User Benefits Application News Evaluation of Microscopic Foreign Matter in Recycled Plastics Using Dynamic Image Analysis, Infrared Microscopy, and SEM-EDS Hiroki Maeda 1 , Masahiro Homma 2 , Hiroyasu Ono 2 , Karen Maruyama 1 , Xu Yan 1 , Zen Miyazaki 1 Dynamic Particle Image Analysis System Fourier Transform Infrared Spectrophotometer Infrared Microscope 1 Shimadzu Corporation, 2 Shimadzu Techno-Research, Inc. Pressure Rise During Melting and Extrusion Increased Burst Frequency Recycled Materials Flakes Pellets Final Product PET Bottle Manufacturing Processes Preform Molding Blow Molding Sorting, Crushing, Washing, Density Separation, Drying Recycling Processes Observed Issues When Foreign Matter is Abundant Fig. 1 iSpect DIA-10 Dynamic Particle Image Analysis System  Analysis Conditions Preparation of Microscopic Foreign Matter Suspensions 100 mg/mL suspensions were prepared by adding HFIP to PET pellets (virgin and recycled) and left to stand at room temperature. Because PET dissolves in HFIP, microparticles that do not dissolve in HFIP remain in the suspensions. The dissolution behavior of pellets is shown in Fig. 4. Due to the different dissolution rates of virgin and recycled materials, pellets became invisible to the naked eye within 4 days for the virgin material and within 6 hours for the recycled material. Acquisition of Particle Images and Evaluation of Particle Size and Particle Concentration by Dynamic Image Analysis The suspensions were measured with a dynamic particle image analysis system (iSpect DIA-10, Shimadzu Corporation) to acquire images of microscopic foreign particles. Particle size and particle concentration were evaluated based on the acquired data. The analysis conditions are indicated in Table 1. As a control, HFIP stored in a glass bottle of the same type used for the suspension preparations was also measured to check for any contributions from glass bottles and solvent.  PET Bottle Recycling and Foreign Matter A typical PET bottle recycling process is shown in Fig. 3. One issue caused by foreign matter contained in pellets during PET bottle manufacturing is bursting during molding. Recycled materials tend to burst more frequently than virgin materials, but because foreign matter is microscopic and scatters, collecting foreign matter after bursting is not possible and identifying the cause is difficult. Another issue is clogging of filters during melting and extrusion processes. Metal filters are used to remove foreign matter during processing, but filter clogging causes pressure to rise, so they must be replaced periodically. However, because the size and quantity of foreign particles differ depending on the pellets, optimizing the filter type and replacement timing is difficult. Information on the size and quantity of foreign particles in pellets is expected to be useful for making process improvements in the following ways: • Improving yield and productivity through optimization of parameters by selecting metal filters matched to pellet quality. • Improving foreign matter removal steps during pellet manufacturing intended to improve recycled material quality.  Introduction One of the quality criteria for recycled plastic flakes and pellets is the content of foreign matter. Quantitatively evaluating the size and quantity of foreign particles contained in flakes and pellets is important for examining foreign matter removal processes intended to improve pellet quality and optimize manufacturing processes for products made with recycled materials. In this article, pellets of virgin and recycled polyethylene terephthalate (hereafter PET) were dissolved in hexafluoro-2-propanol (hereafter HFIP), a solvent for dissolving PET, to prepare suspensions of insoluble microscopic foreign particles. These suspensions were measured with a dynamic particle image analysis (DIA) system (iSpect DIA-10) to evaluate the size and number of insoluble microscopic foreign particles (patent pending). In addition, part of the suspensions were diluted tenfold and filtered through a membrane filter to collect the insoluble microscopic foreign particles on the filter. The morphology and composition of the collected microscopic foreign particles were evaluated using a digital microscope, an infrared microscope system (IRTracer -100 and AIM-9000), and an SEM-EDS system. These evaluations enabled comparison of the sizes, quantities, and types of foreign particles contained in virgin and recycled materials.  