antioxidants & antidegradants

8/15/2019 Antioxidants & Antidegradants

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Antioxidants & Ant idegradants

All polymers & products baded on them are subject to degradation on exposure to the degradativeenvironments such as:

- Storage aging- Oxygen- Heat- UV Light & Weathering

- Catalytic degradation due to the presence of heavy metal Ions (Cu, Mn, Fe etc.)- Dynamic Flex - Fatigue- Ozone (Static / Dynamic / Intermittent exposure)

These factors degrade rubbers / rubber products causing substantial changes in their technical propertiesand ultimately lead to their failure during service or shorten the expected service life in the absence of

Antioxidants.

Type of DegradationInitiating / Accelerating

Factors

Degradation

Causes

Type of Failure

Storage Aging Surrounding conditionsOxygen, Light,Heat, Humidity

Loss of elasticity and tensile strength

Aging due to Heat Heat Oxygen Loss of elasticity and tensile strength

Aging due to Light &Weathering

Light, UV light, heat,humidity, surroundingconditions

OxygenFormation of crazed surface, loss ofelasticity and tensile strength

Soluble Metal ion(Cu,Mn,Fe) catalyzedoxidation

Cu, Mn, Fe, Co & NiIons as their rubbersoluble fatty acid salts

OxygenRapid loss in elasticity and tensile

strength.

Flex-Fatigue crackingIntermittent mechanicalstrains

Oxygen,Ozone, Flaws

Appearance of cracks (crackingpatterns usually complex)

C ti / I t itt t E t i ki t i ht l t th


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C ti / I t itt t E t i ki t i ht l t th


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• Free radicals R.

can undergo following reactions depending on their own relative stability :

- Dimerize (cross link),- Disproportionate (exchange H

. becoming alkane & olefin),

- Abstract H. (chain transfer),

- Cleave (rupture polymer chain),- Rearrange,- React with oxygen.

• Auto-oxidation depends on the relative C – H bond dissociation energy.

Strongest Bond Weakest Bond

Primary Secondary Tertiary Allyic

98.0 kcal. 94.5 kcal 91.0 kcal 85.0 kcal

R – CH2 – H R

2CH – H R

3C – H RCH=CH-CRH-H

• Dimerization causes polymer hardening while cleavage reduces polymer chain lengths (change inhardness & elastic properties and causing fatigue – crack initiation points.

• Cleavage may also release of gases (resulting in separations).

• Since all the vulcanization ingredients are still present; degradation can take place by continuedchanges in the state of vulcanization during the rubber product service.

• This causes Reversion or marching modulus due to changes in the nature of the sulphur cross links.

• The Termination Stage reactions progress as follows :

A) Chain Scission


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2 RO

.

ROORR

. + ROO

. ROOR

• Cross linking predominates in case of polymers like BR, SBR, NBR, CR, etc. which havecomparatively less active double bonds or somewhat deactivated double bonds due to the presenceof electron-withdrawing groups such as halogens (e.g. CR, Chloro/Bromo Butyl Rubbers). Crosslinking results in brittleness, gelation and reduction in elongation of the polymer.

EEf f f f eecctt oof f DDeeggr r aaddaattiioonn oonn EEllaassttoommeer r ss

EEllaassttoommeer r ss EEf f f f eecctt OOf f DDeeggr r aaddaattiioonn

Natural Rubber ( NR ) Scission ( Softens )

Poly Isoprene ( IR ) Scission ( Softens )

Polychloroprene ( CR ) Cross linking & Scission ( Harden )

Styrene Butadiene Rubber ( SBR ) Cross linking & Scission ( Harden )

Acrylo Nitrile Butadiene Rubber ( NBR ) Cross linking ( Harden )

Polybutadiene Rubber ( BR ) Cross linking ( Harden )

Isobutylene Isoprene Rubber ( IIR ) Scission ( Softens )

Ethylene Propylene Rubber ( EPM ) Cross linking & Scission ( Harden )

Ethylene Propylene Ter-polymer ( EPDM ) Cross linking & Scission ( Harden )

Chlorosulfonated Polyethylene ( CSM ) Cross linking ( Harden )

Polyacrylic Rubber ( ACM ) Cross linking ( Harden )

Fluorinated Hydrocarbon Rubbers ( FPM ) Cross linking ( Harden )

Polysulfide Rubbers ( T ) Cross linking ( Harden )


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EFFECT OF OXYGEN:

• Only 1– 2 % of combined oxygen is enough to render the rubber product useless.

• Polymer oxidation is a complex process involving many factors -processing conditions (e.g.temperature, shear rate), presence of catalysts of oxidation, compounding formulation design etc.

• Oxidation causes Chain scission and Cross linking resulting in the loss of elastic properties ofvulcanizates. Both occur simultaneously - the one which prevails, determines the final product

properties.• The ‘cure system’ selection also influences the ageing resistance of the rubber product. The

‘Conventional Cure’ Systems are more prone to oxidative degradation than the ‘Semi EV’ or ‘EVCure’ systems.

EFFECT OF HEAT :

• Heat accelerates the process of oxidation and effects of oxidation are observed sooner and are moresevere as the temperature increases.

• In case of NR, in the absence of oxygen, more cross links are formed initially, followed by ‘Reversion’as cross links and polymer chains are broken.

• The oxidative heat ageing causes loss of Tensile Strength, Elongation at Break and overall Elasticityof the rubber vulcanizates.

Effect of Heat on NR Vulcanizates:

Temperature, °C Combined Oxygen, % Loss of Tensile Strength, %

60 1.2 50

110 0 65 50


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EFFECT OF HEAVY METAL IONS:

• Hydro peroxides (ROOH) are the main source of free radicals for the initiation of autocatalyticoxidation reactions.

• Decomposition of hydro peroxides is accelerated by heat , light and polymer soluble fatty acid salts ofmetals like Cu , Mn , Fe , Co & Ni .

• The rubber soluble metallic compounds catalyze hydro peroxide decomposition to free radicals

according to following scheme.

•

Direct reaction of metallic compound with polymer in the early stage of the degradation may alsoresult in free radicals as follows:

RH + MX2 R. + MX + HX

RH + MX R. + M + HX

• Stearates and Oleates of Cu & Mn are highly active catalysts of oxidative degradation of NR. Lesssoluble forms like Oxides of Cu & Mn react with fatty acids to produce highly rubber solublecompounds.

• The first corrective approach is to eliminate all the sources of these harmful metals or their solublesalts. It is possible to protect polymers by incorporating substances which react with ionic metals togive stable co-ordination complexes.


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• However, SBR based Semi EV & EV cure systems exhibit both good heat ageing & dynamic flex-fatigue resistance.

