MFGT 290MFGT Certification Class Chapters 13, 14, and 15: Engineering Materials- Plastics, Composites, and Ceramics Professor Joe Greene CSU, CHICO MFGT 290
Chap 13: Plastics • Plastics • Polymerization • Polymer Structures • Thermoplastics • Engineering Thermoplastics • Thermoset Polymers • Processing of Plastics • Review Questions
Definition of Plastics All Materials Gases Simple Liquids Solids Polymers (polymeric molecules) Metals Ceramics Thermoplastics Heat Forming Thermosets Heat Setting Fiberglass Resins Elastomers Plastics Rubbers
Introduction • Polymeric materials can be either • Thermoplastics, thermosets, and elastomers. • Each section is presented in appropriate groups • Thermoplastics- Heat Forming materials (Can reheat & form again) • Carbon bonds are Saturated and are single bonds. • Come in a variety of forms • Pellets, powder (1-100 microns), flake, chip, cube, dice, • Shipped in packages of choice • Bags (50 lbs), drums (200 lbs), boxes, cartons, gaylords (1000 lb), • Tank-truck loads (15 tons), rail cars (40 – 80 tons) • Bulk supplies are stored in silos and conveyed pneumatically • Thermosets- Heat Setting materials (Once set can’t reform -like cooked eggs) • Carbon bonds are Unsaturated and have some double bonds. • Supplied in powder or liquid form • Supplied in drums, tank-trucks, and railroad cars. • Rubbers are supplied in bale form.
Commercial Thermoplastics • Olefins • Unsaturated, aliphatic hydrocarbons made from ethylene gas • Ethylene is produced by cracking higher hydrocarbons of natural gas or petroleum • LDPE commercialized in 1939 in high pressure process • Branched, high pressure, and low density polyethylene • HDPE commercialized in 1957 in low pressure process • Linear, low pressure, high density • Medium density PE and other PE, UHMWPE, LLDPE • The higher the density the higher the crystallinity • Higher the crystallinity the higher the modulus, strength, chemical resistance, • PE grades are classified according to melt index (viscosity) which is a strong indicator of molecular weight. • Injection molding requires high flow, extrusion grade is highly elastic, thermoforming grade requires high viscosity or consistency • Other commodity (cheap) plastics • PP, PS, PVC (or vinyl), ABS, PMMA (Acrylic)
Major Plastic Materials1994 • LDPE 6.4 M metric tons • HDPE 5.3 M metric tons • PVC 5.1 M metric tons • PP 4.4 M metric tons • PS 2.7 M metric tons • PU 1.7 M metric tons • PET 1.6 M metric tons • Phenolic 1.5 M metric tons Total 28.6 M metric tons(82% of market)
Recycling of Plastics • State and Federal Legislation • PET bottle recycling • Codes for plastics • 1 PET • 2 HDPE • 3 Vinyl/PVC • 4 LDPE • 5 PP • 6 PS • 7 Other
States of Thermoplastic Polymers • 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) • Usually transparent (Clear bags) • Less shrinkage with amorphous materials. • Amorphous Polymers • ABS Acrylics • Polycarbonate PS • Polyurethanes PPO • Phenoxy PVC • SAN
States of Thermoplastic Polymers • Crystalline- Molecular structure forms regular order (crystals) with molecules or portions of molecules regularly stacked in crystal-like fashion. • Most crystalline polymers are semi-crystalline because very few plastics are 100% crystalline. All have both regions that are crystalline and some that are amorphous • Usually Opaque and not transparent • More molding shrinkage with • crystalline materials. • Crystalline Materials • LDPE HDPE PP • PET PBT • Polyamides • PMO PEEK • PPS PTFE • LCP (Kevlar)
Functional Groups H H H H H H H H C C C C C C C C H H H H CH3 CH3 CH3 CH3 n n n n • Certain chemical characteristics associated with various groups of atoms, called functional groups. • Particular groups of atoms occur in a large molecule, the characteristic chemistry is anticipated. • Example, PP has Functional groups can be attached to basic groups of carbon atoms by replacing on H atom. • Note: PP is Mostly Isotactic- CH3 on one side of polymer chain (isolated). Commercial PP is 90% to 95% Isotactic and not Atactic (random) or syndiotactic
