A method for determining impurity content of recycled plastics and its application

Abstract

The present invention discloses a method for determining the impurity content of recycled plastics, including sample pretreatment, sample detection, impurity analysis, and generating a quantitative estimation model. The method for determining the impurity content of recycled plastics of the present invention combines physical detection with chemical instrument detection, and can not only analyze and detect the apparent visible impurity content in the recycled plastics, but also analyze and detect the invisible impurity content. The present invention not only conducts a qualitative analysis of the impurity content in the recycled plastics, but also conducts a quantitative analysis, and can generally understand the impurity composition and content in the same recycled plastics. According to the impurity analysis results of the recycled plastics, an impurity quantitative estimation model can be generated to estimate the impurity content of the same recycled plastic samples.

Description

Technical Field

[0001] The invention relates to a method for determining the impurity content of recycled plastics and application thereof, and is mainly applied to the field of impurity components and quantitative analysis of recycled plastics. Background Art

[0002] Plastic is an important organic synthetic polymer material. Since its advent in the 20th century, it has been widely welcomed by people for its advantages of light weight, easy processing, beautiful appearance, and economical and practical use. It is widely used in agricultural production, industrial processing and all aspects of people's lives. However, with the widespread application of plastics, the defect of plastics being difficult to degrade has gradually been paid attention to by humans. White pollution is increasingly affecting people's lives. In order to reduce white pollution and protect the environment, recycling and reproducing plastic products is a good way to reduce plastic pollution.

[0003] Plastic products are recycled and reproduced. Due to the impurity of the recycled raw materials, the additives and plasticizers in the recycled plastics are oxidized by external factors such as light, oxygen, heat, and mechanical force during the recycling process, and irreversible chemical changes occur. They need to be removed during the reproduction process, but there are still a small number of impurities remaining in the recycled plastics. Before the recycled plastics are re-used in production and life, they need to be tested for impurities. The existing detection technology only analyzes and detects the apparent visible impurities of the recycled plastics, and it is difficult to distinguish and detect some impurities without color. Therefore, the present application invents a method for detecting impurities in recycled plastics, which can not only analyze the apparent visible impurities, but also analyze and detect colorless impurities. Summary of the invention

[0004] In order to achieve the joint analysis of colored impurities and colorless impurities in recycled plastics, the first aspect of the present invention provides a method for determining the impurity content of recycled plastics, including sample pretreatment, sample testing, impurity analysis, and generating a quantitative estimation model.

[0005] As a preferred embodiment, the sample pretreatment includes weighing the sample to be tested, preparing the sample to be tested, and optimizing the prepared sample.

[0006] As a preferred embodiment, the sample is weighed, and the weighed mass is 50-100 mg.

[0007] As a preferred embodiment, the optimization process for preparing the sample is to prepare the sample to be tested into a pressed sheet with a thickness of 4.5-13 μm and a diameter of 95-135 μm.

[0008] As a preferred embodiment, the sample detection is selected from one or a combination of infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, thermogravimetry, high performance liquid chromatography, gas chromatography, and electron microscopy.

[0009] As a preferred embodiment, the impurity analysis includes analysis of impurity components and quantitative analysis of impurities.

[0010] As a preferred implementation manner, the quantitative analysis formula of the impurities is: W=S impurities / S recycled plastics.

[0011] As a preferred embodiment, the analysis of the impurity components at least includes the analysis of esters, ketones, ethers, acids, peracids, and perester oxides.

[0012] As a preferred implementation, the generation of the quantitative estimation model is to formulate a sample impurity content assessment model based on the content of different impurities in the sample, so as to predict the impurity content of similar samples.

[0013] The second aspect of the present invention provides an application of a method for determining the impurity content of recycled plastics, which is at least applied to the determination of the impurity content of recycled plastics PP, ABS, PVC, PA, PC, PS, PE, and polyester. Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The method for determining the impurity content of recycled plastics of the present invention combines physical detection with chemical instrument detection, and can analyze and detect not only the apparent visible impurity content in the recycled plastics but also the invisible impurity content.

[0015] (2) The method for determining the impurity content of recycled plastics of the present invention optimizes the pre-treatment of samples and can divide the recycled plastics into uniform samples by preparing standardized membranes, so that the difference in impurity content of each sample is not too large, thereby reducing measurement deviation.

[0016] (3) The method for determining the impurity content of recycled plastics of the present invention not only performs qualitative analysis on the sample, but also performs quantitative processing, so that the impurity components and contents in the same recycled plastics can be roughly understood.

