In order to entirely qualify the true shape of fiber particles, several measurement parameters are required.
In order to enable users to more accurately measure their particles, automated image analysis has been developed. For a number of years, results have been rendered by particle size analyzers operating under the assumption that all of the measured particles are spherical.
In several applications, however, both flowability and performance in manufacturing can be affected by particles’ circularity. For example, in certain instances, the performance of abrasives can be influenced by measuring surface smoothness.
Microscopy for shape analysis has become the default method for those in industry who have realized that their particles’ irregularity impacts both efficacy and manufacturability. A laborious and slow method by nature, manual microscopy is an impractical means by which to analyze particles on a large scale.
Consequently, the end-user may end up with a poor representation of the sample. Therefore, while microscopy may be able to provide a vague idea of particle shape, it is ineffective when using particle shape analysis in order to control a process.
Fibers constitute one type of raw material which lends itself to being measured perfectly by shape analysis. Being used to make effective filtration media as well as to strengthen building materials, fiber particles have a wide range of applications.
Whenever raw fibers are used, there is a need to know the width, length, curl, and aspect ratio of the fibers. Vital information relating to the fibers and how they may perform in their final state cannot be provided by particle analysis results expressed in equivalent spherical diameter. Manual microscopy is also an impractical means by which to measure such particles in a quality-controlled environment where both representative and quick analysis is necessary.
Displayed in Figure 1 is a typical fiber from a sample which was analyzed by Particulate Systems’ Particle Insight Dynamic Image Analyzer. All particles are assumed to be spheres when analyzed using a conventional particle size analyzer, and consequently minimal information is reported (a size of 112.1 μm in this case).
When the same particle was analyzed by the Particle Insight Image Analyzer (a proper-shape analyzer which has fiber-shape measures), more information was provided on a high population of particles in mere minutes. Together with the aspect ratio (the length over the width), the measurement of fiber width and length is calculated.
An extra measurement which is able to be calculated is fiber curl - a fractional measure which is equal to 1 when the fiber is completely straight. The lower the value of the fiber curl, the greater its degree of curvature. When determining how fibers will interact with one another during a production process, this value can be extremely useful. These measurements are as follows:
Fiber Length: 449.9 μm
Fiber Width: 22.7 μm
Fiber Aspect Ratio: 19.82
Fiber Curl: 0.984
Figure 1: Fiber sample used for analysis.
Figure 2: Indicates the width of these fibers were rather uniform in nature. A total of 10,000 particles was analyzed in 149 seconds.
Additional data statistics are provided in Figures 2, 3, 4, and 5, as indicated in the figure captions.
Figure 3: Shows the average length of the fibers to have a mean of 123 μm with a standard deviation of 74.8 μm.
Figure 4: Although the width of the fibers is well controlled, the length is not. As a result, the aspect ratio results are broad. Here the aspect ratio shows a mean of 4.450 with a stadard deviation of 2.262.
Figure 5: The mean fiber curl is 0.97 with a mode fiber curl of 0.99. This clearly indicates that the population of fibers is mostly non-curled.
In order to properly analyze the parameters which are important, it is vital that a particle analyzer which is able to do so is selected. As has been shown, operating under the assumption that all particles are spherical is not the most accurate method for quantifying a fiber. In this instance, size was not enough to provide the user with an accurate measure of the fibers.
For the fiber samples in this application, using the four fiber-specific measures was much more revealing. They provided a better understanding of the particles and potentially provided insight into their manufacturing processes. As the analysis is quick, accurate, and able to measure thousands of particles in just seconds, it is also extremely practical to use one or several of these fiber-specific measures as a quality control specification.
This information has been sourced, reviewed and adapted from materials provided by Particulate Systems.
For more information on this source, please visit Particulate Systems.