eng mat chapter 7
TRANSCRIPT
AA
BMM 1523 ENGINEERING MATERIALBMM 1523 ENGINEERING MATERIAL
MUHAMAD MAT NOORMUHAMAD MAT NOOR
JUL 2007JUL 2007
FACULTY OF MECHANICAL ENGINEERINGFACULTY OF MECHANICAL ENGINEERINGUNIVERSITI MALAYSIA PAHANGUNIVERSITI MALAYSIA PAHANG
Group Presentation (A, M05, M06)No. Topics Group When
1 Materials Structure and Bonding 12 Properties of Materials 33 Metal Alloy 104 Ferrous Metals 55 Non-ferrous Metals 66 Polymer : Thermoplastic 97 Polymer : Thermosetting 48 Polymer : Elastomer 89 Ceramics 7
10 Composites 2
W14W14W14W14W14W14W14W14W15W15
Group Presentation (B)No. Topics Group When
1 Materials Structure and Bonding 202 Properties of Materials 113 Metal Alloy 194 Ferrous Metals 125 Non-ferrous Metals 186 Polymer : Thermoplastic 177 Polymer : Thermosetting 148 Polymer : Elastomer 159 Ceramics 16
10 Composites 13
W14W14W14W14W14W14W14W14W15W15
Group Presentation (C) No. Topics Group When
1 Materials Structure and Bonding 2 Properties of Materials 3 Metal Alloy4 Ferrous Metals 5 Non-ferrous Metals 6 Polymer : Thermoplastic7 Polymer : Thermosetting8 Polymer : Elastomer9 Ceramics
10 Composites
28232226212930242725
W14W14W14W14W14W14W14W14W15W15
ENGINEERING MATERIALSENGINEERING MATERIALSBMM1523BMM1523
POLYMERS
CHAPTER 7
Polymeric MaterialsLecture Grp B(M03) – 26Sept
Lecture Grp A(M05) – 26Sept
Polymer
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Polymerization ReactionsPolymerization Reactions Chain Chain
polymerization, also polymerization, also called addition called addition polymerization, with polymerization, with the aid of initiators, the aid of initiators, to form Paraffin or to form Paraffin or Benzene.Benzene.
Step reaction, also Step reaction, also called condensation, called condensation, dissimilar monomers dissimilar monomers joined into short joined into short groups that groups that gradually grow with gradually grow with by-product released.by-product released.
Timeline
Major Polymer ProcessesMajor Polymer Processes Extrusion Extrusion Injection MoldingInjection Molding Blow MoldingBlow Molding ThermoformingThermoforming RecyclingRecycling
Polymer ProcessesPolymer Processes
ExtrusionExtrusion
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Extrusion Product ExamplesExtrusion Product Examples
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Extrusion CharacteristicsExtrusion Characteristics The extrusion machine forms the basis of The extrusion machine forms the basis of
nearly all other polymer processes.nearly all other polymer processes. Basically involves melting polymer pellets Basically involves melting polymer pellets
and extruding them out through a two and extruding them out through a two dimensional die.dimensional die.
Produces long, thin productsProduces long, thin products Coating for electrical wireCoating for electrical wire Fishing LineFishing Line Tubes, etc.Tubes, etc.
Injection MoldingInjection Molding
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Injection Molding Product ExamplesInjection Molding Product Examples
Injection Molding Machine BasicsInjection Molding Machine Basics
Injection Molding Process ControlInjection Molding Process Control Very similar to die Very similar to die
castingcasting Must control heat Must control heat
transfer and fluid flowtransfer and fluid flow Do that by controlling Do that by controlling
temperature and temperature and pressurepressure
Gas Assist Injection MoldingGas Assist Injection Molding
– – Applicable to hollow parts without interior control.Applicable to hollow parts without interior control.
Injection – Compression MoldingInjection – Compression Molding
Injection Molding of ThermosetsInjection Molding of Thermosets Plastics “set” when they coolPlastics “set” when they cool
Mold temperature will be set to allow full cavity fill, while Mold temperature will be set to allow full cavity fill, while increasing production rateincreasing production rate
Thermosets undergo a chemical crosslinking that Thermosets undergo a chemical crosslinking that produces the solid structureproduces the solid structure Mold temperature will be hotter usually – set to allow full Mold temperature will be hotter usually – set to allow full
cavity fill, while accelerating the chemical reaction to cure.cavity fill, while accelerating the chemical reaction to cure. Often called “Reaction Injection Molding” (RIM)Often called “Reaction Injection Molding” (RIM)
Blow Molding Example ProductsBlow Molding Example Products
Blow Molding ProcessesBlow Molding Processes
Injection Blow MoldingInjection Blow MoldingExtrusion Blow MoldingExtrusion Blow Molding
Stretch Blow MoldingStretch Blow Molding
ThermoformingThermoforming
(a) Vacuum, (b) Pressure, (c) Drape-vacuum,(d) Plug-assist, (e) Pressure-bubble plug assist
Thermoforming ProductsThermoforming Products
Polymer RecyclingPolymer Recycling 1998 – Approximately 20% of plastic waste is 1998 – Approximately 20% of plastic waste is
recycled (optimistic estimate)recycled (optimistic estimate) 1998 – Polymers account for approximately 1998 – Polymers account for approximately
18% by volume of material to landfills18% by volume of material to landfills
Needs vs. ChallengesNeeds vs. Challenges
Needs for a viable program:Needs for a viable program: Stable supply of materials with Stable supply of materials with
reliable collection and sortingreliable collection and sorting Economical, proven and Economical, proven and
environmentally sound environmentally sound recycling processrecycling process
End use applications for the End use applications for the recycled materialrecycled material
ChallengesChallenges 10-12 main polymer types10-12 main polymer types Thousands of blendsThousands of blends AdditivesAdditives Impurities in supply (labels, Impurities in supply (labels,
glass, dirt, etc)glass, dirt, etc)
Recycling of PolymersRecycling of Polymers• PET (polyethylene terphthalate) beverage containers, boil-in food pouches, processed meat packages • HDPE (high density polyethylene) milk bottles, detergent bottles, oil bottles, toys, plastic bags • PVC (polyvinyl chloride) food wrap, vegetable oil bottles, blister packaging• LDPE (low density polyethylene) shrink-wrap, plastic bags, garment bags
• PP (polypropylene) margarine and yogurt containers, caps for containers, wrapping to replace cellophane • PS (polystyrene) egg cartons, fast food trays, disposable plastic silverware • Other multi-resin containers
Polymer
• A compound consisting of long‑chain molecules, each molecule made up of repeating units connected together
– There may be thousands, even millions of units in a single polymer molecule
– The word polymer is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part
– Most polymers are based on carbon and are therefore considered organic chemicals
Types of Polymers
• Polymers can be separated into plastics and rubbers
• As engineering materials, it is appropriate to divide them into the following three categories: 1. Thermoplastic polymers2. Thermosetting polymers3. Elastomerswhere (1) and (2) are plastics and (3) are rubbers
Plastics
Plastics are:
● A large and varied group of synthetic materials ● Produced through forming and molding processes ● Classified as either thermoplastic or thermosetting.
