composition and property changes of hnbr & fkm ... - artis · artis 2016 manchester polymer...

© ARTIS 2016 Manchester Polymer Group, 16th May 2016 1

Composition and Property Changes of HNBR & FKM Elastomers after Sour Gas

Ageing

C. Norris, M. Bennett, M. Hale & J. Lynch


Overviewo Demanding Environment Facility

o Ageing Protocol

o Lifetime Predictions

o DMA Assessment

o Extract Analysis

o TGA

o Elemental Analysis

o Degradation Mechanisms

o Conclusions

o Further Work


Sour Gas Testing Capability OverviewEquipment: Six autoclaves (initially) capable of sour gas exposure testing following:

• NORSOK M-710 (ed. 3 Sep 2014)

• ISO 23936-2:2011

• NACE TM0187-2011

Temperature Range: Ambient to +250°C.

Pressure Range: Atmospheric to +110bar.

Gas Mixtures:

• 2% H2S/ 3% CO2/ 95% CH4

• 10% H2S/ 5% CO2/ 85% CH4

• 5% CO2/ 95% CH4

• Others upon request


Oil Price

Oil Price

@ sign-off

Oil Price @

commissioning


Ageing Protocol

10% Distilled Water

30% Gas Phase

60% Solvent Phase


Lifetime Prediction - Example

Example: Cured FKM polymer aged using aggressiveconditions.

50% change in M50% used as the failure criterion.

M50% modulus plotted as a function of time.

Extrapolation often used to estimate time to failure,especially at lower temperatures.

Arrhenius then used to predict lifetime at lowertemperatures.

In this case = 16 years @ 100°C

y = -0.0092x + 2.6551R² = 0.9359

y = -0.0234x + 2.6204R² = 0.9659

y = -0.034x + 2.633R² = 0.9729

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30 35 40 45

M5

0%

(M

Pa)

Time (days)

166°C181°C195°C

y = -9461.3x + 16.676R² = 0.954

-5

-4.8

-4.6

-4.4

-4.2

-4

-3.8

-3.6

0.00212 0.00214 0.00216 0.00218 0.0022 0.00222 0.00224 0.00226 0.00228 0.0023

ln (

1/t

50)

1/TK


Additional Post-Exposure TestingShould we rely on basic physical testing to direct lifetime predictions and product

development?

What additional information can we gain from these testing regimes?The following analytical study was conducted on samples aged under the most

severe conditions.


DMA: Temperature Dependency• Samples tested in tension, 10Hz, 0.1% DSA & -80°C to +80°C.

• HNBR: Reduced tan δ peak height and higher stiffness indicative of higher crosslink density.

• FKM: Reduced stiffness and Tg suggesting molecular weight reductions had occurred; likely

associated with the loss of side-groups .

Opposing effects for the two polymer types

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

-80 -60 -40 -20 0 20 40 60 80

Tan

de

lta

Log

(E'/

Pa)

Temperature (°C)

HNBR Control

HNBR Aged

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

-80 -60 -40 -20 0 20 40 60 80

Tan

de

lta

Log

(E'/

Pa)

Temperature (°C)

FKM Control

FKM Aged


DMA: Strain Dependency• Samples tested in tension, 10Hz, +80°C & 0.06 to 6% DSA.

• HNBR: Significant increase in filler-filler interactions, as indicated by ∆E’ (↑ 79%).

• FKM: Reduced filler-filler interactions observed, possibly due to filler surface modification due to

contact with HF (∆E’ ↓ 7%) .

Opposing effects for the two polymer types

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

0.01 0.10 1.00 10.00

E' (

MP

a)

DSA (%)

HNBR Control

HNBR Aged

0.00

5.00

10.00

15.00

20.00

25.00

30.00

0.01 0.10 1.00 10.00

E' (

MP

a)

DSA (%)

FKM Control

FKM Aged


Extract Analysis GCMS and IR Spectroscopy: • FKM: Unsurprising, the FKM was found to contain very little in the way of soluble matter. No evidence of low

molecular weight polymer was detected but such species may have remained in the ageing vessel fluids.

