Ammonia modification for flotation separation of polycarbonate and polystyrene waste plastics

Hydrogen bonding-mediated interaction underlies the enhanced membrane toxicity of chemically transformed polystyrene microplastics by cadmium

The global attention on microplastic pollution and its implications for human health has grown in recent years. Additionally, the co-existence of heavy metals may significantly alter microplastics' physicochemical characteristics, potentially amplifying their overall toxicity-a facet that remains less understood. In this study, we focused the membrane toxicity of modified polystyrene microplastics (PS-MPs) following cadmium (Cd) pretreatment. Our findings revealed that Cd-pretreated PS-MPs exacerbated their toxic effects, including diminished membrane integrity and altered phase fluidity in simulated lipid membrane giant unilamellar vesicles (GUVs), as well as heightened membrane permeability, protein damage, and lipid peroxidation in red blood cells and macrophages. Mechanistically, these augmented membrane toxicities can be partially ascribed to modifications in the surface roughness and hydrophilicity of Cd-pretreated PS-MPs, as well as to interactions between PS-MPs and lipid bilayers. Notably, hydrogen bonds emerged as a crucial mechanism underlying the enhanced interaction of PS-MPs with lipid bilayers.

A Tug of War between the Self- and Cross-associating Hydrogen Bonds in Neutral Ammonia-Water Clusters: Energetic Insights by Molecular Tailoring Approach

In the present work, the energies of various types of individual HBs observed in neutral (NH₃ )_m (H₂ O)_n , (m+n=2 to 7) clusters were estimated using the molecular tailoring approach (MTA)-based method. The calculated individual HB energies suggest that the O-H…N HBs are the strongest (1.21 to 12.49 kcal mol^-1 ). The next ones are the O-H…O (3.97 to 9.30 kcal mol^-1 ) HBs. The strengths of N-H…N (1.09 to 5.29 kcal mol^-1 ) and N-H…O (2.85 to 5.56 kcal mol^-1 ) HBs are the weakest. The HB energies in dimers also follow this rank ordering. However, the HB energies in dimers are much smaller than those obtained by the MTA-based method due to the loss in cooperativity contribution in the dimers. Thus, the calculated cooperativity contributions, for different types of HBs, fall in the range 0.64 to 5.73 kcal mol^-1 . We wish to emphasize based on the energetic rank ordering obtained by the MTA-based method that the O-H of water is a better HB donor than the N-H of ammonia. The reasons for the observed energetic rank ordering are two folds: (i) intrinsically stronger O-H…N HBs than the O-H…O ones as revealed by dimer energies and (ii) the higher cooperativity contribution in the former than the later ones. Indeed, the MTA-based method is useful in providing the missing energetic rank ordering of various type of HBs in neutral (NH₃ )_m (H₂ O)_n clusters, in the literature.

The impact of chlorination on the tetracycline sorption behavior of microplastics in aqueous solution

Considering the large volumes of treated water and incomplete elimination of pollutants, wastewater treatment plants (WWTPs) remain a considerable source of microplastics (MPs). Chlorine, the most frequently used disinfectant in WWTPs, has a strong oxidizing impact on MPs. However, little is documented, to date, about the impact of chlorination on the transformation of MPs and the subsequent environmental behaviors of the chlorinated MPs when released into the aquatic environment. This study explored the response of the physicochemical properties of specific thermoplastics, namely polyurethane (TPU) MPs and polystyrene (PS) MPs, to chlorination and their emerging pollutant [tetracycline (TC)] adsorption behavior in aqueous solution. The results indicated that the O/C ratio of the MP surface did not significantly change, and that there were increases in the O-containing functional groups of the TPU and PS MPs, after chlorination. The surface area of the chlorinated TPU MPs increased by 45 %, and that of the chlorinated PS increased by 21 %, compared with the pristine ones, which contributed to the TC adsorption. The adsorption isotherm fitting parameters suggested that the chlorinated TPU fitted the multilayer adsorption, and the chlorinated PS was inclined to the monolayer adsorption. The relative abundance of the O-containing functional groups, on the TPU surface, led to the release of CHCl₃ molecules, and the clear surface irregularities and fissures occurred after chlorine treatment. No fissures were found on the surface of the chlorinated PS MPs. The hydrophobicity and electrostatic adsorption were proved to be the major impacts on the TC adsorption of the chlorinated MPs, and the subsequently formed hydrogen bonds led to the stronger adsorption capacity of the chlorinated TPU than the chlorinated PS MPs.

Separation of plastic wastes using froth flotation - An overview

Despite various initiatives and efforts, plastic solid waste (PSW) has become a major global problem due to decades of relentless use of plastics. Since non-biodegradable plastics can persist in the environment for hundreds of years, threatening animal and human life, discarding them into the environment is not a viable option. Plastic recycling is a critical research area that requires urgent attention since less than 10% of the seven billion tons of globally generated plastic waste has been recycled so far. With recent technological developments, it is now possible to recycle many types of PSW using a variety of methods. This review provides an overview of the froth flotation technology that is currently being researched for PSW recycling. Fundamental working principles, the current state of the development, and limitations of this technique are reviewed. It is suggested that froth flotation with continuous development has tremendous potential to result in a more efficient and environmentally friendly approach to PSW recycling.

