Crust Formation On Natural Rubber Shamsul B.Kamaruddin 1, Grant E. Hearn 1, Alan H. Muhr 2, P-Y.Le Gac 3, Y.Marcor 4, 1 University of Southampton; 2 Tun.

Crust Formation On Natural RubberShamsul B.Kamaruddin1, Grant E. Hearn1, Alan H. Muhr2, P-Y.Le Gac3, Y.Marcor4,

1University of Southampton; 2Tun Abdul Razak Research Centre; 3IFREMER, 4ENSTA [email protected]

Fluid Structure Interactions Research Group

Acknowledgement:This project is supported by funds from the Malaysian Rubber Board

FSI Away Day 2012

Motivation• Accelerated ageing tests suggest no crust would be formed at ambient temperature (Lindley & Teo, 1977). This conflicts with some observations on naturally aged natural rubber (NR).

Objectives• Characterise the crust that has formed on rubber aged naturally over a period of 80 years.• Probe the chemical and physical character of the crust and interpret the results to assess the significance of hypothetical mechanisms•Seek to resolve the conflict with extrapolation from accelerated ageing tests by identifying the primary mechanism and modelling it.

References:

Conclusions

Bramfield tyre: aged ~80 years in woodland

Analysis Results

4000.0 3000 2000 1500 1000 680.0cm-1

A

Bulk

4mm depth

2mm depth

1mm depth

Surface

3309.0 1661.6831.01009.2

3363.61703.9

1444.21072.6

1030.3

834.0797.81628.4

1719.0 1447.2

Section showing the hard layer and cracks into the transition layer (~4mm deep)

Rubber (wt%)

Black (wt%)

Ash (wt%) Tmax

Surface 47.2 47.7 5.0 445

1-3mm 55.0 38.3 5.4 446

5-7mm 59.5 31.5 8.6 418

Bulk 59.2 31.9 9.0 413

Table: TGA weight loss and Tmax

FTIR spectra from different depths (labelled in mm) into

rubber

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30

Distance from surface (mm)

I(C=O

)/I(C

H3)

3360 cm-1

-OH

1708 cm-1

C=O ketone

1014 cm-1

C-O831 cm-1

C=CH

Surface 1.67 0.678.3 with

silica0.33

1mm 1.00 0.338.67 with

silica0.67

2mm 0.35 0.29 1.65 0.594mm 0.22 0.04 0.89 0.96Internal bulk

0.07 <0.01 <0.30 0.63

Table : IR Peak ratios /CH2 backbone (1460-1450cm-1)

Normalized C=O intensity, at different distances from the surface (left) to bulk (right)

0

20

40

60

80

100

120

140

160

180

3 6 9 11 14 17 20 23 26 29 32 34 37 40 43 46 49 52 55

Particle diameter, µm

No. o

f Par

ticles

0

1000

2000

3000

4000

5000

6000

Whit

e Ar

ea,µ

m2

Particle size distribution White area distribution

1

10

100

1000

10000

0 5 10 15 20 25 30 35 40

Distance from surface (mm)

EIT(

O&P)

(MPa

)

Distribution of particle diameters and total area contribution of each tranche of particles

Reduced modulus from micro-indentation according to the analysis of Oliver & Pharr

(1992)Discussion

ncxtmrx

cxtmD

xt

c)),(())),(((

t

ndtcxtmrxtm0

)),((),(

for mm(t,x)rr(m(t,x)) o

UV light catalyses oxidation, but doesn’t penetrate deeply:

where I is intensity, is volume fraction of black and L is effective length scale of black agglomerates

I falls to 1% after only ~12mm.

Ozone is too low in concentration and too reactive to penetrate more than ~0.5m.Only oxidation could penetrate as deep as ~1mm to form the crust; with ozone attack, photo-oxidation and loss of scission products by leaching and evaporation contributing to microcracks at the surface.General model for diffusion-limited oxidation:

Needs to be solved numerically, but analytical solutions exist if D and r are at least piecewise constant, that is :

(i) On moving front,

(ii) In steady state,

(iii) In steady state,

KIdx

dI where

mLK

5.0

2.0

0n 0rr

1n 0rr

and

and

0n and for mm(t,x) r(m(t,x)) 0

A crust ~1mm thick has formed on NR aged naturally over 80 years in conflict with the extrapolation of Lindley & Teo (1977). Ozone attack and photo-oxidation could only degrade a layer a few microns thick. The primary mechanism determining thickness is oxidation.A model based on diffusion limited oxidation is being developed.Lindley ,P.B and Teo,S.C., (1977), “High temperature ageing of rubber blocks “, Plastics & Rubber:Materials & Applications, 2, 82-88Li G.Y., Keong J.L., (2005), “A review of rubber oxidation“, Rubber Chemistry Technology, 78, 355-389

Acronym:TGA= Thermogravimetric Analysis, FTIR=Fourier Transform Infrared Spectroscopy (FTIR) , IR = Infrared