Download - Fundamental of Polyethylene and Ultra High Molecular Weight Polyethylene by Peyman Sazandehchi
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Fundamental of Polyethylene
&Ultra High Molecular Weight Polyethylene
(UHMWPE)
April 13, 2023
Prepared By:Peyman Sazandehchi from
April 13, 2023 2
The first step to knowledgeis to know that we are ignorant
Socrates (470-399 B.C.)
Prepared By: Peyman [email protected]
What are polymers, monomers and polymerizations?
Polymers are macromolecules built up by the linking together of large numbers of much smaller molecules.
What is a polymer?
Poly mer
many repeat unit
Polyethylene (PE)
HH
HHH HC C C C C C
H
HH
HH H
Repeat unit
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Types of polymers & polymerizations
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Classification of Polymers
Polymer Structure
Condensation
Polymers
Addition Polymers
Polymerization Mechanism
Step- Polymerizati
on
Chain- Polymerizati
on
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The condensation takes place between two polyfunctional molecules to produce one larger polyfunctional molecule with the possible elimination of a small molecule such as water. The reaction continues until one of the reagents is used up.
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Polymer Structure
The condensation system
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Condensation polymers (New definition)
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Polymers whose repeating units are joined together by functional units such as ester (-OCO-), amide (-NHCO-), urethane (-OCONH-), sulfide (-SO2-) and other linkages.
-R-Z-R-Z-R-Z-R-Z-R-Z-R is aliphatic or aromatic grouping and Z is functional unit.
Polymer Structure
The addition system
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Homopolymer vs. copolymer
Homopolymers are polymers composed of only one repeating unit in their molecules.
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What are homopolymers?
What are copolymers?
Copolymers are polymers composed of two different repeating units in their molecules.
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Homopolymer vs. copolymer
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Types of copolymer systems
Random copolymer
Alternating copolymer
Block
Graft copolymer
random
block
graft
alternating
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Classification of polymers depending on their structure
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What if polymerization conditions are changed or different monomer is used, e.g. ethylene vs. butadiene?
Branched Cross-Linked NetworkLinear
secondary
bonding
Direction of increasing strength
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Classification of polymers depending on their structure
Branched polymers
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What is the effect of branching on polymer properties?Crystallinity
Is it branched polymer?!!!
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• Amorphous State: The polymer chain is randomly oriented
• Crystalline State: The polymer chain has a large degree of orientation, often folded over on itself
• Semicrystalline State: The polymer chain has both amorphous and crystalline regions
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Classification of polymers depending on their structure
Cross-linked polymers
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Using appropriate monomersChemical reactions
Polymer molecules are connected together at points other than their ends
Crosslinked polymers do not dissolve but can be swelled by liquids.
Light crosslinking improves elasticity properties
polymer is used as rubber
High degree of crosslinking gives high rigidity and thermal stability (high melting point).
BOTH CROSSLINKED POLYMERS CANNOT BE RECYLED OR REPOROCESSED
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Thermosets vs. Thermoplastics
What are thermoset polymers?
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Polymers that will not flow when heated. Thermosets have cross-linked structure. Examples are phenolic and epoxy resins.
What are thermoplastic polymers?
Polymers that soften, without chemical change, and take new shapes by the application of heat and pressure and harden when cooled. Thermoplastics have linear and branched structures. Examples are PP, PVC and Nylon
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•Thermoplastics:Spaghetti like structure -- little crosslinking -- ductile -- soften w/heating -- polyethylene polypropylene polycarbonate polystyrene
• Thermosets: Three dimensional crosslinked network which is permanent -- large crosslinking (10 to 50% of mers) -- hard and brittle -- do NOT soften w/heating -- vulcanized rubber, epoxies, polyester resin, phenolic resin
Thermoplastics vs. Thermosets
Callister,
Fig. 16.9
T
Molecular weight
Tg
Tmmobile
liquid
viscous
liquid
rubber
tough plastic
partially
crystalline
solidcrystalline
solid
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Plastics
Thermosets
Highly cross-linked
Thermoplastics
Amorphous Crystalline
Classification of polymers – polymer structure
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Crystalline and amorphous behaviorFringed-Micelle Theory
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Polymers consist of small-sized, ordered crystalline regions (crystallites)These polymers imbedded in amorphous polymer matrix
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April 13, 2023 18
Ex: polyethylene unit cell
• Crystals must contain the polymer chains in some way – Chain folded structure
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Folded-Chain Lamella
Theory
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lamella
A stack of polymer chains folded back on themselves
like this
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Crystalline and amorphous behavior
Spherulites
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amorphousregion
crystalline region
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Crystalline and amorphous behavior
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To have a crystalline polymer:
1. Polymer structure must be highly stereoregular with little or no chain branching.
2. Polymer contain highly polar groups, such as amine, amide, ether and ester groups, that give rise to strong dipole-dipole interactions
For example
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April 13, 2023 22
• Crystalline- Molecular structure forms regular order (crystals)
with molecules or portions of molecules regularly stacked in
crystal-like fashion.
• Most crystalline polymers are semi-crystalline because very
few plastics are 100% crystalline. All have both regions that are
crystalline and some that are amorphous
• Usually Opaque and not transparent
• More molding shrinkage with
– crystalline materials.