[0017] (4) The method for determining the impurity content of recycled plastics of the present invention can generate an impurity quantitative estimation model based on the impurity analysis results of the recycled plastics, and estimate the impurity content of the same recycled plastic samples. DETAILED DESCRIPTION

[0018] In order to achieve the joint analysis of colored impurities and colorless impurities in recycled plastics, the first aspect of the present invention provides a method for determining the impurity content of recycled plastics, including sample pretreatment, sample testing, impurity analysis, and generating a quantitative estimation model.

[0019] As a preferred embodiment, the sample pretreatment includes weighing the sample to be tested, preparing the sample to be tested, and optimizing the prepared sample.

[0020] As a preferred embodiment, the sample is weighed, and the weighed mass is 50-100 mg.

[0021] As a preferred embodiment, the sample is prepared by taking 50-100 mg of the recycled plastic to be tested, putting the recycled plastic into a flat vulcanizer, and pressing it at a pressure of 15-20 MPa for 1-5 minutes.

[0022] As a preferred embodiment, the optimization process for preparing the sample is to prepare the sample to be tested into a pressed sheet with a thickness of 4.5-13 μm and a diameter of 95-135 μm.

[0023] As a preferred embodiment, the sample detection is selected from one or a combination of infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, thermogravimetry, high performance liquid chromatography, gas chromatography, and electron microscopy.

[0024] As a preferred embodiment, the sample detection is a combination of infrared spectroscopy detection, differential scanning calorimetry detection, and electron microscopy detection.

[0025] More preferably, the detection wavelength range of infrared spectrum detection is 0.75-25 μm.

[0026] Further preferably, in the differential scanning calorimetry test, the temperature is increased from room temperature to 210-230°C at a heating rate of 10-15°C / min, and the temperature is kept constant for 1-3 minutes, then the temperature is decreased to 170-190°C at a cooling rate of 10-15°C / min, and the temperature is kept constant for 20-40 minutes, and then the temperature is decreased to 120-150°C at a cooling rate of 10-15°C / min, and the temperature is kept constant for 20-40 minutes.

[0027] As a preferred embodiment, in the electron microscope test, the color impurities with a diameter of ≤0.1 μm are counted as 1 point, the color impurities with a diameter of ≤0.5 μm are counted as 3 points, and the color impurities with a diameter of ≤1 μm are counted as 6 points.

[0028] As a preferred embodiment, the impurity analysis includes analysis of impurity components and quantitative analysis of impurities.

[0029] As a preferred implementation manner, the quantitative analysis formula of the impurities is: W=S impurities / S recycled plastics.

[0030] As a preferred embodiment, the analysis of the impurity components at least includes the analysis of esters, ketones, ethers, acids, peracids, and perester oxides.

[0031] As a preferred implementation, the generation of the quantitative estimation model is to formulate a sample impurity content assessment model based on the content of different impurities in the sample, so as to predict the impurity content of similar samples.

[0032] The second aspect of the present invention provides an application of a method for determining the impurity content of recycled plastics, which is at least applied to the determination of the impurity content of recycled plastics PP, ABS, PVC, PA, PC, PS, PE, and polyester.

[0033] The applicant has found that the oxygen content of recycled plastics will increase due to oxidation reactions, generating a large number of esters, ketones, ethers, acids, peracids, and perester oxides. For organic groups, infrared spectroscopy can be used for detection. The Fourier transform infrared spectrometer provides structural information of different groups. By comparing the peak area of ​​the standard spectrum with the peak area of ​​the test sample, the peak of the impurity can be distinguished, and quantification is performed based on the peak area of ​​the impurity peak.

[0034] Crystallinity can indicate the degree of degradation of the material. Chain breaks produced during the degradation of recycled plastics will increase the crystallinity of the material, while impurities such as oxidation products may affect recrystallization. Recycled plastics containing impurities may have uneven crystal structures. When samples containing impurities are tested by differential scanning calorimetry, multiple peaks will appear, while the melting peaks of samples of recycled plastics without impurities are relatively simple. The samples are pretreated by gradient isothermal crystallization and tested according to a preset heating program to obtain the melting curves of each sample. The melting peak curves of samples containing impurities and samples without impurities are compared, and the impurity content is quantified according to the peak area of ​​the melting peak. The content ratio of impurities in the overall recycled plastic is calculated according to the impurity content calculation formula W=S impurities / S recycled plastics.

[0035] The appearance of heterochromatic impurities in recycled plastics can be inspected by scanning electron microscope or transmission electron microscope, such as black impurities in transparent materials or white materials. The heterochromatic impurities in recycled plastic materials are graded according to the diameter or area of ​​the heterochromatic impurities. The larger the diameter or area, the higher the grade score of the impurity. The heterochromatic impurity diameter ≤ 0.1μm is scored 1 point, the heterochromatic impurity ≤ 0.5μm is scored 3 points, and the heterochromatic impurity ≤ 1μm is scored 6 points. The higher the grade score of the heterochromatic impurities in a recycled plastic sample, the higher the impurity content of the recycled plastic sample. And if two or more heterochromatic impurities appear in a sample, the grade scores of the heterochromatic impurities will be accumulated to calculate the final grade score of the recycled plastic sample.