Functional Groups • Various molecules of carbon, hydrogen and oxygen illustrating the differences properties with different atomic arrangements • isopropyl alcohol- rubbing alcohol • methylethyl ether- anesthetic • acetone- common solvent • methyl acetate- sweet chemical perfume • propionaldehyde- sharp smelling chemical • propanoic acid= related to vinegar • Aromatic group- PBT, PET, PC, PEEK, PS all have aromatic • 6 carbon atoms bonded together with double bonds • Highly aromatic if have several aromatic groups • Aliphatic group- LDPE, HDPE, • single and double bonded carbons with other atoms
Polymers Units H H H H H H H H C C C C C C C C H H H H CH3 Cl H n n n n • Just as 2 carbons atoms are bonded together in ethane, three, four, or more carbons can be bonded in chain-like arrangement, sometimes thousands of atoms long. • Long chains of atoms are poly-mers (many-mers or units) • Figure • Polyethylene PP PS PVC • Note: PP is Mostly Isotactic- CH3 on one side of polymer chain (isolated). Commercial PP is 90% to 95% Isotactic and not Atactic (random) or syndiotactic
Complex Polymers • Polymer chains with atoms other than carbon • Usually polymer chains with C and N, O, S, F, and Cl • PVC has Cl; Nylon has O and N; Polyurethane has O and N • PET has O and benzene ring; PC has O and benzene ring • Bonding in Plastics (No metallic or Ionic bonds_ Just Covalent) • Covalent bonds are dominate bonding between C and other atoms. • Secondary bonding and Intermolecular Forces • Van der Waal’s Forces- weak attraction not in plastics • Dipole interactions- Part of molecule is more electronegative than other part causing one side to be partially negative and the other partially positive. • Hydrogen bonding- Very important for some plastics- Like Nylon • Causes physical properties to change. Like tensile strength and melting point • Nylon 6 has higher tensile strength and melting point than Nylon 12 because • Nylon 6 has 1 dipole + 1 hydrogen bond for every 6 Carbon atoms in chain. • Nylon 12 has 1 dipole and 1 hydrogen bond every 12 Carbon atoms • Dipole induces polarity and occurs if • C-Cl single bond (like PVC); C-Fl single bond (Like PTFE); C=O double bond (like Nylon, PET, PU, PC) • Hydrogen bonds induces polarity and occurs if • C-OH single bond (like PU-polyurethane); N-H Single bond (Like PU, Nylon)
Formation of Polymers • Addition (or Chain-Growth) Polymerization • Most Commodity (cheap) plastics • Instantaneously, the polymer chain forms with no by-products • Chain-reaction mechanism that proceeds by several sequential steps as shown in Figure 2.20. Polymerization begins at one location on the monomer by an initiator • Condensation (or Step-wise) Polymerization • Most Engineering plastics (pellets of Nylon, PC, PET, Polyurethane)and themosets (liquids of epoxy, polyester, polyurethane) • Step-growth polymerization proceeds by several steps which result in by-products. • Monomers combine to form blocks 2 units long • 2 unit blocks form 4, which intern form 8 and son on until the process is terminated. • Results in by-products (CO2, H2O, Acetic acid, HCl etc.)
Nylon (or polyamide) and PC O CH2 C O O C CH2 n • The repeating -CONH- (amide) link • Polymerized with condensation reaction • Nylon 6- Polycaprolactam: [NH(CH2)5CO]x • Nylon 6,6- Polyhexamethyleneadipamide: • [NH(CH2)6NHCO (CH2)4CO]x • Nylon 12- Poly(12-aminododecanoic acid)- [NH(CH2)11CO]x • Polycarbonates are linear, amorphous polyesters because they contain esters of carbonic acid and an aromatic bisphenol (C6H5OH) • Polymerized with condensation reaction
Homopolymers Z F F Y C C C C W F X F n n • Plastics Involving Three+ Substitutions (use Table 3.2) e.g. PTFE polytetrafluoroethylene (Teflon)
Copolymers and Ter Polymers H H H H C C C C m n H H C:::N • Plastics Involving Two mers in chain or 3 mers (ABS) e.g. SAN styrene acronitrile • Structure of two mers can be OR the same three mers with a C • Alternating- ABABABABABABAB • Random copolymer- AABBABBBAABABBBAB • Block copolymer- AABBBAABBBAABBBAABBB • Graft copolymer- AAAAAAAAAAAAAAAAAAAAAAAAAA • B B B • B B B • B B B
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.