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April 13, 2023 23
Properties of polymer
Thermal properties
Mechanical properties
Chemical properties
Electrical & Optical properties
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• Thermal properties
– Dimensional stability- Tg (noncrystalline
portion of the polymer change from
glassy to rubbery)
– Thermal decomposition- occur when
primary covalent bonds are ruptured
– Thermal expansion
– Thermal conductivityApril 13, 2023 24
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• Mechanical properties;
it is categorized based on (also can be
categorized based on tensile, impact,
flexural, etc);
– Stiffness
– Strength
– Toughness
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• Chemical properties
– Solubility- in various solvent
– Permeability to gases or other molecules
– Chemical resistance towards chemicals,
environment & radiation
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• Electrical & Optical properties
– Dielectric properties- most polymers are good
insulators, able to store electrical charge
effectively, thus serving as good dielectric
– Conductivity- most polymers are poor
conductors, because primary chemical bonding
is covalent- thus no free electron or ion to
conduct charge
– Optical properties such as color, transparency,
etc
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April 13, 2023 Introduction to Polymers 28
The ability to bend without
breaking
Thermosets vs. Thermoplastics
Molecular weight and its distribution
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Minimum polymer molecular weight required to produced any significant mechanical strength, ~ 1000 - 2000 g/mol
Minimum molecular weight for a polymer to begin to exhibit sufficient useful strength, ~ 5000 – 10000 g/mol
Limiting value
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Molecular weight and its distribution
xxw MwM
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Average molecular weight is not unique and can be defined in a number of different ways.
Two of the most commonly used averages are:
The number average molecular weight (Mn) and the weight average molecular weight (Mw).
x
xxn N
MNM
Nx is the number of molecules whose weight is Mx
wx is the weight fraction of the molecules whose weight is Mx
xx
xxw MN
MNM
2
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x
xxn N
MNM
xx
xxw MN
MNM
2
lbsM
NnumberTotal
lbs
MNweightTotal
n
x
xx
000,2
5
14
004,10
000,10114
lbsM
lbs
MN
w
x x
000,10004,10
10
10
000,10000,1014
8
8
2
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Illustrative examples….
What do you think ???
9773)10000200()100040()50020()10010(
)10000200()100040()50020()10010(M
7596200402010
)10000200()100040()50020()10010(M
2222
w
n
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Illustrative examples….
Let us say we have:
10 chains of 100 molecular weight
20 chains of 500 molecular weight
40 chains of 1000 molecular weight
200 chains of 10,000 molecular weightMw is much better indicator of the properties to be expected in a
polymer than Mn
Molecular weight and its distribution
1n
w
M
MPDI
aaxxv MwM 1][
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A measure of the breadth of the molecular weight distribution:
n
w
M
MPDI
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Molecular weight and its distribution
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Average degree of polymerization (DP): the number of repeating units in the polymer chain.
Average polymer molecular weight
= DP × Mw,monomer
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xx
2xx
xxw MN
MNMwM
xx
xxx
x
MN
MNw
systemofweighttotal
xlengthofsystemofweightw
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Polymer Additives
Improve mechanical properties, processability, durability, etc.
• Fillers– Added to improve tensile strength & abrasion
resistance, toughness & decrease cost– ex: carbon black, silica gel, wood flour, glass,
limestone, talc, etc.
• Plasticizers – Added to reduce the glass transition
temperature Tg– commonly added to PVC - otherwise it is brittle
April 13, 2023 36Prepared By: Peyman Sazandehchi
• Stabilizers
– Antioxidants– UV protectants
• Lubricants – Added to allow easier processing – “slides” through dies easier – ex: Na stearate
• Colorants – Dyes or pigments
• Flame Retardants– Cl/F & B
Polymer Additives
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Ethylene: how is it made?
In « cracking » furnaces, getting larger & larger:
• 180,000 t/y per furnace,
• by heating, and cracking, very quickly (0.1 second), at
high temp. (800 to 850 °C), 'hydrocarbons', i.e
compounds containing carbon and hydrogen,
• In presence of steam, inert, which 'controls' the
cracking reactions, hence the word 'steam-cracking'
April 13, 2023 39Prepared By: Peyman Sazandehchi
Ethylène : how is it made?
• Then, it’s only separation of the by-products, also, produced during the cracking reactions in the furnaces: hydrogen, methane, propylene, butadiene, fuel-oil and etc…
• By means of compression, cooling/refrigeration, distillation,… in order to isolate each component
• Problems: coke deposits (soot/carbon layers) in the heaters: cyclic shut-down (2/3 days every other 30/50 days)
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Cracking furnace
Boiler Feed Water
Radiant Section
Convection Section
~~
Hydrocarbon
Feed
Dilution Steam
HP Steam
Desuper-heater
Cracked Gas to
Separation Section
Transferline Exchanger
BFW
Radiant efficiency: 40 – 42%
Overall efficiency: 92 – 95 %
850 oC1250 oC
120 oC
620 oC
380 oC
520 oC
Steam Drum
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Olefins complex: a steam-cracking unit
MixedProducts
Quench
Drier
Fuel Oil
Hydrogen
Compressor andChilling
Steam
Quench Methane
AcetyleneConverter
Ethane
Ethylene
Propane
Propylene
NAPDConverter
MixedButanes
Gasoline
CrackingFurnaces
Ethane
Naphtha
Acid Gas
PrimaryFractionator
Feeds
Material Movements
Utilities
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Brief History of Polyethylene
PE synthesis discovered accidentally in 1932 by Imperial Chemical
Company (ICC) Scientists
First High Pressure LDPE plant built in 1939
In 1953, large advancements were made by Scientist Carl Ziegler,
inventor of a new catalyst system. A scientist named Giulio Natta also
shares credit for this catalyst development
Known today as the Ziegler-Natta Catalyst (Z/N), this catalyst facilitated
polymer synthesis at lower temperatures and pressures -High Density
Polyethylene (HDPE) materials were introduced soon after
In the late 1970’s LLDPE materials were introduced to the market
Significant Catalyst advances since that time with the advent of single-
site catalysts 46
ETHENE MOLECULES (MONOMERS)BREAKING BONDSJOINING THE MOLECULES
INTO A POLYMER CHAIN
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April 13, 2023 49
Classification of Polyethylene
Polyethylene is classified into several different
categories
based mostly on its density and branching. The
mechanical properties of PE depend significantly
on variables such as the extent and type of
branching, the crystal structure and the
molecular weight.
