Transcript Polyethylene Ken Anderson Polyethylene R&D The Dow Chemical Company

Polyethylene
Ken Anderson
Polyethylene R&D
The Dow Chemical Company
Freeport, Texas
Invited Lecture for Chem 470 – Industrial Chemistry
Prof. Michael Rosynek, Texas A&M University
April 7, 2006
• My background
– B.S. Chemistry, Tarleton State Univ., Stephenville, TX, 1978
– Ph.D. Polymer Science, Univ. of Southern Mississippi, 1984
– Joined Dow Chemical in 1983 in Epoxy Products R&D then
moved to Polyethylene Product Research in 1996
• My present role at Dow
– Product Research Leader for Solution PE; technical mentor to
younger members of Product Development group
– Design of molecular architecture for new product development
and development of structure-property-performance
interrelationships
– Interface with catalysis, characterization, material science,
intellectual property, process development, pilot plants,
fabrication, Manufacturing, TS&D, and Marketing, with
occasional customer interaction to execute product development
– R&D rep on North American Films Market Management Team
Part of The Ethylene Chain
Natural Gas Liquids (Ethane, Propane)
or Naphtha (from Crude Oil)
Steam Cracking
Ethylene, Propylene
Other Polymers
Chemicals
POLYETHYLENE
H
H
C=C
H
-(-CH2-CH2-)n-
H
Ethylene
Polyethylene
Any Questions?
Polyethylene – The Largest Volume Thermoplastic
2004 Annualized Capacity – Billions of Pounds
151
92
90
75
31
PE
Source: Chem Systems – 2004
PP
Polyester
PVC
PS
PE Demand by Region
2004 Global PE Demand: 136 Billion Pounds
MEAF
7.8%
NA (US & Can)
23.5%
Latin America
8.4%
Western Europe
21.4%
Asia-Pacific
34.8%
SOURCE: Nexant/Chem Systems 2005
Central/Eastern
Europe
4.1%
Markets/Applications for PE
• Rigid and flexible packaging
– Films, Bottles, Food Storage, Shrink film
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•
•
•
•
•
•
•
•
•
Hygiene and medical (nonwovens)
Pipe, Conduit, and Tubing
Fibers
Consumer and industrial liners
Automotive applications
Stretch film and heavy duty shipping sacks (HDSS)
Agricultural films – silage, mulch, bale wrap
Elastomers, Footwear
Wire and Cable
Durables, Toys
Fabrication Versatility
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•
•
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•
•
•
•
•
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Film (blown and cast) extrusion
Injection molding
Blow molding
Sheet, profile, or pipe extrusion
Thermoforming
Rotomolding
Extrusion coating - Lamination
Foaming
Fiber spinning
Wire & Cable
PE Demand by Conversion Process
2004 Global PE Demand: 136 Billion Pounds
Rotational Molding
1%
Blow Molding
14%
Other Extrusion Wire and Cable
2%
3%
Injection Molding
12%
Pipe and Conduit
7%
Sheet
2%
Extrusion Coating
4%
Other Non-Extrusion
3%
Film
51%
SOURCE: Nexant/ChemSystems 2005, PTAI 1/05
Film
• Food Packaging
• Hygiene & Medical
• Consumer & Ind. Liners
• Stretch Films
• Agricultural Films
• HDSS
World Leaders in Polyethylene Production
Dow
ExxonMobil
SABIC
Sinopec
Innovene
Chevron Phillips
Basell
Lyondell/Equistar
Borealis
Total
Formosa Plastics
NOVA Chemical
Polimeri Europa
PetroChina
SOURCE: Nexant/Chem Systems
Types of Polyethylene
HDPE (0.940-0.965)
“High Density”
LLDPE (0.860-0.926)
“Linear Low Density”
O
O
O
C-OH
O
O
O
LDPE (0.915-0.930)
“Low Density”
O
O
O
O
O
High Pressure Copolymers
(AA, VA, MA, EA)
Other Ethylene-Containing Polymers
•
•
•
•
EPDM rubber
Ethylene-Propylene rubber
Impact copolymer polypropylenes
Random copolymer polypropylenes
• Chlorinated PE
• Maleic Anhydride-grafted PE
• Ionomeric salts of EAA or EMA
Classification of PE by Molecular Architecture
PE resins can be distinguished by their unique
combinations of the following attributes:
–
–
–
–
–
molecular weight distribution (MWD)
short chain branch distribution (SCBD)
interrelation of SCBD across MWD
degree of long chain branching
comonomer type and level
These are dictated by polymerization chemistry
and reaction conditions.
