Eng Mat Chapter 7

AA

BMM 1523 ENGINEERING MATERIALBMM 1523 ENGINEERING MATERIAL

MUHAMAD MAT NOORMUHAMAD MAT NOOR

[email protected]

JUL 2007JUL 2007

FACULTY OF MECHANICAL ENGINEERINGFACULTY OF MECHANICAL ENGINEERINGUNIVERSITI MALAYSIA PAHANGUNIVERSITI MALAYSIA PAHANG

mailto:[email protected]

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

ME 355 W. Li

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

ME 355ME 355 W. LiW. Li

Extrusion Product ExamplesExtrusion Product Examples


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


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.

N

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



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

N

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

N

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


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.


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.


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.


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


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


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


Major Polymer ProcessesMajor Polymer Processes

Extrusion Extrusion Injection MoldingInjection Molding Blow MoldingBlow Molding ThermoformingThermoforming

RecyclingRecycling


Polymer ProcessesPolymer Processes


ExtrusionExtrusion


Extrusion Product ExamplesExtrusion Product Examples


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 Molding (See Video)Injection Molding (See Video)


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 Processes (See Video)Blow Molding Processes (See Video)

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

Processing of Polymer CompositesProcessing of Polymer Composites


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(


Fibers dominate composite properties


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)


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


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


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


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


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


Vent Injection Port

Gasket

IndexReceptacle

IndexPin

Resin Transfer Molding (RTM)Resin Transfer Molding (RTM)

Male mold half

Female Mold Half


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


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

http://inventors.about.com/library/inventors/blplastic.htm

http://www.lle.mdx.ac.uk/site/docs/dt/Historyofplastics.html

http://www.americanplasticscouncil.org/benefits/about_plastics/history.html

http://www.americanplasticscouncil.org/benefits/about_plastics/history.html

Thank You

Documents

Eng Mat Chapter 7