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Thermoplastic Polymers - Thermoplastics (TP)
• Solid materials at room temperature but viscous liquids when heated to temperatures of only a few hundred degrees
• This characteristic allows them to be easily and economically shaped into products
• They can be subjected to heating and cooling cycles repeatedly without significant degradation
Thermosetting Polymers - Thermosets (TS)
• Cannot tolerate repeated heating cycles as thermoplastics can– When initially heated, they soften and flow for
molding– But elevated temperatures also produce a chemical
reaction that hardens the material into an infusible solid
– If reheated, thermosets degrade and char rather than soften
Elastomers• Polymers that exhibit extreme elastic extensibility
when subjected to relatively low mechanical stress• Also known as rubber • Some elastomers can be stretched by a factor of 10
and yet completely recover to their original shape• Although their properties are quite different from
thermosets, they share a similar molecular structure that is different from the thermoplastics
Market Shares• Thermoplastics are commercially the most
important of the three types, constituting around 70% of the tonnage of all synthetic polymers produced.
• Thermosets and elastomers share the remaining 30% about evenly, with a slight edge for the former.
• On a volumetric basis, current annual usage of polymers exceeds that of metals.
Polyethylene33%Vinyls16%Polypropylene15%PMMAABSNylonPolycarbonateSaturated PolyesterPEEKPVC
90% of market
Thermoplastics
EpoxyMelamine FormaldehydePhenolicPolyester (unsaturated)PolyimideSiliconeUrea Formaldehyde
10% of market
Thermosets/Elastomers
Polymer Family Tree
Types of PolymersTypes of Polymers
Examples of Polymers• Thermoplastics:
– ABS, Acetals, Acrylics, Cellulosics, Fluorocarbons, Polyamides, Polycarbonates, Polyesters, Polyethylenes, Polypropylenes, Polystyrenes, Polysulfones, Polyurethanes, Polyvinyl Chlorides
• Thermosets: – Alkyds Aminos. Epoxies.Phenolics.
• Elastomers: – Magnetic Rubber. Natural Rubber. Cements. Latex.
Rubberized Fabrics. Vulcanized Rubber.
Range of Mechanical Properties for Various Engineering Plastics
TABLE 7.1
Material UTS (MPa) E (GPa)Elongation
(%)Poisson’sratio ()
ABSABS, reinforcedAcetalAcetal, reinforcedAcrylicCellulosicEpoxyEpoxy, reinforcedFluorocarbonNylonNylon, reinforcedPhenolicPolycarbonatePolycarbonate, reinforcedPolyesterPolyester, reinforcedPolyethylenePolypropylenePolypropylene, reinforcedPolystyrenePolyvinyl chloride
28–55100
55–70135
40–7510–48
35–14070–1400
7–4855–83
70–21028–7055–7011055
110–1607–4020–35
40–10014–837–55
1.4–2.87.5
1.4–3.510
1.4–3.50.4–1.43.5–1721–520.7–2
1.4–2.82–10
2.8–212.5–3
62
8.3–120.1–1.40.7–1.23.5–61.4–4
0.014–4
75–5—
75–25—
50–5100–510–14–2
300–100200–6010–12–0
125–106–4
300–53–1
1000–15500–10
4–260–1
450–40
—0.35—
0.35–0.40————
0.46–0.480.32–0.40
——
0.38—
0.38—
0.46——
0.35—
Reasons Why Polymers are Important:
• Plastics can be formed by molding into intricate part shapes, usually with no further processing required – Very compatible with net shape processing
• On a volumetric basis, polymers:– Cost competitive with metals– Generally require less energy to produce than metals
• Certain plastics are translucent and/or transparent, which makes them competitive with glass in some applications
General Properties of Polymers
• Low density relative to metals and ceramics • Good strength‑to‑weight ratios for certain (but not
all) polymers• High corrosion resistance• Low electrical and thermal conductivity
Limitations of Polymers as Engineering Materials
• Low strength relative to metals and ceramics• Low modulus of elasticity (stiffness)• Service temperatures are limited to only a few hundred
degrees• Viscoelastic properties, which can be a distinct limitation
in load bearing applications • Some polymers degrade when subjected to sunlight and
other forms of radiation
Synthesis of Polymers • Nearly all polymers used in engineering are
synthetic – They are made by chemical processing
• Polymers are synthesized by joining many small molecules together into very large molecules, called macromolecules, that possess a chain‑like structure
• The small units, called monomers, are generally simple unsaturated organic molecules such as ethylene C2H4
Synthesis of polyethylene from ethylene monomers: (1) n ethylene monomers yields (2a) polyethylene of chain length n; (2b) concise notation for depicting the polymer structure of chain length n
Structure of
Polymer Molecules
Figure 7.2 Basic structure of polymer molecules: (a) ethylene molecule; (b) polyethylene, a linear chain of many ethylene molecules; © molecular structure of various polymers. These are examples of the basic building blocks for plastics
Polymerization• As a chemical process, the synthesis of polymers
can occur by either of two methods: 1. Addition polymerization2. Step polymerization
• Production of a given polymer is generally associated with one method or the other
Molecular Weight • The molecular weight (MW) of a polymer is the sum
of the molecular weights of the mers in the molecule; – MW = n times the molecular weight of each repeating
unit – Since n varies for different molecules in a batch, the
molecule weight must be interpreted as an average
Molecular Weight and Degree of Polymerization
Figure 7.3 Effect of molecular weight and degree of polymerization on the strength and viscosity of polymers.