It is easy to evaluate the size and quantity of microscopic foreign particles, which are key quality criteria of recycled plastics.  With the microcell method of DIA, microscopic foreign matter can be detected and counted quickly using a small sample quantity.  Infrared microscope and SEM-EDS systems provide information about the morphology and composition of microscopic foreign matter that is useful for improving recycling processes. Fig. 2 Infrared Microscope System Left: IRTracer -100; Right: AIM-9000 Fig. 3 Recycling Process (PET Bottle Case)

Application News Virgin Recycled Virgin Recycled Start of Dissolution Virgin Recycled After 6 Hours Virgin Recycled After 4 Days Before Dissolution Fig. 4 Dissolution of Pellets in HFIP Table 1 iSpect DIA-10 Analysis Conditions Frame Rate: 8 fps Efficiency: 96.5 % Pump Volume: 250 µL Threshold: 216 (90 % of background brightness) Background Correction: Enabled Morphology Observation and Composition Analysis of Microscopic Foreign Matter by Infrared Microscope and SEM-EDS Due to the high viscosity of the suspensions, 50 µL quantities were diluted tenfold. Insoluble microscopic foreign particles in the tenfold diluted suspensions were collected on a silver membrane filter by suction filtration. Fig. 5 shows the silver membrane filter after collection, observed with a digital microscope. The region within the red dashed circle is where particles were collected. Some of the particles collected on the silver membrane filter were measured by the micro-reflectance method using an infrared microscope system (IRTracer-100 and AIM-9000, Shimadzu Corporation). The measurement conditions are indicated in Table 2. In addition, particles identified as inorganic or metallic based on their images or infrared microscope results were further analyzed using an SEM-EDS system (ProX, Phenom World). Fig. 5 Silver Membrane Filter after Collection Instruments: IRTracer -100, AIM-9000 Resolution: 8 cm -1 Number of Scans: 100 Apodization Function: SqrTriangle Wavenumber Range: 700 - 4000 cm -1 Detector: Liquid nitrogen-cooled MCT Table 2 Infrared Microscope Analysis Conditions  Results and Discussion Acquisition of Particle Images and Evaluation of Particle Size and Particle Concentration by Dynamic Image Analysis Fig. 6 shows a portion of the particle images detected by the iSpect DIA-10. The first images listed when arranged in descending order of area-equivalent diameter are shown. As can be seen from the particle images, the largest particles had area-equivalent diameters of about 10 µm for the virgin material and about 40 µm for the recycled material. The images also show that particle shape and brightness vary from particle to particle. In general, the smaller the relative refractive index between the particle and dispersing medium, and the shorter the particle in the observation direction, the brighter the particle appears. Virgin Recycled Fig. 6 Detected Particle Images Excerpt from the top when arranged in descending order of area-based diameter. Therefore, bright particles are presumed to be either organic materials with a small refractive index, glass fragments that transmit light, or plate-like particles (short in the observation direction), whereas dark particles are presumed to be inorganic or metallic particles or long dense particles (long in the observation direction). In this way, information on particle shape and brightness can be used to infer particle types.