• Ozone cracking and Flex cracking may occur at the same time involving complex mechanisms.

• Para-phenylenediamine antidegradants (PPDs) offer excellent protection to rubber vulcanizates as Antioxidants, Antiozonants &. Antiflexcracking agent.

EFFECT OF OZONE:

• Longer wave length UV light photolyzes Nitrogen Dioxide to yield Oxygen atoms [O.] and Nitrogen

Oxide.

• The Oxygen atoms then combine with Oxygen molecules present in the atmosphere to form Ozone.

• In unpolluted areas the ozone concentration is 2 to 5 pphm. In more polluted areas it can reach to 40to 50 pphm.

• Ozone is also formed in the stratosphere by the action of short wave length UV-light on oxygen. Although the flux of short wave length UV light is absorbed in the upper atmosphere, theconcentration of ozone in the troposphere is still appreciable due to the presence of Nitrogen Oxide.

• Oxygen atoms liberated by this photolysis of oxygen molecules also combine with oxygen molecules to form ozone.

• Since ozone is formed by photolytic reaction, its concentration in the atmosphere peaks at mid-dayand is negligible at night.

• Ozone concentration in the atmosphere is not temperature dependent but it does peak off during thesummer months when the sun light is more directly incident.

Th t h i t ti i d il b i d i d d t th it f th


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• In addition to large number of double bonds present in the highly unsaturated rubbers, ozone alsoreacts with saturated polymers and the polysulphide chains at a comparatively slower rate.

• Unsaturated polymers which contain electron donating groups (e.g. methyl groups in NR) are morevulnerable to ozone attack.

• The unsaturated polymers containing electron-withdrawing groups (e.g. Chlorine in CR, Bromine inBIIR) are less vulnerable to ozone attack due to the deactivating effect imposed on the double bondsby the halogen atoms.

• Ozone reacts with the double bonds in the rubber molecule causing chain scission. The chainscission results in the formation of surface cracks in the direction perpendicular to the applied strain.

• The ozonation reactions proceed as follows :

• Under strain these ozonides easily decompose and break the double bonds resulting in theappearance of surface cracks and as this mechanism repeats, the cracks grow deeper.


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Role of Antidegradants:

• Antioxidants & Antiozonants are used to protect the polymers from degradation.

• Antioxidants are highly effective ingredients and have a dramatic impact on the service life of therubber product although being present at extremely low concentrations (0.5 – 3.5 phr).

• Antioxidants do not completely eliminate oxidative degradation, but they substantially inhibit the rateof auto oxidation by interfering with the radical propagation reaction.

• Depending on the types and combinations of antioxidants used, the polymer can be protected duringthe entire phase of the product’s life cycle.

• The Antioxidants are categorized as :

A) Primary Antioxidants (Chain Terminating)

e.g. Amines & Phenolic.

B) Secondary Antioxidants (Peroxide Decomposers)

e.g. Phosphites & Thioesters.

• Addition of an Antioxidant ( AH ) in small dosage ( 1.0 - 2.0 phr ) interrupts the degradative reactionsas follows :

R˙ + AH RH + A˙ ……………. (Scavenges free radicals.)

ROO˙ + AH ROOH + A˙ …………. (Prevents chain breaking.)

RO˙ + AH ROH + A˙ ……........... (Scavenges alkoxy free radic als.)


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• Thus the Peroxy Radical is offered a more easily abstractable hydrogen by an externally addedhydrogen donor (antioxidant) and the polymer backbone remains unaffected until the H-donor (antioxidant) is consumed.

• In the above process, the Antioxidants themselves get converted to relatively stable radicals which donot propagate further.

• According to the mode of action the antioxidants may be grouped as :


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• The Inert Barrier Theory proposes that the antiozonant migrates from the bulk of the rubber to thesurface to form a film. This film functions as a physical barrier which protects the reactive polymerdouble bonds by keeping ozone out of contact.

• The Inert Barrier Theory Mechanism is similar to ozone protection offered by waxes and non reactivepolymers such as EPDM, Halogenated butyl rubber, halogenation of the surface of rubber vulcanizateetc.

• The ‘Reduced Critical Stress Theory’ proposes that the rubber vulcanizate surface is modified by the

migration of the antiozonant on the surface or just below the surface of the rubber.

• This modification relieves the internal and surface stresses and the vulcanizate behaves as if it wasunstressed or at lower than critical stress required for ozone crack formation.

• The ‘Chain Repair Theory’ proposes that antiozonant reacts directly with the ozonide or the carbonyloxide forming a low molecular weight, inert & self healing film which attaches the antiozonant to therubber.

• The Competitive Reaction Theory is sub divided into ‘Scavenger Theory’ & ‘Protective Film Theory’.

• The ‘Scavenger Theory’ proposes that as the antiozonant migrates to the surface; it selectively reactswith ozone and protects the polymer double bonds until the antiozonant is exhausted.

• ‘Protective Film Theory’ proposes that once the antiozonant has been fully exhausted, the reactionproducts of the antiozonant form an Inert Protective Film over the surface of the rubber vulcanizate.

• The Competitive Reaction theory is substantiated by experiments and is well accepted.

CLASSIFICATION OF ANTIOXIDANTS:

According toFunction

Accord ing toChemical Types

Accord ing to ASTM D4676


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• The antioxidant radical (A.) formed during the above process must be stable to discontinue the

propagation of new radicals.

• The radical (A.) in most cases is stabilized by electron delocalization or resonance.

PARAPHENYLENE DIAMINES ( ASTM : D4676 CLASS-1).

• The general structure of PPDs can be represented as follows :

• Three types of PPDs are used in the Rubber Industry.

1. PPD Type I : N, N’-dialkyl-p-phenylenediamine.2. PPD Type II : N-alkyl-N’-aryl-p-phenylenediamine.3. PPD Type III : N,N’-diaryl-p-phenylenediamine.

• Paraphenylene Diamine antidegradants (PPDs) function as primary antioxidants and are recognizedas the most powerful class of chemical antiozonants, Antiflexcracking agents and Antioxidants.

• PPDs are extensively used in tyres, beltings and molded & extruded rubber products as antiozonants& Antiflexcracking agents at 1.0 – 4.0 phr dosages. However, being highly staining & discoloring type,PPDs are not used in white or colored products.

• PPD antidegradants are also used as polymer stabilizers


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• In case of 77PD both the substituent groups are alkyl groups (branched C7).

• In case of 88PD both the substituent groups are alkyl groups (branched C8).

• Dialkyl PPDs :

- Offer excellent static ozone resistance even in the absence of wax.- Are not very effective under dynamic conditions.- Do not leach out in water.