Classification of PE by Polymerization Chemistry
• Free radical polymerization
– LDPE
• Coordination Polymerization via Catalyst
– HDPE and LLDPE
Classification of PE by Polymerization Chemistry
• Free radical polymerization – LDPE
– extremely high pressures, using organic
peroxides
– formation of both long & short branches by
“side” reactions
– can utilize polar comonomers, e.g. AA, VA
– first practical form of PE, discovered in 1930’s
Discovery of LDPE Reaction
Date:
Company:
Location:
Inventors:
•
•
•
•
•
•
•
•
March, 1933
Imperial Chemical Industries (ICI)
Winnington, England
R. O. Gibson and E. W. Fawcett
High pressure research program (effects on reaction rates)
Ethylene/benzaldehyde system at 170 deg C and 29,000 psi
Unexpected loss of reaction pressure
Obtained minute quantities of waxy, white solid (LDPE)
Two years of research and explosions to reliably reproduce result
Trace oxygen initiated ethylene polymerization
First commercial autoclave train started up in 1939 in England.
Tubular reactor technology developed by UCC during WW II
Free Radical Polymerization of LDPE
Typical Propagation Mechanism
CH2 .
H
H
+ C=C
H
H
CH2-CH2-CH2.
The active center is transferred from the end of the
growing chain to a position on one of the ethylene
carbons and the process continues forming longer
and longer polyethylene chains
Free Radical Polymerization of LDPE
“Back-biting” Mechanism – Short Chain Branching
CH2
CH2
CH2
CH
CH2
H
CH2
.
CH2
CH
CH2
.
CH3
Butyl branch
The active center is transferred from the end of the
growing chain to a position along the back of the
chain and chain growth proceeds from this position.
Free Radical Polymerization of LDPE
Chain Transfer to Polymer – Long Chain Branching
CH2 . + R-CH2-R
.
CH3 + R-CH-R
The active center is transferred from the end of the
growing chain to a position on a dead chain that
allows that chain to begin forming a long chain
branch.
Your class notes have these reactions illustrated in greater detail.
Typical High Pressure, Low Density PE Process
Low pressure recycle
Purge to LHC
High pressure recycle
CTA
Reactor
HPS
(16-39,000 psi)
Compressor
LPS
Ethylene
Secondary or
Hypercompressor
Extruder
Compression  Reaction  Devolatilization  Extrusion
Example of Autoclave PE Reactor
Ethylene
Peroxide
Peroxide
Peroxide
Peroxide
To HPS
Classification of PE by Polymerization Chemistry
• Coordination Polymerization via Catalyst
– Used for
• HDPE
• LLDPE, when using alpha-olefin comonomers
– Can use solution, slurry, or gas phase processes
– Much lower pressures than free radical
– Lower reaction temperatures, esp. in slurry and
gas phase (particle-form processes)
– Must manage heat of reaction to maintain
reaction temperature, esp. in particle-form
– Lower capital cost than LDPE
Three major coordination catalyst types
– Chromium oxide types – so-called Phillips type
• restricted to slurry and gas phase
• dominant type in conventional slurry HDPE
• can be used for LLDPE
– Ziegler-Natta – “conventional” LLDPE
•
•
•
•
discovered in 1950’s for HDPE and PP
effectively commercialized in 1970’s for LLDPE
still predominant type for LLDPE
density limited to ca. 0.900 and above
– Single site catalysts
• constrained geometry and metallocene types (mLLDPE)
• both can be used as homogeneous (soluble) or supported for
particle-form processes (gas, slurry)
• relatively recent innovation, commercialized in 1992
• enables densities all the way down to that of amorphous
• enabling rapid growth in specialty polyolefins
Your class notes illustrate the catalyst chemistry and polymerization mechansims.
Typical Gas Phase PE Process
Vent
Recovery
Reaction
System
Catalyst
Raw
Material
Handling
Pelleting
System
Resin
Purging
Additive
Addition
To Resin
Storage
and
Loadin
g
Typical Solution PE Process
Comonomer
Ethylene
Solvent
Recovery
Reactor
Devo
1
Devo
2
Polymer
Your class notes also illustrate the Phillips slurry loop process.
Linear Low Density Polyethylene (LLDPE)


