Quantitative method for samples containing polypropylene and polyethylene

Abstract

To provide a rapid and simple method for quantifying polypropylene and polyethylene.SOLUTION: This quantitative method is a method for quantifying a sample containing polypropylene and polyethylene using a pyrolysis gas chromatograph mass spectrometer, and quantifies the polypropylene and polyethylene based on the area ratio of the peak attributable to polypropylene and the peak attributable to polyethylene in a mass chromatogram at the mass-to-charge ratio of 252 obtained by ionizing the sample using field ionization.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for quantifying samples containing polypropylene and polyethylene. [Background technology]

[0002] In recent years, interest in environmental issues has been growing worldwide, and various proposals have been made regarding material recycling, which reuses waste plastics as raw materials for new products, as one way to reduce environmental impact.

[0003] Polypropylene processed through material recycling often contains polyethylene because their physical properties are similar and cannot be separated during the recycling process. Although polypropylene and polyethylene are generally incompatible, depending on the type and amount of polyethylene contained in such recycled materials, the mechanical properties and heat resistance life of the polypropylene may be impaired, making it impossible to reuse as a raw material for products. Therefore, when using recycled polypropylene, it is essential to quantify the polyethylene content in the polypropylene and confirm the composition of the recycled material.

[0004] Patent Document 1 discloses an apparatus for analyzing the composition of waste plastics containing multiple types of plastic materials such as polypropylene and polyethylene. Here, the components contained in the waste plastics are assumed in advance, and the retention times and signal intensity vectors of the components are measured by pyrolysis gas chromatography. Matrix calculations are then performed from the measurement results of the waste plastics to determine the content of each component. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-270233 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when quantifying components in waste plastics using a method such as that in Patent Document 1, the measurement accuracy becomes insufficient when the number and amount of pyrolysis components increases, making it impossible to quantify them quickly and easily.

[0007] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide a rapid and simple method for quantifying polypropylene and polyethylene. [Means for solving the problem]

[0008] A quantitative method according to an embodiment of the present invention is a method for quantifying a sample containing polypropylene and polyethylene using a pyrolysis gas chromatograph mass spectrometer, in which the polypropylene and polyethylene are quantified based on the area ratio of the peak derived from polypropylene to the peak derived from polyethylene in a mass chromatogram at a mass-to-charge ratio of 252 obtained by ionizing the sample using field ionization. [Effects of the Invention]

[0009] According to the present invention, a rapid and simple method for quantifying polypropylene and polyethylene can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an example of a total ion chromatogram (TIC) obtained by the quantitative method according to the present embodiment. [Figure 2] 2 is an example of a mass chromatogram at a mass-to-charge ratio (m / z) of 252 extracted from FIG. 1. [Figure 3] 1 shows a total ion chromatogram (TIC) and a mass chromatogram at a mass-to-charge ratio of 252 obtained by measuring homopolypropylene (homoPP) using the quantitative method according to the present embodiment. [Figure 4]1 shows a total ion chromatogram (TIC) and a mass chromatogram at a mass-to-charge ratio of 252 obtained by measuring high-density polyethylene (HDPE) using the quantitative method according to the present embodiment. [Figure 5] 1 shows an example of a total ion chromatogram (TIC) and a mass chromatogram at a mass-to-charge ratio of 252 obtained by measuring a recycled material using the quantification method according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The quantitative method according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for the sake of explanation and may differ from the actual ratios.

[0012] A quantitative determination method according to this embodiment will be described. The quantitative determination method according to this embodiment is a method for quantifying a sample containing polypropylene (PP) and polyethylene (PE) using a pyrolysis gas chromatograph mass spectrometer (Py-GC / MS). That is, the sample to be measured by the quantitative determination method according to this embodiment contains polypropylene and polyethylene.

[0013] The polypropylene is not particularly limited, and examples thereof include homopolypropylene (homoPP), random polypropylene (random PP), block polypropylene (block PP), and copolymers of propylene with other olefins copolymerizable with propylene. Examples of other olefins copolymerizable with propylene include α-olefins such as ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, and 3-methyl-1-hexene.

[0014] The polyethylene is not particularly limited, but examples thereof include high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and the like.

[0015] A pyrolysis gas chromatograph mass spectrometer is an analytical instrument that combines a pyrolysis apparatus, a gas chromatograph, and a mass analyzer, and is used for the compositional analysis of polymeric materials, etc. First, the sample to be measured in the quantification method according to this embodiment is introduced into the heating furnace of the pyrolysis apparatus, where it is thermally decomposed to obtain pyrolysis products. Next, the obtained pyrolysis products are sent to a gas chromatograph and separated into individual components. Each component separated by the gas chromatograph is ionized by field ionization (FI) in a mass analyzer, which determines the mass of each component and outputs information on the molecular weight of each component as a mass spectrum. Compounds can be identified quickly and easily by searching a library of the obtained mass spectra.

[0016] While electron ionization (EI) is commonly used as the ionization method for mass spectrometry, the quantitative method according to this embodiment uses field ionization. In the case of electron ionization, components generated by thermal decomposition undergo fragmentation. In this case, common fragment ions with mass-to-charge ratios of 43 and 57 are generated from both polypropylene and polyethylene. Furthermore, these fragment ions are generated regardless of molecular weight. As a result, it is not possible to extract and depict specific components using a mass chromatogram.

[0017] On the other hand, in field ionization, ionization is performed under milder conditions than in electron ionization, so the components produced by thermal decomposition are less likely to cleave. As a result, molecular ions are generated from polypropylene and polyethylene, and peaks derived from polypropylene and polyethylene are detected in the mass chromatogram at a mass-to-charge ratio of 252.

