Separation Of Polyvinyl Chloride Research Articles

Recent Studies and Technologies in the Separation of Polyvinyl Chloride for Resources Recycling: A Systematic Review

Material recycling and thermal treatment are the two most common recycling methods employed for plastic waste management. Thermal treatment for energy recovery is more widely applied compared with material recycling because the latter requires a high efficiency of separation and a high purity of products. Unfortunately, certain plastics like polyvinyl chloride (PVC) are unsuitable for thermal treatment because they contain additives like chloride (Cl−) that have adverse effects on refractory materials used in boilers. As a result of this, mixed plastic wastes containing PVC generally end up in landfills. PVC-bearing mixed plastics, however, remain valuable resources as championed by the United Nation Sustainable Development Goals (UN-SDGs): Goal 12 “Responsible production and consumption”, and their recycling after the removal of PVC is important. In this paper, recent studies (2012–2021) related to the separation of PVC from other types of plastics were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 66 articles were selected, reviewed, and summarized. The results showed that various separation technologies conventionally applied to mineral processing—selective comminution, gravity separation, magnetic separation, electrical separation, and flotation—have been studied for PVC separation, and the majority of these works (>60%) focused on flotation. In addition, more advanced technologies including sorting and density-surface-based separation were introduced between 2019 and 2021.

Flotation separation of hazardous polyvinyl chloride towards source control of microplastics based on selective hydrophilization of plasticizer-doping surfaces

As the single largest chlorine source of plastics, hazardous polyvinyl chloride (PVC) has become an increasing environmental concern with the rapid microplastics accumulation. An advanced separation method is advocated to purify waste PVC plastics, optimize physical recycling, and protect aquatic and terrestrial environment safety. In this study, we proposed a novel scheme for the flotation separation of PVC plastics with diverse plasticizer contents (PVCs) via regulating hydrophilicity based on a selective ferric deposition. Rigid PVCs were prone to loading ferric ions and generating hydrophilic shells than flexible PVCs. Plasticizers can diffuse freely through the interior and surface of PVC plastics. Abundant plasticizers thereby overlaid the surface of flexible PVC and shielded PVC matrix from ferric ions. By regulating the ferric concentration, the wettability of PVCs was adjusted to separate rigid and flexible PVCs by froth flotation. Waste PVCs could also be separated from each other through the compound process of ferric deposition and flotation, further confirming its feasibility and stability. Thus far, this study supplies distinctive insights into the wettability regulation of plasticizer-doping PVC surfaces, contributes a pioneering hydrophilization method to PVCs separation and recycling, and mitigates hazardous PVC microplastics by source control.

Surface treatment with peroxymonosulfate for flotation separation of waste polyvinylchloride and acrylonitrile-butadiene-styrene: Optimization and mechanism

Polyvinylchloride (PVC) and acrylonitrile-butadiene-styrene (ABS), as common components in waste plastic, are hard to separate due to similar physical and chemical properties, which limits plastic recycling and cleaner production. In this research, a novel approach by using peroxymonosulfate (PMS) was established to modify waste PVC and ABS surface, and separation was successfully realized in flotation process. Key variables closely related to PMS oxidation capacity, namely pH, temperature, and concentration were confirmed through single parameter experiments. Subsequently, response surface methodology (RSM) using Box-Behnken design (BBD) was applied to optimize the above surface treatment conditions. A quadratic model was generated for predicting PVC purity (response value). Mechanism of surface modification was explored by Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). Results showed that the optimal conditions were PMS concentration of 0.026 mol/L, pH value of 9.0, and temperature of 65 °C, respectively. PVC can achieve 99.72% purity and 100.00% recovery, and ABS can reach 100.00% purity and 99.81% recovery in triplicate validation tests, respectively. Additionally, available ranges of particle sizes, mass ratios, and reuse of reagents further show the remarkable application potential of flotation combined with PMS treatment in separating waste PVC and ABS. The mechanism of surface treatment shows that oxygen-containing groups are introduced into ABS surface, enhancing the hydrophilicity of ABS, but PVC is almost unaffected and remains floating in flotation process. This study established a novel surface modification with RSM optimization and reliable mechanisms for the flotation separation of waste PVC and ABS.

