Extraction-Based Pretreatment of End-of-Life Plastics from Waste Electrical and Electronic Equipment for Brominated Flame Retardant Removal and Subsequent Valorization via Pyrolysis

Abstract

Due to the increasing volumes of plastic waste generated from electric and electronic devices, research has focused on the investigation of recycling methods for their safe handling. Pyrolysis converts plastics from waste electric and electronic equipment (WEEE) into valuable products (pyrolysis oil). Nevertheless, the frequent presence of flame retardants, mainly brominated flame retardants (BFR), hinders pyrolysis’s wide application, since hazardous compounds may be produced, limiting the use of pyrolysis oils. Taking the aforementioned into account, this work focuses on the recycling, via pyrolysis, of various plastic samples gathered from WEEE, to explore the valuable products that are formed. Specifically, 14 plastic samples were collected, including parts of computer peripheral equipment, remote controls, telephones and other household appliances. Considering the difficulties when BFRs are present, the study went one step further, applying XRF analysis to identify their possible presence, and then Soxhlet extraction as an environmentally friendly method for the debromination of the samples. Based on the XRF results, it was found that 23% of the samples contained bromine. After each Soxhlet extraction, bromine was reduced, achieving a complete removal in the case of a remote control sample and when butanol was the solvent. Thermal pyrolysis led to the formation of valuable products, including the monomer styrene and other secondary useful compounds, such as alpha-methylstyrene. The FTIR results, in combination with the pyrolysis products, enabled the identification of the polymers present in the samples. Most of them were ABS or HIPS, while only three samples were PC.

1. Introduction

Globally the generated amount of waste electric and electronic equipment (WEEE) has increased, since it became approximately 62 million metric tons (Mt) in 2022, while it was 34 million metric tons (Mt) in 2010 [1,2]. This rise can be attributed to the wide use of electric and electronic devices, including health, energy, transport, security and other applications, along with their short lifespan and the fact that the replacement of the equipment is accelerated, while the repair options are quite limited [1,3]. Consequently, sustainable approaches for the management of WEEE are vitally important.

Until now, the main difficulty in the recycling of WEEE has been the presence of different materials, including glass, metals and plastics. Plastics, which account for almost 30% of a typical WEEE fraction, including mainly acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), polycarbonate (PC), blends of PC/ABS, polypropylene (PP), etc., can be reused or recycled in order to obtain valuable secondary products [4,5]. Nevertheless, the recycling of plastics from WEEE is no mean feat, taking into consideration the fact that WEEE plastics often contain various hazardous additives, including colorants, stabilizers, flame retardants (FR) [mainly brominated flame retardants (BFR)], etc. [6].

It should be highlighted that the presence of BFRs in plastics from WEEE is of great concern, since they are characterized as persistent organic pollutants (POPs) because of their long-range transportation, persistence in the environment and toxicity [7,8,9]. Also, BFRs are responsible for the formation of polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) during the combustion of plastics that contain them [10,11]. Therefore, the presence of the aforementioned toxic substances renders the recycling of plastics from WEEE complex, and so, advanced and environmentally friendly techniques are necessary for their safe handling to avoid environmental issues [11,12].

So far, research has investigated primary recycling, energy recovery, mechanical recycling and chemical recycling for the handling of plastics from WEEE. Among these methods, chemical recycling, and mainly pyrolysis, is an advantageous technique that results in the recovery of monomers or the production of secondary valuable compounds [10,13]. Specifically, pyrolysis takes place in an inert atmosphere, at medium to high temperatures (300–900 °C) and in the absence or presence of catalysts, enabling the conversion of plastic waste into liquid (pyrolysis oil), gas and solid residues [14].

However, if direct thermal pyrolysis of plastics from WEEE occurs, then brominated compounds may be formed, along with the useful pyrolysis products, hindering their reuse. This is due to the frequent presence of BFR in plastics originating from WEEE, and underlines the importance of applying a pretreatment step before or during pyrolysis, in order to overcome this issue [1,15].

