pe additives overview

PE Additives Overview

Polyethylene Film Training Program

Additives for Polyethylene Resins

• What are additives• Selection criteria• Additive types

– Antioxidants & stabilizersPrimary antioxidantsSecondary antioxidantsUV light stabilizers

– Processing aids– Catalyst neutralizers– Slip agents– Antiblocks – Antistatic agents

• Purpose for additives• Additive mechanisms• Typical commercial additives

What Are Additives?

• Materials added to the polymer to– Provide stabilization during processing or end use– Enhance processability– Modify selected physical properties of the final PE film or molded article

• Examples– Antioxidants Reduce Gel Formation During Processing

– Processing Aids Eliminate Melt Fracture in Blown Film

– Slip Reduce COF of Films

– Release/Lubricating Agents Provide Mold Release For IM Resins

Selection Criteria for Additives

• Select the additive that provides the desired performance during processing and/or end-use in the most cost effective manner possible while meeting all safety, handling, regulatory and legal requirements

• Understanding additive mechanism important to – Proper additive selection

– Choosing appropriate concentration

– Minimizing potential interactions w/ other additives

Selection Criteria for Additives

• Additional factors in selection process– Specific customer requirements

– Unique processing conditions, unusual end-use requirements– Performance aspects

– Migration, diffusion, volatility, solubility– Additive form

– Liquid, powder, flake, granule, prill, pastille, pellet, packaging options– Method of addition

– Direct, additive pre-blend, masterblend, masterbatch, hardware requirements– Safety concerns

– Dust generation potential, minimum ignition energy (MIE)– Industrial hygiene

– Personal protective equipment (PPE) requirements, OSHA– Regulatory issues

– Chemical inventories, foodlaw, right-to-know, CONEG (heavy metals), Kosher, endocrine disrupter, BSE (mad cow)

– Legal considerations– FTO, potential patentability

– Cost/performance balance – Total formulation cost vs performance

Antioxidants for Polyolefins

• Principle antioxidant types– Classified by their stabilization chemistry

Primary antioxidants hindered phenolsSecondary antioxidants phosphites

– Other types available for specialized applications

• Why are they needed?– Minimize oxidation of PE and PP during melt processing– Extend lifetime of final product in end use application

provide long term thermal stability (LTTS)

• What do they prevent or minimize?– Excessive polymer crosslinking (MI decrease) or chain scission (MI

increase)– Gel formation– Loss of physical properties– Discoloration (in some cases)

Autoxidation CycleSimplified thermo-oxidative degradation cycle for

Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH

Cycle 1 ROO*RO* + *OH Cycle 2


Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


1 – Polymer is exposed to shearand/or heat, which strips ahydrogen, leaving a radical


Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


2 – Polymer radical reactswith oxygen forming a peroxy group


Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


3 – Peroxy reacts with another polymermolecule creating another radical aswell as a hydro peroxide


Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


4 – By thermal or UV, the hydroperoxide can split apart


Non-stabilized PE

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


5 – these species want to take a hydrogen(to make alcohol or water) from anotherpolymer molecule, resulting in another radical

6 – the number of polymer radicals continues to grow through cycle

The Problems with Radicals (R*)

In polyethylene, an R* will react with another R*, thereby making a polymer molecule with increased (almost doubled) molecular weight (“cross-linking”). This will manifest itself as a gel in the bulk film.In polypropylene, the R* will strip away the hydrogen from a tertiary carbon, thereby encouraging the splitting of the polymer backbone at that point (“chain scission”).

