EXPERTISE OF PYRAMID TEA BAGS BY OPTICAL MICROSCOPY AND FTIR-SPECTROSCOPY METHODS. MICROPLASTICS FORMATION IN BREWED TEA

. Eight brands of pyramid tea bags on the Ukrainian market were studied: Sun Gardens (1), Lovare (2), Curtis for Mc Donalds (3), Curtis (4), Lipton (5), Premiya (6), Sonnet (7) and Loyd (8). Using FTIR spectroscopy, it was found that the pyramids of the bags are made of thermoplastic polymers polyethylene terephthalate (samples 1-7) and polylactic acid (sample 8). The threads attached to the pyramids are made of thermoplastic polymers polypropylene (samples 1,2,4-7), polyethylene terephthalate (sample 4) and polylactic acid (sample 8). The specific optical rotation of polylactic acid [α] D25 is about -150° (c=1, CHCl 3 ), which refers to poly(L-lactic acid). Using optical microscopy, it was established that the structure of the pyramids are divided into those made of plain woven fabrics (samples 1-3) and heat-bonded nonwoven fabrics (samples 4-8). The tea bags (samples 1-3) exhibit a well patterned net structure (mesh) with the pores perceived to be uniform and regular. The tea bags made of nonwoven materials have an irregular network consisting of compact and random arrangement of fibers. The fibers are pleated randomly, generating irregular pores. Nonwoven fabrics are made from fibers with a diameter of 12-18 µm, woven fabrics are made from fibers with a diameter of 48-54 µm. The area density of nonwoven fabrics is 18.5-20.3 g/m 2 , the area density of woven fabrics is 22.0-22.7 g/m 2 . The threads are made by twisting several single-twisted yarns. The structure of threads are a cabled yarn from three 2-ply yarns (samples 1,8), 4-ply yarn (samples 2-4,6,7) and 4-ply multyfilament yarn (samples 5). The final twist of the plied yarn/cord is S-twist. The primary structural element of threads in the case of samples 1-4, 6-8 are staple fibers, of sample 5 are multyfilament fibers. Each empty pyramids and thread was steeped at 95°C for 5 min in 10 mL of water. It has been established that the shape of microplastic particles formed in beverages during tea brewing is determined by the primary structure of tea bags. Both pyramids and threads release irregularly shaped microplastic particles.


Introduction. Formulation of the problem
The negative impact of plastic pollution on the environment (air, land and water) is now beyond doubt.Plastic pollution is a global problem.According to recent estimates, plastic waste that pollutes the aquatic environment (oceans, seas, lakes, and rivers) amounts to 10 to 20 million tons per year, while the global production of synthetic plastic is about 300 million tons per year [1].Part of the plastic pollution is in the form of microplastics (particle size from 0.1 to 5000 μm) and nanoplastics (plastic particle size from 0.001 to 0.1 μm) [2].In recent years, nano-and microplastics have been detected in food products (fish, seafood, honey, sea salt, water, etc.) [1][2][3][4].
When consuming plastic-contaminated food products, micro-and nanoplastics enter the human body and the annual consumption of microplastics ranged from 39000 to 52000 particles per person [5].The presence of micro-and nanoplastics in human tissues has recently been established, which is a risk factor for health [6][7][8][9][10].
Recent studies by scanning electron microscopy (SEM) and Nanoparticle Tracking Analysis (NTA) have shown that steeping a single nylon or polyethylene terephthalate (PET) plastic tea bag at brewing temperature (95°C) for 5 min released about Volume 17 Issue 3/2023 11.6 billion microplastics and 3.1 billion nanoplastics into a single cup of the beverage [11].That is, in this case, the source of micro-and nanoplastic is not the environment, but the packaging of the food product, which contaminates the tea during its preparation.Given this abnormally large amount of nano-and microplastics, it is relevant to study the plastic tea bags.
Using μ-Raman spectroscopy between 5800 and 20400 microplastic particles >1 μm were found in released by one tea bag of nylon plaine fabric with attached string/thread of polypropylene (PP) [12].The formation of micro-and nanoplastic was observed in the case of nylon tea bags [13][14][15], nonwoven PET/polyethylene (PE), nonwoven PP with PET/PE string/thread, woven nylon with PP string/thread tea bags [16].The release of plastic from tea bags made of PET/PE, polylactic acid (PLA) and PET has been shown [17,18].Therefore, it is of interest to study the tea bags on the Ukrainian market.
The purpose of the work is to study pyramid tea bags intended for brewing tea using FT-IR spectroscopy and optical microscopy in order to identify polymeric materials and the structure of tea bags as a source of microplastics.
Objectives of the research: 1) to identify the type of polymer of the tea bags by FTIRspectroscopy; 2) to examine the parameters, structure and morphology of the tea bags samples using optical microscopy.
Packaging material with tea in the form of bags, which consists of such structural elements as a tetrahedron / triangular pyramid (hereinafter pyramid), thread and tag (label), is presented in Figure 1.FTIR spectra of samles were recorded using a Spectrum One spectrometer (Perkin-Elmer).The spectral resolution is 4 cm -1 , the number of scans is 16.
The specific rotation in the case of the Loyd tea bag (sample 8) was determined at a polymer concentration of 0.01 g/cm 3 using a P1000 polarimeter (A.KRÜSS Optronic) with a sodium lamp (wavelength D line 589.3 nm) at a cuvette length of 10 cm and a temperature of 25°C.The polymer for these mesurements was purified by precipitation with methanol from a chloroform solution.
The linear dimensions of the structural elements of the bags were measured according to DSTU EN 1773:2009(EN 1773:1996, IDТ).The area density of textile materials in units of mass per unit area (g/m 2 ) was determined using an electronic balance as the average value for measurements of five bags according to DSTU ISO 7211  The morphology and structure of tea bags were determined by optical microscopy using microscopes.The fiber diameter was determined using the optical microscopy method as the cross-sectional distance of fiber.
The final twist of the plied yarns and the original twist of the single yarn before plying were determined by the procedure given in ISO 2061:2015.
The formation of microplastics was investigated for structural elements of tea bags that come into contact with water during tea brewing.Each pyramid and each thread was steeped at 95°C for 5 min in 10 mL of distilled water.Tea were removed before proceeding.Tags (labels) were not examined due to the fact that they do not come into contact with water during tea brewing.

