High-quality, reproducible and reliable XRF analysis of polymer samples can be achieved using a benchtop pressing system for the sample preparation. This brings the full power of ED- or WDXRF analysis of polymer samples to every lab, assuring constant product consistency from the raw material analysis to the quality control of the final goods.
The most common presentation form for raw polymer materials (virgin or recycled) is as granulates with chips and powders also being of widespread use. The accurate and reliable analysis of such materials by X-ray fluorescence spectrometry requires them to be compression-molded (hot-pressed) into flat, homogeneous disks. Only in that form can XRF spectrometers deliver their full capabilities with maximum reproducibility and accuracy.
The most common presentation form for raw polymer materials (virgin or recycled) is as granulates with chips and powders also being of widespread use. The accurate and reliable analysis of such materials by X-ray fluorescence spectrometry requires them to be compression-molded (hot-pressed) into flat, homogeneous disks. Only in that form can XRF spectrometers deliver their full capabilities with maximum reproducibility and accuracy. High-quality, reproducible and reliable XRF analysis of polymer samples can be achieved using a benchtop pressing system for the sample preparation. This brings the full power of ED- or WDXRF analysis of polymer samples to every lab, assuring constant product consistency from the raw material analysis to the quality control of the final goods.
The Buehler SimpliMet 4000 (Figure 1) is an electrohydraulic automatic compression mounting system for the preparation of solid polymer disks from granulates, chips or powders. The powerful 1900 W heating system provides quick and homogeneous softening of the polymer material, while the accurate pressing unit molds the sample into its final shape. Controlled water cooling contributes to a short total process time, while assuring that a high-quality, un-stressed disk is achieved. A very narrow footprint (31 cm width) minimizes the bench space requirement. The need for a single-phase electrical connection in addition to cooling (tap)water and a drain, make the installation of the system extremely simple and feasible for any lab.
All relevant parameters for the optimization of the sample preparation process can be programmed by the push of a button, and are presented in Table 1.
| Parameter | Operation range | Increment |
|---|---|---|
| Molding pressure | 70 - 300 bar | 5 bar |
| Heating temperature | 50 - 220 °C | 5 °C |
| Heating time | 1 - 20 minutes | 10 seconds |
| Cooling time* | 1 - 30 minutes | 10 seconds |
*If activated, the SmartCool function overrides the cooling time programming, finalizing the cycle once the sample temperature drops below 40 °C, saving processing time.
The heating range up to 220 °C makes possible the preparation of specimens from a wide variety of thermoplastic polymers, such as polyolefins (LDPE, HDPE, UHMWPE, PP), ABS, PBS, PC, PCL, PEO, PHB, PLA, PMMA, POM, PS, PVA, PVC, PVDF, PVF and others, including compounded mixtures.
Specific total process time (heating-up, pressing, cooling down) varies according to the polymer properties, but is usually between 10 and 30 minutes per specimen.
A safe-to-operate, robust and very low-maintenance system, the Simplimet 4000 is CE, PSE, RoHS and WEEE compliant.
High-quality polymer disks (40 mm diameter) were prepared using the Buehler SimpliMet 4000 mounting press. Typically, 7.0 g of polymer granulates were loaded into the pressing chamber. The disks obtained were of around 5 - 7 mm thickness (dependent on the polymer’s density).
In one experiment, fifteen specimens of a homogeneous, virgin LDPE sample were prepared. The total process time was 11 min/disk, with a heating temperature of 180 °C and 80 bar molding pressure. Analysis of the disks was performed with an Epsilon 3XLE ED-XRF spectrometer and provided the following sample preparation repeatability results, depicted for phosphorus and calcium in Figure 2.
Figure 1. Sample preparation repeatability XRF data for 15 specimens of a virgin LDPE sample
From Figure 1, it can be seen that the sample preparation repeatability is very high. The relative standard deviation (RSD) obtained for phosphorus measurements was 4.3 % and for calcium 3.4 %. These values are in the same range as what is normally achieved by using of industrial planar polymer hot-presses.
In a second experiment, ten disks of an additive functionalized PP sample were prepared. The total process time was 24 min/disk, with a heating temperature of 200 °C and 80 bar molding pressure. Analysis of the disks was performed with an Epsilon 3XLE EDXRF spectrometer.
Table 2 presents the relative standard deviations for the XRF measurement repeatability (same specimen measured 10 times) and for the sample preparation repeatability (10 different specimens measured once) of those samples.
| Element | Concentration
(mg/kg) | Repeatability - relative standard deviation (%) | |
|---|---|---|---|
| XRF measurement | Sample preparation | ||
| Mg | 299.7 | 2.4 | 3.7 |
| Al | 245.2 | 1.1 | 2.2 |
| Si | 572.9 | 1.7 | 3.5 |
| P | 32.5 | 3.7 | 4.2 |
| S | 92.3 | 1.0 | 3.2 |
| Ca | 1364.9 | 0.9 | 1.8 |
| Ti | 4218.9 | 0.4 | 0.7 |
| Cr | 5.6 | 3.8 | 4.5 |
| Cu | 14.1 | 2.0 | 4.2 |
| Zn | 92.9 | 1.0 | 1.8 |
| Br | 32.4 | 1.0 | 2.5 |
| Ba | 5111.5 | 0.4 | 0.7 |
The data above shows the high degree of repeatability achieved for the sample preparation, with RSD values always below 5% even at concentrations around 10 mg/kg. This is clearly well within the expected levels for this industry segment, but usually only achieved with bigger industrial pressing systems.
Conclusions
The SimpliMet 4000 Compression Mounting System offers XRF users a cost-effective solution for preparation of highquality polymer disks. It is a simple-to-operate, low-maintenance and small-footprint system which may be welcomed by entry-level or expert users alike. When in combination with Malvern Panalytical XRF spectrometers, highly reproducible results can be achieved, with the same quality level expected from industrial, floor standing planar hot presses. Typical preparation times for disks from polymer granulates are around 10-30 min. In principle, any polymer with softening temperature lower than 220 °C is suitable to be used with this system.