[0036] The present invention is described in detail below by way of examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by professionals and technicians in this field based on the content of the present invention above still belong to the scope of protection of the present invention.

[0037] Example 1

[0038] A method for determining the impurity content of recycled plastics, firstly performing sample pretreatment, weighing 75 mg of recycled polypropylene plastic, putting it into a vulcanizer for tableting, and pressing it for 2 minutes under a pressure of 20 MPa, so that the thickness of the prepared tablet is 9 μm and the diameter is 100 μm. The prepared sample tablet is placed in a scanning electron microscope for scanning detection, and the grade of heterochromatic impurities in the sample tablet is judged, and the grade score of the heterochromatic impurities in the sample tablet is calculated.

[0039] The prepared sample tablet is placed in a Fourier transform infrared spectrometer to scan the infrared spectrum, scan the infrared spectrum at a wavelength of 0.75 to 25 μm, compare the infrared spectrum of the sample with the standard infrared spectrum of recycled plastics, compare the impurity components contained in the sample, and perform quantitative calculation based on the peak area of ​​the impurity peak.

[0040] The prepared sample tablets were placed in a special aluminum sample tray, sealed and covered, and the standard recycled plastic and the test sample were placed in a differential scanning calorimeter. The sample was tested by the gradient isothermal crystallization method. The temperature was raised to 230°C at a heating rate of 15°C / min, kept constant for 2 minutes, then cooled to 180°C at a cooling rate of 15°C / min, kept constant for 30 minutes, and then cooled to 150°C at a cooling rate of 15°C / min, kept constant for 30 minutes. The melting curves of the standard recycled plastic and the test sample were obtained respectively. The impurity content was quantitatively calculated according to the formula W = S impurities / S recycled plastic.

[0041] According to the results of the impurity content determination of recycled polypropylene plastics, a quantitative estimation model for impurities in recycled polypropylene plastics is generated to estimate the impurity content of recycled polypropylene plastics in a targeted manner. The types and quantities of impurities contained in recycled plastics from different raw material sources are roughly the same. The impurities in recycled plastics from different raw material sources are used to generate multiple different impurity type-impurity quantity curves. The corresponding curves are corresponding to specific types of recycled plastics to obtain estimated information on impurities, and then the test methods are selected in a targeted manner.

Claims

1. A method for determining the impurity content of recycled plastics, characterized in that: Including sample pretreatment, sample testing, impurity analysis, and generation of quantitative estimation models; The sample pretreatment includes weighing the sample to be tested, preparing the sample to be tested, and optimizing the prepared sample; Weighing the sample, the mass of which is 50-100 mg; The optimization process of preparing the sample is to prepare the sample to be tested into a pressed sheet with a thickness of 4.5-13 μm and a diameter of 95-135 μm; The sample detection is a combination of infrared spectroscopy detection, differential scanning calorimetry detection, and electron microscope detection; The impurity analysis includes analysis of impurity components and quantitative analysis of impurities; The quantitative analysis formula of the impurities is: W=S impurities / S recycled plastics; The analysis of the impurity components at least includes the analysis of esters, ketones, ethers, acids, peracids, and perester oxides; The quantitative estimation model is generated to formulate a sample impurity content assessment model based on the content of different impurities in the sample; specifically, the impurity content of recycled polypropylene plastic is estimated in a targeted manner; multiple different impurity type-impurity quantity curves are generated for the impurities in recycled plastics from different raw material sources, and corresponding curves are corresponding to specific types of recycled plastics to obtain estimated impurity information, and then a test method is selected in a targeted manner; The differential scanning calorimetry detection method is as follows: placing the prepared sample pressed tablet into a special aluminum sample tray, performing a sealing and pressing process, placing the standard recycled plastic and the test sample into a differential scanning calorimeter, and detecting the sample by a gradient isothermal crystallization method, heating the temperature to 230°C at a heating rate of 15°C / min, keeping the temperature constant for 2 minutes, then cooling the temperature to 180°C at a cooling rate of 15°C / min, keeping the temperature constant for 30 minutes, and then cooling the temperature to 150°C at a cooling rate of 15°C / min, keeping the temperature constant for 30 minutes; respectively obtaining the melting curves of the standard recycled plastic and the test sample; The impurity content is quantitatively calculated according to the formula W=S impurities / S recycled plastics.

2. An application of the method for determining the impurity content of recycled plastics according to claim 1, characterized in that: It is used at least in the determination of impurity content of recycled plastics PP, ABS, PVC, PA, PC, PS, PE and polyester.