H H H H H HI I I I I I

— C—–C–—C–—C–—C–—C—I I I I I I

CH3 H CH3 H CH3 H

Hydrogen on tertiary carbon on PP chain

Stabilization with Hindered Phenol A/O’s

• Hindered phenol antioxidants– First line of defense stabilization

Trap alkoxy (RO*) & peroxy radicals (ROO*) Reaction results in hydroperoxide formation (ROOH)

can lead to further degradation unless secondary A/O is present

– Provide stabilization for PEAt melt processing temperaturesDuring end use at lower temperatures (LTTS)

– Can be regenerated in the polymer may react more than once

– Reaction products can cause discoloration (yellowing)

– Use of hindered phenols at low levels in some LDPE resins can cause V-gels

Stabilization Cycle - PhenolsSimplified antioxidant stabilization cycle for PE stabilized with

Hindered Phenol (ArOH) stabilizers

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


ArO* + ROH

+ ArOH

+ ArOH

ArO* + ROOH



RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


ArO* + ROH

+ ArOH

+ ArOH

ArO* + ROOH

Phenolic antioxidant interrupt the cycles, preventing the formation of R*.ArO* is a relatively stable species because of its aromatic ring.



RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


ArO* + ROH

+ ArOH

+ ArOH

ArO* + ROOH

However, peroxides are still formed

Typical Hindered Phenols Used in PE Resins

HO CH3

C

O

OH CH2CH2 O C18H37

C

O

OOH CH2CH2 CH2

4

C

BHT

Irganox® 1076Anox™ PP18Naugard® 76

Irganox® 1010Anox™ 20Naugard® 10

BHEB HO CH3C2 H5

Stabilization with Secondary AOs

• Typically are Phosphite antioxidants– Second line of defense in stabilization

decompose hydroperoxides

– Provide stabilization only at melt processing temperaturesminimal impact on LTTS

– Normally need hindered phenol antioxidant present to function

– Cannot be regenerated in the polymerneed "active" phosphite to protect polymer

– Can minimize discoloration from hindered phenol reaction products

• Optimum ratio is from 1: 4 to 1: 2 primary:secondary A/O

Stabilization Cycle – with PhosphitesSimplified antioxidant stabilization cycle for PE stabilized with both

Hindered Phenol (ArOH) and Phosphite ((ArO)3 P) Stabilizers

RH (polymer)

ShearHeat

R*

R*+

ROOH

+ RH + Oxygen

+ RH


ArO* + ROH

+ ArOH

+ ArOH

ArO* + ROOH

+ (ArO)3 P

(ArO)3 P=O + ROH

+ (ArO)3PThe phosphite changes the peroxide to an alcohol, becoming a phosphate in the process

Typical Phosphites Used in POs

O P

3

P P OOO

OO

O

Weston® 399 (TNPP)Doverphos® 4-HRAlkanox™ TNPP

Irgafos® 168Alkanox™ 240Doverphos® S-480

Ultranox® 626Alkanox™ P-24

O ]3-PC9H19[

Effects of Antioxidants on Resin Melt Index

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 3 5

Mel

t Ind

ex (d

g/m

in)

250 ppm IR 1076500/500 IR 1076/Wes 399500/1000 IR 1076/Wes 399

Extrusion Pass # at 260°C (pass #0 -= Compounding at 230°C)

- Higher antioxidant loadings are better at retaining MI during multiple extrusion passes

- Phosphite A/O provides additional protection

UV Inhibitors / Light Stabilizers for PE

• Main UVI types– Classified by their stabilization mechanism

Absorbers benzophenones & benzotriazolesQuenchers organo-nickel compoundsRadical traps hindered amine light stabilizers

• Purpose– Prevent degradation of PE during exposure to UV light– HALS may also function as antioxidants at low / moderate temperatures

enhances LTTS

• Typical applications - anything used outdoors– Heavy duty bags– Agricultural films– Rotomolded parts

Typical UV/LS Used in PE Resins

Tinuvin® 622Lowilite® 62

Chimassorb™ 944Lowilite® 94

Cyasorb™ UV3346

Product Lifetimes with use of UV Stabilization

0

1000

2000

3000

4000

5000

6000

7000

0 10 20 30 40 50

Square Root [HALS Concentration (ppm)]

Tinuvin 622Chimassorb 944Tinuvin 783Tinuvin 111Chimassorb 119CGL 116Chimassorb 2020Pr

edic

ted

Life

time

(Xe

WO

M, h

rs)