- Are more sensitive to oxygen and hence suffer from lack of persistency and poor shelf-life(3 to 4 months only).- Are highly basic in nature and hence scorchier.- Used in combination with alkyl-aryl PPDs to obtain static and dynamic ozone protection.- Dosage 1.0 to 2.0 phr.


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• R is a secondary alkyl group and R1 is hydrogen or a primary alkyl substituent (usually methyl). These

PPDs are generally consist of a single component or purposeful mixture of two or more majorcomponents. The products can be liquids or solids.

• In case of IPPD, R is isopropyl group and R1 is hydrogen.

• In case of 6PPD, R is (1,3-dimethylbutyl) group and R1 is hydrogen.

• In case of CPPD, R is cyclohexyl group and R1 is hydrogen.

• In case of 8PPD, R is octyl group and R1 is hydrogen.

Alky l – Aryl PPDs:

- Offer best all-round performance as Antidegradants against all degradative forces.

- Offer excellent antioxidant, static & dynamic ozone resistance and anti-flex cracking properties.

- Exhibit optimum migration rate due to the presence of bulky aromatic ring on one side and a

branched alkyl chain on the other side.

- Are less volatile than di-alkyl PPDs. (Lower losses during storage, processing & cure and henceoffer long term protection to rubber vulcanizates).

- Are slightly basic in nature and hence influence scorch & cure characteristics.

- The water leaching properties depend on molecular weight of the

- PPD and the pH of water. (e.g. IPPD is easily leached out in water but 6PPD does not leach outin water to any appreciable extent.)

- Exhibit high solubility in rubber hence do not exhibit blooming tendencies.


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• Comparatively less basic in nature and hence does not influence scorch or cure rate.

• Generally used in combination with alkyl-aryl PPDs to obtain static and dynamic ozone protection(Dosage 0.5 to 1.0 phr). Resume activity when other PPDs get depleted.

• More stable & good shelf-life (12 months).

Antiozonant Action : Diaryl PPD

N N

H HO3 O2

N N

H H

O

N N

H

O

H

-H2O

N N

O3 O2N N

O

Catalytic process mechanism of polymer protection: How DPPD Antidegradant works.

ROO.

NH NH

PP

NH N

NH N

O


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• PPD antiozonants exhibit following common functi ons :

- All PPDs migrate to the surface of the rubber product to react with ozone directly and competitively.

- The migratory losses of antiozonants can occur by migration to adjacent stock.

- The effectiveness of PPD antiozonants in rubber vulcanizates can be improved by incorporation ofwaxes and synergistic antioxidants. This helps in the reduction of PPD dosages for adequate ozoneprotection.

- The use of higher wax dosages / selection of improper wax grades can be detrimental to theperformance of Antiozonants.

- All PPDs decrease the rate of cut - growth of rubber vulcanizates.

- Di alkyl & Alkyl-Aryl PPDs increase polymer’s critical stress necessary for ozone crack initiation.

- The use of antioxidants along with PPDs protects the PPDs from direct oxidation.

- The Dialkyl-PPDs are initially the most active antiozonants followed by Alkyl-Aryl-PPDs & then theDi-Aryl-PPDs. This order of activity reverses as the ageing progresses due to oxidation and exposureof PPDs.

- For extended protection of rubber vulcanizates blends of PPD antiozonants are often used.

- The solubility of PPD antiozonants depends on the solubility parameter of the rubber itself.(Example: Diaryl PPDs have low solubility in NR and hence bloom above 1.0 phr dosage.)

- All PPDs exhibit high solubility in NBR based compounds and hence do not migrate easilyto the surface to offer ozone protection.

- Diaryl-PPDs are more effective and persistent compared to other PPDs in polychloroprene(CR) b d d H PPD ti t li k CR th


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• In this mechanism, the original diphenylamine antioxidant is converted to diphenylamine-N-oxide.

• The N-oxide can either trap R. and then thermally eliminate diphenylhydroxylamine directly.

• The diphenylhydroxylamine then behaves as a hydrogen donating antioxidant by neutralizing ROO.

and the catalytic cycle is complete.

• This process uses polymer as a source of hydrogen to moderate, compete with and control the

propagating step of the free radical oxidation process.

• The creation of double bonds in the polymer has minimal effect on the overall physical propertiesbecause polymer chains are not being broken or cross-linked.

• This mechanism is often called as ‘Chain breaking hydrogen abstractor / Chain breaking hydrogendonor’ mechanism.

COMPARISONS OF ANTIDEGRADANTS IN NR-TRUCK TREAD COMPOUND @ 2.0 phr.

Antidegradant M.P.,°C MS @ 120°C, minNR Protection SR Protection

Demattia Flex, kcStatic Dynamic Static Dynamic

Control - 27 - - - - 87

IPPD 75 23 100 100 100 100 430

6PPD 48 26 100 90 85 80 300

77PD Liquid 19 160 65 130 75 200

DTPD 105 15 150 65 125 70 225

- DTPD is expected to show comparatively much better performance during long term exposure tests due to itsslower migration rate.

- NR & SR ozone protection under static & dynamic conditions as per standard ASTM procedure indexed @

IPPD = 100 .


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The test results indicate that:

• 6PPD Antidegradant provides high degree of protection against Oxidative Heat Ageing,Flex-Fatigue (Unaged & Aged), and Dynamic Ozone Resistance even at 1.0 phr dosage.

• The degree of protection increases as the dosage is increased further. The test results confirmthat 6PPD Antidegradant is almost three times more effective than TMQ antioxidant in thisrespect.

• TMQ antioxidant offers excellent oxidative heat ageing resistance to rubber vulcanizates which iscomparable to 6PPD.

• Considering the costs involved; one would prefer use of TMQ antioxidant so that the 6PPDantioxidant included in the rubber compound is available for protection against other degradativeforces.

EVALUATION OF TMQ AND 6PPD IN NR/BR -TRUCK TREAD COMPOUND.

Base Formulation: NR - 75, BR1220 - 25, N339 Black - 50, Aromatic Oil - 8, Zinc Oxide - 5, Stearic Acid - 2,

CBS - 0.6, Sulphur - 2.5.6 PPD / TMQ Dosages phr % Tensile Strength

Retention(Aged, 85°C-2days)

Fatigue Life , kc to Failure at 100% Extension

6 PPDphr

TMQphr

Unaged Aged

( 85°C-5 days)% Retention

Of Fatigue Life

1.0 - 60.0 132 135 102

1.0 1.0 72.0 123 137.5 112

1.0 2.0 78.5 118 142 120

1.0 3.0 88.0 113 154 136

2.0 - 77.5 135 137 101

2.0 1.0 84.5 130 150 115

2.0 2.0 88.5 135 132 98


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IPPD REPLACEMENT BY 6PPD. (REASONS)

• 6PPD is not a skin sensitizer like IPPD,

• 6PPD is much less volatile than IPPD (Better retention in rubber compounds),

• 6PPD is not easily leached out in water like IPPD,

• 6PPD is not ‘scorchier’ like IPPD,

• If the losses of IPPD due to volatility & water leaching are taken into account, then at equal dosages6PPD shows better performance than IPPD.

