chemical engineering 378mjm82/che378/fall2019/lecturenotes/lecture_17_notes.pdfancient polymers •...
TRANSCRIPT
-
1
Chemical Engineering 378
Science of Materials Engineering
Lecture 17Polymers and Applications I
-
Spiritual Thought
Isaiah 1:1818. Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.
2
-
Materials Roadmap3
-
4
What is a Polymer?
Poly mermany repeat unit
C C C C C CHHHHHH
HHHHHH
Polyethylene (PE)ClCl Cl
C C C C C CHHH
HHHHHH
Poly(vinyl chloride) (PVC)HH
HHH H
Polypropylene (PP)
C C C C C CCH3
HH
CH3CH3H
repeatunit
repeatunit
repeatunit
-
5
Ancient Polymers
• Originally natural polymers were used– Wood – Rubber– Cotton – Wool– Leather – Silk
• Oldest known uses– Rubber balls used by Incas– Noah used pitch (a natural polymer)
for the ark
-
6
-
7
Unsaturated Hydrocarbons
• Double & triple bonds somewhat unstable – can form new bonds– Double bond found in ethylene or ethene - C2H4
– Triple bond found in acetylene or ethyne - C2H2
C CH
H
H
H
C C HH
-
Organic Chemists8
-
9
Isomerism
• Isomerism– two compounds with same chemical formula can
have quite different structures for example: C8H18
• normal-octane
• 2,4-dimethylhexane
C C C C C C C CHH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
HH H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=
H3C CHCH3
CH2 CHCH2
CH3
CH3
H3C CH2 CH3( )6
⇓
-
10Polymerization and Polymer Chemistry
• Free radical polymerization
• Initiator: example - benzoyl peroxide
CH
HO O C
H
H
CH
HO2
C CH H
HHmonomer(ethylene)
R +
free radical
R C CH
H
H
H
initiation
R C CH
H
H
HC CH H
HH
+ R C CH
H
H
HC CH H
H H
propagation
dimer
R= 2
propagation
-
11
Chemistry and Structure of Polyethylene
Adapted from Fig. 14.1, Callister & Rethwisch 10e.
Note: polyethylene is a long-chain hydrocarbon- paraffin wax for candles is short polyethylene
-
Polymers – Molecular Shape12
-
13
Bulk or Commodity Polymers
-
14
Bulk or Commodity Polymers (cont)
-
15
Bulk or Commodity Polymers (cont)
-
16
To very complicated
-
17
And Super Complicated!
-
18
-
19
MOLECULAR WEIGHT• Molecular weight, M: Mass of a mole of chains.
Low M
high M
Not all chains in a polymer are of the same length— i.e., there is a distribution of molecular weights
-
20
Chain End-to-End Distance, r
Fig. 14.6, Callister & Rethwisch 10e.
-
21
xi = number fraction of chains in size range i
MOLECULAR WEIGHT DISTRIBUTIONFig. 14.4, Callister & Rethwisch 10e.
wi = weight fraction of chains in size range i
Mi = mean (middle) molecular weight of size range i
-
22
Molecular Weight Calculation
Example: average mass of a classStudent Weight
mass (lb)1 1042 1163 1404 1435 1806 1827 1918 2209 22510 380
What is the averageweight of the students inthis class:a) Based on the number
fraction of students in each mass range?
b) Based on the weight fraction of students in each mass range?
-
23
Molecular Weight Calculation (cont.)
Solution: The first step is to sort the students into weight ranges. Using 40 lb ranges gives the following table:
total number
total weight
Calculate the number and weight fraction of students in each weight range as follows:
For example: for the 81-120 lb range
Sheet1
Weight
mass (lb)
104
116
140
143
180
182
191
220
225
380
Sheet2
weightnumber ofmeannumberweight
rangestudentsweightfractionfraction
NiWixiwiStudentWeight
mass (lb)mass (lb)mass (lb)
81-12021100.20.1171104
121-16021420.20.1502116
161-20031840.30.2943140
201-24022230.20.2374143
241-2800-00.0005180
281-3200-00.0006182
321-3600-00.0007191
361-40013800.10.2028220
9225
SNiSNiWiMnMw10380
101881188 lb218 lb
188.1217.7529682793
Sheet2
1
Sheet3
-
24
Molecular Weight Calculation (cont.)
Sheet1
Weight
mass (lb)
104
116
140
143
180
182
191
220
225
380
Sheet2
weightmeannumberweight
rangeweightfractionfraction
WixiwiStudentWeight
mass (lb)mass (lb)mass (lb)
81-1201100.20.1171104
121-1601420.20.1502116
161-2001840.30.2943140
201-2402230.20.2374143
241-280-00.0005180
281-320-00.0006182
321-360-00.0007191
361-4003800.10.2028220
9225
10380
188.1217.7529682793
MnMw
188 lb218 lb
Sheet3
-
25
Degree of Polymerization, DPDP = average number of repeat units per chain
C C C C C C C CHH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
HC C C CH
H
H
H
H
H
H
HH( ) DP = 6
mol. wt of repeat unit iChain fraction
-
26
Adapted from Fig. 14.7, Callister & Rethwisch 10e.