A great number of researchers have investigated different conditions during pyrolysis to reduce the bromine content in the pyrolysis liquid fraction. For instance, catalytic pyrolysis has been widely studied, exploring various catalysts, such as zeolites, all-silica MCM-41 and active Al₂O₃ [11], HZSM-5 and Fe/ZSM-5 [16], ZSM-5, Al₂O₃, MgO, Fe/Al₂O₃ and Fe/MgO [17], etc., for their debromination efficiency. Another alternative is that of co—pyrolysis during which pyrolysis occurs in the presence of two or more materials, to improve the composition of the pyrolysis oils, but without using catalysts or solvents [18]. Other works have studied the application of two-step pyrolysis, for instance, Ma et al. [19] investigated single and two-step pyrolysis of waste computer casing plastics, intending to improve the derived pyrolysis products.

As already mentioned, to reduce the bromine content in the products formed, a pretreatment process can take place before the recycling of the plastics from WEEE. A common pretreatment method for the dehalogenation (e.g., debromination) of plastic waste is solvent extraction, where a solvent is used in order to extract the halogenated (brominated) additives from the native plastics [20]. Until now, various solvents have been investigated for their debromination efficiency. For instance, Evangelopoulos et al. [21] explored isopropanol and toluene as solvents, applying Soxhlet extraction, for the removal of tetrabromobisphenol A (TBBPA) from plastics gathered from WEEE. They found that bromine was reduced, achieving a maximum reduction of 36.5% [21]. In our previous work [12], soxhlet extraction before pyrolysis was investigated for the debromination of polymeric blends that simulated WEEE and for the debromination of real plastics from WEEE [12], respectively, exploring the efficiency of various alcohols as solvents. It was found that all alcohols (isopropanol, ethanol, butanol) were efficient in reducing the bromine content while butanol was the optimal solvent.

Advanced solvent extraction methods can also be applied, including supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), ultrasonic assisted extraction (UAE), as well as microwave-assisted extraction (MAE) [22]. For instance, Kousaiti et al. [23] examined MAE and UAE for the reduction of bromine in some plastic samples gathered from WEEE. The findings showed that MAE resulted in a better debromination efficiency than UAE [23]. Another example is our previous work [24], where MAE was explored before pyrolysis, for the debromination of some polymeric blends that simulated WEEE, investigating different conditions, such as extractive temperatures, times and solvents [24].

Taking into account the fact that dehalogenation prior to recycling of plastics from WEEE is a field that is vitally important for the reduction of the large volumes of end-of-life plastics from WEEE, along with the difficulties associated with their handling, more up-to-date research is still needed. Additionally, in most of the aforementioned research works, complete bromine removal during the pretreatment of the WEEE plastics was not achieved. The maximum bromine reduction observed was quite low, almost discouraging. Therefore, intending to fill this gap, this work focuses on highlighting specific methods for the complete debromination of plastics from WEEE. Furthermore, the products obtained after their recycling via pyrolysis are recorded in an attempt to provide the research community with new data and findings in this field. Thus, it attempts to contribute to the global difficulties that are involved in the recycling of brominated plastics from WEEE. For this reason, 14 plastic samples were collected from end-of-life household appliances, including parts of computer peripheral equipment, remote controls, telephones and others. All samples were analyzed by various techniques, such as Fourier transform infrared spectroscopy (FTIR), evolved gas analysis (EGA), and X-ray fluorescence (XRF) to find which of the samples comprised bromine. All brominated samples were subjected to Soxhlet extraction with isopropanol and butanol to reduce their bromine content. Finally, they were subjected to pyrolysis (chemical recycling method), which enables the recovery of their monomers or the production of other valuable products.

2. Materials and Methods

2.1. Materials

Fourteen (14) plastic samples were collected from household waste electric and electronic devices, including two (2) samples from computer peripheral equipment (mouse and keyboard), five (5) remote control samples, three (3) samples from telephones, telephones’ accessories and other miscellaneous samples from a bathroom ventilator, an iron, a plug and a lamp. All samples gathered, along with their names, are presented in detail in

Table 1. Overview of the samples gathered from WEEE.

