Using FTIR and EDX to Analyze Plastic Pellets

Every day large quantities of water are used for both domestic and industrial purposes. The Earth has abundant water resources but there is only an extremely limited amount of safe, drinkable water. As such, securing drinking water by recycling wastewater is an important issue.

Water treatment processes used at wastewater treatment plants are two-fold. The first treatment, known as physical treatment, is to physically separate and remove solid material. The second, known as biological treatment, is to remove organic matter using microorganisms. With biological treatment, cultivated microorganisms feed on the organic matter in the water, which causes oxidative decomposition. The microorganisms are supported on the surface of the water using plastic pellets. As shown to the left in Figure 1, these pellets are approximately 5 mm in diameter. To the right in Figure 1, a large number of pores are visible upon inspection of the cross section.

(Left) Approx. 5-mm Diameter Plastic Pellet (Right) Cross Section

Figure 1. (Left) Approx. 5-mm Diameter Plastic Pellet (Right) Cross Section

A large number of applications rely on plastic pellets to purify water but there is growing concern that these pellets may flow into the sea and river systems when wastewater overflows and become marine pollution (microplastics etc.).

This article examines the use of FTIR and EDX to analyze plastic pellets prior and post water treatment.

Measurement Samples

The measurement samples of new and used plastic pellets are shown in Figure 2. The shape is distorted on the used pellets and they show significant unevenness on their surface.

(Left) Unused (Right) Used

Figure 2. (Left) Unused (Right) Used

Instruments Used and Measurement Conditions

A system comprised of an IRTracerTM-100 Fourier transform infrared spectrophotometer connected to a Quest single-reflection ATR accessory, and an EDX-8000 energy dispersive X-ray fluorescence spectrometer was used to perform the analysis.

IRTracerTM-100 (Left), Quest (Right)

Figure 3. IRTracerTM-100 (Left), Quest (Right)

EDX-8000

Figure 4. EDX-8000

The appearance of each instrument is shown in Figure 3 and Figure 4 and the conditions under which measurements were carried out are listed in Table 1 and Table 2. No processing or special pre-treatment was carried out prior to analysis on the measurement samples shown in Figure 2.

Table 1. FTIR Measurement Conditions

. .
Instrument : IRTracer-100
  Quest (Diamond prism)
Resolution : 4 cm-1
Accumulation : 100
Apodization function : Happ-Genzel
Detector : DLATGS

Table 2. EDX Measurement Conditions

. .
Instrument : EDX-8000
X-Ray tube target : Rh
Voltage/current : 50 kV (Al-U) / Auto
  15 kV (C-Sc) / Auto
Atmosphere : Vacuum
Analysis diameter : 10 mmφ
Filter : None
Integration time : 100 s

Results of Measurement Using FTIR and EDX

The measurement results using FTIR and EDX are shown in Figure 5. Measurements were taken on both the sample surface and a cross section using FTIR.

The results of FTIR measurement showed that, for both the new and used plastic pellets, the surface is a mixture of polyethylene and cellulose and the cross section is polyethylene.

There was no 15P detected in the used pellets with a qualitative and quantitative analysis using EDX (red frame Figure 5). However, 15P was detected in the new plastic pellets. In terms of composition, there were no significant differences between the two samples. As such, it is believed that trace amounts of contaminants that adhered to the surface or rubbed against the samples may be present.

Measurement Results

Figure 5. Measurement Results

Conclusion

In this article, we examined plastic pellets used as carriers for water treatment. No significant differences were found in composition between new and used pellets.

FTIR is a quick method to identify the main components of plastic pellets, as it is capable of performing qualitative analysis of organic matter and some inorganic matter. Moreover, it was possible to reveal the existence of contaminants and wear due to additives as well as minute material differences through the element information obtained using EDX.

Rapid performing FTIR and EDX are effective for analysis of plastic pellets as carriers for water treatment.

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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