THE ROLE OF WAXES.

• Waxes migrate quickly to the surface of rubber vulcanizates to form a physical barrier against ozoneattack.

• A critical of wax bloom is required to form a continuous film for optimum static ozone protection.

• Solubility and mobility of waxes govern their ability to form a sufficient level of bloom which is alsodependent on polymer & filler type added, loadings, state of cure and time & temperature of storageafter vulcanization.

• Paraffin waxes are produced by solvent extraction of lubricating oil fractions and then separated intodesired sub-fractions by step wise crystallization.

•

Paraffin waxes contain ‘normal’ paraffins (alkanes) with slightly branched chain paraffins (iso alkanes)with generic formula (Cn H2n+2) where n = 18 to 50. The Melting Points vary from 52 to 54°C (C18 toC36) to 66 to 68°C (C22 to C50).

L l l i ht f ti (< C ) i t f t t l t t 0°C b t di l i


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•

Paraffin waxes offer best static ozone protection at low temperatures while MC-Waxes protect best athigh vulcanizate temperatures.

• A blend of Paraffin Wax & MC-Wax would provide best protection at ambient exposure temperaturesof rubber products under static conditions. No chemical reactions are involved between wax andozone.

• Use of waxes in rubber compounds reduces the fatigue life and dynamic ozone resistance of therubber vulcanizates.

• Waxes alone do not offer ozone protection under dynamic conditions due to lack of adhesionbetween wax film & vulcanized rubber surface and the inextensibility of the wax bloom (film).

• The PPD antidegradants do provide ozone protection against both static and dynamic conditions dueto Chemical Reactions with ozone besides film formation.

• Any change in ozone concentration and atmospheric temperature will influence the rate of chemicalreactions between ozone and PPDs.

• Increase in PPD dosages results in slight increase in wax bloom and thus at lower wax dosages theozone resistance is improved significantly.

• The wax bloom thickness is higher in case of NR / BR blends than 100% NR compounds.

• At normal levels of PPD-Wax blends, there is no synergism between PPD and Waxes under static ordynamic conditions. However, significant synergism is observed under intermittent conditions due to acombination of effective static ozone protection of wax and dynamic ozone protection of PPDs.

• Blended Wax & PPD Antidegradants combinations will provide excellent ozone protection over a widerange of temperatures under Static, Dynamic as well as Intermittent (alternating static & dynamic)conditions.


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•

The Contents of Amine Impurities (which cause several processing problems) also differ considerablyfrom supplier to supplier.

• The primary aminic groups (- NH2) do not function as antioxidants. Hence products which contain

higher proportions of primary aminic groups are weaker antioxidants and are responsible to activatesulphur cross linking and scorching of Rubber Compounds.

• Primary aminic groups destabilize Insoluble Sulphur by decreasing its transition temperature tosoluble Sulphur and thus causing scorching and sulphur bloom problems for Rubber compounds.

• The formation of isopropyl-bis-aniline (or bisaniline A) and Monomer-Aniline Adducts during TMQmanufacture; are responsible for dramatically decreasing the ‘Peptization’ activity as well as initiatingcross linking reactions causing viscosity increase of NR based compounds at the rubber processingtemperatures.

• The monomer content in TMQ antioxidant is also considered as an objectionable impurity since it isleached out in water and can cause porosity in thicker cross section extrudates.


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MECHANISM OF TMQ ANTIOXIDANT REACTIONS

• TMQs act as alkyl radical (R.) scavenger which immediately stops auto-oxidation process.

• The hindered aromatic amine antioxidants get oxidized due to peroxy radicals to form nitroxyl radicals

which act as scavengers of alkyl radicals (R.).


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b) Comparison of TMQ against other antioxidants in NR – Tread Compound :

(Base Compound: NR-100, Peptizer-0.15, ZnO – 5, St. Acid – 2, N 330 Black – 45, Aromatic Oil – 5, Wax – 0.5,MBS – 0.5, S – 2.3, Antioxidant – 2.5. )

Tensile Strength Retention After Ageing In Hot Air @ 100 °C

No. of Days Control ADPA (L) TMQ 6 PPD IPPD

1 25.5 50.2 55.3 55.5 55.5

2 10.2 25.5 34.0 38.3 40.8

3 6.8 17.0 21.3 28.1 28.5

4 6.0 10.2 12.8 15.0 17.0

PHENOLIC ANTIOXIDANTS ( ASTM : D4676 CLASS-3)

•

Phenolic antioxidants are primary antioxidants and are classified chemically according to the numberof Phenolic groups in the molecule.

• In general, the more sterically hindered antioxidants are less discoloring but have lower antioxidantactivity in rubber application.

• The Phenolic Antioxidants are Non-Staining type and are used in the Rubber Industry for themanufacture of white/colored rubber products and as stabilizers of raw Synthetic Rubbers.

• Phenolic Antioxidants are of following types:

Mono-functional Phenols (Type 1),Bi-functional Phenols (Type 2),Multi-functional Phenols (Type 3).


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• Sterically Hindered phenols act by scavenging RO. And ROO

. Radicals via Hydrogen atom transfer

from the OH group to form hydroperoxides and phenoxyl radicals. The reaction mechanism is givenbelow:

• The radical (A.) is stabilized by electron delocalization or resonance as shown below:

• The discoloration tendency of Phenolic Antioxidants is due to the formation of Stilbenequinone whichis explained as follows :


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•

Styrenated Phenol is much less volatile & provides long term protection and is widely used in white /coloured latex based goods at the dosage of 1.0 - 2.0 phr.

• BHT is more volatile and provides only short term protection. It is mostly used as an in processstabiliser for synthetic polymers to impart raw polymer storage stability.

• These represent the most important class of non staining antioxidants.

•

These antioxidants have low volatility, good antioxidant activity and exhibit minimal discoloration torubber vulcanizates.

