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Mean elementary particle diameter and specific surface
According to the LEA & NURSE method, air permeability of a pressed tablet is the method used to measure elementary particle size (dp); the results obtained closely correlate with electronic microscopy results.
For non-isometric particles the dp is equal to the smallest dimension; for scalenohedral- calcitic SOCAL®, the ratio between the biggest and smallest dimensions is typically from 5 to 10.
The unit for the elementary size (Dp) is nm.
Nitrogen gas adsorption is used to calculate the multi-point BET surface area. The unit for the specifc surface (SBET) is m²/g.
Both measurements Dp and BET surface reflect the size of the elementary particle.
Size of agglomerates
Elementary particles are usually associated with agglomerates whose size is measured by sedimentation (Sedigraph).
The result of the measurement depends on the operating conditions and in particular on the dispersion environment.
Laser measurement is also possible but more precautions are necessary: the quantity of PCC used is comparable to that of solubility in water. In practice the dispersion environment used is alcohol.
The size of the agglomerate is around dp X 10. Grinding in the final stage of production has a significant influence on the size of the agglomerates.
The unit for the size of agglomerates is µm.
Residue on sieve 45 µm
The residue on sieve measures the residues found on a sieve of 45 µm after mechanical flushing.
A certain amount of SOCAL® is flushed through a sieve with filtered tap water. The residue blocked on the sieve is then dried and weighted. The unit for the residue on sieve is ppm.
Brightness and lightness
These properties are extremely important for application fields such as paper or paint, but also for all applications where the stability of colour properties is expected.
ü lightness is measured at 520 nm; it is Y of the chromacity in the space Yxy.
ü brightness is measured at 457 nm; in the same space Yxy, it is the result of :
(or a similar relation in the space Lab)
Volatile components (at 105° C)
The loss on drying reflects the moisture content of SOCAL® and WINNOFIL® lost at the temperature of 105°C. Loss on drying value is valid at the time of manufacturing.
Respecting the temperature is very important for SOCAL® and WINNOFIL®, because the quantities of volatile water at 105, 120 or 150 °C are completely different. SOCAL® and WINNOFIL® lose water up to 500 °C (after this, measurement is not possible due to decomposition).
Water absorption and desorption by equilibration with relative humidity is very easy. Coating limits these fluctuations.
The unit for loss on drying is g/kg.
Organic coating content
The reference method for organic coating content is based on dissolving a sample in hydrochloric acid and subsequently extracting the organic substances in organic solvent, which is evaporated.
For quality control, measurements are based on IR method or the thermo-gravimetric method. Both methods have been validated as equivalent to our reference.
The unit for coating content is g/kg.
Yield stress and viscosity
Rheological properties are important for many applications such as plastisols, sealants. Yield Value (YV) is a good picture of the achieved rheological properties thanks to SOCAL® and WINNOFIL®, in the defined suspension.
The flow curve (shear stress as a function of shear strain) of a suspension is measured at fixed conditions and YV is calculated based on the Bingham model.
2 methods are carried out to characterize the Yield Value:
ü suspension of a plasticizer, a drying agent and PCC analyzed on controlled shear rate rheometer using coaxial cylinders,
ü suspension of a plasticizer and pre-conditionned PCC analyzed on controlled shear stress rheometer using parallel plate.
The unit for Yield Value is Pa.
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