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Very low density polyethylene (VLDPE)
Low density polyethylene (LDPE)
Linear low density polyethylene (LLDPE)
Medium density polyethylene (MDPE)
High density polyethylene (HDPE)
High molecular weight polyethylene (HMWPE)
Ultra high molecular weight polyethylene (UHMWPE)
Cross-linked polyethylene (PEX)
High density cross-linked polyethylene (HDXLPE)
Classification of Polyethylene
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VLDPE is defined by a density range of 0.880 - 0.915 g/cc. is a
substantially linear polymer, with high levels of short chain branches
LDPE is defined by a density range of 0.910 - 0.940 g/cc. LDPE has a
high degree of short and long chain branching, which means that the
chains do not pack into the crystal structure as well
LLDPE is defined by a density range of 0.915 - 0.925 g/cc. is a
substantially linear polymer, with significant numbers of short
branches
MDPE is defined by a density range of 0.926 - 0.940 g/cc
Classification of Polyethylene
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PEX is a medium- to high-density polyethylene containing cross-link
bonds introduced into the polymer structure, changing the thermoplast
into an elastomer
HDPE is defined by a density of greater or equal to 0.941 g/cc. HDPE
has a low degree of branching and thus stronger intermolecular forces
and tensile strength
UHMWPE is polyethylene with a molecular weight numbering in
the millions, usually between 3 and 6 million. The high molecular
weight results in less efficient packing of the chains into the crystal
structure as evidenced by densities less than high density
polyethylene (e.g. 0.935 - 0.930). The high molecular weight results in
a very tough material
Classification of Polyethylene
HDPEHigh density polyethyleneDensity 935-965 mg/cm3
LLDPELinear low density polyethyleneDensity 915-930 mg/cm3
LDPELow density polyethyleneDensity 910-925 mg/cm3
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Types of Polyethylene Based on Density
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Special Forms of Polyethylene
• Cross-linked PE (XLPE)
– Chemical cross-links improve chemical resistance and improve
temperature properties.
– Cross-linked with addition of small amounts of organic
peroxides
• Dicumyl peroxide, etc.
– Cross-links a small amount during processing and then sets up
after flowing into mold.
– Used primarily with rotational molding
– Extruded Products
• Films (shrink wrap film in particular)
• Pipes
• Electrical wire and cable insulation
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Special High Versions of Polyethylene
• Ultra High Molecular Weight Polyethylene (UHMWPE)
– Extremely high MW at least 10 times of HDPE (MW=3M to 6M)
– Process leads to linear molecules with HDPE
– Densities are 0.93 to 0.94 g/cc and Moderate cost
– High MW leads to high degree of physical entanglements that
• Above Tmelt (130 °C or 266 °F), the material behaves in a
rubber-like molecule rather than fluid-like manner causing
processing troubles, high viscosities• Processed similar to PTFE (Teflon)
– Ram extrusion and compression molding are used.55
Produced through catalyst selection and regulation of reactor conditions
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Ultra High Molecular Weight
Polyethylene(UHMWPE)
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April 13, 2023 57
Ultra high molecular weight polyethylene (UHMWPE)
high-modulus polyethylene (HMPE)
high-performance polyethylene (HPPE)
Prevalent Names of UHMWPE
UHMWPE is a type of polymer classified as a linear
homopolymer and subset of the thermoplastic
polyethylene with extremely long chains, with
molecular weight numbering in the millions,
molecular weight between 3 and 6 million.
The average molecular weight is 10-100 grater than
HDPE.
The longer chain serves to transfer load more
effectively to the polymer backbone by strengthening
intermolecular interactions.
UHMWPE Definition:
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UHMWPE is available commercially either as
consolidated forms, such as :
Powder
Sheets
Rods
Fibers
Advantages and Properties of UHMWPE 15 times stronger than steel and 3 times stronger than Kevlar
Very high impact resistant
High abrasion resistant
non-adherent surface
Very low friction coefficient
Self-lubricating “Wax Like”
Biocompatible (for medical applications)
Good chemical and corrosion resistant
Excellent sound damping and energy adsorption
Excellent dielectric properties
Odorless, tasteless, and nontoxic 60
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• Still susceptible to oxidation with oxidizing acids
(but better than many other polymers)
• Main limitation is operating T (below 100oC) since Tm
~140 oC
• Not a self-supporting material
• High cost for tooling for custom extrusion and custom
parts
UHMWPE Limitations:
Why UHMWPE Can Support Great Tensile Loads?
• It is made up of extremely long chains of polyethylene, which all align in the same direction. Each chain is bonded to the others with so many Van-der-Waals bonds that the whole can support great tensile loads
• When formed to fibers, the polymer chains can attain a parallel orientation greater than 95% and a level of crystallinity of up to 85%. In contrast, Kevlar derives its strength from strong bonding between relatively short molecules
• Because olefins have no polar group, UHMWPE does not absorb water readily
• UHMWPE does not contain chemical groups (such as esters, amides or hydroxylic groups) that are susceptible to attack from aggressive agents, it is very resistant to water, moisture, most chemicals, UV radiation, and micro-organisms
Polymers – Molecular Shape
Configurations – to change must break bonds
• Stereoisomerism
EB
A
D
C C
D
A
BE
mirror plane
C CR
HH
HC C
H
H
H
R
or C C
H
H
H
R
Polymers – Molecular Shape
Conformation – Molecular orientation can be changed by rotation around the bonds– note: no bond breaking needed
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April 13, 2023 Introduction to Polymers 65
Some Properties of UHMWPE Compared to Other Polyethylene
April 13, 2023 Introduction to Polymers 66
Major Trade names and Suppliers
of UHMWPE
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Major Trade names of UHMWPE• Dyneema® (by Royal DSM N.V.)
