"Multi-Technique Problem Solving in an Industrial
Environment"
Shell, Thornton Laboratories, Chester-
Wednesday 6th of January 1999
"Coated Calcium Carbonated Revisited"
D Maton, I Sutherland & D Harrison (Loughborough
University).
Coated Precipitated Calcium Carbonate (PCC) has been used in industry
for over 50 years. As a filler, PCC improves the mechanical properties of a polymer
compared to conventional calcium carbonate. Using a range of bulk and surface specific
analytical techniques, it is possible to examine the mechanism of deposition on the CaCO3
particles and optimize the level of treatment.
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(b) C-H Region Only |
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Figure 14: DRIFT Spectra from the Surface of the Coated PCC
samples
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The standard IR method for the analysis of powders is
DRIFT (Diffuse Reflection Spectrocopy) which can be used to quantitatively assess the
level of coverage using changes in the band intensities. In particular, changes in the C-H
intensity can be used to estimate the coating coverage, to limits of 0.05 monolayers.
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Figure 15: Coating Thickness
as determined by XPS using the Flat (---) and Round (---) Models |
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These measurements were compared against the values
obtained using XPS, a more surface specific technique. In this instance a new model was
developed to determine the overlayer thickness, since the standard model assumes a flat
plate, whilst the particles are essentially round. Figure 15 above shows the effect the
different models have on the calculated coating thickness.
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Uncoated
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Figure 16: Film Coverage
Data using XPS and SEM images of "Optimised" Stearate Coatings on PCC |
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Coated
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Using the different models, attempts were made to both
optimize the amount of material used in the coating process and to understand the
mechanism stearate adsorption on the surface of the calcium carbonate particles. This was
achieved by dispersing the stearate in different solvent and by using different stearate
systems. Using a standard weight of stearate in a given solvent, the coating coverage's
given in Figure 16 were determined using both the "Flat" and the
"Round" models.
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