Sample Category	Samples	Sample Name
Computer peripheral equipment	Mouse	MS
	Keyboard	KB
Remote controls	Television remote	RC1
	Television remote	RC2
	Television remote	RC3
	Television remote	RC4
	PlayStation remote	RC5
Telephones and accessories	Mobile phone	MP
	Wireless phone	WP
	Earphones	EP
Miscellaneous household equipment	Bathroom ventilator	VENT
	Iron	IR
	Plug	PL
	Lamp	LAM

.

Apart from the samples collected, two solvents, isopropanol (CAS# 67-63-0, d = 0.78 g/mL, batch# 21.0810404.4800) and butanol (CAS# 71-36-3, d = 0.811 g/mL, batch# 20H114011) were also used during this work. Both solvents were investigated during the soxhlet extractions, because of their low toxicity, since alcohols are characterized as non-hazardous compounds [25], along with the fact that the findings from our previous work [12] were promising enough.

2.2. Methods

2.2.1. Analytical Methods

Real plastic samples from waste electric and electronic equipment were selected for this study. Therefore, it was necessary to reduce their size, using hand cutting tools. Thus, it was possible to analyze them without further pre-treatment, as the analytical techniques (EGA, FTIR, DSC and XRF) that were applied do not require it.

The method of Fourier transform infrared spectroscopy (FTIR) was initially applied to distinguish the characteristic peaks of the functional groups of the polymers in the received spectra, and thus draw some early conclusions about the identity of the unknown samples. FTIR analysis was performed using a FTIR Spectrum One Spectrometer (by Perkin Elmer, Shelton, CT, USA). The obtained spectra were received within the range of 4000–600 cm⁻¹ and 16 scans per spectrum were applied for higher accuracy.

X-ray fluorescence (XRF) was applied in order to investigate if the samples from WEEE contained bromine, and, therefore, brominated flame retardants as additives. In this case the samples were also analyzed by XRF after the pretreatment method—Soxhlet extraction that was applied, with the aim of estimating the total bromine content and its reduction. Thus, the samples were cut to a suitable size and the analysis was carried out with a S4-Pioneer wavelength dispersive spectrometer (Bruker-AMS, Karlsruhe, Germany) that is located at the Scanning Electron Microscopy Laboratory of Aristotle University of Thessaloniki. To ensure better accuracy in measuring the bromine content of each sample (plastic waste) before and after pretreatment, random and distinct parts of the specific plastic waste were analyzed. The results present mean values and standard deviations of the measurements. Furthermore, prior to the measurements, a calibration process was conducted by measuring known samples containing a specified amount of bromine.

Evolved Gas Analysis (EGA) was applied in order to obtain information about the decomposition temperature range of the samples and find their optimum degradation temperature, in which the degradation becomes maximum. At this temperature, which is mentioned as T_max, pyrolysis process occurs. Thus, the samples were heated to 100–700 °C, with a heating rate of 20 °C/min. A pyrolyser (EGA/PY-3030D Frontier Laboratories, Fukushima, Japan) was used for this technique and a metallic, capillary tube (6 m, 0.25 mm) was placed under purging gas flow He. The mass of the samples in each analysis ranged between 0.3–0.5 mg.

Samples were also subjected to Differential Scanning Calorimetry (DSC), in order to find their glass transition temperature (T_g) or their crystallization temperature (T_c) or melting point (T_m), depending on the sample examined. For this reason, the instrument DSC Spectrum One (Perkin Elmer) was used. The runs took place under nitrogen flow. Samples were heated within the range of 30 to 200 °C, at a rate of 20 °C/min, then they were cooled from 200 to 30 °C applying again a rate of 20 °C/min, and finally they were heated within the range of 30 to 200 °C, at a rate of 10 °C/min. Temperatures (T_g or T_c and T_m) of each sample were estimated taking into account the thermograms that were received during the second heating cycle.