• Spectra® (by Honeywell)
• TIVAR® (by Quadrant EPP Inc.)
• Polystone-M® (by Röchling Engineering Plastics)
• Tensylon® (by Integrated Textile Systems)
• GARDUR® (by Garland Manufacturing)
• Okulen® (by Ottensteiner Kunststoff GmbH)
• Dehoplast® (by Deutsche Holzveredelung)
• Ramex® (by Symplastics Ltd.)
• Chirulen® (by Poly Hi Solidur)
• Ultra ΙΙΙ® (by Plastic Specialties)
• Hi-Zex Million ® (by Mitsui Sekka Engineering Company)
• Hostalen GUR® (by Ticona/Hoechst/Hoechst Celanese)67
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Production of UHMWPE Take Place in 4 Stages:
• Stage 1: Polymerization (Production of Powder)
• Stage 2: Consolidation (Production of Rods, Sheets and Fibers)
• Stage 3: Machining and Polishing (for Rods and Sheets but Not for Fibers)
• Stage 4: Sterilizing (for medical application only)
Introduction to UHMWPE
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Stage 1: Polymerization of UHMWPE
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Stage 1: Polymerization of UHMWPE
• Polymerization is the process of transforming
the ethylene molecules into UHMWPE in a powder form.
• Ethylene gas is fed into a reactor where The processing conditions (temperature, pressure, and proprietary catalysts) in the reactor determine the average molecular weigh, its distribution, the powder particle size and shape.
• Catalyst is the key to producing white UHMWPE powder with reduced impurities
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Polymerization of UHMWPE
Historical Approach of UHMWPE Polymerization
• Polymerization of UHMWPE was commercialized in the 1950s by Ruhrchemie AG (currently known as Ticona) in Germany (Karl Ziegler)
• In 1953, chemists from the nearby Max-Plank Institute approached scientists at Ruhrchemie AG in Oberhausen with a brown, wet (not fully dried) mass that they claimed was a new form of polyethylene, produced in a new low-pressure process. Convinced of the commercial utility of such a material (the dangers of high-pressure polymerization, such as in the production of LDPE, were widely appreciated) development on UHMWPE began shortly thereafter at Ruhrchemie AG. In 1955, the first commercial polymerization of UHMWPE began and during that same year, the material was first introduced at the K55, a polymer trade show
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Catalysts Used for Polymerization of Olefins
• Ziegler-Natta (TiCl3, TICl4) ,supported on MgCl2
• Chromium (CrO2 or VO2 Phillips), supported on Silica
• Metallocene (Zr, Ti), supported on Silica and on MgCl2
• Late-transition metals (Pd, Ni, Fe)
April 13, 2023 74Prepared By: Peyman Sazandehchi
April 13, 2023 75
• Metallocene catalysts
• Modified Ziegler Catalyst
Catalysts Used for Polymerization of UHMWPE
UHMWPE powder is synthesized from monomers of ethylene, based on two kinds of catalysts which are
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Mechanism of Ziegler Catalysts:
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Mechanism of Metallocenes Catalysts:
• Metallocene ⇒ Is theoretically a monosite
catalyst made from well-defined organometallic
compounds.
•Active sites from group 4 (Ti, Zr, Hf) that have at
least one π ligand (Cyclopentadienyl - Cp).
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Polyolefins: Catalysts
Ratio of rate of addition to rate of transfer determines chain length
More monomer = faster reaction and longer chains
Monomer concentration gradients in particle mean wide MWD
Different types of sites with different relative sensitivities to transfer and propagation mean wide MWD
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General Methods of Polymerization
• Bulk Polymerization• Solution Polymerization• Suspension Polymerization (Slurry)• Emulsion Polymerization • Gas Phase Polymerization
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• There are 5 Common Polymerization Methods: – Some polymers have been produced by nearly 4
Methods
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Gas Phase Polymerization
Schematic of Some Commonly Polymerization Methods
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Definition of Five Polymerization Methods
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Definition of Five Polymerization Methods(Con’t)
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Definition of Five Polymerization Methods(Con’t)
April 13, 2023 Introduction to Polymers 86
Types of Reactors Used in Polymerization Methods
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Types of Reactor Used in Polymerization Methods
(Con’t)
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Technical Parameter for All Types of Reactor Used in Polymerization Methods
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Technical Parameter for All Types of Reactor Used in Polymerization of HDPE
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Technical Parameter for All Types of Reactor Used in Polymerization of LDPE
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Technical Parameter for All Types of Reactor Used in Polymerization of LLDPE
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April 13, 2023 95Introduction to UHMWPE
HDPE Process technology category by reactor type
Uni-modal TechnologyUnipol 1Phillips InnoveneSpherilene
Bi-modal Technology
MitsuiLyondell-Maruze-NissanHostalenUnipol 2Borstar
96
April 13, 2023 Introduction to UHMWPE 101
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Polymerization Techniques for UHMWPE
Slurry Polymerization (Suspension)– Most Prevalent Process (More than 95%)
Gas Phase Polymerization
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• In the literatures, there are two commercial
methods for polymerization of UHMWPE which
are:
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Suspension or Slurry Processes (PE and PP)
Diluent (sub, supercritical)
Propane (supercritical), or C4, C6, C7 used as diluents
An obtain high
(90% PP, 95-98%PE) conversions, although mostly used for (HDPE)
Done with autoclaves, loop reactors
Need to purify, separate and recycle diluents.
