Blooming Bob Francis

Responsible Care A Public Commitment

Science & Technology of Blooming of Rubber

Chemicals & its Prevention

Bob Francis – Flexsys Asia Pacific

17/2/2006


Contents

Introduction Mechanism of Blooming Merits & Demerits of Blooming Effect of Rubber Chemicals’ Bloom on Compound

Tack Effect of Blooming Vulcanizing Chemicals on

Vulcanizate Properties Factors affecting Blooming of Rubber Chemicals Detection & Estimation of Rubber Chemical Bloom Summary & Conclusions


Dictionary DefinitionBloom a.

A waxy or powdery whitish to bluish coating on the surface of certain plant parts, as on cabbage leaves or on a plum

or grape.b. A similar coating, as on newly minted coins.c. Grayish blotches or streaks on the surface of chocolate

produced by the formation of cocoa butter crystals.

d. Chemistry See efflorescence.

Efflorescence a. The deposit that results from the process of

efflorescing. Also called bloom. b. The process of efflorescing. c. A growth of salt crystals on a surface caused by

evaporation of salt-laden water.Courtesy of the Free Dictionary by Farlex


Bloom vs Diffusion Bloom: May occur when a partly

soluble additive is used at a loading in excess of its solubility at a given temperature. Bloom doesn’t occur from an unsaturated solution.

Diffusion: The movement of a soluble material prompted by a concentration gradient Fick’s 1st Law: ‘The flux of diffusing particles is proportional to the gradient of their concentration’

Bloom is an outcome of a diffusion process


Bloom For bloom to develop, it needs a surface (typically with air)

Blooms result from a diffusion process to a surface. The molecules migrate through the compound to form a high stability supersaturated solution on the surface

Under favourable conditions this solution destabilises and crystals form

For the molecules to migrate they need to be partially soluble in the matrix

There can be subtleties as to whether a surface ‘film’ is actually a bloom. Blooms are solids not liquids.

Blooms can be bi-products of the vulcanizing reactions (eg ZDCs from thiurams, phthalimide from CTP, resotropin from SRH systems)


Curative Diffusion in NR(17days@45C)

0.001

0.01

0.1

1

10

-1.25 -0.75 -0.25 0.25 0.75 1.25 1.75

Distance From Interface (cm)

Lo

g C

on

c. (

wt.

%)

TBBS

DTDM

MBTS

CTP

With curatives initially No curatives initially


Molecular Weight (size) A study in NR showed the following tendency for

migration:

DTDM (236) > TBBS (238) > CTP (261) > MBTS (332)

Decreasing rate of migration

Larger molecules diffuse slower

(not just MW,also a steric hindrance effect)


Temperature & Concentration

The rate of diffusion increases with increasing temperature

Higher concentration increases the rate of diffusion


Merits & Demerits of Blooming

Influential for tackifying, ozone protection Problematic for:

tack retention interply adhesionvisual appearancecontact stainingantidegradant

loss

Diffusion is necessary for the functionality of tackifiers & antiozonants

Blooming is considered undesirable as it is generally in excess to the need


Antiozonants An antiozonant used in excess of its solubility has

two driving forces affecting its appearance at the surface

Bloom & Diffusion

An ideal antiozonant would be totally soluble & show rapid migration to the surface to replace that depleted by its reactivity & not be easily removed from the surface (high persistence, low volatility)

77PD > 6PPD > IPPD > DTPDDecreasing Solubility


Petroleum Waxes Types

Paraffin (low temp. solubility & mobility)Microcrystalline (high MW,high temp solubility/mobility)

Characterized by balance of:Migration & solubility in rubber, both Temp. dependent

Sufficient bloom formation on surface provides protection Limitations: Can

inhibit tack & adhesion Wax film is brittle & suitable only as static protectant Once film is ruptured the surface is unprotected High concs. (>2.5phr) reduces fatigue resistance


Wax composition Alkanes – give rapid migration but a brittle film

with low adhesion & poor ‘depot’ properties Isoalkanes - improve the film properties Cycloaliphatics - improve plasticity & adhesion

