1 MFGT 104 Materials and Quality Chap 5: Polymers and Elastomers Professor Joe Greene CSU, CHICO MFGT 104

2 Polymers and Elastomers Objectives –Define the common terms associated with polymers and elastomers –List the common properties of a variety of polymer and elastomer families. –List the various manufacturing processes associated with polymers and elastomers. –Describe the various properties used to designate or specify various polymers and elastomers

3 Definition of Plastics All Materials Gases Simple Liquids Solids Metals Polymers (polymeric molecules) Ceramics Thermosets Heat Setting Thermoplastics Heat Forming Elastomers

4 Early Modified Natural Materials Natural Rubber (gum rubber_ natural latex) –Little industrial significance compared to gutta percha –Melted in hot temperatures and cracked in cold temperatures –Vulcanization of rubber with sulfur (1839) by Goodyear –Small amounts of sulfur = rubber; Large amounts = ebonite (hard) –Civil War required large amounts of rubber –Today- Rubber is a multi Billion $ business Celluloid (substitute for horn, ivory, tortoise shell) –Conversion of cotton into nitrocellulose (sulfuric acid and nitric acid): highly nitrated is explosive, moderately nitrated is useful –Pyroxylin is soluble in several solvents, used as a finish. –Solid Pyroxylin called celluloid (powdered Pyroxylinwith pulverized gum camphor) heated and molded for Billiard balls.

5 Automotive Applications of Plastics and Composites n Composite Intensive Vehicles

6 Automotive Plastics and Composites Use

7 Major Plastic Materials 1994 LDPE6.4 M metric tons HDPE5.3 M metric tons PVC5.1 M metric tons PP4.4 M metric tons PS2.7 M metric tons PU1.7 M metric tons PET1.6 M metric tons Phenolic1.5 M metric tons Total28.6 M metric tons (82% of market)

8 Recycling of Plastics State and Federal Legislation PET bottle recycling Codes for plastics – 1 PET – 2 HDPE – 3Vinyl/PVC – 4LDPE – 5PP – 6PS – 7Other

9 Polymer Materials Polymer materials are made up of “many” (poly) repeating “units”(mers). Polymers are mostly based in carbon, oxygen, and hydrogen. Some have Si, F, Cl, S Polymers are considered a bowl of spaghetti or a bag of worms in constant motion.

10 Polymer Materials Polymers are classified broadly as –thermoplastic: form after heat. Over and over again. –thermoset: set after heat. Only sets once. Can’t reform Thermoplastics –crystalline: polymers arranged in a regular order –amorphous: polymers arranges randomly like coil Thermosets –low molecular weight monomers that crosslink and polymerize to for polymer network Elastomers –Can be either thermoplastic and thermoset Thermoset elastomers: natural and synthetic rubbers Thermoplastic elastomers: plastics that mimic rubber (EPDM, TPO, TPE)

11 Macromolecules Simplest Plastic- Polyethylene (PE). –Saturated Hydrocarbon –approx Carbon atoms in backbone (chain) –Length: ~ mm (if stretched out) –Comparison: Typing paper mm (30 PE on end) –Repeating unit- Mer –Degree of Polymerization= n DP= 500 is PE (14,000amu’s) DP= 9 is Paraffin wax (252 amu’s) CC HH HH n

12 Amorphous- Molecular structure is incapable of forming regular order (crystallizing) with molecules or portions of molecules regularly stacked in crystal-like fashion. A - morphous (with-out shape) Molecular arrangement is randomly twisted, kinked, and coiled States of Thermoplastic Polymers

13 Amorphous Materials PVCAmorphous PSAmorphous AcrylicsAmorphous ABSAmorphous Polycarbonate Amorphous PhenoxyAmorphous PPOAmorphous SANAmorphous PolyacrylatesAmorphous

14 Crystalline- Molecular structure forms regular order (crystals) with molecules or portions of molecules regularly stacked in crystal-like fashion. Very high crystallinity is rarely achieved in bulk polymers Most crystalline polymers are semi-crystalline because regions are crystalline and regions are amorphous Molecular arrangement is arranged in a ordered state States of Thermoplastic Polymers

15 Crystalline polymers (PE, PP, PBT, PA,etc) Molecular Chains are in an order Crystalline structure forms from a single point, “spherulite”. Spherulites meet to form crystal. Time dependent process and consumes energy. Most polymers are semi-crystalline with regions of crystals surrounded by amorphous areas. Start IntermediateFully Grown Spherulites