Boiling Monomer
Only used for PP
Done with autoclaves, loop reactors
Absence of diluent lowers part of energy
requirement, but need higher pressures
Low polymer solubility might increase fouling
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Slurry Reactors
Slurry process has a short residence time
Reaction medium is homogeneous, especially in loops so it is rare to find hot spots
The solubility of the polymer into the diluent limits the product range (ρ> 0.93 g/cm3)
The recovery of unreacted materials is sometimes complicated, especially in the case
of a high-boiling diluent.
Use catalyst with high H2 sensitivity, supercritical conditions
Relatively short transitions (CSTR-like RTD still needs to be dealt with)
Fouling may result if have poor control of MFR and/or density due to solubility of
Polymer (more in C6 than with C3/C4)
MFR range can be limited by the solubility of the hydrogen in the solvent (more in C6
than with C3/C4).106
Slurry Reactors Main advantage is simplicity
Very simple to install and operate
More limited in operation flexibility
Operated as a CSTR and is used in slurry, bulk and solution processes
Main disadvantage is low surface to volume (5 m2/m3 vs. 100 m2/m3
for tubes) – OK heat
Removal for low solids, but harder for commercially acceptable
solid contents and reaction rates
Have cooling jackets, but also need external heat exchangers
and/or condensation of diluent
107
Slurry Reactors
• Loop reactors (one – older – or multiple legs) operates at higher monomer and slurry
concentrations than stirred autoclaves and allows for higher space time yield
• Up to 50% of the world’s polyolefin resins are produced in loop reactors because of
Excellent heat removal capacity.
• Operate at slurry concentrations of about 45 – 50 wt % polymer.
• Conversion limited only by quantity of monomer needed to evacuate powder
• Agitation is achieved by pumping the slurry at high velocity through the reactor
• Run full – gives better H2 incorporation because no gas head space.
108
CSTR Autoclaves or Loop Reactors
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• Gas phase processes economical and energy-efficient
alternative to liquid phase polymerization
Separating the polymer from the monomer is easy since no
need
to flash off liquid monomer or diluent (high energy
requirement)
Heat removal is a bigger problem than in slurry Can use
« supercondensed » cooling by injecting inert diluents or
monomer at
the dew point to evaporate on hot spots – good for
production, but
renders grade changes a bit of a challenge
Gas Phase Reactors
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April 13, 2023 115
• Extended product range is also possible with gas phase reactors as
there is no solubility limit for hydrogen and co-monomer in the reaction
medium Densities down to 910 kg/m³ may be produced
• Theoretically, MFR range in a gas phase reactor is unlimited.
• Products with higher melt flow index and increased co-monomer
content
(relative concentrations not limited by solubility in liquid phase).
• Lower densities are possible, need to reduce TR < TSoftening
• Playing with hydrogen sensitivity of catalyst used can enhance this.
Gas Phase Reactors
April 13, 2023 116
Prepared By: Peyman [email protected]
FBR Gas Phase Reactors• Good heat transfer w.r.t. stirred beds b/c have very high gas particle velocity.
• Heat transfer augmented by injection of condensables used for PE,PP,iPP
• Modelling as CSTR (usually OK)… or much more complex(bubble and wake phases) because of multiphase flow.
FBR Gas Phase Reactors• Good temperature control* (high recirculation ratios, vaporization of liquid monomer)
• Lower operation costs For a gas phase reactor!
• Grade flexibility - Easy control over H2 concentration
• Higher comonomer incorporation - no dissolution
• High quality impact copolymers
• Needs particles that can fluidize well - catalyst design
• Control of fluidized-bed is not trivial
• Severe fouling and particle agglomeration can occur
• Large reactors - more off-spec product during (long) grade transitions
• Stable temperature control is extremely important for FBRs
• Hot Spots formed when heat transfer between particle and continuous
• phase is poor, particle overheats and reaches softening point.
• Hot spots must be minimized cause formation chunks and lumps
• small chunks can cause transport and processing problems downstream;
• large lumps can block the outlet of the reactor – immediate shut-down; if
• not shut down properly, total meltdown. 118
FBR Gas Phase Reactors
• Stable temperature control is extremely important for FBRs
• Static charges can also be a significant problem in gas phase reactors in general, and in fluidized bed
reactors in particular.
• Polymer is poor conductor of electricity
• static electricity generated by the intense mixing and high velocity of the circulating monomer may
cause fine particles to stick to the reactor walls
• Heat transfer in FBR at wall already poor and fine particles stuck to the wall can continue to polymerize
and melt to form sheets & chunks (c.f. SPM).
• Polymer sheets can block the outlet of the reactor if they fall off the
• wall, requiring immediate shutdown of the reactor.• Very different flow regimes + multiphase flow
make simulation (full) of FBRs challenging
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UHMWPE powders contemplated under the invention are produced by slurry
polymerization in an inert solvent in the presence of a specific catalyst,
or by gas-phase polymerization substantially without such inert solvent,
but cannot be produced by other polymerization processes involving such
high temperature as to melt or dissolve the formed polyethylene. The
polymerization according to the invention is effected with the use of a
catalyst comprising a component containing either one or both of titanium
and vanadium compounds and an organometallic compound at a
pressure in the range of 0-70 (barg) and at a temperature below the
melting point of polyethylene or usually in the range of -20° -110° C.,
preferably 0° -90° C. and with or without solvents which are organic and
inert to Ziegler catalysts. Specific examples of such solvents include
butane, pentane, hexane, heptane, octane, cyclohexane, benzene,
toluene and xylene. Other high boiling organic solvents such as decalin,
tetralin, decane and kerosine may also be used if necessary depending
upon the particular manner of processing of UHMWPE. The molecular weight
of UHMWPE may be controlled by changing the polymerization temperature
or pressure and with use of hydrogen if necessary.