2.2.2. Chemical Recycling Method—Pyrolysis

Chemical recycling and especially pyrolysis was investigated for the valorization of the plastic waste samples. Pyrolysis was carried out on a pyrolyser, which is coupled with a gas chromatographer/mass spectrometer (Py-GC/MS) (QP-2010 Ultra Plus, Shimadzu, Fukushima, Japan), with helium as the purging gas. The mass of the samples varied in the range between 0.3–0.6 mg. The chromatographic column used for GC was a capillary column Ultra Alloy 5% diphenyl- 95% dimethylpolysiloxane (30 m × 0.25 mm × 0.25 μm) and the software was GC/MS Lab Solutions, version 2.71 (Shimandzu, Fukushima, Japan) and EGA/Py 3030Ex (Frontier Laboratories, Fukushima, Japan). Pyrolysis was performed at the optimum degradation temperature (T_max) that was received from EGA analysis for each sample, and in all measurements the temperature program lasted 40 min. The detailed description of the GC program can be found in [26]. The obtained chromatograms were analyzed with Shimadzu post-run software and the NIST 17 library was used to identify pyrolysis products.

The objective of this technique was twofold: determination of the pyrolysis products (monomers and possibly secondary valuable products) and identification of the polymers present in the unknown samples gathered from WEEE (along with the FTIR, EGA and DSC results).

2.2.3. Soxhlet Extraction Method

Soxhlet extraction was applied as an environmentally friendly method for the debromination of the samples that comprised bromine, according to the XRF results. Two extractive solvents, isopropanol and butanol, were explored for their debromination efficiency. The extractive temperature was based on the boiling point of the solvents, and the extractive time was 6 h. A soxhlet apparatus was used and the solid sample (brominated plastic waste) was put into the thimble, while the spherical flask was filled with the appropriate amount of each solvent. During every soxhlet extraction, the ratio of solid waste/solvent was 1/100. The conditions were selected based on the findings of [12].

3. Results

3.1. Chemical Characteristics of the Samples—FTIR Results

In Figure 1 there are presented the FTIR spectra for all samples examined. As noticed, in all cases two (strong in most cases) peaks within the range of 2846–2940 cm⁻¹ were received. These peaks are attributed to the C–H bond. Additionally, peaks within the range of 1450–1600 cm⁻¹, which are due to the aromatic double bond C=C, were presented. The aforementioned peaks are typical of either styrenic polymers (such as ABS or HIPS) or PC that are very common in WEEE plastics [27,28]. In some cases, for instance RC4 and RC5 samples, a strong peak at ~2290 cm⁻¹ was obtained, which is due to the acrylonitrile units in ABS, proving that these are ABS samples. In other cases, such as in case of the MP sample, a peak at ~1760 cm⁻¹ was observed, which is typical of the C=O bond and is indicative of polyesters, such as PC. These observations played an important role in the identification of the polymers present in the unknown plastic waste samples.

3.2. Thermal Characteristicsof the Samples—EGA Results

In Figure 2 all EGA curves are presented for all samples examined in this work. As it is shown in each case only one degradation peak is observed witnessing a one-step degradation mechanism. EGA analysis enabled the estimation of the initial, maximum and final degradation temperatures for all samples. Pyrolysis was held at the maximum degradation temperature—T_max (

Table 2. T_max for all samples examined according to the EGA results and initial bromine content according to the XRF analysis (mean and standard deviation).

Sample Name	Tmax (°C)	Bromine Content (ppm)
MS	443	2630 ± 154
KB	394	0
RC1	433	0
RC2	436	0
RC3	439	1100 ± 69
RC4	432	0
RC5	434	2300 ± 131
MP	489	0
WP	426	0
EP	432	n.a. *
VENT	420	0
IR	523	0
PL	517	0
LAM	459	0

* Not analyzed because of its size.

) of each sample estimated from the peak of the EGA curves shown in Figure 2. As it can be seen, in all cases tested (with the exception of the sample KB) the maximum degradation takes place at high temperatures, greater than ~400 °C.