Waxes with a low softening point are more soluble & re-dissolve at higher environmental temperatures risking under-protection

Waxes with a high softening point diffuse too slowly risking under-protection

Microcrystalline waxes need careful selection to accomplish static ozone protection


Wax Mobility vs Solubility

Amount of

bloom

Mobility solubility

Temperature


Impact on Tack Tackifiers function to some extent by plasticizing &

softening, reducing the viscosity & elastic behaviour of the rubber

This has the effect of smoothing the surface facilitating inter-surface adhesion

Part of their functionality relies on diffusion of polar molecules to the surface of less-polar elastomers

Chemicals which co-migrate to the surface can interfere with the tack (eg waxes, sulfur, antidegradants, oils)

Environmental factors such as humidity & UV also can result in reactions to reduce tack

Frequently, hydrocarbon solvents are used to ‘freshen’ stocks to remove tack-limiting blooms during tyre construction


TMQ components - Days to form bloom

0 5 10 15 20 25 30 35

1

2

3

4

TMQ

degr

ee o

f co

ndens

ati

on

days

Ref: “Non Blooming High Performance Antidegradant” (N.Inui, H. Nagasaki and T. Yamaguchi, Osaka) presented at Tyretech ‘92


More elastic, fewer points

of inter-surface contact

More plastic, numerous points of

inter-surface contact

Addition of plasticizing resins


Sulfur Bloom One of the major problems in tack retention is sulfur

bloom This is due to the limited solubility of sulfur in rubbers

at room temperature

0

2

4

6

8

10

30 40 50 60 70 80 90 100

Temperature [°C]

So

lub

ilit

y, [

%] SBR

NR

IIR


RHOMBIC SULPHUR

•Only slightly soluble in rubber at room temperatures

- SULPHUR BLOOM

- REDUCED TACK

- REDUCED INTERPLY ADHESION


INSOLUBLE SULPHUR :

• Polymeric (large molecules)

• Insoluble in rubber

• Metastable, slowly reverts to

Rhombic sulphur more-so at high

temps

•


INSOLUBLE SULPHUR

- NO SULPHUR MIGRATION

- NO SULPHUR BLOOM

- TACK RETENTION

- INCREASED SCORCH TIME

But more difficult to disperse


Factors influencing Sulfur bloom

Quality of the Insoluble Sulfur (starting IS content & thermal stability) & its phr in the compound

Degradation of Insoluble Sulfur due to storage near basic chemicals (HMT, HMMM, ammonia, DCBS, TBBS, CBS, DPG…)

Pre-weighing of IS with accelerators in same bag + in-compound effects of these basic chemicals

Temperature & time (heat history) during mixing & processing


Bloom TendencyEvaluation of the risk of bloomingIf final soluble sulfur concentration is equal or greater than 1.5 ---> will bloom Formula phr SS = (100-%I.S) * phr TS /100if in between 1.0 - 1.5 --> possible bloom

phr SOLUBLE SULFUR in compounds** 95.0 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

92.5 0.075 0.150 0.225 0.300 0.375 0.450 0.525 0.600HTS can be considered as 90.0 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800% IS remaining 87.5 0.125 0.250 0.375 0.500 0.625 0.750 0.875 1.000in rubber compound 85.0 0.150 0.300 0.450 0.600 0.750 0.900 1.050 1.200

** = 82.5 0.175 0.350 0.525 0.700 0.875 1.050 1.225 1.400ADDING 100 % of sulfur 80.0 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600in rubber compound 77.5 0.225 0.450 0.675 0.900 1.125 1.350 1.575 1.800

after milling the IS remaining 75.0 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000

is=95.0 %mean that in the compound 72.5 0.275 0.550 0.825 1.100 1.375 1.650 1.925 2.200there is 5 % soluble sulfur 70.0 0.300 0.600 0.900 1.200 1.500 1.800 2.100 2.400 + - 0.050 phr of soluble sulfur 67.5 0.325 0.650 0.975 1.300 1.625 1.950 2.275 2.600 in the mixed compound 65.0 0.350 0.700 1.050 1.400 1.750 2.100 2.450 2.800