• Depending upon the position of linkages, bisphenols are subdivided into ‘ortho’ or ‘para’ bridgedbi h li ti id t


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PHENOLIC ANTIOXIDANTS ( ASTM : D4676 CLASS-3)

Multi-func tional Phenols (Type 3)

• Multifunctional phenolic antioxidants are very high performance antioxidants, exhibit extremely lowvolatility and do not cause contact / migratory staining or discoloration of the rubber products.

• Higher molecular weight of multifunctional phenolic antioxidants also contributes to practically noleaching and extraction from rubber products by water or solvents and ensuring long term protectionagainst oxidation.

• Chemical structure of multifunctional phenols is given below:

• Butylated reaction product of para cresol and dicyclopentadiene (e.g. Wingstay L) is the most popularmultifunctional phenolic antioxidant used both in solid rubber products and latex based products.


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Aromatic Phosphites: ( ASTM : D4676 CLASS-5)

• Aromatic phosphites are phosphphorus esters of aromatic phenols.


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•

There are two different types of ADPA condensates viz. low temperature reaction products and hightemperature reaction products.

• The high temperature reaction products are reactive towards oxygen and provide some flex –cracking resistance but are severely staining and discoloring.

• They are also volatile and do not provide long term protection against the degradative forces thatconstantly act on rubber products.

• These products are mostly used in cheap mechanical rubber products, some non – critical tyreapplications and as a stabilizer for emulsion SBR.

• These antioxidants reduce the building tack of uncured rubber compounds making product (e.g. tyres,conveyor beltings etc) building process more difficult.

• The low temperature condensation products are not very reactive towards oxygen but are lessstaining and discoloring.

• These are comparatively less volatile and can provide medium term protection to the rubber

vulcanizates.

• These types of ADPAs have low solubility in oil and hence suitable for oil resistant compounds basedon NBR.

• The recommended dosage of ADPA antioxidants is 1.0 – 2.0 phr for various rubber productsmanufacture.

PROPERTIES OF ANTIOXIDANTS / ANTIDEGRADANTS

• For selecting a proper Antioxidant/Antidegradant for specific end-use requirements following factorsare considered to be important for the choice.


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•

All these forms of discoloration are due to oxidation products of the antioxidants themselves in nearlyall the cases.• In general, phenolic antioxidants are non-discolouring and the amines are discolouring.

Volatility

• Volatility of antioxidant is related to both the molecular weight and the type of molecule. Generally,greater the molecular weight, less is the volatility.

• The type of molecule however, has a greater effect than the mol. Weight (e.g. .Hindered Phenols) hashigh volatility in comparison with amine antioxidants of the approx. same molecular weight.

• Loss of antioxidants results due to low volatility during processing, curing and usage of the rubberarticle under severe operating conditions.

VOLATALITY OF ANTIOXIDANTS / ANTIOZONANTS AT 100° C

A Annttiiooxxiiddaannttss // A AnnttiioozzoonnaannttssLLoossss oonn HHeeaattiinngg aatt 110000 °° CC,, %% ww // ww

44 DDaayyss 88 DDaayyss 1122 DDaayyss ADPA ( Liquid - Low Viscosity ) 37.00 48.00 54.00

ADPA ( Liquid - High Viscosity ) 28.00 35.00 40.00

ADPA ( Solid - Resin ) 0.60 0.50 0.50

77 PD 7.50 13.20 17.00

IPPD 4.25 6.40 9.00

6 PPD 2.50 4.50 6.20

DTPD 2.50 4.00 6.00

PBNA 2.50 4.70 6.30

TMQ 0.15 0.20 0.20


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Chemical Stability

• The stability of an antioxidant towards, heat, light, oxygen etc. is important if it is supposed to havemaximum effectiveness for long periods.

• Many amine antioxidants are affected by oxidative reactions and phenolic antioxidants are affected byheat in the presence of acidic materials.

• Among the PPDs, dialkyl PPDs are oxidised very fast and are effective for short duration whereasalkyl aryl PPDs and diaryl PPDs are more persistent.

Physical Form

• Solid, free-flowing and non-dusty material are generally preferred over liquid antioxidants because ofease of handling & weighing,

• Health – Safety & Environmental Concerns & change over to automated conveying & weighingsystems.

Antiox idants / Antiozonan ts Concentration

• Determining proper level of Antidegradant to use is a complex question whose answer depends oncost, polymer type, end-use, application, staining requirements, etc.

• Most materials show an optimum level, based on laboratory ageing studies and increased levels arenot required.

• One is encouraged to use sufficient material to ensure the presence of an optimum dosage so thatafter extended use part of the antioxidant may be destroyed or rendered inactive and still the rubberproduct is well protected.


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Health & Toxicity Concerns

• Antioxidants / Antidegradants used in rubber compounds intended for food & drugs contact should beFDA / BGA approved.

• Use of Antioxidants / Antidegradants of known health hazards should be avoided.

• Information on Health, Safety & Environmental Control is updated continuously. One must consult aresponsible chemical manufacturer for the update before selecting the material for intended use orrefer to the latest edition of the BRMA Book.

• The physical form of the antioxidants may vary from supplier to supplier ( e.g. Liquid, Powder,Flakes, Pastilles, Rods etc.). Ease of handling & transportation, clean & dust-free characteristics arethe factors to be considered.

How to select the antioxidant system?

1. Identify Primary Degradation Factors.

- Oxygen,- Heat,- Light, Weathering & Other gases,- Moisture, Steam,- Ozone,- Metal ions,- Flex-Fatigue and other types of Stresses & Strains.

2. Define Service Environments / Requirements.

- Staining & Discoloration,- Temperature,- Static / Dynamic / Intermittent,- Life cycle desired,

T i l i l


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1

Summary Table:

Antidegradants & Antioxidants

Chemicals Structure

Stainingor

Non

Staining

Protection against

NotesHeat &

Oxidation

Ozone Flex

FatigueASTM D 4676

Class 1PPDAnti -

degradants Para phenylenediamines (PPDs)

(General Structure)

ST Excellent Excellent Excellent Primary Antioxidants. Donate reactive Hydrogen (N-H) to the polymer peroxy free radicals(RCOO.) during the propagation stage of polymer degradation. All PPDs migrate to thesurface of the rubber product and react directly and competitively with ozone. Migratory lossescan occur to adjacent compounds. Effectiveness of PPDs can be improved by incorporation ofwaxes and synergistic antioxidants. PPDs decrease the rate of cut - growth of rubbervulcanizates. Use of antioxidants along with PPDs protects the PPDs from direct oxidation. Dialkyl & Alkyl-Aryl PPDs increase polymer’s critical stress necessary for ozone crack initiation.The Dialkyl-PPDs are initially the most active antiozonants followed by Alkyl-Aryl-PPDs

& thenthe Di-Aryl-PPDs. Order of activity reverses as the ageing progresses due to oxidation andexposure of PPDs. The solubility of PPDs antiozonants depends on the solubility parameter ofthe rubber itself. (Example, Diaryl PPDs have low solubility in NR and bloom above 1.0 phrdosage.) All PPDs exhibit high solubility in NBR based compounds and hence do not migrateeasily to the surface to offer ozone protection. Diaryl-PPDs are more effective and persistentcompared to other PPDs in polychloroprene (CR) compounds. However, PPD antiozonants

can cross link CR or other halogenated polymers causing ‘bin cure’. PPD antiozonants areeasily oxidized by oxidizing agents (e.g. Lead Oxide) or even during storage. PPDantiozonants are not added in the Rubber-Carbon black master batch as oxidation of thisblend destroys the activity of PPDs.

