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Polyethylene & PolypropyleneExtrusion Coating Primer
Presented by:
Darrell LandryTechnical ServicesChevron Phillips Chemical Co. LP
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Learning Outcomes
• Description of polyethylene.
• Types of polyethylene resins used in extrusion coating.
• Overview of polyethylene manufacturing processes.
• Understand key PE properties and how these properties relate to both processing and finished properties. – MI, Density, MW, MWD, LCB & Rheology
• Description of polypropylene.
• How to process polypropylene in extrusion coating.
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Extrusion CoatingA Demanding Process!
• Process at temps up to 630F!• Oxidize (burn) surface to achieve chemical bond to
substrate.• Extrude in air gap with unsupported edges.• Draw down to 1/100th of original thickness or less in
milliseconds.• Polymer acceleration rate in the air gap similar to going
from 0-60mph in less than 0.5s!• All of this with minimal neck-in, stable edges, EBR, good
gauge profile, no web breaks, minimal smoke, inclusion free, pinhole free & good release from chill roll….Polyethylene to the rescue!!!
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What is Polyethylene?
H H
H
C C
H
ETHYLENEETHYLENE
Colorless GasOdor = Slightly SweetOrigins = Refinery Gas &Liquefied Petroleum GasesMol. Wt. = 28
World Capacity*128 Million Tons. (2005 est.)
* World Petrochemical Review (Oct 2005)
Colorless GasOdor = Slightly SweetOrigins = Refinery Gas &Liquefied Petroleum GasesMol. Wt. = 28
World Capacity*128 Million Tons. (2005 est.)
* World Petrochemical Review (Oct 2005)
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H H
H
C C
H
Catalyst/InitiatorTemperature
Pressure
Catalyst/InitiatorTemperature
PressureH H
H
C C
H
H H
H
C C
H
H H
H
C C
H
Polyethylene Reaction
H H
H
C C
H
H H
H
C C
H
H H
H
C C
H
H H
H
C C
H
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Polyethylene Structures
HDPEHDPE
LDPELDPE
LLDPELLDPE
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Basic Molecular PropertiesResin Type
MOLECULAR WEIGHT
DISTRIBUTION (MWD)
CRYSTALLINITYHDPE
MOLECULAR WEIGHT
DISTRIBUTION (MWD)
CRYSTALLINITY
COMONOMER TYPE (SCB)
LLDPE
MOLECULAR WEIGHT
DISTRIBUTION (MWD)
CRYSTALLINITY
LONG CHAIN BRANCHING (LCB)
LDPE
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LDPELow Density Polyethylene
• LDPE is characterized by long chain branching.– Density range from 0.915 to 0.925 g/cc
• Autoclave grades offer excellent melt strength for minimal neck-in and excellent drawdown in extrusion coating.
• Typical Applications:– Liquid Packaging– Snack Foods / Laminations– Pouch Stock– Folding Carton / Cup Stock– Sealant Layers
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LLDPELinear Low Density Polyethylene
• LLDPE is characterized by short chain branching.– Density range from 0.916 to 0.925 g/cc
• Enhanced toughness, tear, puncture and stiffness are some attributes over LDPE.
• Typical Applications:– Institutional Foods– Balloon Films– Non-wovens– Enhanced Packaging
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LLDPEComonomer Type
COMONOMER TYPEComonomer type refers to the number of carbons contained in the side chain
attached to the main polymer backbone.
