Few months ago, our customer received, as usually, 1 ton of Melamine resin, a thermosetting plastic material used as the main constituent of high-pressure laminates, such as Formica and Arborite, and of laminate flooring, but also as a component in construction materials or in brakes for automotive industry.
And this was a ‘big’ surprise… (figure 1). The bag was much bigger than the usual one ton bag, they checked the weight… 1 ton confirmed! What could cause this difference?
Fig. 1. Usual (named TWF – left) and new (named TWE – right) one ton bags of melamine resin.
A visual observation of the powder did not show any difference (fig.2). The new (TWE) and the usual (TWF) powders look the same, and the chemical analysis confirmed the same chemical formula… but a different bulk density.
The batch of TWE new melamine resin was used to produce the final product based on was released on the market, but then our customer received several claims and decided to investigate the product in Alfatestlab.
Fig. 2. Usual (named TWF – left) and new (named TWE – right) powders of melamine resin.
Our physical characterization of both usual TWF and new powder TWE started with a particle size analysis by laser diffraction that confirmed a very similar granulometric profile (fig.3). Laser diffraction is the most widely used technique worldwide to characterize particle size distribution of powders and liquid dispersions.
Laser diffraction measures particle size distribution by measuring the angular variation in intensity of light scattered as a laser beam passes through the dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter.
Fig. 3. Particle size distribution by laser diffraction of usual TWF powder (red) and new TWE powder (green).
We thus decided to use Automated Static image analysis to get number-based particle size distribution and shape parameters of the particles. Alfatestlab is equipped with the Morphologi 4-ID from Malvern Panalytical, a powerful instrument that allows to determine size, shape and chemical identification of particles in powders or liquid dispersions. The fully automated Static measurement system vs other Dynamic systems on the market is based on optical microscopy (Nikon, 5 optics from 2.5x to 50x) that guarantees in addition to high quality images, also the orientation of the particles. By analyzing hundreds of thousands of particles with a powerful software, the technique allows in live or post processing to filter and classify any desired shape parameter, generating highly accurate and absolute measurements.
Fig. 4. Particle size distribution in number of usual TWF powder (red) and new TWE powder (green) measured by Automated Static Image Analysis.
The particle size distribution in number of the new sample TWE (fig. 4) showed a slightly highest number of small particles compared to the usual product TWF, but no huge difference in mean particle size. The morphological parameters of the particles are shown in figure 5. The chart details the percentage of spherical, almost spherical (spheroidal) and non-spherical particles in both samples. It clearly appears that sample TWE (new) has less spherical particles than sample TWF, thus more non-spherical particles. This can explain the difference in big bag density, where non spherical particles do not pack as tight as spherical ones.
Fig. 5. Particle shape classification of usual TWF powder (red) and new TWE powder (green) measured by Automated Static Image Analysis.
In fig. 6A and 6B are shown images of particles from sample TWE, first spherical class (6A) and then non-spherical class particles (6B), as they were identified during the morphological analysis. The instrument takes high quality images on statistically representative numbers of particles (in this case more than 179.000 particles) and retrieves accurate shape parameters such as circularity, elongation, convexity, etc., and particle transparency.
Fig. 6A. Spherical class of particles from TWE powder measured by Automated Static Image Analysis.
Fig. 6B. Non-spherical class of particles from TWE powder measured by Static Automated Static Image Analysis.
When looking at Circularity parameter on its own, the difference between both products is even clearer (fig. 7), TWF shows a higher circularity of particles as demonstrated by the classification data in fig. 5.
Fig. 7. HS Circularity shape parameter of usual TWF powder (red) and new TWE powder (green) measured by Static Automated Static Image Analysis.
We ended our characterization process with scanning electron microscopy analysis of both powders, images are reported in fig. 8A and 8B. TWE powder (new) shows more fragments of particles, in agreement with non-spherical particles while fragments are not present in TWF sample, although some non-spherical particles can still be observed.
Fig. 8A. Scanning electron microscopy image of TWE powder (mag x 1350).
Fig. 8B. Scanning electron microscopy image of TWF powder (mag x 2000).
Conclusion
Our customer came with a very interesting issue, two Melamine resins with the same chemical formula showed different powder density, one ton of TWE occupied a much higher volume than one ton of TWF. A complete powder characterization including not only particle size by laser diffraction method, but also particle shape, by optical imaging and SEM analysis, helped understand the origin of such a difference been 2 products expected to be the same.
Alfatestlab is specialized in powder and solid-state characterization, as well as liquid dispersions and materials characterization in general. Alfatestlab has also a bioscience division, to know more about our services visit our website Analytical services – AlfatestLab or contact us directly info@alfatestlab.com