3.3. XRF Results and Debromination Efficiency

Table 2 also presents the initial bromine content of all samples examined, according to the XRF analysis that was applied. It was found that 23% (3/13) of the samples comprised bromine, which is due to the presence of BFR in the plastics from WEEE. The fact that some samples contained bromine while others did not may be attributed to various reasons, such as their different use, differences in their composition and the year of manufacturing [23]. Furthermore, the possible co-existence of other flame retardants, apart from the BFR, may play an important role in the results [23]. According to XRF, almost all samples (except for MS and LAM) contained chlorine and almost all of them (except RC2 and RC3) comprised phosphorus. Therefore, they possibly contain chlorinated and phosphorus-based flame-retardants, respectively.

As already mentioned, the brominated samples (MS, RC3 and RC5) were subjected to soxhlet extraction with isopropanol and butanol and were finally analyzed by XRF for the estimation of their debromination efficiency. In

Table 3. Bromine content (mean and standard deviation) and bromine reduction, according to the XRF analysis, after the soxhlet extractions with isopropanol and butanol.

Sample Name	Solvent: Isopropanol		Solvent: Butanol
	ppm Br	% Br Reduction	ppm Br	% Br Reduction
MS	729 ± 42	72	408 ± 22	85
RC3	428 ± 25	61	BDL *	100
RC5	669 ± 40	71	654 ± 37	72

* BDL: below detection limit.

, the bromine content measured, along with the bromine reduction that was achieved after the Soxhlet extractions with isopropanol and butanol, are presented. It should be highlighted that in all cases (different samples and solvents), great debromination results were noticed, showing that all solvents have good debromination efficiency. Butanol seems to be the optimal solvent that presents higher bromine reduction in each case. The latter observation follows the results obtained during our previous work [12]. Since both alcohols present similar properties, the higher tendency of butanol to dissolve and extract bromine could be attributed to its higher boiling point (near 118 °C) compared to isopropanol (i.e., 82 °C). Extraction takes place in boiling solvents, so the higher temperature employed when using butanol may result in better extraction of bromine from the plastics. It should be highlighted that the findings are very encouraging, since they prove that Soxhlet extraction using alcohols, which are environmentally friendly solvents, may be a solution for the debromination of plastics from WEEE.

3.4. Thermal Pyrolysis Results

Figure 3 presents the chromatograms obtained after the thermal pyrolysis of the samples, at the T_max estimated by the EGA results. In

Table 4. Pyrolysis products of all samples examined.

Peak	Retention Time (min)	Compound
KB (computer peripheral equipment)
1	0.59	Acrylonitrile
2	0.96	Methyl methacrylate
3	2.40	Styrene
4	12.70	2-Heptenoic acid, 7-(methylenecyclopropyl)-, methyl ester
5–6	14.50; 14.73	2-Methyl-4-phenyl-butyric acid, methyl ester
7	15.36	Pentadecanoic acid, 14-methyl-, methyl ester
8	15.59	Cyclohexane, 1-ethenyl-3-methylene-5-(1-propenylidene)-
9	15.86	1,6-Heptadiene, 2-methyl-6-phenyl-
MS (computer peripheral equipment) and RC2 and RC3 (remote controls)
1	3.00	Styrene
2	13.41	3-Butynylbenzene
3	20.22	Cyclohexane, 1,3,5-triphenyl-
RC1, RC4 and RC5 (remote controls); WP and EP (telephones and accessories); and VENT (miscellaneous household equipment)
1	2.92	Styrene
2	8.97	Propanedinitrile, (1-methylethenyl)(phenylmethyl)-
3	13.41	3-Butynylbenzene
4	15.01	4-Isopropylphenylacetonitrile
5	17.33	7-Ethyl-1,3,5-cycloheptatriene
6	17.78	4-Isopropylphenylacetonitrile
7	18.02	[1-(3-Phenyl-3-butenyl)cyclopropyl]benzene
8	20.07	Cyclohexane, 1,3,5-triphenyl-
MP (telephones and accessories) and IR (miscellaneous household equipment)
Peak	Retention Time (min)	Compound
1	8.61	Phenol, p-tert-butyl-
2	15.25	Phenol, 4-(1-methyl-1-phenylethyl)-
3	18.40	Bisphenol A
4	20.03	Cyclohexane, 1,3,5-triphenyl-
PL (miscellaneous household equipment)
1	4.38	Phenol
2	7.67	p-Isopropylphenol
3	8.53	Phenol, p-tert-butyl-
4	8.89	2-(2-Propenyl)-phenol
5	18.49	Bisphenol A
LAM (miscellaneous household equipment)
1–3	8.16; 8.38; 10.90	1-Undecene, 7-methyl-
4	11.74	Cyclohexane, 3-ethyl-5-methyl-1-propyl-
5–7	13.34; 13.65; 13.98	1-Undecene, 7-methyl-
8	14.09	Cyclohexane, 1,1′-(1,2-dimethyl-1,2-ethanediyl)bis-
9–10	15.50; 15.76	Cyclooctacosane
11	16.22	Cyclopentane, 1,2-dibutyl-
12	18.16	Cyclohexane, 1,3,5-trimethyl-2-octadecyl-
13–14	19.92; 21.56	Cyclooctane, 1-methyl-3-propyl-
15	23.08	Cyclohexane, 1,3,5-trimethyl-2-octadecyl-
16	24.49	Cyclooctane, 1-methyl-3-propyl-
17–19	25.81; 27.18; 29.07	1-Cyclopentyleicosane