LLDPE is ethylene/alpha-olefin copolymer.
-olefin typically 1-butene, 1-hexene and 1-octene
-CH2-CH2-CH2-CH-CH2-CH2-CH2-CH2-
CH2
CH2
CH2
CH2
CH2
CH3
Branch length =
Comonomer length - 2
INSITE* Catalyst Technology
• A novel constrained geometry, single-site catalyst
technology introduced in 1992 that has transformed the
polyolefins industry
• An innovation that continues to deliver new families of
plastics offering new combinations of performance and
processability
• Exceptional control of molecular architecture and polymer
design sparking innovation and unique solutions
Si
N
* Trademark of The Dow Chemical Company
Ti
LLDPE Molecular Structure Comparison
Heterogeneous chain length
distribution + Heterogeneous
short chain branch distribution
Homogeneous chain length
distribution + Homogeneous
short chain branch distribution
Conventional LLDPE
via Ziegler-Natta
INSITE* Technology Polymer
(typical mLLDPE lacks long
chain branches)
* Trademark of The Dow Chemical Company
Semi-Crystalline Morphology
Since SCB disrupt crystallinity, more branching means fewer and
smaller crystals. Conventional LLDPE is a mixture of small and large
crystals while metallocene LLDPE has more uniform crystal size
distribution
TIE CHAIN
INTERFACE
CRYSTAL CORE
AMORPHOUS
MATERIAL
A 3-d representation of chain-folded lamellae in semi-crystalline PE is shown in your class notes.
DSC
Melting
Endotherms
Heat Flow (Watts/gm)
ITP, 0.92 g/cc
2
1.5
ITP, 0.908 g/cc
1
LLDPE, 0.92 g/cc
ITP, 0.902 g/cc
VLDPE,
0.905 g/cc
ITP, 0.896 g/cc
0.5
0
40
60
80
100
Temperature (oC)
120
140
Solid State Properties
Solid state properties are determined by:
 Percent crystallinity (density) & crystal size
distribution
– Amount of Short Chain Branching
 Tie-chain concentration (Toughness)
– Short Chain Branching Distribution
– Molecular Weight
 Orientation of both crystalline and amorphous
phases
– Molecular Weight Distribution
– Long Chain Branching
Engineering Stress-Strain Response - ITP resins
(Strain Rate - 2.4 min-1)
40
15
0.9180
0.9099
0.9016
30
0.8960
Stress, MPa
0.8817
0.9550
10
20
0.8730
0.8702
10
5
0.8630

0
0
250
500
750
Strain, %
1000
0
1250
0
50
Strain, %
Samples were cooled at 1 oC/min.
ALLS50. 21.3.93
100
Decreasing the Crystallinity (Density)
 Is accomplished by...
– Increasing the amount of short chain branching by
adding comonomer
 And results in...
–
–
–
–
Decreasing the modulus (stiffness)
Decreasing the yield strength
Improving optics (haze, gloss, clarity)
Lowering the melting & softening points
Increasing Tie Chain Concentration
 Is accomplished by
– Optimizing Short Chain Branching Distribution
– Increasing the molecular weight
 Increases…
– Toughness
• Impact
• Tear (needs balance of tie chain & high dens)
– Environmental Stress Crack Resistance (ESCR)
Properties vs. Density
Gloss, Clarity, Haze Impact
strength, Tear strength,
ESCR
Modulus (stiffness),
Softening point, Moisture
Barrier
Density
What is Molecular Weight ?
• One of the most important properties of a
polymer is molecular weight.
• The MW is simply the weight of all the atoms
in a molecule. (The weight of the chain).
• Due to the random nature of the
polymerization process, all of the polymer
chains are not exactly the same length.
• This requires that molecular weight be defined
as an average and as a distribution function
(MWD).
Molecular Weight Distribution Comparison
by Gel Permeation Chromatography
Typical mLLDPE
Mw = 73800, Mn = 37400, MWD = 2.0
Mw = 124600, Mn = 33200, MWD = 3.8
Conventional LLDPE
16
18
20
22
24
26
28
ELUTION VOLUME (mls)
Increasing Molecular Weight
* Trademark of The Dow Chemical Company

Melt properties are determined by:
– Molecular Weight, esp. viscosity = k M
3.6
Doubling Molecular weight leads to ten fold increase in viscosity

– Molecular Weight Distribution
– Long Chain Branching
As molecular weight increases:





Processability becomes more difficult
Melt strength, bubble stability improves
Tensile strength improves
Impact strength improves
ESCR increases