Application of froth flotation in the separation of polyvinyl chloride and polycarbonate for recycling of waste plastic based on a novel surface modification

The complicated stream of waste plastic impedes the recycling of polyvinyl chloride (PVC) and polycarbonate (PC), which can be settled by flotation separation. We proposed a novel chlorine dioxide (ClO2) pretreatment to assist the separation of PVC and PC by froth flotation, and clarified possible surface reactions of hydrophilic PC by contact angles, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The hydrolysis and further rearrangement of carbonic esters (O(CO)O) may be deemed as the main reason for hydrophilic PC, introducing oxygenated functional groups, such as hydroxyl groups (COH), carboxyl groups (COOH), and tiny acyl chloride (ClCO), on PC surfaces. The robustness of this process was proved by efficient flotation separation of PVC and PC under various conditions of size fractions, frother concentration, mass ratio, and flotation time. The optimal pretreatment conditions for flotation separation of PVC and PC are temperature of 70 °C, ClO2 concentration of 0.5 g/L, and treatment time of 70 min. The optimal recovery and purity of PC in sunken plastic can stably maintain 97% and 99%, respectively. Compared with waste plastic, raw PC embraces a high floatability after ClO2 pretreatment, revealing that ageing is conducive to surface modification.

Separation of hazardous polyvinyl chloride from waste plastics by flotation assisted with surface modification of ammonium persulfate: Process and mechanism

Plastic separation becomes an effective method to improve the plastic recycling by concentrating a single component from complex plastic mixtures. Based on advanced oxidation process, surface modification assisted by ammonium persulfate ((NH4)2S2O8) was applied to selectively wet plastic surface, achieving the separation of hazardous polyvinyl chloride (PVC) from acrylonitrile butadiene styrene (ABS), polystyrene (PS), and polycarbonate (PC) in forth flotation. The mechanisms were investigated through contact angle, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), as well as scanning electron microscope (SEM). The floatability of PS, PC, and ABS reduces owing to the introduction of carbonyl (O = CO), hydroxyl (−OH), and amide (O = C–NH2) on plastic surfaces, which is the result of the oxidation by sulfate radical (SO4∙-) and the hydrolysis of nitrile group (CN) and butadiene (CC). Then, available reaction equations of ABS, PS, and PC were established to supplement the mechanisms of surface modification. The optimal conditions for flotation separation of PVC are (NH4)2S2O8 concentration 0.2 M, temperature 70 °C, pretreatment time 30 min, pH 10, flotation time 4 min, terpineol dosage 20 mg/L, and particle size 3–4 mm. The recovery and purity of PVC reach 100 % and 99.7 ± 0.2 % respectively, favoring the reuse of separated waste plastic.

Green flotation of polyethylene terephthalate and polyvinyl chloride assisted by surface modification of selective CaCO3 coating

Abstract Plastic flotation was a promising separation method for efficient recycling of waste plastics. Aiming to avoid the destruction of original surface and secondary pollution, a novel flotation process based on calcium carbonate (CaCO3) coating was proposed for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The mechanism of CaCO3 coating was researched via scanning electron microscope (SEM), X–ray photoelectron spectroscopy (XPS), X–ray diffraction (XRD), zeta potential, Fourier transformed infrared spectroscopy (FT–IR), and solution chemistry analysis. High polarity of C–Cl on PVC surface resulted in selective adherence of Ca2+ on PVC surface, and Ca2+ was a bridge between plastic surface and CaCO3 particles. The separation of PVC and PET was optimized by response surface methodology (RSM) combining Box–Behnken design (BBD). Optimal pretreatment conditions for flotation separation of PVC and PET were 0.11 g CaCO3, temperature 50.6 °C, treatment time 20 min, and pH 10.1. The purity and recovery of PVC could be 100% and 99%, respectively.

