mseasuslides: muddiest points: polymers i - introduction
TRANSCRIPT
Muddiest Points
Muddiest Points:• “I don’t get the difference between a monomer, a
mer, and a polymer?”• “How do I calculate degree of polymerization?”• “How does degree of polymerization affect polymer
properties?”• “I don’t get polymer microstructures and how they
affect properties?”• “I don’t get the different techniques for processing
polymers.”
Polymers I: Introduction to Polymers
What is a Polymer?
Poly merMany Units
repeatunit
repeatunit
repeatunit
What is a Polymer?Definition:
PE Milk Container PVC Pipe PP Rope
•C-C rotations along the chain give the polymer molecule a loosely-coiled, string-like shape
Polymer Chain Geometry
CarbonHydrogen
What are Important Polymer Concepts & Terminology?Monomers, Mers, Polymers, and Degree of PolymerizationDegree of Polymerization:
Concept and Definition
• Monomer - small, unreacted single molecule for polymer.
Ethylene Monomer:
• Mer – single repeat unit of a polymer
Polyethylene Mer:2 C-C chain bonds / mer
• Polymer – entire polymer chain
Polyethylene Molecule: n mers / chain molecule
n = degree of polymerization (DP) = n mers / chain molecule n= DP =
n = DP =
• n is typically 100 10,000 but may go higher than 100,000
number of mer units polymer molecule
molecular weight of polymer molecule molecular weight of mer
Hydrogen
Carbon
Ethylene Monomers
Candle (Paraffin)
Container (HDPE)
n (DP) 10 10,000
MW Chain (g/mol)
(28 g/mol )(10) =280 g/mol
(28 g/mol)(10000) = 280,000 g/mol
Tm (°C)
MW of Molecule = n * MW Mer
2.Why does the Tm increase with more C atoms in chain?
1. What are the similarities and differences of candles and plastic milk containers?
How Degree of Polymerization Affects Properties: Melting Point
n= Degree of Polymerization (DP) Molecular Weight= MW
Tem
pera
ture
(°C)
Number of carbons= 2n = 2* DP
What are the Four Different Types of Polymer Structure and Morphology?
• Polymer – a long chain molecule of 1-D covalently bonded repeat units or a network of 3-D covalently bonded repeat units
• Length of molecule varies from 1,000s to 100,000s of atoms long.
• Four main classes of polymer solids we will consider are:
–Thermoplastic AMORPHOUS polymers are 1-D covalently-bonded chains. They are randomly-oriented and form a glassy solid. When heated, they melt; when cooled, they solidify; and they can be remelted (melt recyclable).
- Thermoplastic SEMICRYSTALLINE polymers also have 1-D covalently-bonded chains. They form layers of thin, chain-folded crystalline lamellae separated by amorphous regions and are connected with tie molecules. When heated, they melt. When cooled, they solidify and can be remelted (melt recyclable).
– Heat Set ELASTOMERS are 3-D LIGHTLY to MODERATELY crosslinked networks of long chain molecules that are covalently crosslinked during a curing chemical reaction. After the cure, the 3-D network maintains its structural integrity when heated (not melt recyclable).
–Heat Set THERMOSETS are 3-D HIGHLY crosslinked networks of covalently-bonded molecules. The thermoset reaction forms a rigid amorphous solid with very good thermal resistance (not melt recyclable).
PS Glass
PE Trash Bag
Rubber Shoe Sole
Bakelite Billiard Balls
How can Polymers be Classified?
What is the Effect of Structure & Morphology on Mechanical Properties?
Polymer E (MPa)
TS (MPa) %EL
Natural Rubber 2.5 20 600-
1000%
HDPE 830 28 300-600%
Polystyrene 3100 40 1.2-2.5%
Bakelite 6900 55 0.1%
A
B
CPS Glass PE Trash Bag
Rubber Shoe SoleD
Bakelite Billiard Balls
Morphology and Thermal & Mechanical Properties
Lightly X-linkedElastomer
Heavily X-linkedThermoset
Semicrystalline Polymer
Amorphous Polymer
Thermoplastic Polymers Heat Set Polymers
Tg = 100CT25 < TgGlassy
Tg = -103CTg < T25
Elastic
Tg = -90C; Tm = 130CTg < T25 < Tm
Flexible
Tg = 163CT25 < Tg
Rigid
Tg = Glass Transition Temperature, below which a polymer is rigid and brittle
PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls
1010
What is the Effect of Structure on Processing of Plastics?
• Thermoplastics – Amorphous & Semicrystalline• Processing can be continuous – only cooling required• Heat to melt, shape & cool below Tg or Tm• Can be reversibly melted and solidfied, i.e. recyclable• Ex: PE, PP, PS.
• Heat Sets – Thermosets and Elastomers– Processing not continuous – one part at a time– Heating & crosslink reaction require time in fixed shape mold– Permanent 3-D crosslinked network – not recyclable– Shape is permanent – does not change with heat; will only degrade
– Elastomer + crosslink agent (S, O) mixed, shaped, reacted– Ex. polybutadiene, polyisoprene– Thermoset prepolymer pressed into a shape & reacted – Ex: Bakelite, urethane, epoxy
For additional information on polymer processing terminology go to: GOOGLE “matsciasu” and get Quizlet.com vocabulary e-flash cards for 6.2 Polymers II – Processing
PS Glass
PE Trash Bag
Rubber Shoe Sole
Bakelite Billiard Balls
Processing for Thermoplastic and Crosslinked Polymers
PS Glass PE Trash Bag
Rubber Shoe Sole
Bakelite Billiard Balls
ThermoplasticAmorphous
ThermoplasticSemicrystalline
Heat SetElastomers
Heat SetThermosets
Processing: Film Blowing
Processing: Injection Molding
Processing: Transfer Molding
Processing: Compression Molding
Effect of Molecular Weight and Bonding on Properties
Metals Ceramics Polymers
0.2
8
0.6
1
Wood( grain)
AFRE( fibers)
CFRE*GFRE*
Glass fibers only
Carbon fibers only
A ramid fibers only
Epoxy only
0.4
0.8
2
46
10
20
406080
100
200
600800
10001200
400
C FRE( fibers)
G FRE( fibers)*
G FRE(|| fibers)*
A FRE(|| fibers)*
C FRE(|| fibers)*
Why is elastic modulus of polymers two orders of magnitude less than metals or ceramics?
How do Polymer Properties Compare to Metals and Ceramics?
Property Polymer Metal Ceramic
E (GPa) 0.2-4 40-400 10-1200
Tensile Strength (Mpa)
26-60(Fibers~700)
200-3400 70-140
Ductility (% elongation)
2-500 1-8 1<
Tm (°C) 100-250 200-2800 500-4000
Coefficient of Thermal
Expansion(m/m-K)
15 x10-6 -100 x10-6
5x10-6 -12x10-6
1x10-6 -5x10-6
E (G
Pa)
Wrap-Up
• “What is a polymer?”
• “I don’t get the difference between a mer and a monomer.”
• “How do I calculate degree of polymerization?”
• “How does degree of polymerization affect polymer properties?”
• “I don’t get polymer microstructures and how they affect properties.”
• “I don’t get the different techniques for processing polymers.”
Polymers I: Introduction to Polymers