fundamental of polyethylene and ultra high molecular weight polyethylene by peyman sazandehchi

1

Fundamental of Polyethylene

&Ultra High Molecular Weight Polyethylene

(UHMWPE)

April 13, 2023

Prepared By:Peyman Sazandehchi from

[email protected]

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


Types of polymers & polymerizations

April 13, 2023 4

Classification of Polymers

Polymer Structure

Condensation

Polymers

Addition Polymers

Polymerization Mechanism

Step- Polymerizati

on

Chain- Polymerizati

on


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.

April 13, 2023 5

Polymer Structure

The condensation system


Condensation polymers (New definition)

April 13, 2023 6

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


Homopolymer vs. copolymer

Homopolymers are polymers composed of only one repeating unit in their molecules.

April 13, 2023 7

What are homopolymers?

What are copolymers?

Copolymers are polymers composed of two different repeating units in their molecules.


Homopolymer vs. copolymer

April 13, 2023 8

Types of copolymer systems

Random copolymer

Alternating copolymer

Block

Graft copolymer

random

block

graft

alternating


Classification of polymers depending on their structure

April 13, 2023 9

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



Branched polymers

April 13, 2023 10

What is the effect of branching on polymer properties?Crystallinity

Is it branched polymer?!!!


• 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

April 13, 2023 11



Cross-linked polymers

April 13, 2023 12

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


Thermosets vs. Thermoplastics

What are thermoset polymers?

April 13, 2023 13

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


•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

April 13, 2023 15

Plastics

Thermosets

Highly cross-linked

Thermoplastics

Amorphous Crystalline

Classification of polymers – polymer structure


Crystalline and amorphous behaviorFringed-Micelle Theory

April 13, 2023 16

Polymers consist of small-sized, ordered crystalline regions (crystallites)These polymers imbedded in amorphous polymer matrix


Polymers rarely exhibit 100% crystallin

e

April 13, 2023 17


April 13, 2023 18

Ex: polyethylene unit cell

• Crystals must contain the polymer chains in some way – Chain folded structure


Folded-Chain Lamella

Theory

April 13, 2023 19

lamella

A stack of polymer chains folded back on themselves

like this


Crystalline and amorphous behavior

Spherulites

April 13, 2023 20

amorphousregion

crystalline region


Crystalline and amorphous behavior

April 13, 2023 21

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


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.


April 13, 2023 23

Properties of polymer

Thermal properties

Mechanical properties

Chemical properties

Electrical & Optical properties


• 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


• Mechanical properties;

it is categorized based on (also can be

categorized based on tensile, impact,

flexural, etc);

– Stiffness

– Strength

– Toughness

April 13, 2023 25


• Chemical properties

– Solubility- in various solvent

– Permeability to gases or other molecules

– Chemical resistance towards chemicals,

environment & radiation

April 13, 2023 26


• 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

April 13, 2023 27


April 13, 2023 Introduction to Polymers 28

The ability to bend without

breaking

Thermosets vs. Thermoplastics

Molecular weight and its distribution

April 13, 2023 29

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



xxw MwM

April 13, 2023 30

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


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

April 13, 2023 31

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

April 13, 2023 32

Illustrative examples….

Let us say we have:

10 chains of 100 molecular weight



200 chains of 10,000 molecular weightMw is much better indicator of the properties to be expected in a

polymer than Mn


1n

w

M

MPDI

aaxxv MwM 1][

April 13, 2023 33

A measure of the breadth of the molecular weight distribution:

n

w

M

MPDI



April 13, 2023 34

Average degree of polymerization (DP): the number of repeating units in the polymer chain.

Average polymer molecular weight

= DP × Mw,monomer


xx

2xx

xxw MN

MNMwM

xx

xxx

x

MN

MNw

systemofweighttotal

xlengthofsystemofweightw

April 13, 2023 35


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

[email protected]

• 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

April 13, 2023 37


Ethylene,

What is it, actually?

April 13, 2023 38


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'


[email protected]

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)

April 13, 2023 40

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

April 13, 2023 41

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

April 13, 2023 42

Ethylène Dérivatives

43April 13, 2023Prepared By: Peyman Sazandehchi

[email protected]

April 13, 2023 44

April 13, 2023 45

Polyethylene or Polythene


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

MAKING POLYTHENE

(A POLYMER)

FROM ETHENE

47


ETHENE MOLECULES (MONOMERS)BREAKING BONDSJOINING THE MOLECULES

INTO A POLYMER CHAIN

48


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.


50

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)


April 13, 2023 51

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


April 13, 2023 52

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


HDPEHigh density polyethyleneDensity 935-965 mg/cm3

LLDPELinear low density polyethyleneDensity 915-930 mg/cm3

LDPELow density polyethyleneDensity 910-925 mg/cm3

April 13, 2023 53

Types of Polyethylene Based on Density


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

54

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

April 13, 2023 56

Ultra High Molecular Weight

Polyethylene(UHMWPE)


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:

April 13, 2023 58

April 13, 2023 59

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

April 13, 2023 61

• 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



Some Properties of UHMWPE Compared to Other Polyethylene


Major Trade names and Suppliers

of UHMWPE


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

April 13, 2023 68

Processing Of UHMWPE

Introduction to UHMWPE


April 13, 2023 69

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


Stage 1: Polymerization of UHMWPE


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

April 13, 2023 71

April 13, 2023 72

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

73

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)


[email protected]

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

April 13, 2023 76

Mechanism of Ziegler Catalysts:

April 13, 2023 77

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).