Typical Values of DP and MW for Selected Polymers
PolymerPolyethylenePolyvinylchlorideNylonPolycarbonate
DP(n)10,000 1,500 120 200
MW300,000100,000 15,000 40,000
TutorialWhat are some advantages and disadvantages of the injection-molding process for molding thermoplastics?
Advantages :Potential for creating high quality parts at a high production rate; Low labor costs; good surface finishes; Capability for a highly automated process; Ease of producing intricate shapes.
The primary disadvantages: The large initial investment required to purchase the machine necessitates a large volume of production; The process must be closely controlled to produce a high quality part.
Tutorial1. Define the following terms: chain polymerization, monomer, and
polymer.
Answer : Chain polymerization is the process by which monomers are
chemically combined into long-chain molecular polymers.
A monomer is the simple molecule that is covalently bonded with other monomers toform long molecular chains.
A polymer is the long-chain molecule formed from monomer units.
• Since molecules in a given batch of polymerized material vary in length, n for the batch is an average; its statistical distribution is normal
• The mean value of n is called the degree of polymerization (DP) for the batch
• DP affects properties of the polymer: higher DP increases mechanical strength but also increases viscosity in the fluid state, which makes processing more difficult.
Lecture Grp C(M01) – 27Sept
Lecture Grp B(M03) – 27Sept
Degree of Polymerization
Tutorial
Degree of Polymerization
Degree of Polymerization
Tutorial
Linear, Branched, and Cross-linked Polymers
• Linear structure – chain-like structure – Characteristic of thermoplastic polymers
• Branched structure – chain-like but with side branches – Also found in thermoplastic polymers
• Cross-linked structure– Loosely cross-linked, as in an elastomer– Tightly cross-linked, as in a thermoset
Polymer ChainsFigure 7.4 Schematic illustration of polymer chains. (a) Linear structure--thermoplastics such as acrylics, nylons, polyethylene, and polyvinyl chloride have linear structures. (b) Branched structure, such as in polyethylene. (c) Cross-linked structure--many rubbers or elastomers have this structure, and the vulcanization of rubber produces this structure. (d) Network structure, which is basically highly cross-linked--examples are thermosetting plastics, such as epoxies and phenolics.
• Linear structure of a thermoplastic polymer
Various structures of polymer molecules: (a) linear, characteristic of thermoplastics
• Branched structure that includes side branches along the chain
Various structures of polymer molecules: (b) branched
• Cross-linked polymers, in which primary bonding occurs between branches and other molecules at certain connection points
Various structures of polymer molecules: (c) loosely cross‑linked as in an elastomer
• Tightly cross-linked or network structure - in effect, the entire mass is one gigantic macromolecule
Various structures of polymer molecules: (d) tightly cross‑ linked or networked structure as in a thermoset
• Copolymers – A polymer which has two types of mer in the same molecule. Eg: styrene-butadiene, which is used widely for automobile tires.
• Terpolymers – Contains three types of mer. Eg: ABS (acrylonitrile-butadiene-styrene), which is used for helmets, telephones and refrigerator liners
• Terpolymers- in effect, the entire mass is one gigantic macromolecule
Illustrate the following types of copolymers by using filled and open circles for their mers: (a) random, (b) alternating, (c) block, and (d) graft.
Tutorial
Crystallinity in Polymers• Both amorphous and crystalline structures are
possible, although the tendency to crystallize is much less than for metals or non‑glass ceramics
• Not all polymers can form crystals • For those that can, the degree of crystallinity (the
proportion of crystallized material in the mass) is always less than 100%
CrystallinityFigure 7.6 Amorphous and crystalline regions in a polymer. The crystalline region (crystallite) has an orderly arrangement of molecules. The higher the crystallinity, the harder, stiffer, and less ductile the polymer.