Type 1Dialkyl PPD

Antidegradant77PD

N,N’-Bis (1,4-dimethylpentyl)-p-phenylenediamine

ST Excellent Excellent Fair A liquid at room temperature. Excellent static ozone resistance. Offers long term static ozoneprotection. Not very effective under dynamic conditions. Highly basic nature& hence scorchy.Does not leach out in water. High volatility at elevated temperatures. More sensitive to oxygenand heat hence poor persistency & shelf-life. A metal ion (Cu, Mn, Fe) deactivator. Causessevere contact & migration staining. Used with alkyl-aryl PPDs to obtain static and dynamicozone protection for NR based tire compounds.Dosage:1.0 to 2.0 phr.


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2

Chemicals Structure

Stainingor

NonStaining

Protection against

NotesHeat &Oxidation

Ozone FlexFatigue

Type 2

Alkyl-Aryl PPD Antidegradant6PPD

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine

ST Excellent Excellent Excellent Offer excellent antioxidant, static & dynamic ozone resistance and anti-flex cracking

properties. Exhibit optimum migration rate. Are less volatile than di-alkyl PPDs. Lower lossesduring storage, processing & cure. Offer long term protection to rubber vulcanizates.IPPD is highly basic in nature and influence scorch & cure. IPPD is easily leached out in waterbut 6PPD does not. 6PPD is much less volatile & basic than IPPD. If the losses of IPPD due tovolatility & water leaching are taken into account, then at equal dosages 6PPD shows betterperformance than IPPD. 6PPD exhibits high solubility in rubber hence no blooming. IPPD is askin irritant hence is substituted by 6PPD in most parts of the world. IPPD & 6PPD are stable& have good shelf-life. Dosages: 1.0 phr to 4.0 phr.Effectiveness of these PPDs increases as the dosages are increased.Type 2

Alkyl-Aryl PPD Antidegradant

IPPD N-phenyl-N’ isopropyl-p-

phenylenediamine

ST Excellent Excellent Excellent

Type 3Diaryl PPD

Antidegradant DPPD

N,N’-diphenyl- ppd

ST Very Good Very Good Excellent Slower migration rate hence persistent, non-extractable by fuels & solvents and retained in thecompound to offer long term protection. Limited solubility in rubber hence bloom over 0.7 phrin NR & 1.0 phr in SRs. Good antioxidant, static & dynamic ozone resistance and anti-flexcracking properties. Does not influence scorch or cure rate. Used in combination with alkyl-aryl PPDs. Resume activity when other PPDs get depleted. Dosage: 0.3 to1.0 phr.

Type 3Diaryl PPD

Antidegradant DTPD+DPPD

ST Very Good Very Good Very Good

ASTM D 4676Class 2

PolymerizedTrimethylQuinoline

AntioxidantTMQ

Polymerized 2,2,4-Trimethyl-1,2-dihydroquinoline

MildDiscolor

ation

No

Contactstaining

Excellent Modest(Static)

Modest TMQ is widely used in the Rubber Industry as general purpose, high activity amine classantioxidant. TMQ is highly persistent, non-blooming antioxidant and has minimal effects onprocessing and curing characteristics of rubber compounds. TMQ offers excellent resistanceto thermo-oxidative ageing of elastomers. Its low volatility (due to polymeric nature) ensuresmaximum retention, low mobility, and minimized losses through diffusion and extraction by

solvents / fuels / oils. Due to Very high activity TMQ is effective even at lower dosages. TMQantioxidant along with 6PPD offers improved oxidative heat ageing resistance proportional tothe dosages of 6PPD and TMQ. TMQ is only mildly discoloring and does not cause contactstaining. TMQ also exhibits a weak antiozonant activity. The composition and performance ofTMQ varies from supplier to supplier.Dosage: 0.7 – 2.0 phr.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

ASTM D 4676

Class 2 AntidegradantETMQ

6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline

ST

Discolor

Excellent Excellent Very

good

A liquid at room temperature.

ETMQ is used in the Rubber Industry as Antiozonant & Antioxidant for general purpose rubberbased compounds (e.g. Tire side walls, cushion gums etc. & Beltings). Particularly effective inSBR compounds. Non blooming. Causes severe contact staining. Also used as an antioxidantfor animal feeds.Dosage: 2.0-3.0 or higher (alone) , Or 2:1 ratio with 6PPD/IPPD.

ASTM D 4676Class 3

PhenolicType 1

Monofunctional

General Structure

NonStaining

PaleYellowOr pinkDiscolor

ation

Good Modest(Static)

Fair Phenolic antioxidants are primary antioxidants. Classified by the number of phenolic groups inthe molecule. More Sterically hindered antioxidants are less discoloring but have lowerantioxidant activity in rubber application. The Phenolic Antioxidants are Non-Staining type andare used for the manufacture of white/colored rubber products and as stabilizers of rawSynthetic Rubbers. The Phenol radical can cause polymer degradation but this is preventedby the hindered physical structure (e.g. substitution by styrene) at 2, 6 position. StericallyHindered phenols act by scavenging RO. And ROO. Radicals via Hydrogen atom transfer from

the OH group to form hydro peroxides and phenoxyl radicals.

Type 1Monofunctional

Antioxidant SPH

n=1-3Styrenated Phenol

NonStaining

PaleYellow

Discolor ation

Good Modest(Static)

Fair Low cost, comparatively weaker, less persistent antioxidant. Slight discoloration tendency onlong term ageing of the rubber vulcanizates. Styrenated Phenol is much less volatile &provides long term protection and is widely used in white / coloured latex based goods,general mechanical goods and footwear products. Dosage:1.0 - 2.0 phr.