April 13, 2023 78

April 13, 2023 79


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

April 13, 2023 80

General Methods of Polymerization

• Bulk Polymerization• Solution Polymerization• Suspension Polymerization (Slurry)• Emulsion Polymerization • Gas Phase Polymerization

April 13, 2023 81

• There are 5 Common Polymerization Methods: – Some polymers have been produced by nearly 4

Methods


Gas Phase Polymerization

Schematic of Some Commonly Polymerization Methods

April 13, 2023 83

Definition of Five Polymerization Methods

April 13, 2023 84

Definition of Five Polymerization Methods(Con’t)

April 13, 2023 85

Definition of Five Polymerization Methods(Con’t)


Types of Reactors Used in Polymerization Methods

April 13, 2023 87

Types of Reactor Used in Polymerization Methods

(Con’t)

April 13, 2023 88

Technical Parameter for All Types of Reactor Used in Polymerization Methods


April 13, 2023 89

Technical Parameter for All Types of Reactor Used in Polymerization of HDPE


April 13, 2023 90

Technical Parameter for All Types of Reactor Used in Polymerization of LDPE


April 13, 2023 91

Technical Parameter for All Types of Reactor Used in Polymerization of LLDPE


April 13, 2023 92

Process Overview of HDPE


April 13, 2023 93


April 13, 2023 94

PE Process Technology …


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

April 13, 2023 102


April 13, 2023 103

Polymerization Techniques for UHMWPE

Slurry Polymerization (Suspension)– Most Prevalent Process (More than 95%)

Gas Phase Polymerization

April 13, 2023 104

• In the literatures, there are two commercial

methods for polymerization of UHMWPE which

are:


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

April 13, 2023 105

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

April 13, 2023 109


April 13, 2023 110

April 13, 2023 111


April 13, 2023 112


April 13, 2023 113


• 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


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


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

119Prepared By: Peyman Sazandehchi

[email protected]

April 13, 2023 120

April 13, 2023 121


[email protected]

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 )


UHMWPE Polymerization Reactors Compared with Other PE Polymerization Reactors

(Summary )

April 13, 2023 128

UHMWPE Plant in China

Stage 2:Consolidation of UHMWPE


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


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)


[email protected]

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)

135


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.

April 13, 2023 136

April 13, 2023 137

Ram Extrusion Technique (for Producing Rods)


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


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.

•

April 13, 2023 139

Direct Compression Molding Technique (DSM) (for Producing Direct Parts)


[email protected]

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)


[email protected]

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


April 13, 2023 146

Additives of UHMWPE


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


[email protected]

Stage 3:Machining and Polishing of UHMWPE


Machining Processes

April 13, 2023 149

• Sawing

• Turning

• Milling

• Drilling

• Grinding/Sanding

• Planing


150

• 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


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

April 13, 2023 152


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:

April 13, 2023 153


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


Cross linked PE


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


Cross linked PE


PE Oxidation

Extensive chain-scission, weakening and embrittling the PE Directly, reduce wear resistance, delamination and fracture Indirectly, reduce cross-linking

Cross linked PE


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


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


[email protected]

http://en.wikipedia.org/wiki/Anneal

http://en.wikipedia.org/wiki/Silicone_oil

http://en.wikipedia.org/wiki/Glycerine

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


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


Cross linked PE


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


XLPE, Smith & Nephew

Gamma Radiation-Cross-

Linked and Remelted PE

Same manner as

Marathon

Except, final sterilization

with ethylene oxide

Cross linked PE


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


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


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


April 13, 2023 172

Applications Of UHMWPE


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

173

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

176

Sport Applications

Snowboard Manufacturing Running Sport

Sky

Tennis

Rock Climbing Fishing

Yachting LinesBow stringsClothing (Fencers and skaters)

Kite and Sails

Example of Snowboard Manufacturing Process


[email protected]

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.

178


179

Medical Applications

Hip and Spine Implants

Surgical Cables and Orthopedic sutures

180

Medical Applications (Cont’d)

Artificial Knee Joints

Artificial Bone Artificial Foot UHMW-PE Tibia inserts

Prepared By: Peyman Sazandehchi

[email protected]

181

Cordage, Ropes and Belt Applications

Strong Ropes Powerful Cordages

Ropes of 4WD Cars Strong Belts


http://www.qx100.com/showimg.htm?img=/en_sj/2008-11/3/2008113145459197.jpg

182

Lining Applications

Truck Bed Liners Flow Lining


183

Supreme Protector Fabric Worlds Strongest Woven Textile...

Protective Clothing


184

Engineering Parts’ Applications

wheel, bearing bushes, sliding elements, chute liners, bunker liners, chain wear strip, guide strips, rings and liners

185

Packing, Conveying and Food Processing Applications


Other Applications

Fender Applications

Screw For Labeling Applications and Cutting Applications

Some Dock and Bridge Part Applications

187

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)


[email protected]

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


191

Pipeline Handling Applications


April 13, 2023 192

Thank you for your kind attention

The end


fundamental of polyethylene and ultra high molecular weight polyethylene by peyman sazandehchi

Documents

polymers peyman sazandehchi

polymers iran

structurebranched polymers

thermoset polymers

thermoplastic polymers

structurecrosslinked

polymers polyester resin

nylon41412 introduction