62.5 0.375 0.750 1.125 1.500 1.875 2.250 2.625 3.00060.0 0.400 0.800 1.200 1.600 2.000 2.400 2.800 3.20057.5 0.425 0.850 1.275 1.700 2.125 2.550 2.975 3.40055.0 0.450 0.900 1.350 1.800 2.250 2.700 3.150 3.60052.5 0.475 0.950 1.425 1.900 2.375 2.850 3.325 3.80050.0 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.00047.5 0.525 1.050 1.575 2.100 2.625 3.150 3.675 4.20045.0 0.550 1.100 1.650 2.200 2.750 3.300 3.850 4.400

soluble S 42.5 0.575 1.150 1.725 2.300 2.875 3.450 4.025 4.600< 1.0 phr : no bloom 40.0 0.600 1.200 1.800 2.400 3.000 3.600 4.200 4.800

1-1.5 phr : bloom possible 37.5 0.625 1.250 1.875 2.500 3.125 3.750 4.375 5.000>1.5 phr : bloom likely 35.0 0.650 1.300 1.950 2.600 3.250 3.900 4.550 5.200

32.5 0.675 1.350 2.025 2.700 3.375 4.050 4.725 5.40030.0 0.700 1.400 2.100 2.800 3.500 4.200 4.900 5.60027.5 0.725 1.450 2.175 2.900 3.625 4.350 5.075 5.80025.0 0.750 1.500 2.250 3.000 3.750 4.500 5.250 6.000

1 2 3 4 5 6 7 8phr TOTAL SULFUR in compound


%Sol. Sulfur through steel skim processing(factory example)

0

0.1

0.2

0.3

0.4

0.5

0.6

Ex Banbury into warm up calender feedstrip

cal. Wind-up Tyre building

% S

S

Theoretical max soluble sulfur of this cmpd is 3.2%

Prior to mixing sol. S is 0.08%

Bloom likely > 0.8% (1.5phr)


Sulfur Migration Migration of IS only occurs after it has reverted to

a soluble form The rate of migration depends on concentration &

temperature Above 130°C there is no difference in the

migration characteristics of insoluble & soluble S (its one & the same)

Soluble sulfur will readily migrate across a rubber interface to equilibrate concentration differences. The magnitude is a function of time, temp. & distance


Effect of blooming vulcanizing chemicals on vulcanizate

performance Visual

Ozone protection

Contact staining (esp. PPDs)

ES&H

Interply adhesion (durability, retreadability etc)


Relation of wax bloom to static ozoneprotection

0

50

100

150

200

250

0 50 100 150 200

Ozo

ne

Re

sis

tan

ce

, h

ou

rs

Wax Bloom, g/cm2

NR/BR Sidewall1 phr Santoflex6PPD

>208


Diffusion of Antiozonant in Passenger Tyre Carcass & Sidewall

0

0.5

1

1.5

2

0 2 4 6 8

% B

y W

eig

ht

6PP

D

Weeks aging at R.T.

Carcass

Sidewall

0

0.5

1

1.5

2

0 2 4 6 8

Weeks aging at R.T.

Carcass

Sidewall


0

1

2

3

4

5

6

7

8

0 0.5 1 1.5 2

Sid

ew

all

Cra

ckR

atin

g

phr Antiozonant in Carcass

Road Test

Wheel Test

Carcass Reservoir Concept : Tyre Tests

Bad

Good


Change in Antidegradant Concentration

in Tyre Sidewall Area (due to migration)

0

10

20

30

40

50

60

70

80

90

100

AfterProcessing

AfterCuring

3 MonthsAging

7 MonthsAging

12 MonthsAging

% R

etai

ned

An

tid

egra

dan

t

6PPD in Carcass

6PPD in Sidewall

DTPD in Sidewall

DTPDin Carcass


Change in Antidegradant Concentration

In Tyre Tread Area (due to migration)