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 CO2 and H2O. • 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 CO2 and H2O. • 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.
Thermoplastic Elastomers, Natural Rubber • 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. • Natural Rubber is an elastomer that comes from rubber trees in Asia • Properties are increased by vulcanization with sulfur to make it strong. • Automobile tires use a large amount of Natural rubber and SBR
Plastics Questions • A bond between 2 carbon atoms is a _______ bond. • A CH3 groups is called a __________ group. • A dash between atoms indicates a ______ bond. • The small repeating units that make up a plastic molecule are called ___________ • What does poly mean? ___________ • 3 types of intermolecular forces found in plastics are ___________ , ____________, and ____________. • What type of bonding makes Nylon 6 stronger than nylon 12? _____________ • Crystalline plastics are more rigid and not as transparent as _________ plastics. • A _______ material may be softened repeatedly when heated and hardened when cooled. • The term used to describe tying together adjacent polymer chains is _______ • If the different mers make up the composition of a polymer , it is called a ______. • A Hydrogen molecule which contains some double bonds is called ________. • Is PVC a copolymer? _________ Explain- _____________________________. • What is the general structure of an alternating copolymer? __________________. • If a carbon chain has a methyl side group, is it branched? _________ Explain- _____________________________. • If a material is transparent, is it crystalline? ____________ • What effect do dipoles and hydrogen bonds have on melting point of polymers ___________ • Is residual stress synonymous with orientation? ____________________ • How does the tensile strength and melting point change with increasing crystallization? ______
Processing of Polymers • Thermoplastics • injection molding, extrusion, blow molding, thermoforming, rotational molding, compression molding • Usually uses high pressure processes and imparts high residual stresses on the material which an cause warping in part. • Thermosets • compression molding, reaction injection molding, resin transfer molding, casting, hand layup, etc. • Elastomers • compression molding, extrusion, injection molding, casting.
Extruder Equipment Die Swell • 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
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
Resin Transfer Molding ProcessRef: MSU Tutorial- http://islnotes.cps.msu.edu/trp/liquid/rtm/ • Materials • Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber
Polyurethane Processing • Polyurethane can be processed by • Casting, painting, foaming • Reaction Injection Molding (RIM)
Thermoset Reacting Polymers • Process Window • Temperature and pressure must be set to produce chemical reaction without excess flash (too low a viscosity), short shot (too high a viscosity), degradation (too much heat)
Compression Molding • Compression molding was specifically developed for replacement of metal components with composite parts. The molding process can be carried out with either thermosets or thermoplastics. However, most applications today use thermoset polymers. In fact,compression molding is the most common method of processing thermosets.
Resin Transfer Molding • In the RTM process, dry (i.e.,unimpregnated ) reinforcement is pre-shaped and oriented into skeleton of the actual part known as the preform which is inserted into a matched die mold. • The heated mold is closed and the liquid resin is injected • The part is cured in mold. • The mold is opened and part is removed from mold.