Application News Skin 0 5000 10000 15000 20000 25000 Particle Concentration (count/mL) Table 3 Particle Concentration by Size Range (count/mL) Morphology Observation and Composition Analysis of Microscopic Foreign Matter by Infrared Microscope and SEM-EDS Selected results from analyzing the composition of the virgin material are shown in Figs. 8 and 9. Brown particles were observed in the infrared microscope images. Based on the IR spectra, they were presumed to be amide-type compounds or cellulose. These particles could have been introduced during handling/processing at the time of measurement, making it difficult to determine whether they originated from the sample itself. For the recycled material, the infrared microscope suggested the presence of particles that were not organic substances. SEM-EDS results for those particles are shown in Figs. 10 and 11. For the particle in Fig. 10, the EDS spectrum showed mainly C (carbon), Ca (calcium), and O (oxygen), suggesting a carbonate or similar substance. The Ag (silver) peak is from the filter substrate. For the particle in Fig. 11, a metallic luster was observed under an optical microscope and Al (aluminum) was detected in the EDS spectrum, indicating metallic aluminum. Recycled materials may come into contact with various substances during the collection process. Therefore, composition information for foreign matter can be used to investigate the origin of foreign matter, evaluate measures for reducing foreign matter, and evaluate the impact of the foreign matter on final products. Furthermore, the particle in Fig. 10 was confirmed to have a similar shape and major axis length to the particles shown in the second to fourth images from the left in the top row of iSpect DIA-10 particle images in Fig. 6. Based on the morphological similarity, iSpect DIA-10 particle images may also be useful for inferring particle composition. Fig. 7 Particle Concentration Measurement Results Average of three measurements with standard deviation indicated by error bars. Sample Particle Concentration by Size Range (count/mL) All 5-10 μm 10-25 μm 25-50 μm 50-100 μm >100 μm HFIP 104 91 12 0 0 0 Virgin 286 257 23 3 0 0 Recycled 20240 19523 699 18 0 0 Sample Number of Particles Gram of Pellets by Size Range (count/g) All 5-10 μm 10-25 μm 25-50 μm 50-100 μm >100 μm Virgin 2860 2570 230 30 0 0 Recycled 202400 195230 6990 180 0 0 Table 4 Number of Particles per Gram of Pellets by Size Range (count/g) Note: Average of three measurements. Note: Average of three measurements. Note: Calculated from 100 mg/mL suspension concentration used for sample preparation. a) Observation Image by Infrared Microscope b) IR Spectrum Fig. 8 Composition Analysis Result Virgin Material: Human Skin-Derived Component a) Infrared Microscope Observation Image b) IR Spectrum Fig. 9 Composition Analysis Result Virgin Material: Cellulose Virgin_Brown 1 Virgin_Brown 2 Cellulose

Application News www.shimadzu.com/an/ Shimadzu Corporation © Shimadzu Corporation, 2025 For Research Use Only. Not for use in diagnostic procedures. This publication may contain references to products that are not available in your country. Please contact us to check the availability of these products in your country. The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. See https://www.shimadzu.com/about/trademarks/index.html for details. Third party trademarks and trade names may be used in this publication to refer to either the entities or their products/services, whether or not they are used with trademark symbol “TM” or “”. Shimadzu disclaims any proprietary interest in trademarks and trade names other than its own. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice. First Edition: Dec. 2025 01-00861-EN iSpect, IRTracer, and AIMsight are trademarks of Shimadzu Corporation or its affiliated companies in Japan and/or other countries.  Conclusion By using an iSpect DIA-10 system to measure suspensions prepared by dissolving two types of PET pellets (virgin and recycled) in HFIP, we obtained particle images of insoluble foreign matter and evaluated size and concentration of particles. That enabled quantitative comparison of particle size and count in microscopic foreign matter contained in virgin and recycled materials. In addition, after diluting the pellet suspensions, the insoluble microscopic foreign matter in the diluted suspensions was collected on filters. The morphology and composition of the microscopic foreign matter were evaluated using an infrared microscope and SEM-EDS system. The results indicated that the suspensions contained organic substances, such as cellulose and amide-based compounds, and inorganic substances and metals that contain elements such as C, O, Ca, and Al (suggestive of carbonates and metallic aluminum). Thus, the iSpect DIA-10 enables simple quantitative evaluation of the size and number of microscopic foreign particles in PET pellets using only small sample quantities. Furthermore, composition evaluation by infrared microscope and SEM-EDS systems provides useful information for investigating the origin of foreign matter, examining measures to reduce foreign matter, and evaluating impacts on final products. If similarities in size and shape are observed, particle images obtained with iSpect DIA-10 can also potentially be used to estimate particle composition. a) Infrared Microscope Observation Image b) SEM Image Fig. 10 Composition Analysis Result Recycled Material: Particle Containing Mainly C, Ca, O c) EDS Spectrum a) Infrared Microscope Observation Image b) SEM Image Fig. 11 Composition Analysis Result Recycled Material: Particle Containing Al c) EDS Spectrum

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