0

10

20

30

40

50

60

70

80

90

100

AfterProcessing

AfterCuring

3 MonthsAging

7 MonthsAging

12 MonthsAging

% R

etai

ned

An

tid

egra

dan

t 6PPD in Carcass

6PPD in Base

DTPDin Base

77PDin Carcass77PD

in Tread

6PPD in Tread


Effect of Storage/Service conditionson Antidegradant Concentration

% Retention of AntidegradantAkron Texas TexasOne Static 1 Year StaticYear 16 Mos. +48,000 Miles

Tread6PPD 98.4 71.6 22.87PPD 12.8 0.0 0.0

Tread Base6PPD 66.5 48.7 22.07PPD 42.8 37.8 17.0

Carcass Under Tread6PPD 88.6 75.7 20.3

Sidewall6PPD 46.0 22.0 8.0DTPD 28.6 17.8 11.8

Carcass Under Sidewall6PPD 97.1 59.6 18.3(None Added) DTPD 11.4 6.3 3.8


O3 Protection vs. 6PPD level

60

70

80

90

100

110

3.0 phr 2.5 phr 2.0 phr 1.5 phr

% R

elat

ive

Ozo

ne

Res

ista

nce


Reservoir Effect It is generally recognized that the carcass needs

some level of 6PPD to act as a ‘reservoir’ to be able to migrate through to the tread or sidewall to replace reacted & lost 6PPD


ES&H

Dangerous for the environment

EU Classification based on ecotoxicological properties

N

Several antidegradants & accelerators are environmentally hazardous


Skin contact Many individuals suffer skin allergies (Type IV

hypersensitivity)

Bloom presents the chemical to the surface where it can be transferred to skin through handling

Whilst this is not ‘life-threatening’, it can cause severe inconvenience & discomfort to sensitised individuals


Interply Adhesion Exposure of NR & IR to sunlight or O3 produces a thin film

on the surface of the compound. This film restricts migration of the polymer chains across a plied-up interface

Consequently both tack in the uncured compound & interply bond strength in the cured compound are reduced

The effects of sunlight can be greatly reduced through the use of antidegradants such as 6PPD

But Antiozonants react with O3 to form a protective film which acts as a barrier to the mobility of the polymer chains & thereafter reduces interply adhesion

Also, as the number of double bonds at the surface is reduced after O3 attack, a lower crosslink density is expected


Effect of Sunlight on the Tack of NR and SBR

0

40

80

120

160

200

0 15 30 45 60

Sunlight Exposure Time, minutes

Ta

ck

(lb

s/in

2 )

SBR

NR


Effect of Ozone on Tack--15pphmConcentration

Exposure

0

10

20

30

40

50

60

70

SBR NR/SBR NR

Ta

ck

(lb

/in2 )

1 Day 2 Days


Effect of Ozone/Humidity on Interply

Adhesion

Adhesion Rating

Compound Initial 16hrs @15pphm O3 and

30% RH

16hrs @25pphm O3 and

30% RH

16hrs @ 15pphmO3 and 60% RH

NR 5 2 - 3 1 1

IR 5 4 - 5 2 - 1 2 - 1

SBR 5 4 - 5 3 - 4 3 - 4

Adhesion Rating: 1 2 3 4 5

Bad Good

NR stock more affected by O3 + humidity


Effect of 5pphm Ozone on Interply

Adhesion

0

1

2

3

4

5

0 4 8 12 16 20

Exposure Time, hours

Ad

hes

ion

Rat

ing


Effect of Sunlight on Cured Interply

Adhesion-NR

ExposureTime, minutes 0 15 60 90

Rating 5 4 - 5 1 - 2 1

Green compound exposure to Sunlight is quite damaging to

subsequent ply adhesion


Effect of Antiozonants in NR on cured

Interply Adhesion After O3 Exposure

Antiozonant(1 phr)

InitialRating

Rating after 16h @15pphm O3

None 5 1TMQ 5 16PPD 5 1IPPD 5 177PD 5 1

No apparent benefit!