Results of the research and their discussion
The FTIR spectra were used to identify the tea bag material.Figure 2 shows the FTIR spectra of the pyramids, and Figure 3 shows the FTIR spectra of the threads.The absorption bands in the FTIR spectra were compared with the known spectra of polymers.The FTIR spectra of the pyramids (samples 1-7) as well as the threads (sample 3) show the corresponding infrared absorption bands of PET.
The FTIR spectra of threads (samples 1-7) show the corresponding infrared absorption bands of PP.The FTIR spectrum of PP exhibits large peaks in the wavenumber range 3000-2800 cm −1 : the peaks at 2955 and 2873 cm −1 can be attributed to CH 3 asymmetric and symmetric stretching vibrations, ν as (CH 3 ) та ν s (CH 3 ), respectively, while the peaks at 2922 and 2843 cm −1 are due to CH 2 asymmetric and symmetric stretching vibrations ν as (CH 2 ) та ν s (CH 2 ), respectively.The FTIR spectrum also shows two intense peaks at 1460 and 1378 cm −1 : the peak at 1460 cm −1 is caused by CH 3 asymmetric deformation vibrations, δ as (CH 3 ), while the peak at 1378 cm −1 refers to CH 3 symmetric deformation vibrations, δ s (CH 3 ).The FTIR spectrum of PP also exhibits numerous less intense absorption bands in the wavenumber range 1370-700 cm −1 : in the region 1370-1200 cm -1 there are wagging and twisting vibrations of CH 2 groups) and deformation vibrations of CH 2 and CH groups, which strongly interact with each other; absorption bands in the region of 1200-700 cm -1 are caused by the interaction of rocking vibrations of CH 3 and CH 2 groups with stretching vibrations of the carbon skeleton, ν(CC) ) [19,24,25].
In the case of sample 8, the FTIR spectra of the pyramid as well as the thread show the corresponding polylactide (PLA) infrared absorption bands.
PLA is a thermoplastic aliphatic polyester derived from lactic acid, which is optically active and has two optical isomers, namely L-and D-lactic acid.In this regard, there are optically active isomers of PLA: the L-isomer of PLA, if the polymer is obtained from Llactic acids, and the D-isomer of PLA, if the polymer is obtained from D-lactic acids [30,31].
The structure and composition of plastic tea packages were determined by optical microscopy.The material of the pyramids of samples is shown in the following photomicrographs (see Figure 4).The materials are used to separate tea from a moving fluid passing through the media.From the given microphotographs, it can be seen that the samples are divided into two groups by structure: pyramids made of plain weave fabrics (samples 1-3) and made of nonwoven fabrics with random fiber structures in sheet form (samples 4-8).Plain weave is a weave in which 57 Volume 17 Issue 3/2023 each weft thread passes alternately over and under the warp thread, and each warp thread alternately passes over and under the weft thread [37].Nonwoven fabrics are fabrics that are produced by mechanical, thermal or chemical processes, but without being woven and without the need to convert fibers into yarn, since the fiber webs are bonded together as a result of the inherent friction (entanglement) from one fiber to another thanks to these non-conventional processes [37][38][39][40].The weft and warp threads of samples 1-3 are monofilaments which, as a result of interweaving, form a well patterned net structure (mesh) with the pores perceived to be uniform and regular.
The nonwoven material of the pyramids with the pore structure is formed by point thermal bonding of fibers on a calender.A point-bonded nonwoven material consists of randomly interwoven fibers joined together at discrete points, forming sections of thermal contact bonding uniformly distributed throughout nonwoven fabric.Other bridging fibers that connect the junctions retain their structural properties.The partial thermal contact connection of samples 4-7 has a rhombic shape, while in the case of sample 8 it has a round ones [40].There is no complete melting of the fibers at the bonding points, which is characteristic of commercial nonwoven materials that are obtained under conditions of insufficient pressure in the inter-Volume 17 Issue 3/2023 roller gap, high speed of rotation of the rollers, or insufficiently high temperature, which does not ensure complete melting of the fibers at the bonding points. of contact (usually about 10 ms) [39].Areas of partial thermal contact bonding of the studied samples have a rhombic shape with a diagonal length of about 500 μm.