Crystallized regions in a polymer: (a) long molecules forming crystals randomly mixed in with the amorphous material; and (b) folded chain lamella, the typical form of a crystallized region
Crystallinity and Properties• As crystallinity is increased in a polymer:
– Density increases– Stiffness, strength, and toughness increases– Heat resistance increases – If the polymer is transparent in the amorphous state, it
becomes opaque when partially crystallized
Low Density vs. High Density Polyethylene
Polyethylene type Low density High density
Degree of crystallinity 55% 92%
Specific gravity 0.92 0.96
Modulus of elasticity 140 MPa(20,000 lb/in2)
700 MPa(100,000 lb/in2)
Melting temperature 115C (239F)
135C (275F)
General Properties of Polymers
• Low density relative to metals and ceramics • Good strength‑to‑weight ratios for certain (but not
all) polymers• High corrosion resistance• Low electrical and thermal conductivity
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Limitations of Polymers as Engineering Materials
• Low strength relative to metals and ceramics• Low modulus of elasticity (stiffness)• Service temperatures are limited to only a few
hundred degrees• Viscoelastic properties, which can be a distinct
limitation in load bearing applications • Some polymers degrade when subjected to sunlight
and other forms of radiationN
Thermoplastic Polymers (TP)• A thermoplastic polymer can be heated from a solid
state to a viscous liquid state and then cooled back down to solid– This heating and cooling cycle can be repeated
multiple times without degrading the polymer • The reason is that TP polymers consist of linear
(and/or branched) macromolecules that do not cross‑link upon heating
• By contrast, thermosets and elastomers change chemically when heated, which cross‑links their molecules and permanently sets these polymers
General Properties and Characteristics of Thermosets
• Rigid - modulus of elasticity is two to three times greater than TP
• Brittle, virtually no ductility• Less soluble than TP in common solvents• Capable of higher service temperatures than TP • Cannot be remelted ‑ instead they degrade or burn
Elastomers• Polymers capable of large elastic deformation
when subjected to relatively low stresses • Some can be extended 500% or more and still
return to their original shape • Two categories:
1. Natural rubber - derived from biological plants 2. Synthetic polymers - produced by polymerization
processes similar to those used for thermoplastic and thermosetting polymers
• Model of long elastomer molecules, with low degree of cross‑linking: (a) unstretched, and (b) under tensile stress
Vulcanization• Curing to cross‑link most elastomers• Vulcanization = the term for curing in the context of
natural rubber (and certain synthetic rubbers)• Typical cross‑linking in rubber is one to ten links per
hundred carbon atoms in the linear polymer chain, depending on degree of stiffness desired – Considerable less than cross‑linking in thermosets
• Increase in stiffness as a function of strain for three grades of rubber: natural rubber, vulcanized rubber, and hard rubber
Natural Rubber (NR)
• NR consists primarily of polyisoprene, a high molecular‑weight polymer of isoprene (C5H8)
• It is derived from latex, a milky substance produced by various plants, most important of which is the rubber tree that grows in tropical climates
• Latex is a water emulsion of polyisoprene (about 1/3 by weight), plus various other ingredients
• Rubber is extracted from latex by various methods that remove the water
• Properties: Good resistance to abrasion and fatigue, high frictional properties, but has low resistance to oil, heat, ozone and sunlight.
Natural Rubber Products• Largest single market for NR is automotive tires• Other products: shoe soles, bushings, seals, and shock
absorbing components• In tires, carbon black is an important additive; it
reinforces the rubber, serving to increase tensile strength and resistance to tear and abrasion
• Other additives: clay, kaolin, silica, talc, and calcium carbonate, as well as chemicals that accelerate and promote vulcanization
Synthetic Rubbers• Today, the tonnage of synthetic rubbers is more
than three times that of NR• Development of synthetic rubbers was
motivated largely by world wars when NR was difficult to obtain
• The most important synthetic is styrene‑butadiene rubber (SBR), a copolymer of butadiene (C4H6) and styrene (C8H8)
• As with most other polymers, the main raw material for synthetic rubbers is petroleum
Thermoplastic Elastomers (TPE)• A thermoplastic that behaves like an elastomer • Elastomeric properties not from chemical
cross‑links, but from physical connections between soft and hard phases in material
• Cannot match conventional elastomers in elevated temperature strength and creep resistance
• Products: footwear; rubber bands; extruded tubing, wire coating; molded automotive parts, but no tires
Mechanical Properties of Thermoplastics
• Low modulus of elasticity (stiffness)– E is two or three orders of magnitude lower than
metals and ceramics• Low tensile strength
– TS is about 10% of the metal• Much lower hardness than metals or ceramics • Greater ductility on average
– Tremendous range of values, from 1% elongation for polystyrene to 500% or more for polypropylene
Thermoplastics Products
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Thermosets
• THERMOSETS are distinguished by their highly cross‑linked three‑dimensional, covalently‑bonded structure within the molecule
• Chemical reactions associated with cross‑linking are called curing or setting
• In effect, the formed part (e.g., pot handle, electrical switch cover, etc.) becomes one large macromolecule
• Always amorphous and exhibits no glass transition temperature
Mechanical Properties of Thermosets
• Rigid - modulus of elasticity is two to three times greater than thermoplastics
• Brittle, virtually no ductility• Less soluble than thermoplastics in common solvents• Capable of higher service temperatures than
thermoplastics • Strength and hardness not effected by temperature or
rate deformation. If temperature raise sufficiently, it will burn up, degrade.
Thermosets Applications• Thermoset products include countertops, plywood
adhesives, paints, molded parts, printed circuit boards and other fiber reinforced plastics.
Tutorial1. What are some of the advantages of plastics for use in
mechanical engineering designs?
Answer : The incorporation of plastics in engineering designs often allows for the elimination of many parts and finishing operations, the reduction of weight and noise, and the simplification of assembly processes. In some cases, plastics eliminate the need for
lubrication of parts.
Tutorial1. What are some of the advantages of plastics for use in electrical
engineering designs?
