Characterizing the Thermomechanical Degradation of a Filled Elastomer by Morphology and X Ray Photoelectron Spectroscopy
- PDF / 65,605 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 56 Downloads / 300 Views
Characterizing the Thermomechanical Degradation of a Filled Elastomer by Morphology and X Ray Photoelectron Spectroscopy GIOVANNI F CROSTA1, ART J NELSON2, MARINA C CAMATINI1 1
2
Dept. of Environmental Sciences, Università degli Studi Milano - Bicocca, 1, Piazza della Scienza, I 20126 MILAN, Italy; contact: [email protected] Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, LIVERMORE, CA.
ABSTRACT Three types of debris particles, denoted by L2, H2 and K3 respectively, originated from the abrasion of silica-filled, vulcanized rubber under different test conditions (severity) were analyzed and compared. The structural fractal dimension, DFS , of the particle perimeter was chosen as a morphological descriptor (but not necessarily as an intrinsic property of the fractured material !). Said dimension was estimated by processing light microscopy images. A value of the morphological threshold, TST , which separates the textural from the structural domain in the RICHARDSON plot was determined in order to maximize discrimination between the three particle types and rank them by increasing values of DFS . Particles from the highest severity test (K3) exhibited the highest value of DFS . X ray photoelectron spectroscopy (XPS) provided elemental composition, core level binding energies and the speciation of C, N, O, Si and S. As a result, L2 debris was found to originate from two processes: fracture of rubber and segregation of extender oil. Evidence has come both from morphology and XPS. Particles of H2 and K3 were ascribed to fracture alone. Comparison between K3 and the reference material, rasped rubber (RAS), shows the following: a) increase of the [S]/[C] surface atomic concentration ratio from RAS to K3; b) existence of multiple bonding states of S in K3 with energy peaking at 162.9 ± 0.3 eV ([-S-S-]n) ; c) weak contribution of R-S-O-R oxidized S species in K3 at 165 eV, not seen in RAS; d) no evidence of either SO3 or SO4 groups in any material. Although preliminary, these results prove the ability of morphological analysis and XPS to characterize the surface properties of debris particles non destructively. INTRODUCTION For a long time mineral fillers have been added to elastomers with the aim of improving the mechanical properties of the composite. One example is rubber in the tread of a passenger car tire, where the main elastomer is the styrene - butadiene - rubber (SBR) filled with amorphous silica and subject to sulfur vulcanization. Abrasion and wear of said material give rise to debris, which consists of particles. The latter bear information about the mechanical degradation process: for this reason the morphology of tire debris particles was investigated by [1] ,[2], [3] and [4], just to mention a few, and by some of the co-authors [5]. Herewith the morphological characterization and classification of said material particles are achieved by fractal analysis. Non destructive chemical characterization is attained by X ray photoelectron spectroscopy (XPS): some prelimi
Data Loading...
