polyethylene henrique de almeida torres. introduction polyethylene is the simplest of all commercial...
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PolyethyleneHENRIQUE DE ALMEIDA TORRES
Introduction• Polyethylene is the simplest of
all commercial polymers, and yet, it is the most popular plastic in the world.
• It is a versatile material that can be used in grocery bags, shampoo bottles, children's toys, and even bullet proof vests
• Where does the monomer, ethylene (ethane) come from?
• Ethane, propane, naphta, gas oil and ethanol
http://www.elmhurst.edu/~chm/vchembook/401addpolymer
Types of Polyethylene
LDPE – Low-density Polyethylene
HDPE – High-density Polyethylene
LLDPE – Linear low density Polyethylene
UHMWPE – Ultra high molecular weight Polyethylene
Annual production of Polyethylene/Million tons LDPE HDPE LLDPE
World 23.3 25.5 7.4
Europe 6.7 5.1 1.1
US 3.5 6.5 2.8
Russia Total 1.41
Middle East
1.9
China 3.5 1.4 1.6
Rest of Asia
4.36.4 1.8
1. Federal State Statistics Service: Russian Federation 2011Table from: www.essentialchemicalindustry.org/polymers/polyethene
LDPE – Low density Polyethylene The commercial LDPE process is a free radical polymerization that uses organic
peroxide initiators 420-570 K and 1000 - 3000 atmospheres of pressure. Ethene (purity in excess of 99.9%) is compressed and passed into a reactor together
with the initiator. The molten polyethylene is removed, extruded and cut into granules
Density : 0.91-0.94 g/cm3
Average LDPE chain length: 400 – 40000 carbon atoms LDPE is generally amorphous and transparent with about 50% crystallinity LDPE has about 20 branches per 1000 carbon atoms
Representation of the LDPE – Image from: www.essentialchemicalindustry.org/polymers/polyethene
HDPE- High Density Polyethylene
http://www.ecvv.com/product/2377724www.polyethylenepepipes.com
Image1: HDPE beads Image2: HDPE pipes
HDPE Density: 0.94 g/cm3
Low branching allows better stacking of the molecules
HDPE’s synthesis is done via Ziegler-Natta or Phillips catalysis.
Ziegler-Nattta catalyst: organometallic catalyst (titanium compounds with an aluminum alkyl).
Phillips-type catalyst: A well-known example is chromium(VI) oxide on silica.
HDPE is produced by three types of processes: Slurry process(2-methylpropane (isobutane) or hexane as solvent), Solution process (a C10 or C12 alkane as solvent) and the Gas phase process
Slurry process (using a loop reactor)
Image from: www.essentialchemicalindustry.org/polymers/polyethene
Gas phase process(Phillips catalyst)
Image from:www.essentialchemicalindustry.org/polymers/polyethene
LLDPE – Linear Low density Polyethylene
LLDPE is actually a copolymer of ethylene and 1- butane (with lesser amounts of others alkenes)
LLDPE’s production is more energetically favorable energy than the production of LDPE
The structure is essentially linear but because of the short chain branching it has a low density. The structure gives the material much better resilience, tear strength and flexibility without the use of plasticizers
LLDPE is produced by the same processes as HDPE
LLDPE
Structure of LLDPE with 1-butane as copolymer and a representation of the polymer molecule.
Images from: www.essentialchemicalindustry.org/polymers/polyethene
Polyethylene ApplicationsProcess HDPE LDPE LLDPE
Making filmFood packagingShopping bags
Cling filmMilk carton lining
Stretch film
Injection molding
DustbinsCrates
BucketsBowls
Food boxes
Blow mouldingDetergent bottlesDrums
Squeezable bottles
Extrusion Water pipes
Flexible water pipesCable jacketing
Cable coating
Table from: www.essentialchemicalindustry.org/polymers/polyethene
UHMWPE – Ultra high molecular weight Polyethylene
Ultra–high molecular weight polyethylene (UHMWPE) is a unique polymer with outstanding physical and mechanical properties. Most notable are its chemical inertness, lubricity, impact resistance, and abrasion resistance. These characteristics of UHMWPE have been exploited since the 1950s in a wide range of industrial applications
Its molecular weight is generally around 4-7 millions g/mole
Density: 0.930–0.935 g/cm3
UHMWPE The polymerization is done by Ziegler- Natta catalysis (titanium
tetra chloride as catalyst). The polymerization takes place in a solvent, used for mass and heat transfer, at low pressures.