Answer : Plastics are used extensively in electrical designs primarily because of their outstanding insulating properties and low cost. However, their low density and facilitation of
assembly processes are also important to electronic applications.
2. What are some of the advantages of plastics for use in chemical engineering designs?
Answer : Chemical engineering designs take advantage of the corrosion resistant and thermal
insulating properties of plastics.
Biodegradable Plastics●Most plastics are renewable, not biodegradable and difficult to recycle. ●Biodegradability means the microbial species in the environment will degrade a portion or entire polymeric material, under the right environmental conditions and without producing toxic. ●The end products of the degradation of the material are carbide and water. There are 3 different biodegradable plastics:
1. Starch based, extracted from potatoes, wheat, rice, corn 2. Lactic based, fermenting feed stocks produce lactic acid, the polymerize to form polyester resin.3. Fermentation of sugar. Organics acids are added to sugar feed stock. Resultant of highly crystalline and very stiff polymer.
Biodegradable Plastic Bag
www.aichi-inst.jp/ ~mikawa/biodegrade/
Before buried in sand After buried in sand
www.biotech.wisc.edu/.../ Poster/feedstocks.html N
TutorialWhat are some of the advantages of thermosetting plastics for engineering design applications? What is the major disadvantage of thermosets that thermoplastics do not have?
Answer :General advantages of thermosetting plastics include one or more of the following: high thermal stability; high rigidity; high dimensional stability; resistance to creep and deformation under load; light weight; and high electrical and thermal insulating properties.
TutorialWhat are some of the advantages of epoxy thermoset resins? What are some of their applications?
Answer :Advantageous properties of epoxy resins include: good chemical and environmental resistance, good mechanical properties, good electrical insulating properties, low cure shrinkage, strong adhesive properties and exceptional wetting characteristics.
This set of attributes makes epoxies a natural choice for a wide variety of protective and decorative coatings, adhesives, fiber-reinforced matrix materials, electrical potting and encapsulating applications.
TutorialWhat are elastomers? What are some elastomeric materials?
Answer : Elastomers (rubbers) are polymeric materials whose dimensions can be significantly altered under stress yet return to nearly or exactly their original dimensions once the stress is removed.
Examples of elastomeric materials include natural rubber, syntheticpolyisoprene, styrene-butadiene rubber, nitrile rubbers, polychloroprene, and the silicones.
TutorialWhat is natural rubber latex?Briefly describe how natural rubber is produced in the bulk form?
Answer : Natural rubber latex is a milky liquid, collected from trees and diluted to approximately 15 percent rubber content.
This mixture is coagulated with formic acid, and the material is then compressed into sheets by rollers and dried.
Subsequently, milling between heavy rolls is performed to break up some of the long polymer chains and thus reduce their average molecular weight.
Tutorial1. How does the average molecular mass of a thermoplastic affect
its strength?2. How does the amount of crystallinity within a thermoplastic
material affect (a) its strength, (b) its tensile modulus of elasticity, and (c) its density?
3. Explain why low-density polyethylene is weaker than high-density polyethylene.
4. Explain why thermosetting plastics have in general high strengths and low ductilities.
Also pls do some DP and MW calculation. Do remember some g/molExample H=1g/molC=12, N=14, O=16
Tutorial (Answer)1. How does the average molecular mass of a thermoplastic affect its strength?The average molecular mass of a thermoplastic directly affects its strength as it is indicative of the degree of polymerization of the solid; the
plastic must attain a critical molecular mass to become a stable solid. However, increasing the mass beyond this minima does not appreciably increase the thermoplastic.s strength.
2. How does the amount of crystallinity within a thermoplastic material affect (a) its strength, (b) its tensile modulus of elasticity, and (c) its density?
(a) As the amount of crystallinity increases, the polymer chains become more tightly packed and the tensile strength increases.(b) The tensile modulus of elasticity is also directly related to crystallinity; the modulus increases with increasing crystallinity.(c) Increased crystallinity corresponds to an increase in density.
2. Explain why low-density polyethylene is weaker than high-density polyethylene.Low-density polyethylene is weaker than high-density because the molecular chains aremore branched and farther apart from each other, causing weaker bonding forces and thuslower strength.
2. Explain why thermosetting plastics have in general high strengths and low ductilities.In general, thermosetting plastics have high strengths and low ductilities because their molecular structure is comprised of a covalently
bonded network produced by chemical reaction within the material after casting or during pressing under heat and pressure.
Also pls do some DP and MW calculation. Do remember some g/molExample H=1g/molC=12, N=14, O=16
Thank You
Thank You
Extra Note for Polymer
Polymer and Polymer ProcessingPolymer and Polymer Processing
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Polymer, Resin, and PlasticsPolymer, Resin, and Plastics A A polymerpolymer is any substance made up of many of is any substance made up of many of
repeating units, building blocks, called repeating units, building blocks, called mersmers.. When in form ready for further working, they are When in form ready for further working, they are
called called resinsresins.. Polymers are seldom used in their neat form, most Polymers are seldom used in their neat form, most
often compounded with various additives. The often compounded with various additives. The resulting material is usually referred to as a plastic.resulting material is usually referred to as a plastic.
Frequently, polymers, resins, plastics are used Frequently, polymers, resins, plastics are used interchangeably.interchangeably.
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Properties and ApplicationsProperties and Applications Low density, high corrosion resistance, Low density, high corrosion resistance,
electrical insulation.electrical insulation. Ease of manufacturing into complex shapes.Ease of manufacturing into complex shapes. Widely used for consumer products.Widely used for consumer products. Emerging as structural polymers (T<150-Emerging as structural polymers (T<150-
250C).250C). Sales of plastics, on a volume basis, has grown Sales of plastics, on a volume basis, has grown
more than double the steel production in the more than double the steel production in the U.S. U.S.