Stage 1: Polymerization of UHMWPE (Summary )
April 13, 2023 Introduction to UHMWPE 127
UHMWPE Polymerization Reactors Compared with Other PE Polymerization Reactors
(Summary )
April 13, 2023 128
UHMWPE Plant in China
Stage 2:Consolidation of UHMWPE
Prepared By: Peyman [email protected]
Limitation of UHMWPE for Consolidation
• The extremely high molecular weight (EHMW) limits UHMWPE to
use conventional processing techniques (such as: Screw
extrusion, Injection molding, blow molding and etc) for converting
this materials from powder to a final product. Because EHMW
reduces the ability of material to flow; actually, UHMWPE does not
flow like lower molecular weight polyethylenes when raised above
its melting temperature; for this reason, new methods of
consolidating was applied (such as: Ram Extrusion, Compression
Molding and etc) .
130
Stage 2: Consolidation of UHMWPE
There are Six Commercial Method for Consolidated
Forms of UHMWPE (Sheets, Rods, Fibers)Compression Molding (For Producing Sheets)
(Generally Used by Quadrant, PPD, Hutchinson, NorthAmerican)
Ram Extrusion (For Producing Rods)
(Generally Used by Quadrant, Garland Manufacturing, Artek)
Gel Spinning (For Producing Fibers)
(Exclusively Used by DSM)
Direct Compression Molding (For Producing Parts)
(Exclusively Used by Perplas)
Hot Isostatic Pressing (HIP'ing) (For Producing Rods)
(Generally Used by Biomet and Warsaw)
Sintering (Especially Used in Medicine)
(Generally Used by Quadrant, Solus, Perplas)
• The process of consolidation in UHMWPE requires the proper combination of temperature, pressure, and time. The precise combinations of these variables used to produce commercially available molded and extruded stock materials remain proprietary, but the scientific principles underlying consolidation of UHMWPE are generally well-understood. The governing mechanism of consolidation is self-diffusion, whereby the UHMWPE chains (or chain segments) in adjacent resin particles intermingle at a molecular level. The kinetics of intergranular diffusion is promoted by close proximity of the interfaces (at elevated pressures) and thermally-activated mobility of the polymer chains (at elevated temperatures). As a diffusion-limited process, consolidation of UHMWPE requires sufficient time at elevated temperature and pressure for the molecular chains to migrate across grain boundaries. In contrast with grain boundaries, which reflect the normal ultrastructure of UHMWPE, consolidation defects may arise when the proper combination of pressure, temperature, and time are not used
April 13, 2023 Introduction to UHMWPE 132
Polyethylene fibers
The theoretical elastic modulus of the covalent C-C bond in the fully extended PE molecule is 220 Gpa. Experimental value in PE fibres - 170 Gpa.
Entanglement network Fibrillar crystal
Dyneema or SpectraOrientation > 95%Crystallinity up to 85%
Normal PEOrientation lowCrystallinity < 60%
Stretching
Compression Molding Technique (for Producing Sheets and Slabs)
134April 13, 2023Prepared By: Peyman Sazandehchi
Compression Molding (History and Definition)
• This manufacturing technique originated in Germany in the
1950’s. Although this technology is the main processing
method used with thermoset resins, it can also be employed to
process UHMWPE
• Consolidation of the materials is a direct result of the Heat,
Pressure and Time combination used by the processors this
however is dependant upon the size of hydraulic presses and
mould dimensions used
• Generally Used by Quadrant, PPD, Hutchinson, North American)
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Prepared By: Peyman [email protected]
Compression Molding Process Description
• The equipment is commonly situated in a clean and controlled environment
• Virgin powder is loaded into the clean reciprocating mould used in the press.
• The mould is retracted into the press housing.
• Once situated pressure is applied to the mould at a controlled rate.
• A Temperature profile is applied to the mould using electric or fluid heated systems
• The mould is opened and the compression moulded product removed from the
mould, which is cleaned and the process repeated.
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Ram Extrusion Technique (for Producing Rods)
Prepared By: Peyman [email protected]
Ram Extrusion (History and Definition)
• Conventional screw extrusion techniques cannot be used with UHMWPE due to the high melt viscosity, during the 1970’s in the United States a process called ram extrusion was developed.
• Using this technique UHMWPE can be extruded up to 350 mm in diameter
• Generally Used by Quadrant, Garland Manufacturing, Artek
138
Prepared By: Peyman [email protected]
Ram Extrusion Technique• Virgin UHMWPE powder is transferred to the extruder hopper from the storage silos
• The extrusion equipment is commonly situated in a clean controlled environment
• The hopper is mounted on the extrusion die and semi-continuously feeds the powder
into the heated die chamber
• The extrusion die consists of a heated die with a horizontal reciprocating ram at the
rear, during the reverse ram cycle the powder is accepted into the die.
• The forward motion of the ram applies pressure to the UHMWPE powder, which
forces the material through the die section where temperature is applied.
• Back pressure within the die is a direct result of the frictional forces of the molten
resin against the heated die wall.
• The molten extrudate manufactured at very low production rates (mm/min) is
supported and cooled within the clean environment.