• HNBR: Naugard 445 antioxidant (↓90%) and a trimellitate plasticiser were found to be deficient in the aged material, confirming migration of soluble matter to have occurred. The extract was noted as being gummy in nature – IR spectroscopy revealed the presence of acrylonitrile groups (-C≡N), almost certainly arising from low molecular weight polymer.

E59505_A.sp - 30/09/2014 - UNAGED HNBR EXTRACT, SP_ATR

E59505_B.sp - 30/09/2014 - AGED HNBR EXTRACT, SP_ATR

L59410_A.002 - 17/04/2014 - TOTM/TNTM BLEND, SP_ATR

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600.0

52.92

55.0

60.0

65.0

70.0

75.0

80.0

85.0

90.0

95.0

100.00

cm-1

%T


TGA: HNBR

• No significant impact on bulk composition (other than reduced extract content).

• The cumulative weight loss profile reveals some modification of the polymer decomposition behaviour, with more rapid weight loss being recorded for the aged sample over much of the temperature range – further confirmation of formation of lower molecular weight species.

-30

-25

-20

-15

-10

-5

0

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80

dW

/dt

We

igh

t /(

%)

Time (mins)

HNBR Control

HNBR Aged

0.1

1

10

100

200 300 400 500 600

Cu

mu

lati

ve w

eig

ht

loss

(%

)

Temperature (°C)

HNBR Control

HNBR Aged


TGA: FKM

• No significant impact on bulk composition.

• Increase in carbonaceous residue formed during polymer volatilisation.

• Increased carbon black oxidation rate, typically associated with the attachment or formation of pro-oxidative species.

• More rapid polymer decomposition indicating some level of chain scission.

-60

-50

-40

-30

-20

-10

0

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80

dW

/dt

We

igh

t (%

)

Time (mins)

FKM Control

FKM Aged

0.1

1

10

100

100 200 300 400 500 600

Cu

mu

lati

ve w

eig

ht

loss

(%

)

Temperature (°C)

FKM Control

FKM Aged


SEM EDX Analysis

Presence of localised surface degradation on both compounds.

↑O & S at surface. Low-level oxidative ageing.

↑O & F at surface. Possible bloom of low molecular weight fragments. Low-level oxidative ageing.

Sulphur content of sectioned samples show both to have ↑ sulphur content

FKMHNBR


Elemental Microanalyses Quantitative elemental microanalyses of extracted samples

(aged – unaged values in wt%)

C -1.36 -3.5

H 0.1 -0.29

N -0.12 Not tested

S 0.55 0.73

F Not tested -0.67

• Sulphur content increased for both HNBR and FKM = permanently bound.

• HNBR – Reduction in N content further confirmation of loss of low MW polymer.

• FKM – Reduction in H & F content confirms dehydrofluorination. Significant reduction in carbon content suggests loss of polymeric fragments.


Mechanisms Summary: HNBRData suggests that additional C-Sx-C is the dominant mechanism with regard to increased stiffness. No evidence of H reduction to support additional C-C linkages.

*arbitrary numbers


Mechanisms Summary: FKM

*arbitrary numbers

Data suggests molecular weight reductions and dehydrofluorination to be the dominant mechanisms:


Conclusionso The test fluids outlined in NORSOK M710 ed.3/ ISO 23936-2:2011 were found to impart

muliple modes of degradation to both HNBR and FKM compounds after relatively short exposure times.

o Stiffening of HNBR attributed to additional crosslinking, plasticiser extraction and increased filler-filler interactions.

o Softening of FKM attributed to dehydrofluorination and loss of polymer fragments.

o Crosslinking, chain scission, dehydrofluorination, oxidative ageing, filler surface modification and extraction all likely to be occurring at different rates.

o Understanding of the mechanisms involved can be used to develop more robust formulations for sour service conditions.


Further Work• Currently running a Box-Behnken experimental

design to further understand the effects of temperature, H2S concentration and time on the different modes of degradation.• HNBR material compounded at ARTIS –

therefore, composition fully understood.

• Can we use parameters other than standard physical properties to estimate lifetimes?

• Can we correlate the ageing mechanisms occurring during service with those of the accelerated ageing?

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Thank You!

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composition and property changes of hnbr & fkm ... - artis · artis 2016 manchester polymer...

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