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Polymerization ReactionsPolymerization Reactions Chain Chain
polymerization, also polymerization, also called addition called addition polymerization, with polymerization, with the aid of initiators, the aid of initiators, to form Paraffin or to form Paraffin or Benzene.Benzene.
Step reaction, also Step reaction, also called condensation, called condensation, dissimilar monomers dissimilar monomers joined into short joined into short groups that groups that gradually grow with gradually grow with by-product released.by-product released.
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Polyethylene33%Vinyls16%Polypropylene15%PMMAABSNylonPolycarbonateSaturated PolyesterPEEKPolyurethaneSome are thermosets as well.PVC
Not Cross-Linked90% of market
ThermoplasticsWill reform when melted
EpoxyMelamine FormaldehydePhenolicPolyester (unsaturated)PolyimidePolyurethaneSome are thermoplastic as well.SiliconeUrea Formaldehyde
Cross-linked10% of market
Thermosets/ElastomersWill not reform
Polymer Family Tree
Types of PolymersTypes of Polymers
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Basic ConceptsBasic Concepts Molecular weight (MW)Molecular weight (MW) Degree of polymerization (DP)Degree of polymerization (DP) Chain structuresChain structures Crystalline and amorphous polymersCrystalline and amorphous polymers Glass transition temperature (Tg) and melting Glass transition temperature (Tg) and melting
temperature (Tm)temperature (Tm) Mechanical properties Mechanical properties
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Source of Strength of PolymersSource of Strength of Polymers Primary Bond - Covalent Primary Bond - Covalent
BondingBonding Secondary Bonds –Secondary Bonds –
van der Waalsvan der Waals Dipole BondsDipole Bonds Hydrogen BondsHydrogen Bonds PE - mer
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Major Polymer ProcessesMajor Polymer Processes
Extrusion Extrusion Injection MoldingInjection Molding Blow MoldingBlow Molding ThermoformingThermoforming
RecyclingRecycling
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Polymer ProcessesPolymer Processes
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ExtrusionExtrusion
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Extrusion Product ExamplesExtrusion Product Examples
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Extrusion CharacteristicsExtrusion Characteristics The extrusion machine forms the basis of The extrusion machine forms the basis of
nearly all other polymer processes.nearly all other polymer processes. Basically involves melting polymer pellets Basically involves melting polymer pellets
and extruding them out through a two and extruding them out through a two dimensional die.dimensional die.
Produces long, thin productsProduces long, thin products Coating for electrical wireCoating for electrical wire Fishing LineFishing Line Tubes, etc.Tubes, etc.
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Injection Molding (See Video)Injection Molding (See Video)
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Injection Molding Product ExamplesInjection Molding Product Examples
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Injection Molding Machine BasicsInjection Molding Machine Basics
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Injection Molding Process ControlInjection Molding Process Control Very similar to die Very similar to die
castingcasting Must control heat Must control heat
transfer and fluid flowtransfer and fluid flow Do that by controlling Do that by controlling
temperature and temperature and pressurepressure
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Gas Assist Injection MoldingGas Assist Injection Molding
– – Applicable to hollow parts without interior control.Applicable to hollow parts without interior control.
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Injection – Compression MoldingInjection – Compression Molding
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Injection Molding of ThermosetsInjection Molding of Thermosets Plastics “set” when they coolPlastics “set” when they cool
Mold temperature will be set to allow full cavity fill, while Mold temperature will be set to allow full cavity fill, while increasing production rateincreasing production rate
Thermosets undergo a chemical crosslinking that Thermosets undergo a chemical crosslinking that produces the solid structureproduces the solid structure Mold temperature will be hotter usually – set to allow full Mold temperature will be hotter usually – set to allow full
cavity fill, while accelerating the chemical reaction to cure.cavity fill, while accelerating the chemical reaction to cure. Often called “Reaction Injection Molding” (RIM)Often called “Reaction Injection Molding” (RIM)
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Blow Molding Example ProductsBlow Molding Example Products
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Blow Molding Processes (See Video)Blow Molding Processes (See Video)
Injection Blow MoldingInjection Blow MoldingExtrusion Blow MoldingExtrusion Blow Molding
Stretch Blow MoldingStretch Blow Molding
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ThermoformingThermoforming
(a) Vacuum, (b) Pressure, (c) Drape-vacuum,(d) Plug-assist, (e) Pressure-bubble plug assist
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Thermoforming ProductsThermoforming Products
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Polymer RecyclingPolymer Recycling 1998 – Approximately 20% of plastic waste is 1998 – Approximately 20% of plastic waste is
recycled (optimistic estimate)recycled (optimistic estimate) 1998 – Polymers account for approximately 1998 – Polymers account for approximately
18% by volume of material to landfills18% by volume of material to landfills
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Needs vs. ChallengesNeeds vs. Challenges
Needs for a viable program:Needs for a viable program: Stable supply of materials with Stable supply of materials with
reliable collection and sortingreliable collection and sorting Economical, proven and Economical, proven and
environmentally sound environmentally sound recycling processrecycling process
End use applications for the End use applications for the recycled materialrecycled material
ChallengesChallenges 10-12 main polymer types10-12 main polymer types Thousands of blendsThousands of blends AdditivesAdditives Impurities in supply (labels, Impurities in supply (labels,
glass, dirt, etc)glass, dirt, etc)
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Recycling of PolymersRecycling of Polymers• PET (polyethylene terphthalate) beverage containers, boil-in food pouches, processed meat packages • HDPE (high density polyethylene) milk bottles, detergent bottles, oil bottles, toys, plastic bags • PVC (polyvinyl chloride) food wrap, vegetable oil bottles, blister packaging• LDPE (low density polyethylene) shrink-wrap, plastic bags, garment bags
• PP (polypropylene) margarine and yogurt containers, caps for containers, wrapping to replace cellophane • PS (polystyrene) egg cartons, fast food trays, disposable plastic silverware • Other multi-resin containers
Processing of Polymer CompositesProcessing of Polymer Composites
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What are Composites• Composites are often classified
by the type of matrix: polymer, metal or ceramic
• In addition, composites my be classified by the type of embedded material (a.k.a., reinforcement) fiber, particle, whisker, flake, etc.
