Sample preparation for XRF analysis – polymers, granulates, fluffs and related materials

A large variety of materials that are not already available in powder, liquid, or solid disc form, will need preparation for X-ray fluorescence (XRF) analysis. Examples are plastics, fibers, alternative fuels, and materials that are subject to RoHS/WEEE legislation. In most cases the fundamentals apply, namely; crushing, grinding and pressing or fusing, to produce a robust, homogeneous, and representative sample.

Crushing

Crushing of the material is required to reduce its size allowing further processing, such as representative sub-sampling, homogenization and grinding.

Grinding

Grinding of the material to a fine powder is required to minimize undesired particle size effects and to allow further processing like pressing or fusion. Soft and malleable materials, which cannot be ground, may require cutting to be brought to a homogeneous, fine-grained condition. You may need a special cutting- or knife mill to prepare such samples.

Loose powders and granulates in liquid cups

For screening or quick control of raw materials, you could analyze granulates and powders ‘as is’ in liquid cups. This practical and quick solution has its advantages when accuracy and reproducibility are not the driving factors. There will be a loss of intensity for light elements though.

Pressing

Pressed powders are often very successfully used in production control, especially if the calibration ranges are narrow.

Pellets can be pressed free, into Al cups or steel rings. The use of binders is usually required to achieve the necessary mechanical stability and robustness. Malvern Panalytical also offers the ultra-wax binder, for the preparation of high-quality pellets for the most demanding applications.

Hot-pressing

Granulates, fibers or powders from hot-moldable polymers, like PE or PP are ideally prepared by hot-pressing into solid homogeneous disks. The choice of the correct temperature and pressure is fundamental for the reproducibility of the analytical method.

Previously in the seven-part series on ‘Sample preparation for XRF analysis’:

• Cement and building materials
• Metallic materials
• Liquids
• Food products, animal feed, premixes and related materials

Watch out for more blogs in the series on “Sample preparation for XRF analysis” in the course of this year