- Performance ≈

square root of HALS concentration- Based on % elongation in 5 mil thick clear mLLDPE films

Discoloration of Polyethylene Products

Antioxidant interactions sometimes result in discoloration– Oxidative yellowing

• Auto-oxidation of hindered phenol A/Os can generate chromophores• Aggravated by high melt temp and air exposure during processing

– Pigment interactions• TiO2 pigments can react directly/induce oxidation of hindered phenols • Can minimize by using high quality coated TiO2 pigments

– Gas fading• NOx vapors can react with hindered phenols to create discoloration• Aggravated by the presence of basic additives such as HALS

– Cardboard yellowing• Oxidation of phenol-like materials that have migrated from cardboard

boxes • Use of PE liner will eliminate problem

Proper use of phosphite A/Os and catalyst neutralizers can minimize color formation

Gas Fade Mechanism for BHT Discoloration

CH3

hO

+ NO2 + HONO

NO2

H2 O R.T.

+ HONO

Slightly Yellow| |CH2

O⏐⏐

O⏐⏐

CH3

O⏐⏐

CH3 NO2

Conjugated Dimer

Intensely Yellow

HO

CH3

h

NOx Gas Fade Exposure Discoloration

0

2

4

6

8

10

0 25 50 75 100NOx Exposure Time (hrs)

Yello

wne

ss In

dex

NOx exposure should be minimized during polymer processing, storage & transport

Possible NOx sources include exhaust from

– Corona discharge treaters– Furnaces and gas burners– Propane-powered fork-lifts– Gasoline or diesel engines

Can reduce NOx discoloration by use of appropriate antioxidant type & level

Standard A/O package (hind. phen. + phosphite)

Standard A/O package + additional phosphite

Gas fade resistance hindered phenol + additional phosphite

Auto-oxidation of Hindered Phenol A/O

-8-6-4-202468

1012

Extrusion Pass

Yello

wne

ss In

dex

Melt processing at high temp in air can lead to auto-oxidation of hindered phenol A/O

Oxidized form of hindered phenol is more susceptible to NOx gas fading

High levels of regrind or reprocessed materials can intensify discoloration

If reprocessed materials are necessary, consider use of additional phosphite A/O

0 1 3 5

Pass 0 - Compounding @ 450°F in N2

@ 550°F in air

Polymer Processing Aids

• Purpose– Reduce / eliminate melt fracture– Increase processability

Lower melt temperatureReduce melt pressure / motor load / torque

– May reduce die buildup (blown & cast film applications)

• Function– Polymeric process aids (PPA’s) form a thin layer on film die surfaces– Coating allows molten polymer to exit die more uniformly / quickly– Slightly reduces apparent shear stress/viscosity of resin improved processability– PPA performance can be affected by

PE base resin (MI, MWD, A/O stabilization level)Concentration and degree of dispersion of the processing aid in the resin Interfering additives (antiblocks, HALS, TiO2 pigments, antistats, fillers)

Polymer Processing Aid Effect on PE Rheology

PPA reduces shear stress resulting in less melt fracture

1

10

1 10log Shear Rate

(Output)

log

Shea

r Str

ess

(Gat

e Pr

essu

re)

Smoo

th Mat

te Shar

kski

n

CM

F

“Slip

”

No PPA

w/ PPA

Typical PPAs Used in PE Resins

• Typical PPA’s used in PE resins– Fluorine based polymers like poly (vinylidene fluoride/hexafluoro propylene)

– Poly (vinylidene fluoride/hexafluoro propylene)– Dynamar® FX9613– Dupont-Dow Viton® Free Flow™ 23

– Poly (vinylidene fluoride/hexafluoro propylene) + synergist– Dynamar® FX5920A– Dupont-Dow Viton® Free Flow™ RC

– Poly (vinylidene fluoride)

– Kynar®

F

F H

H

CF3

F

F

Fn

m

Functionality of PPAs

Reference: S. Woods*, R. King**, J. Kunde; Proceeding from Polyolefin XI Conference; Houston; 1999; p. 591-610.