Type 1Monofunctional

Antioxidant BHT

Butylated hydroxytoluene

NonStaining

PaleYellow

Discolor ation

Good - - BHT is more volatile and provides only short term protection. It is mostly used as ‘in processstabiliser’ for synthetic polymers to impart raw polymer storage stability. BHT also finds non-rubber applications (e.g. Food) and is used as polymer stabilizer at 0.5 to 1.5 phr dosage.Dosage: 1.0 to 2.0 phr for rubber products manufacture.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

ASTM D 4676

Class 3PhenolicType 2

Bifunctional

General Structure

Non

StainingPalePink

Discolor ation

V. Good - - These antioxidants have low volatility, good antioxidant activity and exhibit minimal

discoloration to rubber vulcanizates.Depending upon the position of linkages, bisphenols are subdivided into ‘ortho’ or ‘para’bridged bisphenolic antioxidants.

Type 2Bifunctional Antioxidant

22M46

2.2’-methylenebis (6-t-butyl-4methylphenol)

NonStaining

PalePink

Discolor ation

V. Good - - 22M46 is a highly potent and is most effective antioxidant for sulfur cured rubber products.22M46 is also an effective antioxidant for polychloroprene based products. 22M46 has a verylow volatility and is most suitable for high temperature processing or product performance.22M46 does not bloom on uncured stocks and gives protection against Copper andManganese ion catalyzed oxidative ageing. These properties of 22M46 make it an interestingantioxidant even for critical carbon black reinforced rubber compounds! 22M46 is used incolored compounds; however; white colored products may show slight pink coloration on

prolonged exposure to light. 22M46 is an excellent polymer stabilizer and is also used as anantioxidant for Hot Melt Adhesives based on EAM, EVA etc. Dosage: 0.5-2.0 phr

Type 2Bifunctional

Thiobis phenols Antioxidant

TBMC

4,4’-thiobis-6-(t-butyl metacresol

NonStaining

PalePink

Discolor ation

V. Good - - Thiobisphenols exhibit high antioxidant activity compared to similar bisphenols.Thiobisphenols generate sulphur compounds which react with polymers during antioxidantprotection reaction and compliment antioxidant activities of thiobisphenols. Thiobisphenolscause comparatively higher discoloration of rubber vulcanizates than bisphenols.Dosage: 0.5-2.0 phr

ASTM D 4676Class 3

PhenolicType 3

MultifunctionalOrtho bridged

General Structure

NonStaining

PalePink

Discolor ation

V. Good - - Multifunctional phenolic antioxidants are very high performance antioxidants, exhibit extremelylow volatility and do not cause contact / migratory staining or discolorations of the rubber

products.Higher molecular weight of multifunctional phenolic antioxidants also contributes to practicallyno leaching and extraction from rubber products by water or solvents and ensuring long termprotection against oxidation.The ‘ortho’ bridged bisphenolic antioxidants exhibit excellent antioxidant performance butshow discoloration (pinking) tendency to rubber vulcanizates.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

Type 3

Multifunctional Polyphenol AntioxidantWingstay L(Goodyear)

Reaction product of Butylated p-cresol & dicyclopentadiene.

Non

Staining

NoDiscolor

ation

V. Good - - Butylated reaction product of para cresol and dicyclopentadiene ( Wingstay L ) Is the most

popular multifunctional phenolic antioxidant used both in dry rubber and latex based productswhere color stability, low volatility and long term protection against heat and oxidativedegradation is desired. The resistance to oxidative degradation is due to a particularlyfavorable pattern of substitution on the phenolic group. Color stability is due to the stearicimpossibility to form highly conjugated and colored by-products like quinones.Dosage: 1-2 phr.

ASTM D 4676Class 3

PhenolicType 3

MultifunctionalPara bridged

General Structure

NonStaining

NoDiscolor

ation

V. Good - - The ‘para’ bridged bis phenolic antioxidants show slightly lower antioxidant performance butdo not exhibit discoloration effect on rubber vulcanizates.

Type 3MultifunctionalPara bridged

AntioxidantIrganox 1010

(Ciba)

Tetrakis [Methylene 3-(3,5 di-t-butyl -4 hydroxyphenyl) propionate]

methane

V. Good - - Irganox anti-oxidants are phenolic based anti-oxidants that hinder thermally induced oxidationof polymers where high temperature applications are used. Unlike hindered amines, anti-oxidants are consumed - and not regenerated - in the stabilization process. Irganox 1010offers excellent protection against over bake yellowing by terminating free radicals inconventional solvent-based and powder coating systems. The major usage of Iraganox 1010is in Thermoplastics rather than rubbers. Dosage: 0.5-1.0 phr

ASTM D 4676Class 4

Alkylated DPAs(Antioxidant)

Diphenyl amines(General Structure)

STDiscolor

Good - - This class of antioxidants represents ‘Substituted Amine Antioxidants’ which are complexreaction products of diphenylamine and various alkylating agents.The substituents are selected to achieve a desired balance of cost and performancecharacteristics. Alkylated Diphenyl Amines are moderately staining and discoloring. Theseantioxidants are generally used as stabilizers of raw synthetic polymers and as generalpurpose antioxidants for rubber vulcanizates.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

Diphenyl Amines

(DPAs)(Antioxidant )

Alkylated diphenylamines(Styrenated, Octylated, Heptylated,

Nonylated)

NST

Discolor

Good - - Styrenated Diphenyl amine a straw colored-amber liquid. Is highly active, low volatility

antioxidant and protects rubbers against degradation due to heat, light and oxygen. It is nonblooming, non hydrolysable, non staining but discoloring type antioxidant and does notinfluence the cure rate of the rubber compound. Styrenated Diphenyl amine is widely used asa polymer stabilizer for the manufacture of staining type synthetic rubbers. It is used in somenon critical tire compounds, automotive & mechanical molded goods. Dosage: 1.0 – 3.0 phr.

AntioxidantSDPA

Wingstay 29(Goodyear)

p-oriented Styrenated Diphenyl amine

NSTDiscolor

Good - - Dark tan liquid. Mostly di substituted with some mono & tri substitution. Some orthosubstitution. Highly active non-staining & mildly discoloring antioxidant for NR & SyntheticRubbers. Low volatility. Offers very good heat resistance to rubber vulcanizates. Non-blooming. Suitable for CR based compounds. Dosage:1.0-2.0 phr

AntioxidantDCDPA

Naudard 445(Chemtura)

4,4, bis (α,α-domethylbenzyl)diphenylamine

STDiscolor

Good - - 4,4’-Bis (α,α-dimethylbenzyl) diphenylamine (DCDPA) is a grayish white powder with meltingpoint of 90 deg C. DCDPA is a slightly staining type antioxidant which offers good heat and

flex-cracking resistance to rubber vulcanizates and is used in the rubber products based onNR, IR, BR, SBR, NBR, CR & ACM. DCDPA is less discoloring than ODPA and is especiallyeffective against heat for ACM based compounds. Dosage: 1.0 – 4.0 phr.