• Rule of mixtures says that each constituent contributes to the properties of the composite in proportion to its volume fractionmfc ff )1(
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Fibers dominate composite properties
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Components of Polymer CompositesComponents of Polymer Composites Polymer ResinPolymer Resin
Usually a thermosetUsually a thermoset EpoxyEpoxy BismaleimideBismaleimide PolyimidePolyimide
Thermoplastics Thermoplastics PolyesterPolyester VinylesterVinylester
Reinforcing fiberReinforcing fiber FiberglassFiberglass Graphite (Carbon)Graphite (Carbon)
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Fabrication of Composites (See Video)Fabrication of Composites (See Video) Fabrication of polymer-matrix compositesFabrication of polymer-matrix composites
Open-mold processesOpen-mold processes PultrusionPultrusion Closed-mold processes (Matched-die molding)Closed-mold processes (Matched-die molding)
Metal-matrix compositesMetal-matrix composites Ceramic-matrix compositesCeramic-matrix composites
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Open-Mold ProcessesOpen-Mold Processes Shaping:Shaping:
Male or female moldMale or female mold Hand lay-upHand lay-up Spry moldingSpry molding Tape layingTape laying Filament windingFilament winding
Curing:Curing: Open airOpen air Vacuum bagVacuum bag High pressure bagHigh pressure bag Heated pressure vesselHeated pressure vessel
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Filament WindingFilament Winding Control the orientation Control the orientation
of the fiber using a of the fiber using a relative motion of relative motion of rotation and linear rotation and linear motionmotion
Example Products:Example Products: Pressure VesselsPressure Vessels Fishing PolesFishing Poles Light PolesLight Poles
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PultrusionPultrusion Fibers or cloth are Fibers or cloth are
pulled through a resin pulled through a resin bathbath
Heated in a die with a Heated in a die with a shaped profileshaped profile
Cured to shapeCured to shape Cut to lengthCut to length
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Closed MoldingClosed Molding Can be done using Pre-Can be done using Pre-
preg or wet layuppreg or wet layup Process:Process:
Resin impregnated fibers Resin impregnated fibers cut to proper geometrycut to proper geometry
Heated Die sets close on Heated Die sets close on partpart
Part is cured at Part is cured at temperaturetemperature
Die opens and part is Die opens and part is ejected from moldejected from mold
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Vent Injection Port
Gasket
IndexReceptacle
IndexPin
Resin Transfer Molding (RTM)Resin Transfer Molding (RTM)
Male mold half
Female Mold Half
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The Resin Transfer Molding Process:
• Fiber reinforcement is placed in the mold • The mold is closed and clamped
• Resin is injected into the mold cavity under pressure
• The resin cures
• The part is removed from the mold
PressurizedResin
Air Air
The RTM ProcessThe RTM Process
Steps of RTM ProcessSteps of RTM Process
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Open vs. Closed MoldingOpen vs. Closed Molding Open MoldingOpen Molding
Only one sided moldOnly one sided mold Limited temperature Limited temperature
controlcontrol Lower capital cost for Lower capital cost for
moldsmolds
Closed molding – or Closed molding – or compression moldingcompression molding Two sided mold – part is Two sided mold – part is
sandwiched between two sandwiched between two mold halvesmold halves
Pressure appliedPressure applied Improved material Improved material
properties (fewer voids)properties (fewer voids) Higher Capital costHigher Capital cost
Definition
• Plastic is broadly defined as– Any inherently formless material that can be molded
or modeled under heat or pressure
As early as…
• Go back as far as the Old Testament– References of:
• Fillers• Adhesives• Coatings
Good Ol’ Enoch Noyes
• 1760• Opened business with the use of natural polymers• Made combs out of organic proteins (Keratin and
Albuminiod) derived from animal horns, hoofs, an tortoise shells
In the beginning…
• Greek word plastikos• First natural plastics
– Tortoise shell– Tree resins– Shellac
• Insect secretion
Natural Rubber
• Natural rubber: mainly polyisopropene
• Tends to be sticky when hot, brittle when warm
• Does not reform when stretched
isoprenen
polyisoprene
Natural RubberNatural Rubber Natural rubber: mainly Natural rubber: mainly
polyisopropenepolyisopropene
Tends to be sticky when Tends to be sticky when hot, brittle when warmhot, brittle when warm
Does not reform when Does not reform when stretchedstretched
isoprenen
polyisoprene SS
SS
SS
Sulfur crosslinking
Charles Goodyear, 1839Oven cleaning
Ebonite bracelet from 1880Ebonite bracelet from 1880
1851: Hard Rubber— 20-30% Sulfur
Christian Schoenbine• Swiss Chemist• 1840’s• Developed Cellulose nitrate
– Mix of cotton (wife’s apron), nitric acid, and sulfuric acid
Early FilmsHighly flammable and explosive
Parkes Invents Celluloid
• The first man-made plastic was unveiled by Alexander Parkes at the 1862 Great International Exhibition in London. – Parkesine- organic material derived from cellulose that
could be molded in heat and retain its shaped when cooled• Buttons• Combs• Pens
Alexander Parkes- 1855
• Rights sold to Daniel Spill (1865)– Patented
• Downfall- high cost of the raw materials needed in its production.