Effect of Antioxidants in NR on Cured

Interply Adhesion After O3 Exposure

Antiozonant(1 phr)

InitialRating

Rating after 16h @15pphm O3

None 5 1TBMC 5 2TMQ 5 2

Antioxidants do not form an ozonide

film to limit subsequent cured adhesion


Effect of Fast Blooming Waxes in NR on

Cured Interply Adhesion After O3 Exposure

WaxLoading

InitialRating

Rating after 16h @ 15pphm O3

None 5 1Wax #1 -1phr

5 5

Wax #2 -1phr

5 5

Wax is beneficial in protecting in-process

components


Effect of antioxidants in NR on Cured

Interply Adhesion After UV Exposure

Exposure Time,minutes

0 15 60 90

Antioxidant (1phr)

Ratings

None 5 4 - 5 1 - 2 1TMQ 5 5 5 56PPD 5 5 5 5ADPA 5 4 - 4 2 1DTPD 5 5 5 5MBI 5 - - 1 - 2TBMC 5 4 3 2


Effect of Fast Blooming Wax in NR onCured Interply Adhesion After UV

Exposure

RatingWax/ AOLoading

0 MinutesUV

Exposure

60 Minutes UV Exposure

None 5 1Wax- 2phr 5 3Wax- 2phr;6PPD - 1phr

5 5


Lab Measurements of Diffusion

Uncured stocks, butt-joined, pressed & stored for differing conditions

12.7 12.763.5 mm 63.5 mm

Stock #1

Stock#1

5 phr

5 phr

Stock #2

No curative

Stock #2

No curative


Test methodology After 3, 7, or 17 days @ either 23°C or 45°C, strips

were cut at measured distances from the interface

2 mm3 pieces were cut, weighed into amber bottles & extracted for 24hrs

The quantitative assessments were made by reverse phase HPLC


Compound with experimental AO

Compound with experimental AO

Control without AO

Diffusion coefficient determination (mould)

Procedure 2


Determination of diffusion coefficient, D, cm2/sec(Classical diffusion theory)

D = (l2/16) * (Tan2 (from plot)/m2 )

l= thickness of the vulcanizate plate, cm

Tan = Determine from the plot

m = Weight increase in the central plate at equilibrium


The method:• The increase of AOz in central vulcanizate plate to be followed by the measurement of the weight increase. The decrease of the mass of the side plates to be measured simultaneously. The equilibrium will occur when “central” and “side” plates each reach a constant weight.

•Plot the increase mass (mt, gram) versus square root of t½

From the plot determine tangent


A typical plot

α


Diffusion coefficient (cm2/s) of IPPD and 6PPD determined by this technique, effect of temperature

Rubbers Temp. °C IPPD 6PPD

NR 1038

3.40 * 10-9

2.56* 10 -81.70 * 10-9

1.39* 10 -8

SBR 1500 38 1.03* 10 -8 6.13* 10 -9

NR/BR 1038

1.16 * 10-8

6.89* 10 -87.82 * 10-9

4.55* 10 -8


The time required for the saturation of the central plate

Rubber Temperature, °C IPPD 6PPD

NR 10°CSaturation days

3.40*10-9

571.70*10-9

60

38°CSaturation days

2.56*10-8

131.39*10-8

16

62°CSaturation days

1.19*10-7

47.05*10-8

4

Mobility greatly affected by temperature


Other Test Methods Visual assessments

Radioactive tracing

Microinterferometry (an optical method, suitable only for gum stocks)

Wet swabs or dry scraping followed by extract analysis via instrumental techniques such as FTIR, GC/Flow Injection Analysis-MS


Developments Flexsys has done considerable R&D on the

development of long-lasting antioxidants & antiozonants

Polymer-bound products slow the diffusion (eg Q-Flex QDI)

Molecular size is another strong variable

Flexsys continues to improve the thermal stability of our Crystex Insoluble Sulfur to maintain this as the most bloom resistant IS


Chemical Additives’ Migration

Curatives & antidegradants will migrate throughout a rubber compound, both in the uncured & cured states

The extent of migration is a function of additive type, loading, its reactivity with other ingredients, & the environmental / service conditions

Optimum compound performance is, in part, a result of designing the compound taking these factors into account


Documents

Blooming Bob Francis