ODPA(Antioxidant)

Octylated Diphenyl amine

ST Good - Good Octylated diphenylamine (ODP) is a brownish to purple colored antioxidant (Flakes) withmelting point of 75 deg C. Octylated diphenylamine (ODP) is used as a stabilizer in themanufacture of synthetic rubbers. Octylated diphenylamine (ODP) is a staining and bloomingtype antioxidant which offers good heat and flex-cracking resistance to rubber vulcanizatesand is used in the rubber products based on NR, IR, BR, SBR, NBR, & CR. It is most widelyused antioxidant in CR based rubber compounds since it does not influence the bin storageproperties.Dosages: 1.0 – 2.0 phr.

ASTM D 4676

Class 5Aromatic

Phosphites

General Structure

NST Good - - Phosphite antioxidants are hydro peroxide (ROOH) decomposers and are always used in

combination with H-donors e.g. hindered phenols. The phosphites are oxidized to phosphatesand RO

. & ROO

. Radicals are reduced by the reaction with the formation of trivalent

phosphorus compounds.The phosphites are hydrolyzed easily in presence of acidic materials. They are also destroyedduring sulphur vulcanization and hence are not effective with sulphur cured products.


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Chemicals Structure

Staining

or

Non

Staining

Protection against

NotesHeat &

Oxidation

Ozone Flex

Fatigue

Antioxidant

TNPP

Trinonyl phosphate

NST Good - - Phosphite antioxidants are used as in-process stabilizers and as stabilizers during Synthetic Rubber

e.g. SBR manufacture.Phosphites can be used with non-sulphur cured products.

Phosphites give excellent color retention properties because they act as reducing agents.

Phosphite antioxidants are also widely used in the manufacture of adhesives for tack retention.

The recommended dosages are 1.0 – 2.0 phr.

ASTM D 4676

Class 6

Diphenylamine -

Ketone

Condensates

(Antioxidant)

Acetone Diphenyl amine condensates

(ADPA)

ST Modest Modest Modest These antioxidants are complex reaction products of diphenylamine and alkyl ketones (primarily

acetone), some of which are further condensed with formaldehyde to produce products of high

molecular weight. These antioxidants are low melting point resins or liquids.

There are two different types of ADPA condensates viz. low temperature reaction products and h igh

temperature reaction products. The high temperature reaction products are reactive towards oxygen

and provide some flex – cracking resistance but are severely staining and discoloring. They are also

volatile and do not provide long term protection against the degradative forces that constantly act

on rubber products. These products are mostly used in mechanical rubber products, some non

critical tyre applications and as a stabilizer for emulsion SBR. These antioxidants reduce the building

tack of uncured rubber compounds making product (e.g. tyres, conveyor beltings etc) building

process more difficult.

The low temperature condensation products are not very reactive towards oxygen but are less

staining and discoloring. These are comparatively less volatile and can provide medium term

protection to the rubber vulcanizates. These types of ADPAs have low solubility in oil and hence

suitable for oil resistant compounds based on NBR. Dosages: 1.0 – 2.0 phr.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

Other

AntioxidantsNapthylAmines

PAN(Antioxidant)

Phenyl –α-napthyl amine

ST Good - - Highly effective antioxidants, but toxicological risk! (Carcinogenic).

Usage discontinued in the Rubber Industry.

PBN(Antioxidant)

Phenyl –ß-napthyl amine

ST Very Good - -

MMBI& ZMMBI

Antioxidants

and

1,2-Mercapto-4(5)-methylbenzimidazole

Zinc salt of 1,2-Mercapto-4(5)-methylbenzimidazole

NST Very Good - - These are heterocyclic SH-compounds and are different from the usual phenol/amineantioxidants.

These are used with other antioxidants for synergistic effect on heat resistance properties &metal as metal deactivators. This effect depends on the vulcanization system. x MMBI is moreeffective in vulcanizates produced with Thiuram and Dithiocarbamate accelerators than insulfenamide or thiazole accelerators.

The combinations are particularly suitable for compounds which contain low levels of sulfurand high levels of accelerators.

These products offer no protection from cracking, whether caused by flexing, ozone or theaction of light and oxygen.

MMBI and ZMMBI give little protection from heavy metal poisoning when used individually.However, the protection is enhanced by using combinations with other antioxidants like22M46. TMQ & MMBI and ZMMBI combinations ore suitable antioxidants for rubber productsbased on peroxide-cured rubber products.

Dosage: 1:1 in combination with phenolic antioxidants/amine antioxidants.


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Chemicals Structure

Stainingor

NonStaining

Protection against


Ozone FlexFatigue

Other

AntioxidantsThioestersTDPE type

DIdodecyl 3.3’ thiodipropionate

NST Good - - The Thioesters are esters of thiodipropionic acid. These are secondary antioxidants and are

used with phenolic or amine antioxidants.Thioesters are highly effective peroxide decomposers for long term heat resistance when usedin combination with phenolic antioxidants.Thioesters are destroyed during sulphur vulcanization. Hence, not used for Sulphur vulcanizedrubber products. Thioester antioxidants find applications in Plastics and TPE s. Exhibitblooming tendency at higher dosages.

DIoctadecyl 3.3’ thiodipropionate

NST Good - -

OtherAntioxidants

Dithio

Carbamates

ZDBC

Zinc dibutyl dithiocarbamate

NST Good - - Dithiocarbamates are moderate antioxidants but their use is limited due to the activating effecton sulphur based cure systems.One of the widely used dithiocarbamate is Nickel Dibutyl dithiocarbamate (NBC). It is used as

an antiozonant for SBR, BR, NBR, ECO and CR based compounds. It is also used as anantioxidant and heat age resistor for CSM and EPDM.Nickel Dibutyl dithiocarbamate should not be used with NR since it is a pro-oxidant with NR.

Another dithiocarbamate is Zinc dibutyl dithiocarbamate. This product is used as a stabiliserfor Butyl rubber production and as an antioxidant for rubber based adhesives.

NiDBC(NBC)

Nickel dibutyl dithiocarbamate

NST Good - -

For selecting a proper antioxidants / antidegradants for specific end-use requirements following factors are considered to be important for the choice.a ) Discoloration & Stainingb ) Volatilityc ) Solubilityd ) Chemical Stabilitye ) Physical formf ) Antioxidant/Antidegradant concentrationg ) Costh ) Health & Toxicity concerns

antioxidants & antidegradants

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