Carbon Black Dispersion
Measurement via Interferometric Microscopy
Old
reliable technology – New exciting application
History
of Dispersion Measurement [1]
Characterization
of the filler dispersion within a rubber compound has been of documented
interest for nearly a century due to the need for compound mixing optimization.
Over-mixing increases the compound cost while poor filler dispersion decreases
product lifetimes and can cause catastrophic failure in extreme cases. One of
the oldest and most fundamental techniques for characterizing filler dispersion
is analysis of microtomed thin sections with light microscopy. The use of this
technique is limited, however, by the required microtoming, which is labor and
time intensive and is not suitable for routine, quick analyses. Faster and
relatively inexpensive methods for characterizing filler dispersion rely on
surface roughness created when samples are razor cut. The main advantage of
these techniques is the ease of sample preparation,
however, it is often difficult to quantify the resulting surface roughness of
the sample.
New
Innovations
To combine the
quantitative results from light microscopy with the speed of the surface
roughness techniques, the method of interferometric microscopy (IFM) has been
applied to carbon black dispersion characterization in vulcanized elastomeric
systems by Columbian Chemicals Company [1] and the resulting technique has been
licensed to Ambios Technology.
The Ambios
Xi-100 IFM uses white light interference to generate a three-dimensional topographic
map of the razor cut rubber surface (See Figure 1). The peaks and valleys
observed in this figure correspond to the undispersed carbon black agglomerates
within the sample. Based on this surface topography, data analysis techniques are
utilized to characterize the surface roughness, and carbon black dispersion. IFM
results from carbon black compounds correlate extremely well (R2=0.954)
with those obtained via light microscopy according to the study by Columbian[1]. Although the initial correlation was performed
for carbon black only samples, this
technique can be applied to other fillers besides carbon black.
Interferometric Microscope Characterization
Once the Xi-100 topographic map of the
sample is obtained, the analysis software is used to isolate, define and
characterize the peaks and valleys found on the sample surface. The acquired
topographic maps often have long-range variation of the sample surface, which interferes
with identification of the peaks associated with the carbon black agglomerates.
To remove this long-range variation, the as-acquired data is processed using a
band-pass Fast Fourier Transform filter and the height scale origin is set to
the mean height of the image.
The next step is to isolate the surface features and quantify them.
Since the base surface of the data has been flattened and set to zero, setting
a minimum height displacement from the image mean plane can identify the peaks
(positive height) and valleys (negative height) present in the data (See Figure
2). Parameters to describe the carbon black agglomeration such as the number of
peaks, the peak area, the aspect ratio of each peak, and the height of each
peak, as well as others are obtained and cataloged by our program. The ability
of the Xi-100 to provide true three-dimensional topographic information is
invaluable for carbon black dispersion characterization.
Sample Preparation and Processing
A key factor to
this technique is a measurement time of only minutes. A rubber sample is placed
in a guillotine sample cutter and cut with a razor blade, exposing the peaks
and valleys due to the undispersed carbon black agglomerates. The fresh-cut
surface is then placed under the Xi-100 objective and quickly scanned. The customizable
software enables the user to automate the acquisition of several measurements
using a motorized stage. The topographic data from each measurement location is
then automatically processed and the surface roughness characterized. Finally,
a printable report is generated displaying 3D images of the sample, the
dispersion index, roughness, and many other key statistics.
Primary Reference:
[1] Carbon Black Dispersion Measurement in Rubber
Vulcanizates Via Interferometric Microscopy
Rubber Chemistry and
Technology Vol. 77 Num. 4 pg. 691-710 Sept – Oct 2004.
Ambios
Technology
Ph: 831-429-4200
Fax: 831-427-1160
info@ambiostech.com
The Columbian logo is a
registered trademark of Columbian Chemicals Company.