a chain.”

Addition Polymerization Commonly: thermoplastics Examples: PP: Polypropylene PE: Polyethylene PVA: Poly(vinyl acetate) PVC: Poly(vinly chloride) ABS: Acrylonitrile butadiene styrene

Example: Polyethylene Bifunctional Ethylene (C2H4) Ethylene mer Polyethylene

FIGURE 6-4 (a) Monomer of ethylene (C2H4) FIGURE 6-4 (a) Monomer of ethylene (C2H4). Carbon atoms with four valence electrons have four arms (shared electrons) for covalent bonding. Two shared electrons hold another carbon atom in a double bond. Two other shared electrons, each covalently bonded, hold one shared electron of hydrogen, which has only one valence electron for single bonds. Double bonds are not stable and form reactive sites. (b) Polyethylene, chain of ethylene monomers. During polymerizaton, heat and pressure break the hold of one shared electron on each of the double-bonded (reactive sites) carbon atoms, thereby leaving each carbon atom of the monomers free to grasp another carbon atom (covalent bond) from other ethylene monomers, which form into a chain of thousands of ethylene monomers (polyethylene). The single bonds satisfy the carbon bond arrangement and produce the most stable saturated polymers because they have no reactive sites. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-5 (a) Typical polymers produced through addition (chain) polymerization. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-5 (b) A portion of a modern polymer processing plant showing some of the complex apparatus and piping necessary to produce resins. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Condensation Polymerization Aka: Step Reaction “Polymerization in which monomers are linked together with the splitting off of water or other simple molecules.” ASTM

FIGURE 6-6 Graphical illustration of condensation (step) polymerization of a polyamide (nylon). James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Condensation Polymerization Thermoset Examples PF: Phenolic PET: Polyester PUR: Polyurethane SI: Silicone Thermoplastic Examples PC: Polycarbonate PA: White Nylon

Molecular Weight of a Polymer Polyethylene Molecule: [C2H4]n=2000 Using 12 for wt of C and 1 for wt of H: Weight of C2H4 mer = (2x12) + (4x1) = 28 Molecular wt = 2000 x 28 = 56,000

Determine the Molecular Weight of: Polypropylene with n = 1500 (Use Table 10-9)

Polypropylene C3H6 Mer weight = (3x12) + (6x1) Mer weight = 42 At n=1500, molecular weight = 63,000

Determine the Molecular Weight of: Acrylic with n = 1600 (Use Table 10-9)

Acrylic CH2O Mer weight = 12 + (2x1) + 16 Mer weight = 30 At n=1600, molecular weight = 48,000

General Relationship Between Plastics’ Molecular Weight and Mechanical Properties

The Melting Point of Plastics Generally Increases with Molecular Weight

FIGURE 6-7 Degrees of crystalline structure of polymers FIGURE 6-7 Degrees of crystalline structure of polymers. (a) Mostly amorphous (b) Semicrystalline (crystallites encircled) (c) Mostly crystalline (d) Liquid crystal polymer (Luther Gammon, Boeing Materials Technology) (a) (b) (c) (d) James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-7 Degrees of crystalline structure of polymers FIGURE 6-7 Degrees of crystalline structure of polymers. (e) Ultra-thin section of transmitted, cross-polarized, light circles, polymer matrix composite—carbon fiber (cut at 90 and seen as black circles) in a matrix of PEEK thermoplastic with liquid-crystalline spheroids at 2000x/100x obj. (Luther Gammon, Boeing Materials Technology) (d) James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

FIGURE 6-8 Polymers and crystallinity FIGURE 6-8 Polymers and crystallinity. (a) Properties: relation to molecular weight and crystallinity. (b) Effect of pulling an amorphous polymer through a die. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Vulcanization “an irreversible process during which a rubber compound…becomes less plastic and more resistant to swelling by organic liquids and elastic properties are conferred…” ASTM Typically, through the addition of sulfur

FIGURE 6-36 Vulcanized rubber. (a) Natural rubber—thermoplastic FIGURE 6-36 Vulcanized rubber. (a) Natural rubber—thermoplastic. (b) Vulcanized (cross-linked) rubber—thermoset. James A. Jacobs & Thomas F. Kilduff Engineering Materials Technology, Fourth Edition Copyright ©2001 by Prentice-Hall, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.