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Comonomers for LLDPE
Octene (+6)
Hexene (+4)
Butene (+2)
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Effect of Comonomer Typeon Properties
BUTENE (+2) HEXENE (+4) OCTENE (+6)
STR
ENG
TH
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Metallocene LLDPE’s
• Metallocene LLDPE was developed for improved abuse resistance– Tear, dart impact and Spencer impact– Hot tack and heat seal
• Some tie properties, e.g. OPP• Two types of metallocenes:
PlastomersPlastomers density <0.915 g/cc
Enhanced LLDPEmLLDPE density >0.915 g/cc
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High Density Polyethylene
• HDPE is also characterized by short chain branching – Density range from 0.940 to 0.965 g/cc
• Properties improved over standard LDPE:– MVTR - Grease resistance - Temperature resistance– Higher stiffness - Lower COF
• Typical Applications:– Release Liners– Temperature Resistant Applications– Multi-wall Bags– MVTR Applications
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Resin ManufacturingProcesses
LDPE LLDPE HDPE mLLDPECopolymer
LDPE
Autoclave x xTubular x
Particle Form x x x
Gas Phase x x x
Solution Form x x x
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High Pressure AutoclaveHigh Pressure Autoclave
PrimaryCompressor
SecondaryCompressor
Telogen VAMonomer MA
Monomer
REACTOR SEPARATOR
VoluntaryPurge
DEPROPANIZER
DEMETHANIZER
C2
SPLITTER
HOPPER
Gear Pump andPelletizer
HourlyHold-UpHoppers
RAWPRODUCT
SILO
To Finishing
Ethane toFlare
Solvent/MonomerRemoval
C2
< C3Methaneto Flare
Initiator
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Low Pressure Gas PhaseLow Pressure Gas Phase
CATALYST
COMONOMER
HYDROGEN
ETHYLENE GASRECYCLE GASCOMPRESSOR
GranularPolyethylene
Vent
GASPHASE
REACTOR
Operating Conditions200 - 250 o F100 - 300 psi
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Low Pressure SlurryLow Pressure Slurry
GranularPolyethylene
Operating Conditions200 - 250 o F500 - 600 psi
CirculatingPump
EthyleneHydrogenComonomer(Hexene or Butene) Flash Tank
Vapors
LOOPREACTOR
DRYER
RECYCLE STREAM
Catalyst
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Low Pressure Solution
RawProduct
300-350 F400-600 psiDissolved in Hydrocarbon Solvent
Vapors
Comonomer
Hydrogen
Ethylene
Recycle Stream
Catalyst Catalyst
1
23
5
4
1. Stirred Reactors2. Filtration3. Separator4. Drier5. Compressor
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Critical Polyethylene Properties
• Melt Index / Molecular Weight • Density / Crystallinity• Molecular Weight Distribution• Long Chain Branching• Rheology
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Melt Index (MI)
• Melt Index is a simple and traditional measure of polymer flow (viscosity).
• This flow value correlates with molecular weight.– the higher the molecular weight, the lower the melt
index.• Higher melt index resins are used for lower coating
weights. • Higher melt index resins have a higher degree of neck-in.
HIGH MIGood Drawability
LOW MILow Neck-In
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Effect of MWw (Melt Index) on Properties
Freq
uenc
y
Increasing Molecular Weight
Effect of Weight Average Molecular Weight IncreasesThese Properties
Increase in Avg. Mol. Wt.
Impact StrengthTensile StrengthHeat Seal StrengthHeat Seal RangeMelt Strength
Chemical ResistanceTD Tear StrengthSeal InitiationPuncture ResistanceExt. Load / Amps/ Back Pressure
Decrease in Avg. Mol. Wt.
Processability (Ease of Flow)Melt Extension / Drawdown
Neck-inEdge Bead
Melt Index Melt Index
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Density
• Density is a measure of the crystallinity of the polymer.• Higher density polymers have more closely packed
molecules and are more stiff in nature.• Lower density polymers have loosely packed molecules
and are more flexible.• Density is measured as the weight of material occupying a
specific volume (g/cc).
No Branching – High Density
Short Chain Branching –Med Density
Short & Long Chain Branching –Low Density
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Crystalline and Amorphous Structure
CrystallineRegions
AmorphousRegions
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Density Test
Density is an indirect measure ofthe crystallinity of a polymer.
Standard Procedure : ASTM D1505Units = g/cc
Calibrated Density Standards
Sample
Controlled TemperatureGradient Column
Other accepted techniques for measuring density include ultrasonic velocity and buoyancy (densimeter).