16 Crystalline Materials LDPECrystalline HDPECrystalline PPCrystalline PETCrystalline PBTCrystalline PolyamidesCrystalline PMOCrystalline PEEKCrystalline PPSCrystalline PTFECrystalline LCP (Kevlar)Crystalline

17 Carbon Chain Polymers Homopolymers –Simplest plastic containing one basic structure –If X = H then Polyethylene –If X = Cl the PVC –If X = CH 3 then PP –If X = Benzene Ring The PS CC HX HH n

18 Homopolymers Table 3-2 Plastics Involving Single Substitutions

19 Carbon with Other Elements in Backbone Many backbones include O, N, S, or benzene rings in the main chain. Most are homopolymers with some copolymers and fewer terpolymers. e.g. Polycarbonate m O C CH 2 C O O n

20 Thermosets Thermosets are polymers that undergo a chemical reaction during the polymerization. Thermosetting reaction is not reversible under heat. Epoxy –Standard epoxy is based on bisphenol A and epichlorohydrin. –Properties include good adhesion to many substrates, low shrinkage, high electrical resistivity, good corrosion resistance, and thermal. –Processing is achieved without generation of volatiles.

21 Polyester and Polyurethane Polyester –Thermoset reaction between a difunctional acid (or anhydride) and a difunctional alcohol (glycol) –Heat or radiation can trigger the cross linking reaction –Accelerators (or promoters) speed up the reaction. –Condensation Reaction results in CO 2 and H 2 O. –Monomer required to polymerize, e.g., Styrene at 30% to 50% in commercial polyester systems Polurethane –Reaction between isocyanate and alcohol (polyol). Condensation Reaction results in CO 2 and H 2 O. –Crosslinking occurs between isocyanate groups (-NCO) and the polyol’s hydroxyl end-groups (-OH) –Thermoplastic PU (TPU) have some crosslinking, but purely by physical means. These bonds can be broken reversibly by raising the material’s temperature, as in molding or extrusion.

22 Polyurethane Chemistry Reaction between isocyanate and alcohol (polyol). Crosslinking occurs between isocyanate groups (-NCO) and the polyol’s hydroxyl end-groups (-OH) Thermoplastic PU (TPU) have some crosslinking, but purely by physical means. These bonds can be broken reversibly by raising the material’s temperature, as in molding or extrusion. Ratio between the two give a range of properties between a flexible foam (some crosslinking) to a rigid urethane (high degree of crosslinking). In PUR foams density can range from 1 lb/ft3 to 70 lb/ft3. Foams are produced by chemical blowing agents. Catalyst are used to initiate reaction. RIM process is used to produce fenders and bumper covers

23 Applications for Thermosets Epoxy –Protective coatings: maintenance coatings for industrial and marine, tank linings, industrial floorings, beer and beverage can coatings, food cans, appliance primers, hospital and laboratory furniture. –Bonding and adhesives: Automotive and aircraft industries adhesive to metals and composites. –Molding, casting and tooling: Molding compounds in electrical and electronic industries, casting resins, potting resins. Prototype and master model tools. –Laminating and composites: Binders in fiber reinforced laminates and composites. Laminates are used in printed wiring boards. Composite applications include filament winding (high performance pipes in oil fields, pressure vessels, tank and rocket motor housings), pultrusion, casting, and molding (graphite composites for aerospace applications) –Building and construction: Flooring (seamless, self-leveling, or epoxy terrazzo floors), repair of bridges and roads with glass and carbon fiber wraps, concrete crack repair, coat reinforcing bars, binders for patios, swimming pool decks, and soil around oil-well drills.

24 Applications for Thermosets Polyester –Boat hulls, shower stalls, electrical components, appliances –Recreation vehicles, automotive body panels, floor pans; SMC –Soft tooling, patterns –Cultured marble, buttons, corrosion resistant tanks and parts, –Corrugated and flat paneling, simulated wood furniture, bowling balls, polymer concrete, and coatings Polyurethane –Rigid foams: (MDI) Laminated board stock, Moldings, Bun, Foam in place insulation, sprayed foam, packaging –Semi-flexible foam: (MDI and TDI) Moldings, Integral-skin moldings –Flexible foam:(TDI) Moldings, integral skin molding, carpet underlay –Packaging: (TDI) Furniture cushioning –Microcellular foam: (MDI) RIM parts, shoe soles –Non-foam cast elastomers –Coatings, binders, thermoplastic elastomers, sealants, paints