Surface treatment by the Fe(III)/sulfite system for flotation separation of hazardous chlorinated plastics from the mixed waste plastics.

A novel advanced oxidation process by a combination of Fe(III) and sulfite for surface treatment of waste plastic mixtures is proposed. The Fe(III)/sulfite system has been found to enhance hydrophilicity of the mixed waste plastics, including acrylonitrile butadiene styrene (ABS), polystyrene (PS) and polycarbonate (PC), while it has little effect on hazardous polyvinyl chloride (PVC), thus promoting separation of PVC from the mixed waste plastics by flotation. Radical scavenging experiments indicate that sulfate radicals are the main reactive species. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) results imply the formation of CO or CO groups on the treated plastics surface except for PVC and a plausible mechanism for oxidizing plastics with sulfate radicals is proposed. PVC with 100.00% recovery and 99.84% purity is achieved under optimum surface treatment conditions of sodium sulfite concentration 10 mM, ferric sulfate concentration 0.4 mM, pH 6.0, temperature 25 °C and treatment time 15 min. Consequently, surface treatment by the Fe(III)/sulfite system is an effective technology for separating hazardous PVC from the mixed waste plastics by flotation.

Separation of polyvinylchloride and acrylonitrile-butadiene-styrene combining advanced oxidation by S2O82−/Fe2+ system and flotation

A combining technology of advanced oxidation by S2O82−/Fe2+ system and flotation was proposed for separating polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS). In this research, sodium persulfate was activated by heating and ferrous ions. The separation efficiency of PVC/ABS oxidized by S2O82−/Fe2+ was higher than that by sodium persulfate. The mechanism of this process was investigated through contact angle, Fourier transform infrared spectroscopy (FT-IR) inductively coupled plasma (ICP), nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS). The floatability of ABS reduced owing to the introduction of oxygen-containing functional groups such as carbonyl (OCO) and hydroxyl (OH), which was a result of oxidation by sulfate radicals (SO4·-). The optimal conditions for separating PVC and ABS were: Na2S2O8 concentration 0.1 M, molar ratio (S2O82−/Fe2+) 200, treatment time 10 min, flotation time 4 min, frother concentration 14.7 mg L−1 and airflow rate 6.8 mL min−1. Novel kinetics of pretreatment time and flotation were proposed and researched in this work. The max rate constant of PVC/ABS flotation was 0.64 min−1. In addition, the pretreatment solution can be reused for three times with superior performance. The recovery and purity of PVC reached 100% and 99.7%, respectively. According to reasonable evaluation, the combination of S2O82−/Fe2+ advanced oxidation and flotation is a practical and efficient technology for separating PVC and ABS.

Novel method for sustainable and selective separation of PVC and PET by the homogeneous dissociation of H2O2 using ultrasonication

This paper presents a one-step selective separation of polyvinyl chloride (PVC) from PVC/PET mixture based on hydrophilicity building on the PVC surface using H2O2/ultrasonication. After the combined treatment, the decrease of PVC contact angle (from 87.2° to 71.5°) is consistent with the increase in hydrophilic functional groups that is evidenced by Fourier transform infrared and X-ray photoelectron spectroscopy results on the PVC surface. The H2O2/ultrasonic treatment generates oxidizing agent and increases hydrophilicity on the PVC surface, which allows to selectively separate the treated PVC by its submerging on the reactor bottom. Meanwhile, the treated PET is easily floated off because it is not affected by the combined treatment and still maintains the hydrophobic surface. The combined treatment of H2O2 and ultrasonic irrigation obtains 100% purity and recovery of the PVC separation under the optimum conditions. The optimized separation conditions are H2O2 concentration 3%, ultrasonic irrigation time 30 min and temperature 30 °C, floating agent concentration 0.4 mg/L and intermittent mixing at 50 rpm. Reusing of H2O2 is also feasible to save cost and environmental benefits. The combination of ultrasonication and H2O2 is an effective and inexpensive method for PVC separation to improve plastic recycling quality.

Sustainable hydrophilization to separate hazardous chlorine PVC from plastic wastes using H2O2/ultrasonic irrigation

Polyvinyl chloride (PVC) products comprise a large portion of plastic wastes and cause severe environmental burdens in thermal recycling such as toxic release and disposal difficulties. Selective separation methods for PVC containing hazardous chlorine are required for the development of suitable disposal or material recycling processes. However, separating PVC selectively from municipal plastic waste mixtures is difficult due to their similar hydrophobic surface and appearance densities. This study presents a one-step, selective separation technique for PVC using H2O2 solution under ultrasonic irrigation to promote the selective development of hydrophilicity only on the PVC surface. The combined treatment helped to decrease air bubbles attached on the PVC surface because of increased wettability, which allowed the treated PVC to settle on the bottom of the flotation reactor. However, the remaining plastic wastes were easily floated off because they maintained their hydrophobicity. The combined treatment with a low concentration of 3% H2O2 and ultrasonic irrigation for 30 min afforded 100% purity and recovery of the PVC separated from the municipal plastic waste mixture. This proposed treatment is therefore a promising and inexpensive way to improve plastic recycling quality through selective PVC separation by the selective development of hydrophilicity on its surface.

Separation of polyvinyl chloride from waste plastic mixtures by froth flotation after surface modification with sodium persulfate

A new method of surface treatment based on advanced persulfate oxidation technology is proposed for separation of plastics by froth flotation. By means of sodium persulfate treatment, waste plastic mixtures, including polyvinyl chloride (PVC), polycarbonate (PC) and polystyrene (PS), were selectively modified to achieve effective flotation separation. After sodium persulfate treatment, flotation percentage of PS and PC decreased significantly, while flotation percentage of PVC was not affected. The mechanism of sodium persulfate treatment was examined by contact angle, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The flotability reduction of PS and PC was in virtue of the increase of surface hydrophily. FT-IR analysis and XPS analysis demonstrated the introduction of oxygen-containing functional groups on the surface of PS and PC. The optimum conditions for separating PVC from plastic mixtures were sodium persulfate (Na2S2O8) concentration 0.1 M, temperature 70 °C, pH 10.5, treatment time 30 min, frother concentration 15.8 mg/L and flotation time 4 min. The impacts of particle size, mass ratio and reusability of Na2S2O8 solution were also studied. The results demonstrated that under optimum conditions, PVC was efficiently separated from plastic mixtures. The purity and the recovery of PVC were up to 99.77% and 100%. The proposed method is a simple, environmentally friendly and efficient way to promote the separation of PVC from waste plastic mixtures.

Validation of a deplasticizer–ball milling method for separating Cu and PVC from thin electric cables: A simulation and experimental approach

There is increasing demand in the electronics recycling industry for an effective method to separate polyvinyl chloride (PVC) and Cu from thin electric cable waste. Herein, a novel separation technique involving PVC embrittlement via plasticizer extraction and crushing by ball milling is proposed. The method was developed by varying the size, quantity, and hardness of the cables, as well as the size and quantity of the milling balls, to determine a combination that resulted in complete separation of PVC and high-purity Cu (>99.9%) from thin electric cables. The experimental crushing behavior was demonstrated via a sphere-to-cylinder discrete element model combined with a statistical approach. The mechanism of PVC crushing generated cracks from the edge to the center of the cable via ball impacts that were strong enough to overcome the elastic repulsion force of the PVC. The resulting method was found to be effective at separating PVC and high-purity Cu (>99.9%) from de-plasticized thin electric cables with diameters of 1.5–2.7 mm.

Separation of polyvinylchloride (PVC), polystyrene (PS) and polyethylene terephthalate (PET) granules using various chemical agents by flotation technique

Abstract A mixture of traditional virgin (unused) plastics ordinarily available in municipal wastes, polyvinylchloride (PVC), polystyrene (PS) and polyethylene terephthalate (PET) was treated with several chemical agents, i.e., polyvinyl alcohol (PVA), polyethylene glycol (PEG), methyl cellulose (MC), tannic acid (TA) and methyl isobutyl carbinol (MIBC), individually or combine with each other. The effects of various parameters on the floatability of the used plastics, namely, chemical agent type and concentration, conditioning temperature and time and liquid media pH, were studied and the results were discussed. It revealed that in most experiments, the PET sustained the least flotation change for the studied chemical agents and was sunk at the bottom of the flotation tank. The TA was useful on the PVC flotation through surface adsorption and changing the PVC surface hydrophobic behavior in different ways depending on the TA concentration. With the PET exception, the increasing temperature improved floatability of the studied plastics for used chemical agents. The raising the pH of the liquid media changed the floatability of the studied plastics in different ways depending on the pH value and the used chemical agent. In most cases, the increasing conditioning time was beneficial to the plastic flotation up to 15 min. As an essential conclusion, the PVC and PS could be separated from PET in their mixture by using TA-PEG with 0.2–0.8 ratio and TA-PEG with equal ratio plus 2 ml/L MIBC in two stages completely. The comparison of the results with other studies showed the shape and size of the used plastics were crucial factors on the separation of the studied plastics by the flotation technique.

Fenton treatment for flotation separation of polyvinyl chloride from plastic mixtures

Abstract The generation of waste plastics has been radically promoted by large-scale consumption and rapid upgrading of plastic products in the last decades, which brings serious threats to environment and management. Combined with Fenton treatment, froth flotation was evaluated to separate polyvinyl chloride (PVC) from waste plastics for recycling. The floatability of polystyrene (PS) and polycarbonate (PC) has a dramatic decrease after Fenton treatment, while the floatability of PVC is not affected. Contact angle, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were conducted to ascertain the mechanism of Fenton treatment. The reduction of PS and PC floatability is attributed to the increase of surface wettability confirmed by contact angle measurement. FT-IR and XPS analysis confirmed that hydrophilic oxygen-containing groups were introduced on PC and PS surface. SEM images indicated that Fenton treatment considerably increased the surface roughness of PC and PS. With respect to flotation separation PVC from plastic mixtures, optimum conditions are molar ratio (H 2 O 2 /Fe 2+ ) 7500, H 2 O 2 concentration 0.2 M/L, treatment 2 min, temperature 25 °C, pH 5.8, frother concentration 15 mg/L and flotation time 4 min. Particle size, mass fractions and reuse of plant effluent were also investigated. After Fenton treatment under optimum conditions, floatation separation of PVC from plastic mixtures was accomplished with high purity and recovery. The purity and the recovery of PVC are up to 99.26% and 100% respectively. The purity and the recovery of other plastics are up to 100% and 97.20% respectively. Consequently, flotation combined with Fenton treatment is a simple, environmental friendly and cost-effective method for separation of PVC from plastic mixtures.

Selective sequential separation of ABS/HIPS and PVC from automobile and electronic waste shredder residue by hybrid nano-Fe/Ca/CaO assisted ozonisation process

The separation of plastics containing brominated flame retardants (BFR) like (acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), and polyvinyl chloride (PVC)) from automobile and electronic waste shredder residue (ASR/ESR) are a major concern for thermal recycling. In laboratory scale tests using a hybrid nano-Fe/Ca/CaO assisted ozonation treatment has been found to selectively hydrophilize the surface of ABS/HIPS and PVC plastics, enhancing ABS wettability and thereby promoting its separation from ASR/ESR by means of froth flotation. The water contact angles, of ABS/HIPS and PVC decreased, about 18.7°, 18.3°, and 17.9° in ASR and about 21.2°, 20.7°, and 20.0° in ESR respectively. SEM-EDS, FT-IR, and XPS analyses demonstrated a marked decrease in [Cl] and a significant increase in the number of hydrophilic groups, such as CO, CO, and (CO)O, on the PVC or ABS surface. Under froth flotation conditions at 50rpm, about 99.1% of combined fraction of ABS/HIPS in ASR samples and 99.6% of ABS/HIPS in ESR samples were separated as settled fraction. After separation, the purity of the recovered combined ABS/HIPS fraction was 96.5% and 97.6% in ASR and ESR samples respectively. Furthermore, at 150rpm a 100% PVC separation in the settled fraction, with 98% and 99% purity in ASR and ESR plastics, respectively. Total recovery of non-ABS/HIPS and PVC plastics reached nearly 100% in the floating fraction. Further, this process improved the quality of recycled ASR/ESR plastics by removing surface contaminants or impurities.

Heterogeneous nano-Fe/Ca/CaO catalytic ozonation for selective surface hydrophilization of plastics containing brominated and chlorinated flame retardants (B/CFRs): separation from automobile shredder residue by froth flotation.

One method of weakening the inherently hydrophobic surface of plastics relevant to flotation separation is heterogeneous nano-Fe/Ca/CaO catalytic ozonation. Nano-Fe/Ca/CaO-catalyzed ozonation for 15min efficiently decreases the surface hydrophobicity of brominated and chlorinated flame retardant (B/CFR)-containing plastics (such as acrylonitrile-butadienestyrene (ABS), high-impact polystyrene (HIPS), and polyvinyl chloride (PVC)) in automobile shredder residue (ASR) to such an extent that their flotation ability is entirely depressed. Such a hydrophilization treatment also stimulates the ABS, HIPS, and PVC surface roughness, wetting of the surface, and the thermodynamic equilibrium conditions at the surface and ultimately changes surface polarity. SEM-EDS, AFM, and XPS analyses of the PVC and ABS surfaces demonstrated a marked decrease in [Cl/Br] and a significant increase in the number of hydrophilic groups, such as C-O, C=O, and (C=O)-O. Under froth flotation conditions at 50rpm, about 99.5% of ABS and 99.5% of HIPS in ASR samples settled out, resulting in a purity of 98 and 98.5% for ABS and HIPS in ASR samples, respectively. Furthermore, at 150rpm, we also obtained 100% PVC separation in the settled fraction, with 98% purity in ASR. Total recovery of non-B/CFR-containing plastics reached nearly 100% in the floating fraction. The amount of nano-Fe/Ca/CaO reagent employed during ozonation is very small, and additional removal of surface contaminants from the recycled ASR plastic surfaces by ozonation makes the developed process simpler, greener, and more effective.

Processing plastics from ASR/ESR waste: separation of poly vinyl chloride (PVC) by froth flotation after microwave-assisted surface modification

The feasibility of the selective surface hydrophilization of poly vinyl chloride (PVC) using microwave treatment to facilitate the separation of PVC via froth flotation from automobile shredder residue (ASR) and electronic waste shredder residue (ESR) was evaluated. In the presence of powder-activated carbon (PAC), 60-s microwave treatment selectively enhanced the hydrophilicity of the PVC surface (i.e., the PVC contact angle decreased from 86.8° to 69.9°). The scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results are consistent with increased hydrophilic functional groups (i.e., ether, hydroxyl, and carboxyl), amounting to significant changes in the morphology and roughness of the PVC surface after treatment. After only 60 s of microwave treatment, 20 % of the PVC was separated in virgin and ASR/ESR plastics with 33 and 29 % purity, respectively, as settled fractions by froth flotation at a 150 rpm mixing speed. The microwave treatment with the addition of PAC had a synergetic effect with the froth flotation, which brought about 100 and 90 % selective separation of PVC from the other virgin and ASR/ESR plastics, with 91 and 82 % purity. The use of the combined froth flotation and microwave treatments is an effective technology for separating PVC from hazardous waste plastics.

Development of hydrophobicity and selective separation of hazardous chlorinated plastics by mild heat treatment after PAC coating and froth flotation

Polyvinyl chloride (PVC) containing chlorine can release highly toxic materials and persistent organic pollutants if improperly disposed of. The combined technique of powder activated carbon (PAC) coating and mild heat treatment has been found to selectively change the surface hydrophobicity of PVC, enhancing its wettability and thereby promoting its separation from heavy plastic mixtures included polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS) and acrylonitrile butadiene styrene (ABS) by means of froth flotation. The combined treatments helped to rearrange the surface components and make PVC more hydrophobic, while the remaining plastics became more hydrophilic. After the treatments at 150°C for 80s the contact angle of the PVC was greatly increased from 90.5 to 97.9°. The SEM and AFM reveal that the surface morphology and roughness changes on the PVC surface. XPS and FT-IR results further confirmed an increase of hydrophobic functional groups on the PVC surface. At the optimized froth flotation and subsequent mixing at 150rpm, 100% of PVC was recovered from the remaining plastic mixture with 93.8% purity. The combined technique can provide a simple and effective method for the selective separation of PVC from heavy plastics mixtures to facilitate easy industrial recycling.

Optimization of surface treatment for flotation separation of polyvinyl chloride and polyethylene terephthalate waste plastics using response surface methodology

A simple process for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) waste plastics was investigated for sustainable development of plastic industry. Surface treatment with potassium permanganate (KMnO4) solution selectively decreases the flotation rate of PVC, promoting flotation separation of PVC and PET. Flotation rate represents the mass percentage of float particles. Oxidization action and migration of calcium carbonate on PVC surface as major mechanism of surface treatment are confirmed by scanning electron microscope and X-ray photoelectron spectroscope determinations. Single factor experiments demonstrate that the flotation rate of PVC is affected significantly by the factors of KMnO4 concentration, treatment time, temperature and stirring rate. The effects of variables, including KMnO4 concentration, treatment time and temperature, on the flotation rate of PVC are evaluated by response surface methodology with a Box–Behnken design. A modified quadratic model is achieved for predicting the flotation rate of PVC plastic. The optimum conditions are potassium permanganate concentration 4.60 mmol/L, temperature 66.5 °C, treatment time 38 min and stirring rate 200 r/min. PVC and PET mixtures with different mass ratio were separated efficiently through one-stage flotation combined with surface treatment. The purity of PET is above 97.87% and the recovery of PVC is above 97.90%. Effective separation by the proposed method enables recycling of PVC and PET waste plastics.

Flotation separation of polyvinyl chloride and polyethylene terephthalate plastics combined with surface modification for recycling

Surface modification with potassium permanganate (KMnO4) solution was developed for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) waste plastics. The floatability of PVC decreases with increasing of KMnO4 concentration, treatment time, temperature and stirring rate, while that of PET is unaffected. Fourier transform infrared (FT-IR) analysis confirms that mechanism of surface modification may be due to oxidization reactions occurred on PVC surface. The optimum conditions are KMnO4 concentration 1.25mM/L, treatment time 50min, temperature 60°C, stirring rate 300r/min, frother concentration 17.5g/L and flotation time 1min. PVC and PET with different particle sizes were separated efficiently through two-stage flotation. Additionally, after ultrasonic assisted surface modification, separation of PVC and PET with different mass ratios was obtained efficiently through one-stage flotation. The purity and the recovery of the obtained products after flotation separation are up to 99.30% and 99.73%, respectively. A flotation process was designed for flotation separation of PVC and PET plastics combined with surface modification. This study provides technical insights into physical separation of plastic wastes for recycling industry.