• PPAs function by hydrogen bonding to die surface• Oxidized PE and other additives can interfere reducing

effectiveness performance improves with clean die

OOO OOO O.. .. .. .. .. .. .. .. .. .. .. .. .. ..

: :.... .. .... .. .... OO O OOO O O O OO

H H HH H H HH

..

..

Phenol

NH

..

Hindered Amine

OP

O

ORO

HH P OR

OROR

..

Phosphite (Hydrolysis)

H2O

Fluoropolymer

OH :..

. .

: :..

F

F H

H

F

FF F

F

F

: :..: :..

..: :..: :

..: :

..: : ..: :

..

H :O:

HMoisture

H:O:

:O::O:

:O::O:

Polyethylene OxideH

:O:

:O:

Metal Stearate / Stearic Acid

Oxidized PolymerH

:O::O: :O:H

O

:O:H

MxOy (H2O)z(Partially Hydrated

Metal Oxide Surface)

MxOy (Metal OxideSub-Surface)

M (MetalSub-Surface)

Polymer Melt

Impact of A/B & TiO2 on PPA Effectiveness

• Addition of antiblock and/or TiO2 pigments often reduce the effectiveness of PPAs may require higher PPA use level

Effect of Antiblock & TiO2 on Elimination of Melt Fracture in PE Blown Films

0

20

40

60

80

100

0 20 40 60 80 100 120

Extrusion Time (min)

800 ppm PPA800 ppm PPA + 5000 ppm A/B1200 ppm PPA + 5000 ppm A/B + 3.5% TiO2

Catalyst Neutralizers• Purpose

– Neutralize trace level acidic compounds due to catalyst residues in PE Minimizes corrosion on processing equipmentImproves PE colorMinimizes side reactions between A/O’s and catalyst residues

– Mold release agents for PE injection molding and blow molding grades

• Function by neutralizing HCl resulting from catalyst residue– Ziegler catalyzed PE should contain acid neutralizer

LLDPE, MDPE & HDPE– Catalyst neutralizer not necessary for

Metallocene PE Free radical based PE (LDPE, EVA, EMA, etc)

• Typical catalyst neutralizers used PE resins– Metal stearates Calcium, Zinc– Metal oxides Zinc– Dihydrotalcites DHT-4A, L55RII

Catalyst Neutralizer Effects on Resin Color

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

w/o Zinc Stearate w/ 500 ppm Zinc StearateAdditive Formulation

(Base Stabilization = 500 / 1000 ppm Irganox 1076 / Irgafos 168)

1st Pass

5 th Pass

Yello

wne

ss In

dex

- Addition of neutralizer greatly helps reduce discoloration

Slip Additives

• Purpose– Reduces the coefficient of friction (COF) of blown film surfaces– May also function as an antiblock (reducing film reblock) although excessive levels may

actually cause blocking

• Function– Incompatible slip additive begins migration to surface as film is extruded– Slip molecules form crystallized layer on surfaces of extruded film– Solidified layer results in smoother/firmer film surface thereby reducing COF

• Typical slip additives– Fatty amides with alkyl chain length ranging from C18 to C22– May be totally saturated or contain 1 or more unsaturation groups (C=C)– Best overall slip additive is erucamide (C22:1)

Typical Slip Additives Used in PE Resins

NH2

O

O

NH2

O

NH2

Stearamide (C18:0)Kemamide® S, Crodamide® SR

Oleamide (C18:1)Kemamide® U, Crodamide® OR

Erucamide (C22:1)Kemamide® E Ultra, Crodamide® ER,

Armoslip® E

Functionality of Slip Additives

Schematic of slip migration mechanism

Additive in molten polymer

Migrationafter solidification

Equilibriumafter time

COF Measurement

Measured by sled test

Test reference: ASTM D-1894A lower numerical value of COF is called “low COF”but represents the “high slip” film