Textile fabric parameters of samples 1-8 presented in table 2. The area density of nonwoven materials is 18.0-19.4g/m 2 , the area density of plain fabrics is 21.8-22.3g/m 2 .Nonwoven and plain weave fabric structures are composed of fibers.The fiber diameter of nonwovens is 13-16 µm, while mesh-type woven fabrics are made from fibers with a diameter of 50-52 µm.It must be noted that reducing fiber diameter is the dominant way of increasing filtration efficiency of a nonwoven filter medium [40].
The tea bag threads/strings are shown in Figure 5.The threads to the pyramids of all tested samples are attached using the thermal bonding method.The pyramids of samples 1,2,4-7 made of PET are connected to threads of another plastic, namely PP.It can be assumed that this is due to the fact that PP is more low melting thermoplastic material than PET.
The melting point of PP is about 165°C, and the melting point of PET is 260°C [40].
The characteristics of the threads are given in Table 3. Threads made of multiple structures such as ply yarns (samples 2-7) and cabled yarns (samples 1,8) [41][42][43].The primary structural element of the threads in the case of samples 1-4, 6-8 are staple fibers (elementary fibers of limited length), of sample 5 -filament fibers (elementary fibers of unlimited length).
Thus, the primary structural element of tea bags (pyramids and threads) are fibers, which are produced from thermoplastic polymers.Figures 6 and 7 shows the longitudinal morphology of PET, PP and PLA fibres.Obvious randomly distributed micro-sized defects in the form of irregularly shaped particles and fibrils (Figure 7 5b) can be observed on the surface of the fibers.Microparticle size is usually smaller or comparable to the diameter of the fibers.These particles on the surface of the fibers are potential microplastic, which is formed during tea brewing (see figure 8).It has been established that microplastics are formed from both pyramids and threads.These results are in agreement with results of other studies [11][12][13][14][15][16][17].It should be noted that after steeping in hot water not all these microparticles on the fibers transfer into solution as microplastic indicating a strong interaction between the fiber surface and microparticles.On the other hand, the thread structure of samples 1-3,5-8 shows a helical arrangement of fibres with a lot of projecting ends [42].This structure allows the threads to collect debris, including microplastic due to electrostatic and mechanical attraction by the assembly of staple fibers of the threads.Fig. 8b presents black microfiber in the thread.When the threads come into contact with hot water, some of the debris gets into the tea.

Conclusion
The structure, morphology and parameters of plastic tea packages were established.The tea bags for all studied samples are made of thermoplastic materials: pyramids of PET and PLA, threads of PET, PP and PLA.No bags made of nylon were found.PET mesh filter bags of samples 1-3 have a woven structure of single filaments.Nonwoven filter bags have a nonwoven structure of single filaments which are thermofixed.Threads made of multiple structures such as ply yarns and cabled yarns.The primary structural elements of tea bags are fibers.On the surface of fibers situated particles of microplastic debris.In some cases, the presence of a small amount of microplastics, which does not belong to the materials from which the structural elements of the tea bags are made: pyramids or threads, has also been established in the composition of ready-made tea drinks.
Thus, all tea bags made of plastic textile materials (nonwoven and plain woven fabrics, yarn) are a source of microplastics.It should be noted that to date no textile plastic materials have been created that would not pollute water with microplastics [44,45].It is therefore appropriate that information about this special characteristic of tea bags be part of the food product labeling as a tool to protect consumer health [8,9,46,47].

Table 1 -Description of the tea bags used in this study No. Brand EAN-13 barcode Batch number Production date Best before date Recomented method of tea brewing
o C), brew for 5 min Volume 17 Issue 3/2023