25 Elastomers Elastomers are rubber like polymers that are thermoset or thermoplastic –butyl rubber: natural rubber –thermoset: polyurethane, silicone –thermoplastic: thermoplastic urethanes (TPU), thermoplastic elastomers (TPE), thermoplastic olefins (TPO), thermoplastic rubbers (TPR) Elastomers exhibit more elastic properties versus plastics which plastically deform and have a lower elastic limit. Rubbers have the distiction of being strenched 200% and returned to original shape. Elastic limit is 200%

26 Rubbers Rubbers have the distinction of being stretched 200% and returned to original shape. Elastic limit is 200% Natural rubber (isoprene) is produced from gum resin of certain trees and plants that grow in southeast Asia, Ceylon, Liberia, and the Congo. –The sap is an emulsion containing 40% water & 60% rubber particles Vulcanization occurs with the addition of sulfur (4%). –Sulfur produces cross-links to make the rubber stiffer and harder. –The cross-linkages reduce the slippage between chains and results in higher elasticity. –Some of the double covalent bonds between molecules are broken, allowing the sulfur atoms to form cross-links. –Soft rubber has 4% sulfur and is 10% cross-linked. –Hard rubber (ebonite) has 45% sulfur and is highly cross-linked.

27 Rubber Additives and Modifiers Fillers can comprise half of the volume of the rubber –Silica and carbon black. –Reduce cost of material. –Increase tensile strength and modulus. –Improve abrasion resistance. –Improve tear resistance. –Improve resistance to light and weathering. –Example, tires produced from Latex contains 30% carbon black which improves the body and abrasion resistance in tires.

28 Synthetic Rubber Isoprene- basic structure of rubber molecule Butadiene- basis for synthetic rubber (SBR) Styrene- Butadiene Rubber co-polymer

29 Synthetic Rubber Polychloroprene- neoprene rubber, closest sythetic to natural rubber. Used for fuel lines, hoses, gaskets. Butyl rubber- addition polymer of isobutylene. Thiokol- ethylene dichloride polymerized with sodium polysulfide. Sulfur makes thiokol rubber self vulcanizing.

30 Thermoplastic Elastomers Thermoplastic Elastomers result from copolymerization of two or more monomers. –One monomer is used to provide the hard, crystalline features, whereas the other monomer produces the soft, amorphous features. –Combined these form a thermoplastic material that exhibits properties similar to the hard, vulcanized elastomers. Thermoplastic Urethanes (TPU) were the first Thermoplastic Elastomer (TPE) used for seals gaskets, etc. Other TPEs –Copolyester for hydraulic hoses, couplings, and cable insulation. –Styrene copolymers are less expensive than TPU with lower strength –Styrene-butadiene (SBR) for medical products, tubing, packaging, etc. –Olefins (TPO) for tubing, seals, gaskets, electrical, and automotive.

31 Processing of Polymers Thermoplastics –injection molding, extrusion, blow molding, thermoforming, rotational molding, compression molding Thermosets –compression molding, reaction injection molding, resin transfer molding, casting, hand layup, etc. Elastomers –compression molding, extrusion, injection molding, casting.

32 Injection Molding Process and Cycle Time

33 Extruder Equipment Exit zone- die –die imparts shape on the material, e.g., rod, tube, sheet, channel –exit material is called extrudate –extrudate swells at end of die due to normal forces from the polymer flow, called die swell Cooling zone –water bath or air cooled to lower the temperature below Tg Auxiliary equipment –puller –rollers for proper thickness –Wind-up or cut off Die Swell

34 Compression Molding Process Materials Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber Sheet Molding Compound (SMC), Bulk Molding Compound (BMC) Thermoplastics: Polypropylene, polyester, or others with glass fibers Glass Mat Thermoplastic (GMT), thermoplastic BMC Elastomers: Thermoplastic or Thermoset rubbers Thermoplastic Olefin (TPO), Thermoplastic Elastomer (TPE), Thermoplastic Rubber (TPR) Thermoset Styrene Butidiene Rubber Thermoplastic: Heat Plastic prior to molding Thermosets: Heat Mold during molding

35 Resin Transfer Molding Process Ref: MSU Tutorial- Materials Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber