Recycling of Polycarbonate/Acrylonitrile Butadiene Styrene Blends with Flame Retardant Additives for 3D Printing Filament

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Introduction
Recycling of plastic waste plays a signifcant role in circular economy and sustainability practices [1].Recycling plastic is helpful for resource efciency by lowering the need for new raw materials, thereby addressing resource scarcity and promoting sustainability [2,3].Plastic recycling can also help mitigate environmental pollution and improve waste management processes [4].Recycled plastics are valuable materials covering a wide range of applications in everyday life and can be found everywhere, from households to industry.Vital economic activities as diverse as packaging, construction, transportation, healthcare, and electronics depend heavily on plastics as raw materials [5].Due to the considerable increase of waste from electrical and electronic equipment (WEEE) in the world each year, further eforts have been made to recycle materials.Te management of electronic waste (e-waste) is a signifcant topic for consideration on the circular economy agenda [6].Studies carried out in 2016 show that on a global scale, 15 million tons of waste from the total WEEE was occupied by plastic materials [7,8].Disposable plastic materials are commonly used in printer machines, and the generation of solid waste is substantial due to their short life cycle [9,10].Of the total WEEE, 25% is occupied by plastic materials, from which a signifcant share was taken by waste PC-ABS blends [11].To overcome the problem, recycling waste plastic materials was taken as the best option.Several advantages will be obtained through the recycling of materials [12].Recycling metals from WEEE requires signifcantly less energy compared to virgin metal production, leading to lower greenhouse gas emissions and reduced pressure on the energy grid [13].Te constant evolution of electronic devices necessitates continuous adaptation of recycling technologies to handle new materials and components [14].Te development and marketing of recycled plastic extruders, which produce 3-D printing flament from recycled materials, have signifcantly broadened the range of materials available for prosumer 3-D printers [15].Additionally, WEEE also holds expensive materials, including rare earth metals, and recycling ofers the possibility of reusing these materials again.Plastic recycling can be done either energetically, chemically, or mechanically [16].
Nemours researchers developed 3D printing flament from recycled plastics such as high-density polyethylene [17], polypropylene [18], and polyethylene terephthalate [19].Te most used materials in fused deposition modeling (FDM) are Acrylonitrile Butadiene Styrene (ABS), polylactic acid (PLA), and polycarbonate (PC) [20][21][22], ABS/Silicon [18].Dani et al. conducted a study on the ABS polymeric material derived from the computer cover and examined its recycling process under various processing conditions.Te fndings suggest that a signifcant decrease in impact strength was observed, likely attributable to the molecular crosslinking and chain fragmentation within the rubber component [23].Imbernon et al. investigated on reprocessing of fame-retardant additive-free pellet PC-ABS using an injection molding process.Te fndings showed that the tensile properties of products were signifcantly afected by the product cycle [24].Woern et al. discovered that recycled waste plastic has the potential to be transformed into flament for 2.5 cents per kilogram, making it signifcantly less expensive compared to the commercial flament.Tis process involves producing flament from polymers with extrusion temperatures below 250 °C, allowing for the creation of customized flament using various homopolymers and composites.Tis development has signifcant implications for material science research, recyclability studies, and exploring new applications of fused flament-based 3-D printing [25].
Chiu et al. investigated the characterization of a PC/ ABS blend over 20 reprocessing cycles and the subsequent restoration of its functionality using virgin additives.Te recovery of the waste material, which had been reprocessed 20 times, was accomplished by introducing approximately 30% (by weight) of virgin PC and ABS, along with 1.5% (by weight) of a chain extender and 2% (by weight) of styrene maleic anhydride, simultaneously [26].Cafero et al. analyzed WEEE plastics and their potential for 3D printing flaments.Tey found that plastic is the most challenging fraction of WEEE to manage, and the market for recycled plastics from WEEE is limited.WEEE samples showed good similarity to virgin polymers with fewer halogens and inorganic fllers.Test objects printed with WEEE flaments showed no signifcant deviation from model design compared to commercial flaments [27].Chawla et al. fabricated fused flaments for the FDM technique of additive manufacturing from recycled ABS by using a twin-screw extruder.Termal analysis performed to estimate the heatcarrying capacity of recycled ABS highlighted that the heat capacity of ABS increases signifcantly from 0.28 J/g to 3.94 J/g during the heating cycle [28].Oliveira et al. tested how recycled ABS (rABS) from e-waste was mixed with virgin ABS (vABS) at various ratios for 3D printing flament application.Diferential scanning calorimetry revealed that the glass transition temperatures for vABS/ rABS blends were between those of vABS and rABS.Torque rheometry investigation revealed that the addition of rABS did not afect the processability of vABS.Increased rABS content up to 50 wt% resulted in higher impact strength (IS) in 3D printed samples [29].Mishra et al. produced and analyzed 3D printing flaments made from recycled/virgin ABS mixes, and the results revealed that the breakdown of the styrene-acrylonitrile and butadiene components in ABS induces strain hardening and material stifening.Te 80% rABS/20% vABS flament has a Young's modulus of 2329 MPa, yield strength of 34.814 MPa, and ultimate tensile strength of 40.82 MPa, similar to vABS flament [30].
1.1.Research Objective.As technology advances, the volume of electronic plastic waste, such as PC-ABS waste, is increasing.However, the correct recycling methods and applications for this waste are still a matter of concern.In particular, the mechanical recycling of waste PC-ABS mixes with fame-retardant additives for 3D printing applications has not yet been thoroughly investigated.Terefore, the primary focus of this research is to study the mechanical recycling of waste polycarbonate/acrylonitrile butadiene styrene blends with brominated fame-retardant additives (PC-ABS-FR), a topic of signifcant importance in the feld of plastic waste recycling.

Materials.
A scrap of waste PC-ABS-FR with product code RC3-0794 and material code > PC + ABS-FR (40) <#1 or in short symbol PC-ABS-FR (GL) Moreover, dark black color waste PC-ABS-FR with product code RC3-0792 and material code > PC + ABS-FR (40) <#1 or explained in short form as PC-ABS-FR (DB) materials were selectively taken from HP printer hardware cover from waste printer store.

Waste Preparation and
Recycling.Te procedure that was utilized for the characterization of PC-ABS-FR consists of sorting of blends, cleaning or washing of sorted material for removal of organic and inorganic contaminants, size reduction (fake production), plastic processing (remelting), and sample preparation for characterization.Material identifcation was done by looking at the tag/trademark stamped on the surface of the sample, and further approval was performed using FTIR analysis.Following the identifcation of the materials, cleaning was carried out using 300 g detergents to remove the surface impurities of the samples.Finally, washed samples were placed in an oven at 50 °C temperature for drying and, successively, to prepare for size reduction, obtaining approximately 7-10 mm fakes in order to continue analysis (see Figure 1).

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Journal of Engineering

Extrusion of Recycled Granules and Filament
Manufacturing.Termo-Hake PTW16 intermeshing corotating twin screw extruder with a screw diameter of 16 mm and die diameter of 3 mm was used for the extrusion of fakes of waste PC-ABS-FR samples (Figure 2(a)).Te processing temperature was regulated in order to obtain a fnal diameter of the extruded flament of 1.75 ± 0.10 mm targeted for 3D printing application.Extrusion analysis of PC-ABS-FR (GL) and PC-ABS-FR (DB) was carried out.However, because of poor results obtained through many trials, only PC-ABS-FR (GL) extruded flament products were reported in Figure 2(b).

Extruded Filament Analysis.
Te chemical composition, functional groups, and thermal and mechanical properties of recycled plastic materials were assessed using EDX, FTIR, TGA, DSC, and tensile strength tests.Tese evaluations play a critical role in determining the quality and characteristics of recycled plastic products [31,32].

FTIR Analysis. FTIR analysis was measured using
Perkin Elmer ATR-FTIR Spectrum diamond-covered refection to characterize functional groups of the PC-ABS blend.Here, the identifcation of samples was done by directing infrared rays toward the sample and looking at the vibration of their chemical compounds.Te scan was done between 4000 cm −1 and 600 cm −1 averaged for each spectrum at intervals of 1 cm −1 with a resolution of 4 cm −1 .

EDX (Energy Dispersive X-Ray Analysis
). Analysis of the chemical composition of waste PC-ABS-FR plastics was carried out by using an SEM Jeol IT300 instrument.It is done to detect compositions of toxic and environmentally hazardous elements that may originate from additives added during the manufacturing of products.

TGA (Termo-Gravimetric Analysis).
Weight loss as a function of the temperature of waste PC-ABS-FR plastics was analyzed using a Q5000 IR thermos-gravimetric analyzer.Sample weight of 10 mg waste PC-ABS -FR was taken, and analysis was done with an airfow rate of 15 ml/min, and temperature ranging from RT to 700 °C at the rate of 10 °C/ min was used during analysis.Intersections of the two tangent lines were taken, and the onset of degradation temperature was evaluated.

DSC (Diferential Scanning Calorimetry).
Heat fow into and out of the system as a function of the temperature of samples was evaluated using a Mettler DSC 30 Swiss Mettler Toledo calorimeter.During the test, 10 mg of samples of plastic were taken, and a nitrogen fow of 100 ml/min was applied.Meanwhile, the glass transition temperature (Tg) of waste PC-ABS-FR samples was measured by taking thermogram infection points.

EDX Analysis Results
. After taking 20 mg waste PC-ABS-FR samples and performing EDX analysis, elemental compositions were presented.As shown in Figure 4 and Table 1, waste PC-ABS-FR (GL) contains more bromine, i.e., 0.96%, in comparison to PC-ABS-FR (DB), which is 0.07%.However, PC-ABS-FR (DB) contains more titanium (0.06%) and phosphorus (0.49%) compared to PC-ABS-FR (GL), according to the European directive (12).Te threshold value for toxic elements, particularly Cd, Br, Cr, Ti, P, and Hg, must be 0.1% for recycling.Te chemical compositions of toxic elements in samples are below the minimum threshold level, and the recyclability of waste samples is not afected [33].

TGA Analysis Result.
From the thermogram, taking the intersection of the two tangent lines, the onset of decomposition of the two samples, namely, PC-ABS-FR (DB) and PC-ABS-FR (GL), was analyzed, and the fnal result is indicated in Figure 5. Two-stage thermal degradation peaks have been seen in both PC-ABS-FR (DB) and PC-ABS-FR (GL).In the case of PC-ABS-FR (DB), the frst degradation starts at 200 °C and ends at 473 °C.However, the second 2nd stage degradation starts from 475 °C and ends at 550 °C.On the other hand, in the case of PC-ABS-FR (GL), the frst phase degradation starts at 225 °C and ends at 425.5 °C.However, the 2nd stage degradation takes place between 425.5 °C and 550 °C.In both cases, the frst phase degradation corresponds to the degradation of ABS, and the 2nd phase degradation corresponds to the degradation of the PC component [34][35][36].Further decomposition has been seen in both samples, starting from 550 °C to 675 °C.Tis further decomposition may have been expected to be the decomposition of additives added during plastic manufacturing.Te onset degradation temperature of both wastes of PC-ABS blends is around 50% lower than the pellet one, and it is expected to be the efect of aging of materials.Since the melting temperatures of ABS and PC plastics are approximately 200 °C and 475 °C, respectively [37,38], from a thermal resistance point of view, recycling of waste PC-ABS-FR(GL) sample is comparatively more acceptable.

DSC Analysis Result.
Figure 6 shows the DSC analysis of PC-ABS-FR (GL) and PC-ABS-FR (PL) samples of thermograms.Te thermal transition results of the two samples are reported in Table 2. From the frst heating thermograms of PC-ABS-FR (GL) and PC-ABS-FR (PL), two peaks were diferentiated from each item, i.e., at 104 °C and 151 °C from PC-ABS-FR (GL) and at 114 °C and 158 °C from PC-ABS-FR (PL) which corresponds to the glass transition temperature of ABS and PC phases, respectively, and the result was noted by taking the midpoint of infection.However, in the second scan, heating thermal transitions were seen between 95 °C and 112 °C in PC-ABS-FR (GL) and PC-ABS-FR (PL), respectively.Tis transition is expected to be the glass transition of the ABS phase of samples remaining from the frst scan.Here, the onset of the glass transition temperature of ABS in the second scan is 5-10% lower than the pellet one, which is 100-105 °C [39].A designer has to take this reduction into account during product design.On the other hand, the glass transition temperature was seen during the cooling scan, and it is expected to be the glass transition of additives added during product manufacturing.Finally, the glass transition temperature of PC-ABS-FR (GL) is nearly consistent with the glass transition temperature of version (pellet) samples; recycling is expected to be acceptable.

Cone Calorimetry Analysis.
Cone calorimeter analysis results of PC-ABS-FR (GL) and PC-ABS-FR (DB) were reported in Table 3. Te cone calorimeter result confrms that the two waste PC-ABS blends consist of brominated fame retardants with Sb 2 O 3 + TiO 2 .

Melt Flow Analysis.
Table 4 shows the melt fow of control and recycled plastics (PC-ABS-FR (DB) and PC-ABS-FR (GL)).Te test was carried out according to the ASTM D1238-A standard using a melt fow rate in g/10 min, temperature of 260 °C, and load of 2.16 kg for three samples, namely, PC-ABS-FR (DB), PC-ABS-FR (GL), and PC-ABS-FR (PL).Te melt fow rate of waste PC-ABS-FR (GL) and PC-ABS-FR (DB) samples shows approximately 3.5% higher melt fow rate in comparison with PC-ABS-FR (PL).Since the viscosity of amorphous polymers was primarily infuenced by the age of the materials (20), the slight increase     Journal of Engineering in the melt fow rate of waste PC-ABS-FR samples mainly corresponds to the aging efect of materials.Tis increase in the melt fow rate can be adjusted by controlling process parameters such as temperature and operating time.
Table 5 shows the linear density, diameter, and productivity of 3D printer flament made from PC-ABS-FR (GL).Similar temperature settings were used during the extrusion of both PC-ABS-FR (DB) and PC-ABS-FR (GL), and the setting was adjusted according to the extrusion temperature setting for PC-ABS blends [40].Here, the initial temperature setup (T 1 ) was modifed by looking at results obtained after the frst and second trials.A gradual increase in melting temperature was carried out in order to get flaments of uniform and suitable diameter for 3D printing applications.Normally, a uniform and 1.75 ± 0.1 mm diameter flament is recommended for 3D printing applications [41].Finally, the PC-ABS-FR (DB) samples do not have a regular cross section, and there is no continuity in flaments.However, PC-ABS-FR (GL) shows the best cross-sectional homogeneity and continuity during flament production.

Mechanical Properties of 3D Printer Filaments.
Tensile strength and modulus analyses of recycled compression molded PC-ABS-FR samples were carried out by using an Instron 5969 electromechanical testing machine with a 50 KN load cell and stress-strain curve, which is reported in Figure 7 and Table 6.
Young's modulus of tensile dumbbell-shaped plastic products was carried out by taking the frst linear segment (slop) of the stress-strain curve through a linear ftting   Journal of Engineering procedure [42].As a result, as indicated in the result section, the tensile strength of PC-ABS-FR (GL) is comparatively better than PC-ABS-FR (DB).Since the tensile strength and modulus of PC-ABS primarily depends on the ratio of mix of PC to ABS and the anisotropic nature of the product, this diference in tensile strength and modulus of products were expected to be primarily anisotropy and mix ratio beyond efects of processing machine, molding process, orientation, and properties of fed materials.Table 7 presents the statistical analysis of the mechanical properties of recycled 3D printing flaments.Te result of the analysis of variance (ANOVA) indicates that the tensile modulus, tensile strength, and extension of the two types of samples displayed statistically signifcant diferences, with P values of 0.002, 0.003, and 0.001, respectively, at a signifcance level of 0.05.
Te 3D printing flaments that were produced were compared to those available commercially and those previously published.Te results are presented in Figure 8.It was found that the flament made from recycled PC-ABS-FR (GL) exhibited a higher strength of 52 MPa, which is comparable to most reported results except for PLA, which had a strength of 65 MPa.Additionally, the tensile strength of the PC-ABS-FR (DB) sample was better than the reported results of PP, HIPS (Blue), and Nylon-618 flaments.In conclusion, the 3D printing flaments made from PC-ABS-FR electronic waste demonstrated mechanical properties that were comparable to both virgin and recycled flaments.

Conclusions
Te main aim of this work was to investigate the mechanical recycling of two specifc waste PC-ABS blends, namely, PC-ABS-FR (DB) and PC-ABS-FR (GL), through chemical (FTIR, EDX), thermal (TGA and extrusion) and mechanical such as tensile strength and modulus analysis.In this study, the recyclability of the two waste samples was checked by using the same process parameters and machine.Te waste PC-ABS blends are thermoplastic polymers, and their applications were always designed far below the glass transition temperature; the results of TGA and DSC analysis of the two samples were acceptable for recycling waste materials.However, during extrusion, waste PC-ABS-FR (DB) shows high diametrical homogeneity and melts fow ability.In this regard, the material is not suitable for flament production.On the other hand, PC-ABS-FR (GL) shows a prominent result during extrusion, which is 1.8 ± 0.03 mm; the product was suitable for 3D printing of products, particularly children's toy cars.In general, light gray color waste PC-ABS-FR, having product code RC3-0794 and material code > PC + ABS-FR (40) <#1 or symbolized as PC-ABS-FR (GL) in this paper, are promising materials with better melt fow ability and cross-sectional uniformity for 3D printing of a variety of products.
During measurement, the barrel length of 162 mm, barrel diameter of 9.55 mm, die length of 8.0 mm, die diameter of 2.096 mm, load of 5 kg, sample weight of 5 g, and melting temperature of 200 °C were used for analysis of both PC-ABS-FR items.Five test replicates were taken in each type of plastic.
2.4.5.Cone Calorimetry Analysis.Cone calorimeter analyses of waste PC-ABS-FR plastics were performed to verify the existence of fame-retardant additives within the samples.Here, material fammability parameters, namely, time to ignition (TTI), heat release rate (HRR), peak heat release rate (PHRR), total heat release (THR), and fnal mass of samples, were analyzed beyond verifcation of fame-retardant additives.2.4.6.Melt Flow Index Analysis.Melt fow index analysis (MFI) of PC-ABS-FR plastics was done using Kayeness Capillary Rheometer (Model 4003DE, Morgantown, PA, USA) according to the ASTM D1238 standard.

Table 1 :
Elemental analysis results of PC-ABS-FR samples.

Table 3 :
Cone calorimetry analysis results of PC-ABS samples.

Table 4 :
Melt fow analysis results of PC-ABS-FR samples.

Table 6 :
Tensile strength and extension of recycled PC-ABS-FR flaments.