[0018] Although polypropylene and polyethylene have the same mass of pyrolysis products, their molecular structures are different, and therefore they are detected at different times by gas chromatography. Due to this difference, the peaks attributable to polypropylene and polyethylene are detected separately in a mass chromatogram at a mass-to-charge ratio of 252. Therefore, the quantification method according to this embodiment can quantify polypropylene and polyethylene based on the area ratio of the peak attributable to polypropylene and the peak attributable to polyethylene in a mass chromatogram at a mass-to-charge ratio of 252 obtained by ionizing a sample using field ionization.

[0019] Figures 1 and 2 show an example of measuring a sample containing a mixture of polypropylene and polyethylene. The sample containing polypropylene and polyethylene was pyrolyzed at 600°C to obtain pyrolysis products. The pyrolysis products were separated into individual components by gas chromatography using a glass capillary. The total ion chromatogram (TIC) in Figure 1 shows the elapsed time (retention time) and peak area of ​​each component separated by gas chromatography. Figure 2 shows a mass chromatogram at a mass-to-charge ratio of 252 extracted from Figure 1. The peaks in Figure 2, i.e., the peaks at elapsed times of 9.308 min and 10.703 min, are those of polypropylene (PP) and polyethylene (PE), respectively.

[0020] Meanwhile, Figures 3 and 4 show the total ion chromatogram (TIC) obtained by separately measuring homopolypropylene (homoPP) and high-density polyethylene (HDPE), and the mass chromatogram extracted at a mass-to-charge ratio of 252, respectively. In Figure 3, the peak at an elapsed time of 9.332 min was identified as coming from polypropylene, and in Figure 4, the peak at an elapsed time of 10.721 min was identified as coming from polyethylene.

[0021] The pyrolysis gas chromatograph mass spectrometer (Py-GC / MS) used was a JMS-T100GCv (manufactured by JEOL Ltd.) The measurement conditions were as follows:

[0022] [Py-GC measurement conditions] Pyrolysis temperature: 600℃ Sample amount: 0.2 mg Split ratio: 50:1 Inlet temperature: 320℃ Oven temperature: Initial temperature 40°C (hold for 2 minutes), heating rate 20°C / min, final temperature 320°C (hold for 14 minutes) Carrier gas: Helium Flow rate: 1mL / min Column: Agilent DB-5MS (inner diameter 0.25 mm, length 30 m, film thickness 0.25 μm)

[0023] [MS measurement conditions] Interface temperature: 280℃ Measurement mass range: m / z 29-800 Counter electrode voltage: -10000V Detector voltage: 2700V Probe current: bake-out time 30 msec, emitter current 40 mA

[0024] In this way, by using the quantification method according to this embodiment, the peak derived from polypropylene and the peak derived from polyethylene are detected separately in the mass chromatogram at a mass-to-charge ratio of 252, as shown in Figure 2. Therefore, the amounts of polypropylene and polyethylene can be quantified based on the area ratio of the peak derived from polypropylene and the peak derived from polyethylene.

[0025] The quantification method according to this embodiment may be used to measure the polyethylene content in polypropylene. That is, the polyethylene content in polypropylene processed by material recycling may be measured. Polypropylene processed by material recycling varies greatly in the type and content of polyethylene contained therein. Therefore, by using the quantification method according to this embodiment to confirm the composition of such recycled material and perform quality checks and sorting, it becomes easier to reuse it as a raw material for products. Furthermore, the quantification method according to this embodiment also makes it possible to add polyethylene to the recycled material to adjust the polyethylene content in the polypropylene.

[0026] An example of quantifying polyethylene contained in commercially available recycled polypropylene using the quantification method according to this embodiment is shown. Figure 5 shows a total ion chromatogram (TIC) and a mass chromatogram at a mass-to-charge ratio of 252 obtained by measuring a recycled material containing polyethylene in block polypropylene (block PP) using the quantification method according to this embodiment. Based on the information in Figures 3 and 4, it was confirmed that the peaks derived from polypropylene and the peaks derived from polyethylene were detected separately in Figure 5. Therefore, the amount of polyethylene contained in the polypropylene could be quantified based on the area ratio of the peaks derived from polypropylene and polyethylene. As a result, it was found that the polyethylene content of this recycled material was approximately 9%. Thus, the quantification method according to this embodiment can measure the polyethylene content of polypropylene.

[0027] As described above, the quantification method of this embodiment is a method for quantifying a sample containing polypropylene and polyethylene using a pyrolysis gas chromatograph mass spectrometer, and quantifies the amounts of polypropylene and polyethylene based on the area ratio of the peak attributable to polypropylene and the peak attributable to polyethylene in a mass chromatogram at a mass-to-charge ratio of 252 obtained by ionizing the sample by field ionization. Therefore, a rapid and simple method for quantifying polypropylene and polyethylene can be provided.

[0028] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

Claims

1. A method for quantifying a sample containing polypropylene and polyethylene using a pyrolysis gas chromatograph mass spectrometer, the method comprising: ionizing the sample by field ionization; quantifying the amounts of polypropylene and polyethylene based on the area ratio of a peak derived from polypropylene to a peak derived from polyethylene in a mass chromatogram at a mass-to-charge ratio of 252.

2. 2. The method for quantifying a sample containing polypropylene and polyethylene according to claim 1, wherein the content of polyethylene contained in polypropylene is measured.

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