•
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Direct Compression Molding Technique (DSM) (for Producing Direct Parts)
141April 13, 2023Prepared By: Peyman Sazandehchi
Direct Compression Molding (DSM)
• Utilising a similar principle to the large-scale compression mould method, this uses a small-scale operation to mould the orthopedic implant directly, thus enabling the manufacture of a component with a highly polished direct moulded surface therefore removing the machining surface definition present on conventionally machined products articulating surface.
• By undertaking the compression moulding operation over a smaller projected area it was possible to attain greater control over the Pressure and Temperature cycles than simple bulk compression moulded, thus in theory improving the properties of the product although micro testing evaluation is only possible due to the sample size.
• Exclusively Used by Perplas142
Gel Spinning Technique (for Producing Fibers)
143April 13, 2023Prepared By: Peyman Sazandehchi
Gel Spinning Technique
• Fibers are made using a DSM patented (1979) method called
gel spinning.
• A precisely-heated gel of UHMWPE is processed by an
extruder through a spinneret.
• The extrudate is drawn through the air and then cooled in a
water bath. The end-result is a fiber with a high degree of
molecular orientation, and therefore exceptional tensile
strength. Gel spinning depends on isolating individual chain
molecules in the solvent so that intermolecular entanglements
are minimal. Entanglements make chain orientation more
difficult, and lower the strength of the final product.
144April 13, 2023
Dyneema® and Spectra® Fibers
• Dyneema and Spectra are gel spun through
a spinneret to form oriented-strand
synthetic fibers of UHMWPE, which have
yield strengths as high as 2.4 GPa and
density as low as 0.97 kg/l
145April 13, 2023
Prepared By: Peyman [email protected]
Additives of UHMWPE
• UHMW-PE properties can be enhanced through the use of additives such as colorants, UV and heat stabilizers, anti-static agents, wear-resistant fillers and friction-reducing lubricants. Metals or ores can be used to increase the weight and make the polymer magnetically detectable, while other fillers increase the environmental operating temperature
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Stage 3:Machining and Polishing of UHMWPE
Prepared By: Peyman [email protected]
Machining Processes
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• Sawing
• Turning
• Milling
• Drilling
• Grinding/Sanding
• Planing
Prepared By: Peyman [email protected]
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• Sawing: For circular sawing, carbide-tipped blades give the best results. A 12-14” diameter blade should have approximately 24 teeth. Feed speeds can range from 10 to 40 feet per minute. For band sawing a blade with three teeth per inch, raker set and positive rake angel are recommended. Feed speeds range from 10 to 40 feet per minute.
• Turning: Use high-speed steel tool bits with 10” front and side clearance and 15-30” rake. Lower cutting speeds of between 600 and 1,000 feet per minute are required. However, it is often necessary to run at a higher rpm to keep chips clear of the machine. Cutting fluids should not be necessary, but a blast of compressed air will sometimes aid in chip removal. When trying to achieve close tolerances or a very thin walled part in UHMW-PE, machine in passes. Remove most of the material on the first pass, then let the piece sit and rest overnight.
• Milling: Cutters designed for machining aluminum give the best results. Cutting speed of 600 to 1,800 feet per minute are suggested, with a fed rate of approximately 0.01 inches per revolution. Router bits work well for slotting and light milling.
• Planing: Wood planers readily reduce the thickness and true-up the surface of UHMW-PE. A rigid machine with sharp blades will give very efficient stock removal and good surface finish. To minimize the potential to warp when machining UHMW-PE, plane half of the desired thickness from each side of the sheet.
• Drilling: Conventional high-speed drills are adequate for most drilling applications. For optimum performance, use special low helix drills with polished flutes. Drilling pilot holes prior to drilling a large hole is not recommended for UHMW-PE, because its properties cause the drill to grab and pull itself into material.
• Grinding/Sanding: Due to UHMW-PE’s abrasion resistant properties, grinding and sanding are usually ineffective. In fact, grinding may cause the material to melt and smear, resulting in a clogged grinding wheel.
Stage 4:Sterilizing of UHMWPE in medical applications
Prepared By: Peyman [email protected]
Major Impurities of UHMWPE Powder
• The trace impurities of titanium, aluminum,
and chlorine are residuals from the catalyst,
whereas the trace levels of calcium, as well as
the ash content, depend upon the storage and
handling of the powder after polymerization
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Sterilizing of UHMWPE
• In medical applications of UHMWPE, surgery
and joint replacements, after consolidation
polymer should not have any free radicals and also
should be sterilized , so some sterilizing techniques
would be applied which are:
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UHMWPE Sterilization
Ethylene oxide (initially) & Gas plasma (recently) – little effect on PE physical property
Gamma Radiation in air : majority
- Dose : 2.5 – 4 Mrads - Markedly affect physical properties
of UHMWPE - Produce Free Radicals
Cross linked PE
Prepared By: Peyman [email protected]
Cross linked PE
Prepared By: Peyman [email protected]
April 13, 2023 Introduction to Polymers 156
Free Radicals Generated by Radiation Surface layer: oxidative degradation and very little cross-linking Oxidative degradation continues during storage and use in vivo Deep layer (beneath oxidation): cross-linking
Cross linked PE
Prepared By: Peyman [email protected]
Cross linked PE
Prepared By: Peyman [email protected]
Cross linked PE
Prepared By: Peyman [email protected]
PE Oxidation
Extensive chain-scission, weakening and embrittling the PE Directly, reduce wear resistance, delamination and fracture Indirectly, reduce cross-linking
Cross linked PE
Prepared By: Peyman [email protected]
How to Remove Free Radicals ?
Annealing :
Reduced by heating below its melting temperature (about 135oC).
Remelting : Eliminated by heating
above its melting temperature.