, the pyrolysis products of all samples examined, from all the categories (computer peripheral equipment, remote controls, telephones and accessories, and miscellaneous household equipment) are presented in detail.

According to Table 4, after the thermal pyrolysis of the KB sample (computer peripheral equipment), the monomers methyl methacrylate, along with styrene and acrylonitrile, were obtained, proving the co-existence of poly(methyl methacrylate) (PMMA) and of ABS. The presence of PMMA is also verified by the formation of various methyl esters [29]. Regarding the second sample of the category “computer peripheral equipment”, MS (Table 4), it seems to be a HIPS sample, since the monomer styrene is received, along with other aromatic hydrocarbons, such as cyclohexane, 1,3,5-triphenyl-(styrene trimer), and in the meantime, no nitrogenated compounds were formed, excluding the possibility of being an ABS sample.

The next category of the samples studied included “remote controls”. Among them, RC2 and RC3 (Table 4) were found to be HIPS samples, since their thermal pyrolysis led to the formation of the same products that were received after the thermal pyrolysis of MS. On the other hand, RC1, RC4 and RC5 were identified as ABS samples due to the formation of nitrogenated compounds (e.g., 4-Isopropylphenylacetonitrile, etc.), along with the monomer styrene and other aromatic hydrocarbons. It should be reported here that, in the case of RC5, a peak at 15.54 min was also obtained, which is attributed to benzene, (1-methylenebutyl)-.

Moving on to the next category, “telephones and accessories”, it was observed that the samples WP and EP were ABS samples since their pyrolysis led to the aforementioned products, styrene (monomer), other aromatic hydrocarbons and nitrogenated compounds as well. On the other hand, MP consists of PC, since, as observed in Table 4, various phenolic compounds were formed, such as bisphenol A (monomer).

With regard to the last category, “miscellaneous household equipment”, IR and PL samples (Table 4) were PC samples, since bisphenol A and other phenolic compounds were obtained. On the other hand, VENT and LAM samples consisted of other polymers. Specifically, the pyrolysis products of VENT included styrene (monomer) and acrylonitrile (monomer) at 2.9 min, other aromatic hydrocarbons and nitrogenated compounds, characterizing it as an ABS sample. The LAM sample, on the other hand, seems to be a PP sample, since non-aromatic hydrocarbons were formed, such as 1-Undecene, 7-methyl- and Cyclohexane, 1,1′-(1,2-dimethyl-1,2-ethanediyl)bis-, which are produced during the pyrolysis of PP [26].

3.5. DSC Results

All samples were analysed by DSC, and it was observed that one T_g was obtained, except for sample LAM. For instance, in the case of the category “computer peripheral equipment”, for sample MS, which consists of HIPS, one T_g was received, and in the meantime one T_g was also received in the case of the KB sample that was found to be a blend of ABS/PMMA.