Injection Molding Glass Reinforced Composites • Plastic pellets with glass fibers are melted in screw, injected into a cold mold, and then ejected. Glass filled resin pellets
Chap 14: Composites • Composite Materials • Composite Construction • Composite Applications • Processing of Composites • Review Questions
Polymers Composites • Objectives • Define the components and difference types of composites. • Explain the different types of composite construction and the reasons behind them. • Describe the various manufacturing methods used to produce composites. • List the different reinforcing materials used in composites. • List the various matrix materials used in composites. • Excellent Web sites • Michigan State http://islnotes.cps.msu.edu/trp/ • U of Delaware http://www.ccm.udel.edu/publications/CU/99/ • Cornell University http://www.engr.siu.edu/staff2/abrate/NSFATE/links.htm
Composites • Composite definition • A composite is a material comprised of two or more physically distinct materials with at least one material providing reinforcing properties on strength and modulus. • Natural Composites • Bone • Wood • Bamboo: Natures fiber glass due to pronounced fibrillar structure which is very apparent when fractured. • Muscle and other tissue • Engineering Composites • Reinforced concrete beams • Thermoset composites: Thermoset resins (polyurethanes, polesters, epoxies) • Glass fibers, Carbon fibers, Synthetic fibers, metalfibers, or ceramic fibers • Thermoplastic composites (polypropylene, nylon, polyester,TPU,polyimide) • Glass fibers, Carbon fibers, Synthetic fibers, metalfibers, or ceramic fibers
Composite Classifications • Reinforcement Type • Discontinuous (fibers are chopped and dispersed in matrix resin) • Short fibers: fiber lengths 3mm or less (most injection molded materials) • Long fibers: fiber lengths greater than 6 mm. (Some injection molded materials with 6mm fibers, Sheet Molding Compound (SMC) with 1” fibers, DFP Directed Fiber Preforms for RTM and SRIM) • Particulates: fibers is forms as spheres, plates, ellipsoids (some injection molded materials reinforced with mineral fibers) • Continuous (fibers are throughout structure with no break points) • Glass roving: glass bundles are wound up in a packet similar to yarn. • Roving is woven into several weaves using a loom machine like in apparel. • Mat products: random swirl glass pattern. • Woven product: roving is woven into machine direction (warp) and cross direction (weft) • Uni product: roving is woven in one direction with a cross thread given to hold mat together.
Glass Fiber Applications • Discontinuous (Chopped) Fiber • Short fiber (L= 3mm) reinforcement for thermoplastic materials that are injection molded (PP and Nylon) • Long Fiber (L=6mm) reinforcement for thermoplastic materials that are injection molded (Nylon) • Chopped Fiber (L=12 mm to 25 mm) reinforcement for thermoset (SMC and BMC) and thermoplastic BMC that are compression molded into parts for Corvette hoods and doors, bumpers, Ford Truck box, and consumer box shapes • Continuous (Mat) Fiber • Many types of weaves for automotive or aerospace applications • Automotive: Viper hood with RTM, GM Truck box with SRIM, Corvette floor pan with RTM • Aerospace: Prepregs, Wings, Fuselages with RTM and SCRIMP
Carbon/Graphite Fibers • Need for reinforcement fibers with strength and modulii higher than those of glass fibers has led to development of carbon • Thomas Edison used carbon fibers as a filament for electric light bulb • High modulus carbon fibers first used in the 1950s • Carbon and graphite are based on layered structures of hexagonal rings of carbon • Graphite fibers are carbon fibers that • Have been heat treated to above 3000°F that causes 3 dimensional ordering of the atoms and • Have carbon contents GREATER than 99% • Have tensile modulus of 344 Gpa (50Mpsi)
Carbon/Graphite Fibers • Need for reinforcement fibers with strength and modulii higher than those of glass fibers has led to development of carbon • Thomas Edison used carbon fibers as a filament for electric light bulb • High modulus carbon fibers first used in the 1950s • Carbon and graphite are based on layered structures of hexagonal rings of carbon • Graphite fibers are carbon fibers that • Have been heat treated to above 3000°F that causes 3 dimensional ordering of the atoms and • Have carbon contents GREATER than 99% • Have tensile modulus of 344 GPa (50Mpsi)