Cross linked PE
Prepared By: Peyman [email protected]
Annealing• To anneal UHMWPE, the material should be
heated to 135 °C to 138 °C in an oven or a liquid bath of silicone oil or glycerine. The material must then be cooled down at a rate of 5 °C/h to at least 65 °C. Finally, the material should be wrapped in an insulating blanket for 24 hours to bring to room temperature
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Annealing vs. Remelting
Annealing :
Induce less change in material morphology and properties Not effective in extinguishing free radicals as remelting
Remelting : Not clear in negative mechanical effect
Cross linked PE
Prepared By: Peyman [email protected]
Alternative Sterilization Techniques
Ethylene oxide or gas plasma: no free radicals & no cross-linking Gamma radiation sealed in low-oxygen atmosphere Heat in the nitrogen packaging
(37oC- 50oC/ 6days) after radiation
Cross linked PE
Prepared By: Peyman [email protected]
Cross linked PE
Prepared By: Peyman [email protected]
Cross-Linked, Thermally Stabilized PE
Marathon, Depuy
XLPE, Smith & Nephew
Longevity, Zimmer
Durasul ,Sulzer
Crossfire, Stryker-
Howmedica
Cross linked PE
Marathon, Depuy
Gamma Radiation-Cross-Linked and Remelted PE Extruded bars of UHMWPE cross linked by 5 Mrads of gamma radiation heated to 155oC for 1 day slow cooling to room temp. Heating above the melt temp.: removes free radicals Remove surface oxidized material & Manufacturing Final sterilization with gas plasma
Cross linked PE
Prepared By: Peyman [email protected]
XLPE, Smith & Nephew
Gamma Radiation-Cross-
Linked and Remelted PE
Same manner as
Marathon
Except, final sterilization
with ethylene oxide
Cross linked PE
Prepared By: Peyman [email protected]
Longevity, Zimmer
Electron Beam-Cross-Linked and Remelted PE
Compression molded sheets of UHMWPE cross linked by 10 MeV electron beam remelting manufacturing sterilize with gas plasma
Cross linked PE
Prepared By: Peyman [email protected]
Durasul, Sulzer Electron Beam-Cross-Linked and Remelted PE Similar to Longevity Process with two exceptions PE pucks are cross-linked from both sides with 10 MeV electron beam to a total 9.5 Mrads Preheated ( 125oC) while electron beam-cross-linking
Cross linked PE
Prepared By: Peyman [email protected]
Crossfire, Stryker-Howmedica
Gamma-Cross-Linked and Annealed
PE 7.7 Mrads gamma radiation Annealing : heating just below the melt temp. Sterilized by 2.5 to 3.5 Mrads gamma radiation while packaged in nitrogen
Cross linked PE
Prepared By: Peyman [email protected]
Growing Applications of UHMWPE • Military Services• Personal Protection• Vehicle Protection• Protective Gloves• Commercial Fishing• Offshore• Heavy Marine• Industrial• Sports• Medical• Packing• Transporting and Handling• Agricultural Equipments• Food and Beverage• Pump and Pipeline • Civil engineering and earthmoving equipment• Membrane Technology• Bearings and bushings• Hopper, chute, truck bed, and railcar liners
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Personal Protection Applications
• Bullet-resistant vests
• Helmets
• Inserts
• Bulletproof fabric
174
Vehicle Protection Applications• Military vehicles (Body)
• Police vehicles (Panels)
• VIP vehicles (Panels)
• Aircraft (Cockpit Doors)
• Ships (Body)
• Helicopters (Floor and Seat)
• Spall liners175
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Sport Applications
Snowboard Manufacturing Running Sport
Sky
Tennis
Rock Climbing Fishing
Yachting LinesBow stringsClothing (Fencers and skaters)
Kite and Sails
Why Medical Application of UHMWPE Is Growing:
• The diverse uses of lot-controlled UHMW-PE range from standard wear applications to implantable products.
• Biocompatibility, self-lubrication, and wear resistance are among the major requirements of articulating surfaces made from UHMW-PE.
• The biological response to UHMW in soft tissue and bone has been well characterized by a history of clinical use.
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Medical Applications
Hip and Spine Implants
Surgical Cables and Orthopedic sutures
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Medical Applications (Cont’d)
Artificial Knee Joints
Artificial Bone Artificial Foot UHMW-PE Tibia inserts
Prepared By: Peyman Sazandehchi
181
Cordage, Ropes and Belt Applications
Strong Ropes Powerful Cordages
Ropes of 4WD Cars Strong Belts
Prepared By: Peyman [email protected]
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Supreme Protector Fabric Worlds Strongest Woven Textile...
Protective Clothing
Prepared By: Peyman [email protected]
184
Engineering Parts’ Applications
wheel, bearing bushes, sliding elements, chute liners, bunker liners, chain wear strip, guide strips, rings and liners
Other Applications
Fender Applications
Screw For Labeling Applications and Cutting Applications
Some Dock and Bridge Part Applications
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Other Applications
Food Grade UHMWPE Cutting Board
Tractor Lifting Devices
Transport Applications
Sprockets
Bearing and Bushing
Commercial Fishing
• Trawl nets, purse seine nets and aquaculture nets
• Fishing Ropes (warp lines, bridles, headlines, footropes, rib line)
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189
Other Applications
Flexible Multipurpose Suction Hose (16 bar)
and Handle Chemicals
Butterfly Valve Sealing
Radial Cartridge Filter
Wastewater Treatment Application
April 13, 2023 190
Gar-Dur® UHMW applications for.
Wastewater Treatment Plant Equipment. Primary and Secondary Sedimentation and Clarifier Tanks, Chain and Flight Systems
Prepared By: Peyman [email protected]