UHMWPE is produced as powder and must be consolidated under elevated temperatures and pressures because of its high melt viscosity.
Schematic of a ram extruder
Image from: www.uhmwpe.org/lexicon/processing_uhmwpe
Compression Molding Press (along with the author, for scale) for production of 1 m by 2 m sheets of UHMWPE. This press is located at Poly Hi Solidur MediTECH in Vreden, Germany, and was originally used by Ticona in the production of Chirulen® sheets of UHMWPE. The press is still used today in the production of medical grade UHMWPE
Image from: www.uhmwpe.org/lexicon/processing_uhmwpe
Morphological features of UHMWPE
TEM micrograph of UHMWPE showing amorphous and crystalline regions (lamellae)
Images from: www.uhmwpe.org/lexicon/a_primer
UHMWPE’s applications
Pickers for textile machinery, lining for coal chutes and dump trucks, runners for bottling production lines, as well as bumpers and siding for ships and harbors. Over 90% of the UHMWPE produced in the world is used by industry. UHMWPE is also used in orthopedics as a bearing material in artificial joints.
Stainless steel and ultra high molecular weight polythene hip replacement
Image from: en.wikipedia.org/wiki/Polyethylene
The Dyneema® brandDyneema® is respected as the premium brand for Ultra-High Molecular Weight Polyethylene (UHMwPE), and we manufacture and sell products in several forms including fiber, tape and uni-directional (UD) sheets.
Image from: www.dyneema.com/americas/applications/life-protection/personal-armor
Typical Average Physical Properties of High Density Polyethylene (HDPE), Ultra-High Molecular Weight Polyethylene (UHMWPE)
Property HDPE UHMWPE
Molecular Weight (106 g/mole) 0.05–0.25 3.5–7.5
Melting Temperature (°C) 130–137 132–138
Specific Gravity 0.952–0.965 0.925–0.945
Tensile Modulus of Elasticity* (GPa) 0.4–4.0 0.5–0.8
Tensile Yield Strength* (MPa) 26–33 21–28
Tensile Ultimate Strength* (MPa) 22–31 39–48
Tensile Ultimate Elongation* (%) 10–1200 350–525
Impact Strength, Izod* (J/m of notch; 3.175 mm thick specimen)
21–214 >1070 (No Break)
Degree of Crystallinity (%) 60–80 39–75
Table from: www.uhmwpe.org/lexicon/a_primer
True-stress strain behavior in uniaxial tension (room temperature, 30 mm/min) for two grades of UHMWPE, in comparison with HDPE
Graph from: www.uhmwpe.org/lexicon/processing_uhmwpe
Green Polyethylene – Braskem’s “I’m GreenTM” Polyethylene
Polyethylene can be produced from renewable sources
Brazilian chemical company Braskem, produces polyethylene from sugar cane ethanol since 2007
U$290 million dollars in the biopolymer production plant in Triunfo–RS
Image from: www.braskem.com.br/site.aspx/Onde-e-produzido
The green cycle
Image from:www.braskem.com.br/site.aspx/Como-e-Produzido
References •Polymer Chemistry: an introduction/ Malcolm P. Stevens. 2nd ed. P.271-275 •www.pslc.ws/macrog/pe.htm•www.uhmwpe.org/lexicon•www.unomaha.edu/tiskochem/Chem4310/Notes/PDF_Files/Free_Radical_Synthesis-Properties•www2.dupont.com/Tyvek/en_US/assets/downloads/tyvek_handbook•www.essentialchemicalindustry.org/polymers/polyethene•www.dyneema.com
Revision questions
List and describe two other microscopy techniques that could be used to analyze UHMWPE’s cristallinity.
What are the similarities between suspension and solution polymerization?
Explain the differences in HDPE’s and LDPE’s properties considering their chain structures.