Diagram from ASTM procedure

COF Development with Time and Type

0.00

0.20

0.40

0.60

0.80

0.1 1.0 10.0 100.0 1000.0

Elapsed Time (hrs)

CO

F

StearamideOleamideErucamide

Slip agents bloom (migrate to the surface) with time

Saturated amides (such as Stearamide)yield higher COFs than unsaturatedamides (such as Oleamide)

Oleamide (C18) blooms faster thanerucamide (C22) due to its lower molecular wt but eventually results in a higher COF(on an equal weight basis)

COF Development with Additive Level

Increasing the slip agent levelwill generally reduce COF

Too much slip additive can also make the film surface tacky and start toincrease the COF. This typically does not happen with the levels present inresin but can occur if a film producer adds additional slip agent.

0.00

0.20

0.40

0.60

0.1 1.0 10.0 100.0 1000.0

Elapsed Time (hrs)

CO

F

500 ppm Oleamide

1000 ppm Oleamide

500 ppm Erucamide

1000 ppm Erucamide

Slip Requirements for Various Film Gauges

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40

Film Gauge (micron)

CO

F

For given amount of slip additive in resin, COF generally decreases with increased film thickness

– decreasing surface/volume ratio– more slip additive available for

migration to film surface

At certain film thickness, surface will be entirely covered with slip agent and there will be no further reduction in COF

- Base resin 2 MI, 0.922 LDPE- 500 ppm slip

Slip Agents in Coextruded Films

Generally, slip agents are used in the skin layers of a coextruded film and migrate from there to coat the film’s surface.To the first order, COF of the film is based on the thickness and slip agent level of the skin layer, not the overall structure.It is possible to make films with a low COF on one side and a high COF on the other, by including the slip agent only in the skin layer of the low COF side.Although, the slip agent wants to migrate out of the PE, it willoccasionally have low level migration to an adjacent layer whichdoesn’t have slip. This is called “Scalping”. It can be addressed by adding a low level (~100 ppm) of slip to that layer or by using a higher density resin in that layer.

Common Problems with Slip AdditivesSome common problems seen with the use of slip additives

– Slip concentration too high• Poor ink adhesion• Film blocking• Build-up on processing equipment• Color formation• Poor hot tack strength/sealing

– Slip concentration too low• High COF

– High film drag (sticking) during converting– Films sticking in end use

• Film blocking

Antiblock Additives

• Purpose– Reduce the blocking force needed to separate two films (blocking and reblock)– May also reduce film COF

• Function– Traditional antiblocks are non-migratory and function by roughening film surface with

numerous discrete particles (~1- 20 µm) – Organic antiblocks (saturated slip additives) function by forming layer on outer surface

reducing film to film adhesion

• Typical antiblock additives– Minerals of various types which are mined and classified by size. Some are surface

treated– Saturated fatty amides (stearamide & behenamide)– Organic non-migratory antiblocks based upon silicone or methacrylate specialty

polymers

Typical Antiblocks Used in PE Resins

• Antiblocks used in PE resins– Diatomaceous Earth (Silica A/B) Superfloss®, Micro-Ken™– Talc ABT2500, Clear-Bloc® 80– Treated Talc Optibloc®, Polybloc®– Kaolin (China clay) Polestar®– Nepheline Syenite Minex®– Fumed Silica Sylobloc®

• Selection is based upon – Film properties (blocking, COF, optics, physical properties)– Dispersability– Abrasiveness– Physical handling characteristics– Industrial hygiene

Antiblock Size and Shape

The antiblock size and shape is determined by the mineral type as well as grinding / classification process

Talc is a ‘platy’ mineral so it yields a flat antiblock particle, while diatomaceous earth shows range of diatom particle morphologies.

Superfloss (DE)ABT-2500 (untreated talc)

Antiblock Size

Antiblock suppliers specify an average or median particle size as well as a top size.

Too large a particle can cause gels, film breaks, screen pack pluggage and may be optically unappealing.Too small a particle will be ineffective for blocking resistance.