John Wesley Hyatt
• Billiard Co. in U.S.– Needed substitute for ivory in making balls
• John Wesley Hyatt developed collodion– Upon spilling a bottle of collodion in his workshop, he
discovered that the material congealed into a tough, flexible film
– Camphor and cellulose nitrate– Occasional Explosion upon impact
Formed the American Celluloid Company
which is today the Plastics Division of the
Celanese Corporation
H3C
H2CCH3
O
Bakelite
• Dr. Leo Baekeland– First totally synthetic plastic (1907)– Didn’t throw away his foul glassware
• Patented in 1909• Thermoset resin• Replaced rubber for insulation in
electrics
Bakelite
OHOH OH +
: O: OH OH :OHH+
OH OH2
+
OOHOHOH
OHOH
HO
HO OH
OH
OH
Bakelite
• Phenol-formaldehyde resins which he called Bakelite.
Polyvinyl Chloride (PVC)
• PVC was first created by the German chemist Eugen Baumann in 1872.
• Patented in 1913 • Waldo L. Semon, invented a
way to make polyvinyl chloride (PVC) useful
Polyvinyl Chloride (PVC)
Cl Cl Cl Cl Cl Cl Cl
R
Cl
ClR
Cl Cl
sunlight
Baumann's 1872 experiment
sealed tube
•R
• •
Applications of PVC
Applications of PVC
O
O
O
O
plasticizers
Polymerization
• In 1920, German Hermann Staudinger published theories on polyaddition
• Nine year later published the polymerization of polystyrene.
Ph Ph Ph Ph Ph
1%
+ Ph PhPh
Polystyrene• Dow Chemical brought
polystyrene to the U.S. in 1937
Toy shark, in Polystyrene, with moving jaw, Made in USA around 1950
Merrifield resinsMerrifield resins
StyrofoamStyrofoam Foam egg cartons, burger containers, coffee cups , Foam egg cartons, burger containers, coffee cups ,
"peanuts" used in packing and the lightweight foam "peanuts" used in packing and the lightweight foam pieces that cushion new appliances and electronics. pieces that cushion new appliances and electronics.
Gas is blown in during the polymerization-- 95 % of Gas is blown in during the polymerization-- 95 % of styrofoam is air (try dissolving in acetone)styrofoam is air (try dissolving in acetone)
CFC’s were used until the 80’s: phased out and CFC’s were used until the 80’s: phased out and replaced with pentane or CO2replaced with pentane or CO2
Polystyrene up close
Dr. Wallace H. Carothers
• 1930’s research on polymer chains at DuPont Chemical Department
• Invented Neoprene and Nylon
Nylons• Condensates of aliphatic diacids with aliphatic
diamines • Introduced in the 1939 Worlds Fair• “Nylonmania” interrupted during WWII, but
resumed after the war (the infamous Nylon riots of 1946)
O
OHO
HO H2NNH2
O
NH
O
HN
HN
NH
O
Oetc. . .
+
- H2O
Nylon 66Nylon 66co-crystalline
Fibers are spun (showerhead)
Neoprene: The first Synthetic Rubber
Cl
R•Cl
R
•
Cl
Cl
R
Cl •
etc
benzoyl peroxideinititates free radicalpolymerization
Synthetic Rubbers
Gasoline pump hoses,Hoses for automobile engines
Styrene/Butadiene copolymer (SBR) is the most important synthetic rubber, and was the first and most widely produced rubber of WWII
Plexiglass: anionic polymerization
Me CO2Me
Polymethylmethacrylate:
cat Nu –
Me
CO2Me
Nu
Me CO2Me
Me CO2Me
MeO2C Me
Windshields, plastic coatings, hard and soft contact lenses
Ok, but how can I make a leisure suit
• Polyesters
O
OMe
MeO
O OH
HO
O
O
O
OO O
OO OO O
O
Dacron
Teflon
• Teflon– Polytetrafluoroethylene
(PTFE)– Dupont Chemical
Department– First used for artillery shell
coversF F
F F
World War II• Polyethylene (1933)
– Imperial Chemical Industries in England– E.W. Fawcett & R.O. Gibson– First used for underwater cable coatings and insulation
for radar
High density polyethyleneZiegler-Natta catalysts
Low density polyethylene1939
Polyethylene
• 1943 Karl Ziegler changed polymerization of polyethylene– Use of catalysts
• Now is most widely produced and perhaps most versatile plastic
Polypropylene
• Guilio Natta continued Ziegler’s work• Created polypropylene in 1957• Substituted for polyethylene where high temperatures
were involved– Ex. Dishwasher safe dishes
Car’s front bumper made of polypropylene in 1978
Stereochemistry and Polymer Properties
isotactic
syndiotactic
atactic
Isotactic: fabrics for carpets, automobile parts, battery casings, medicine bottlesSyndiotactic: new applications are emergingAtactic: soft, and not very useful
Relevant Additional Links
• History of Plastic and Leo Bakeland– inventors.about.com/library/inventors/blplastic.htm
• History of Plastics– www.lle.mdx.ac.uk/site/docs/dt/Historyofplastics.html
• About Plastics– www.americanplasticscouncil.org/benefits/about_plasti
cs/history.html
Thank You