On the other hand, in the case of the LAM sample (miscellaneous household equipment), the DSC thermograms verified the fact that it is a PP sample, since during the second heating cycle a strong peak at 160 °C was received, which is due to its melting point, and during the cooling cycle it was found that its T_c was at 113 °C.

As a result, the identification of the polymers present in the unknown plastic samples (

Table 5. Final identification of the polymers present in the samples.

Sample Category	Samples	Sample Name	Polymer Type
Computer peripheral equipment	Mouse	MS	HIPS
	Keyboard	KB	ABS/PMMA
Remote controls	Television remote	RC1	ABS
	Television remote	RC2	HIPS
	Television remote	RC3	HIPS
	Television remote	RC4	ABS
	PlayStation remote	RC5	ABS
Telephones and accessories	Mobile phone	MP	PC
	Wireless phone	WP	ABS
	Earphones	EP	ABS
Miscellaneous household equipment	Bathroom ventilator	VENT	ABS
	Iron	IR	PC
	Plug	PL	PC
	Lamp	LAM	PP

) was finally achieved, based mainly on the products formed during the pyrolysis of the samples, and on the FTIR, EGA and DSC results.

4. Conclusions

This work investigated the possible valorization of various plastics gathered from waste electric and electronic equipment (WEEE) via thermochemical recycling and, especially, pyrolysis. Soxhlet extraction was explored as a pretreatment method before the pyrolysis of the samples, for the removal of brominated compounds that are often present in the plastic waste. During this study, 14 plastic samples from different categories: computer peripheral equipment, remote controls, telephones and accessories, as well as miscellaneous household equipment, were collected and analysed by various techniques, such as FTIR, for the identification of the polymers that comprised each sample, since they were unknown. They were also analysed by XRF analysis to find which samples contained bromine, due to the presence of brominated flame retardants (BFR). Finally, the brominated samples were subjected to soxhlet extraction using alcohols (butanol and isopropanol), which are environmentally friendly, as the extractive solvents.

It was found that 23% of the samples contained bromine, and therefore BFR. The variations regarding the absence or presence of bromine in the examined samples could be attributed to several reasons, such as the differences in their composition, the year of their manufacturing, as well as the co-existence of other flame-retardants, apart from the BFR. Results showed that both solvents were efficient in reducing the bromine content of the samples, since in both cases the bromine reduction was greater than 60%. Nevertheless, butanol seems to be the optimal solvent, since it led to better debromination results in all cases studied, reaching an almost complete removal of bromine in the case of the sample RC3. This observation is of significant importance, and is very promising too, since it displays the great debromination efficiency of Soxhlet extraction and may provide insights for future work that explores the debromination of plastics gathered from WEEE, enabling the recycling of the polymers. Nevertheless, for better accuracy, additional research and sampling are needed.

All samples were subjected to pyrolysis to obtain monomers or other useful products. In all cases, monomers were received, such as styrene or bisphenol-A, depending on the polymer that comprised each sample. Additionally, other valuable compounds were formed during pyrolysis, including, for example, various aromatic hydrocarbons and/or nitrogenated compounds, etc., depending again on the sample examined. These results proved that pyrolysis is a fruitful method for the recycling of plastics from WEEE. Finally, yet importantly, based on the products formed, along with the results of all methods applied (FTIR, EGA, DSC), all samples were identified. It was found that most of them (6/14) were ABS samples, while the rest of them were HIPS (3/14), PC (3/14), PP (1/14), or a blend of ABS/PMMA (1/14).

In summary, the results of this work showed that the application of Soxhlet extraction before recycling, via pyrolysis, of plastics from WEEE may be considered as a solution for the handling of the large volumes of brominated plastics from WEEE generated. The efficiency of both methods (Soxhlet extraction as the pretreatment and pyrolysis as the recycling method) was great, since bromine was reduced a lot, almost removed, and pyrolysis enabled the recovery of monomers and other important products. However, future research is needed in an attempt to scale up this project by applying it to a larger number of samples, on a larger scale and evaluating its efficiency.