ABT-2500 particle size distribution

Typically, the median particle size of antiblocks is 2-5 μm, with a top sizeof 20-30 μm.

Functionality of Antiblock Additives

Polyethylene films with smooth surfaces tend to stick together, or “block”

Antiblocks disrupt the film surface to prevent blocking

Antiblocks Roughen Film Surfaces

Antiblock additives roughen the surface of an otherwise smooth plastic film

The rougher film surface also shows up as a lowered gloss for the sample

LL1002KW Film with kaolin antiblock

Effect of Antiblock Type & Level on Blocking

- Base resin 1 MI, 0.917 Exceed mLLDPE, 0.9 mil films

0

20

40

60

80

100

120

0 1000 2000 3000 4000 5000 6000 7000 8000

Antiblock Concentration (ppm)

TalcTreated TalcNo A/B Line

Effect of Antiblock Type & Level on Haze

- Base resin 1 MI, 0.917 Exceed mLLDPE, 0.9 mil films

2

4

6

8

10

12

0 1000 2000 3000 4000 5000 6000 7000 8000

Antiblock Concentration (ppm)

Talc

Treated Talc

No A/B Line

Combined Effects of Slip and Antiblock

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000Slip Level (ppm)

CO

F

0

100

200

0 2000 4000Antiblock Level (ppm)

Reb

lock

(g)

No antiblock1000 ppm antiblock

No slip500 ppm slip

Antistatic Agents

• Purpose– Dissipate static charge which may accumulate on PE films or molded articles

Minimizes dust accumulation on final articleUsed more frequently in injection or blow molded PE resins

– At low levels, may be used as catalyst neutralizer

• Function– Traditional antistats function by migrating to surface of PE film or molded article and

forming thin layer– Hygroscopic nature of antistat attracts moisture from the air which dissipates static

charge requires certain humidity level to function effectively– Non-hygroscopic antistats are available for specialty applications

• Potential problems– If antistat agent concentration is too high may cause problems

– Tacky (blocky) films– Printing issues (ink adhesion)

Typical Antistatic Agents Used in PE Resins

• Types of antistats– Ethoxylated amines Atmer® AS974, Armostat® 310

Atmer® AS990, Armostat® 1800

– Polyethylene glycols Carbowax® PEG

– Glycerol derivatives Dimodan, Atmer® 122

• Selection is based upon – Static dissipation performance

– Foodlaw (FDA) restrictions

Additives Found in End-use Applications• Fillers

– Usually finely divided inorganic solids used to improve polymer properties or reduce costs

– Examples - calcium carbonate, kaolin, talc

• Pigments– Used to add color to polymer product and may also provide UV protection– Examples - titanium dioxide, carbon black, chromium oxide, iron oxide

• Antifog agents– Used in packaging and greenhouse films to impart hydrophilicity to film

surface and promote the formation of a continuous,less opaque film of water

– Examples - fatty acid esters (e.g. polyoxyethylene sorbitan ester, Atmer® 112, POE sorbitan derivatives)

Summary

• Many different additive types needed for different polyethylene end-uses– Antioxidants, primary and secondary

Prevent polymer degradation during processing and long term– UV light stabilizers

Prevent degradation during long term exposure to sunlight– Processing aids

Minimize melt fracture during processing– Catalyst neutralizers

Prevent corrosion, discoloration– Slip agents

Control COF for more efficient converting– Antiblocks

Prevent films from sticking to themselves– Antistatic agents

Eliminate static, prevent dust accumulation• Key reasons for selecting an additive

– Selection based upon polymer requirementsProvide stabilization during processing or end useEnhance processabilityModify selected physical properties of the final film or article

Summary

• Numerous additional factors in selection process– Specific customer requirements– Performance aspects – Additive form– Method of addition– Safety concerns– Industrial hygiene– Regulatory issues– Legal considerations– Cost/performance balance

• Overall goal is to provide the desired performance in the most cost effective manner possible while meeting all safety, handling, regulatory and legal requirements

pe additives overview

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