Carbon/Graphite Fibers • Manufacturing Process • Current preferred methods of producing carbon fibers are from polyacrylonitrile (PAN), rayon (regenerated cellulose), and pitch. • PAN • Have good properties with a low cost for the standard modulus carbon • High modulus carbon is higher in cost because high temperatures required • PITCH • Lower in cost than PAN fibers but can not reach properties of PAN • Some Pitch based fibers have ultra high modulus (725 GPa versus 350GPa) but low strength and high cost (Table 3-2)
Carbon/Graphite Fibers • PAN Manufacturing Process Figures 3-3 and 3-4 • Polyacrylonitrile (PAN) is commercially available textile fiber and is a ready made starting material for PAN-based carbon fibers • Stabilized by thermosetting (crosslinking) so that the polymers do not melt in subsequent processing steps. PAN fibers are stretched as well • Carbonize: Fibers are pyrolyzed until transformed into all-carbon • Heated fibers 1800°F yields PAN fibers at 94% carbon and 6% nitrogen • Heated to 2300°F to remove nitrogen yields carbon at 99.7% Carbon • Graphitize: Carried out at temperatures greater than 3200° F to • Improve tensile modulus by improving crystalline structure and three dimensional nature of the structure. • Fibers are surface treated • Sizing agent is applied • Finish is applied • Coupling agent is applied • Fibers are wound up for shipment
Carbon/Graphite Fibers • PITCH Manufacturing Process • Pitch must be converted into a suitable fiber from petroleum tar • Pitch is converted to a fiber by going through a meso-phase where the polymer chains are somewhat oriented though is a liquid state (liquid crystal phase) • Orientation is responsible for the ease of consolidation of pitch into carbon • Stabilized by thermosetting (crosslinking) so that the polymers do not melt in subsequent processing steps • Carbonize: Fibers are pyrolyzed until transformed into all-carbon • Heated fibers 1800°F • Heated to 2300°F • Graphitize: Carried out at temperatures greater than 3200° F to • Improve tensile modulus by improving crystalline structure and three dimensional nature of the structure. • Fibers are surface treated • Sizing agent is applied • Finish is applied • Coupling agent is applied • Fibers are wound up for shipment
Carbon Fiber Mechanical Properties • Table 3-2 (from MFGT 104)
Composites Have a Fiber Preform • Fiber type • Roving form that can be sprayed into a 3-D preform • Roving form that is woven into a glass sheet and then formed to shape (preform)
Sheet Molding Compound (SMC) • SMC is the paste that is compression molded • 33% polyester resin and stryrene, which polymerizes and crosslinks • 33% glass fibers (1” fibers) • 33% Calcium Carbonate
Processing of Composites • Open Mold processes • Vacuum bag, pressure bag, SCRIMP • autoclave: Apply Vacuum Pressure and Heat in an oven which can be 5 feet to 300 feet long
Structural RIM • Fiber preform is placed into mold. • Polyol and Isocyanate liquids are injected into a closed mold and reacted to form a urethane.
Processing of Composites • Open Mold processes • Hand lay-up and Spray-up • Filament winding
Composite Classifications • Resin (or matrix) type • Thermoset resins- those that undergo a chemical cross-linking reaction • Epoxy; Polyester; Polyurethane; Phenolic • Silicone; Melamine • Thermoplastic resins- those that are formed under heat • Polyamines (nylon) (short and long fibers) • Polyesters (short and long fibers) • Polypropylene (short, long fibers and continuous fibers) • Other thermoplastic resins (short and long fibers) • Fiber Reinforcements • Glass for reinforced composites with concentrations less than 50% weight • Carbon fiber for Advanced (aerospace) composites with concentrations greater than 60% by weight. • Kevlar fiber for Advanced (aerospace) composites. • Core or Laminate structures • A foam core material can be added (sandwiched) between the layers of resin and fiber. • Composite laminate has a core material with resin and fiber combinations
Processing and Composites Questions • A composite material is a combination of a reinforcing element and ___________. • How are advanced composites are distinguished from reinforced plastics?_________ • The fibers in advanced composites are usually made from what? ____________ • What two functions does the matrix of a composite serve? ________________ • Under what conditions should graphite fibers versus carbon fibers be used? _______
Chap 15: Ceramics • Ceramic Applications • Ceramic Structures • Glass • Advanced Ceramics • Processing of Ceramics • Review Questions