Polyethylene Ken Anderson Polyethylene RD The Dow Chemical

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 C=C H H -(-CH 2 -)n- H Ethylene Polyethylene Any Questions?

Polyethylene – The Largest Volume Thermoplastic 2004 Annualized Capacity – Billions of Pounds 151 92 90 75 31

PE Demand by Region 2004 Global PE Demand: 136 Billion Pounds

Markets/Applications for PE • Rigid and flexible packaging – Films, Bottles, Food Storage, Shrink film • • • 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 • 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 Film • Food Packaging • Hygiene & Medical • Consumer & Ind. Liners • Stretch Films • Agricultural Films • HDSS

World Leaders in Polyethylene Production Dow Exxon. Mobil SABIC Sinopec Innovene Chevron Phillips Basell Lyondell/Equistar Borealis Total Formosa Plastics NOVA Chemical Polimeri Europa Petro. China

Types of Polyethylene HDPE (0. 940 -0. 965) “High Density” LLDPE (0. 860 -0. 926) “Linear Low Density” O C-OH O O O LDPE (0. 915 -0. 930) “Low Density” 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 CH 2. H H + C=C H H CH 2 -CH 2. 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 CH 2 CH CH 2 . CH 3 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 CH 2. + R-CH 2 -R . CH 3 + 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 (16 -39, 000 psi) HPS Compressor LPS Ethylene Secondary or Hypercompressor Extruder Compression Reaction Devolatilization Extrusion

Example of Autoclave PE Reactor Ethylene 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 (m. LLDPE) • 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 Loading

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 -CH 2 -CH 2 -CH 2 CH 2 CH 2 CH 3 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 m. LLDPE 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

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) Samples were cooled at 1 o. C/min.

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 m. LLDPE Mw = 73800, Mn = 37400, MWD = 2. 0 Mw = 124600, Mn = 33200, MWD = 3. 8 Conventional LLDPE 16 18 20 22 24 ELUTION VOLUME (mls) Increasing Molecular Weight 26 28

· 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