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Effect of Crystallinity (Density)on Properties
As Crystallinity IncreasesThese Properties
Increase
DensityStiffnessTensile StrengthSoftening PointDead FoldCurl
Chemical ResistanceHeat ResistanceWrinkling TendencySeal Initiation Temp.Barrier (Moisture, Light, & Grease)
Decrease
MD Tear StrengthImpact
Puncture ResistanceCOF
Optics (Clarity)
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Molecular Weight Distribution
• Molecular weight distribution (MWD) is a measure of the fractions of the various molecular weights in a polymer.
• Polymers can be produced to have a narrow or broad molecular weight distribution with the same average molecular weight.
Narrow MWD Broad MWD
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Effect of MWD on Properties
Freq
uenc
y
Increasing Molecular Weight
As Molecular Weight Distribution IncreasesThese Properties
IncreaseProcessibility
Melt Strength & StabilityLower Neck-in
DecreaseBackpressure & Motor Load*
Melt ExtensionReduced Draw
Physical PropertiesPuncture – Tear - Tensile
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Long Chain Branching
Long Chain BranchingRefers to the amount of long chains (those
greater than ~150 carbons long) that are attached to the main polymer backbone.
Critical for melt strength in extrusion coating.
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Long Chain Branching Illustration
Long ChainBranches
Short ChainBranches
Main Polymer Backbone
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Long Chain Branching on Properties
As the Degree of Long Chain Branching IncreasesThese Properties
IncreaseProcessabilityMelt Stability
Edge Tear TendencyHaze (Poor Optics)
Die Swell
DecreaseDrawdown
Impact & PunctureGloss (Poor Optics)
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Rheology
• The study of flow is called rheology.• Different polymers have different rheological
properties. • A rheometer is used to measure rheology.
– Measures changes in viscosity caused by changes in flow rate.
• So what does it mean to you ?– Rheology data can tell you how the polymer will
extrude relative to other polymers.– Excellent tool for coextrusion (viscosity matching).
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Effect of MWD on Processing
BROAD MWD
NARROW MWD
LOG Shear Rate (Output)
LOG
App
aren
t Vis
cosi
ty
Mel
t Ind
ex
NormalProcessing
Range
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Polyethylene Summary
• LDPE – excellent processing, general purpose resin• LLDPE – strength• HDPE – temp resistance, moisture and grease barrier • LDPE produced via high pressure processes• LLDPE & HDPE lower pressure processes• PE is characterized by:
– Melt Index (Mw)– Density (Crystallinity)– Rheology (MWD & Branching)
• When to use PE (LDPE)?...Whenever Possible!
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PolypropyleneWhy use PP in E/C?
• Higher Temp Resistance than PE• Grease Resistance• Stiffness & Abrasion Resistance• MVTR Similar to HDPE• Adhesion to PP Substrates….challenge to process.
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Polypropylene Types
• Basic Types of PP used in Extrusion Coating– Homopolymer– Random Copolymer
• Little Difference in Density
• Properties are Dependent on Level of Comonomer
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Polypropylene Homopolymer
• Polypropylene Homopolymer– Produced from propylene only, no comonomer– Wide range of MFR (fractional to 120)– High stiffness, low elongation– High melt temperature, 165° C– High heat deflection temperature– Most commonly used in extrusion coating– Melt stabilized for E/C by addition of LDPE
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Polypropylene Random Copolymer• Random Copolymer
– Uses ethylene as a comonomer usually in the 2-5% range
– MFR range 2-35– “Softer” than homopolymer– Better impact than homopolymer– Lower melt temperature, ~148° C– Better seal than a homopolymer
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Processing PP in E/C
• More heat in feed zone• Does not oxidize like LDPE
– Mechanical Adhesion - Increase Nip Pressure– Minimize Air Gap – Increase Line Speed– Die Position Towards Substrate – Warmer Chill Roll
• Process cooler (590F) to minimize neck-in and stabilize edges.
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Thank you
PRESENTED BY
Darrell LandryTechnical ServicesChevron Phillips Chemical Co. [email protected]
Polyethylene and PolypropylenePolyethylene and Polypropylene