Molecular Structures for Polymers
Branched Cross-Linked NetworkLinear
secondarybonding
-
27
Molecular Configurations for Polymers
Configurations – to change must break bonds• Stereoisomerism
EB
A
D
C C
D
A
BE
mirror plane
C CR
HH
HC CH
H
H
R
or C CH
H
H
R
Stereoisomers are mirrorimages – can’t superimposewithout breaking a bond
-
28
Tacticity
Tacticity – stereoregularity or spatial arrangement of R units along chain
C CH
H
H
R R
H
H
HCC
R
H
H
HCC
R
H
H
HCC
isotactic – all R groups on same side of chain
C CH
H
H
RC CH
H
H
RC CH
H
H
R R
H
H
HCC
syndiotactic – R groups alternate sides
-
29
Tacticity (cont.)
atactic – R groups randomlypositioned
C CH
H
H
R R
H
H
HCC
R
H
H
HCC
R
H
H
HCC
-
30
cis/trans Isomerism
C CHCH3
CH2 CH2C C
CH3
CH2
CH2
H
ciscis-isoprene
(natural rubber)
H atom and CH3 group on same side of chain
transtrans-isoprene (gutta percha)
H atom and CH3 group on opposite sides of chain
-
31
Copolymers
two or more monomers polymerized together
• random – A and B randomly positioned along chain
• alternating – A and B alternate in polymer chain
• block – large blocks of A units alternate with large blocks of B units
• graft – chains of B units grafted onto A backbone
A – B –
random
block
graft
Fig. 14.9, Callister & Rethwisch 10e.
alternating
-
Thermoplastic or Thermosetting32
-
33
Crystallinity in Polymers
• Ordered atomic arrangements involving molecular chains
• Crystal structures in terms of unit cells
• Example shown– polyethylene unit cell
Fig. 14.10, Callister& Rethwisch 10e.
-
34
Polymer Crystallinity
• Crystalline regions – thin platelets with chain folds at faces– Chain folded structure
Fig. 14.12, Callister& Rethwisch10e.
≈ 10 nm
-
35
Polymer Crystallinity (cont.)
Polymers rarely 100% crystalline• Difficult for all regions of all chains to
become aligned
• Degree of crystallinityexpressed as % crystallinity.-- Some physical properties
depend on % crystallinity.-- Heat treating causes
crystalline regions to grow and % crystallinity to increase.
Fig. 14.11, Callister 6e. (From H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)
crystalline region
amorphousregion
-
36
Polymer Single Crystals
• Electron micrograph – multilayered single crystals (chain-folded layers) of polyethylene
• Single crystals – only for slow and carefully controlled growth rates
Fig. 14.11, Callister & Rethwisch 10e. [From A. Keller, R. H. Doremus, B. W. Roberts, and D. Turnbull (Eds.), Growth and Perfection of Crystals. General Electric Company and John Wiley & Sons, Inc., 1958, p. 498. Reprinted with permission of John Wiley & Sons, Inc.]
1 μm
-
37
Semicrystalline Polymers
Spherulitesurface
Fig. 14.13, Callister & Rethwisch 10e.
• Some semicrystallinepolymers form spherulite structures
• Alternating chain-folded crystallites and amorphous regions
• Spherulite structure for relatively rapid growth rates
-
38Photomicrograph – Spherulites in Polyethylene
Fig. 14.14, Callister & Rethwisch 10e.
Cross-polarized light used -- a maltese cross appears in each spherulite
Cou
rtesy
F. P
. Pric
e, G
ener
al E
lect
ric C
ompa
ny
100 μm
Chemical Engineering 378��Science of Materials Engineering��Spiritual ThoughtMaterials RoadmapWhat is a Polymer?Ancient PolymersSlide Number 6Unsaturated HydrocarbonsOrganic ChemistsIsomerismPolymerization and �Polymer ChemistryChemistry and Structure of PolyethylenePolymers – Molecular ShapeBulk or Commodity PolymersBulk or Commodity Polymers (cont)Slide Number 15Slide Number 16Slide Number 17Slide Number 18MOLECULAR WEIGHTChain End-to-End Distance, rMOLECULAR WEIGHT DISTRIBUTIONMolecular Weight CalculationMolecular Weight Calculation (cont.)Molecular Weight Calculation (cont.)Degree of Polymerization, DPMolecular Structures for PolymersMolecular Configurations for PolymersTacticityTacticity (cont.)cis/trans Isomerism CopolymersThermoplastic or ThermosettingCrystallinity in PolymersPolymer CrystallinityPolymer Crystallinity (cont.)Polymer Single CrystalsSemicrystalline PolymersPhotomicrograph – Spherulites in Polyethylene