Separation of virgin plastic polymers and post-consumer mixed plastic waste by sinking-flotation technique

The main objective of this research is to separate virgin polymers (PA, PC, PP, HDPE; PS, and ABS) and post-consumer plastic waste from municipal solid waste (MSW) using the sinking-flotation technique. Separation was carried out on a pilot scale in an 800-l useful volume container with 160 rpm agitation for one hour. Tap water, ethanol solutions, and sodium chloride at different concentrations were used as densification medium. Virgin polymers were separated into two groups: low-density (HDPE and PP) and high-density polymers groups (PS, ABS, PA, and PC). Polymers whose density was less than that of the medium solution floated to the surface, while those whose density was greater than those of the medium solution sank to the bottom. The experimental results showed that complete separation of HDPE from PP achieved 23% ethanol v/v, whereas high-density polymers separated up to 40% w/v sodium chloride. Polymer recovery ranged from 70 to 99.70%. In post-consumer recycled plastic waste, fractions of 29.6% polyolefins, 37.54% PS, 11% ABS, 8% PA, 12% PC PET, and PVC were obtained. Finally, cast plates were made of the post-consumer waste to properly identify the polymer type present in the separated fractions.

Polymer Composites Based on Polycarbonate (PC) Applied to Additive Manufacturing Using Melted and Extruded Manufacturing (MEM) Technology

As part of the present work, polymer composites used in 3D printing technology, especially in Melted and Extruded Manufacturing (MEM) technology, were obtained. The influence of modified fillers such as alumina modified silica, quaternary ammonium bentonite, lignin/silicon dioxide hybrid filler and unmodified multiwalled carbon nanotubes on the properties of polycarbonate (PC) composites was investigated. In the first part of the work, the polymer and its composites containing 0.5–3 wt.% filler were used to obtain a filament using the proprietary technological line. The moldings for testing functional properties were obtained with the use of 3D printing and injection molding techniques. In the next part of the work, the rheological properties—mass flow rate (MFR) and mechanical properties—Rockwell hardness, Charpy impact strength and static tensile strength with Young’s modulus were examined. The structure of the obtained composites was also described and determined using scanning electron microscopy (SEM). The porosity, roughness and dimensional stability of samples obtained by 3D printing were also determined. On the other hand, the physicochemical properties were presented on the basis of the research results using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray scattering analysis (WAXS) and Fourier Transform infrared spectroscopy (FT-IR). Additionally, the electrical conductivity of the obtained composites was investigated. On the basis of the obtained results, it was found that both the amount and the type of filler significantly affected the functional properties of the composites tested in the study.

Enhanced hepatic cytotoxicity of chemically transformed polystyrene microplastics by simulated gastric fluid

Microplastics pollution has emerged as one of the top-ranked global environmental issues, receiving worldwide attention in recent years. However, knowledge about the detrimental effects of microplastics on human health is still limited. In real-world settings, the physicochemical characteristics of microplastics were modified by environmental and biological transformation, largely changing their ultimate toxicity. Nonetheless, the toxicity change related to transformation of microplastics has not been considered in most published studies thus far. In the current study, we investigated the cytotoxicity of transformed polystyrene microplastics in hepatocytes. Our results revealed that 500 nm polystyrene microplastics, which were chemically transformed by simulated gastricfluid, exacerbated their adverse effects on SMMC-7721 cells at 20 μg/mL for 24 h treatment, including morphological alteration, membrane damage and increased cell apoptosis via oxidative stress. This exacerbated cytotoxicity could be at least partially explained by the degradation, changed surface charge and altered surface chemistry of these polystyrene microplastics after transformation. In conclusion, our study demonstrates that the hepatic cytotoxicity of polystyrene microplastics is enhanced after transformation.

Hydrophilic modification of polycarbonate surface with surface alkoxylation pretreatment for efficient separation of polycarbonate and polystyrene by froth flotation

Waste polystyrene (PS) and polycarbonate (PC) are crucial components arising from mixtures of plastic products, whose recycling is significantly limited by separation efficiency. In this work, to assist the flotation separation of PC and PS, we proposed a novel modification technology of surface alkoxylation pretreatment (SAP) where PC surface reacted with glycerol and urea. The SAP could selectively transform the hydrophobic PC into hydrophilic plastic, while the PS remained its hydrophobic surface owing to the exclusion from SAP process. Benefiting from the hydrophilic PC, the separation efficiency of PS and PC could reach the maximum of 99.34% under optimum conditions (urea dosage of 5 g, pretreatment temperature of 130 °C, pretreatment time of 10 min, flotation time of 2.5 min, frother concentration of 16.5 mg/L, and airflow rate of 7.2 mL/min). The mechanism of SAP was systematically analyzed by wettability, surface morphology, molecular weight, and chemical reactions. Compared with PS plastic, the pretreated PC presented better wettability, rougher surface, and significantly reducing molecular weight. The improvement of PC hydrophilicity can be attributed to the cleavage of ester bonds on backbone chains and the introduction of hydrophilic hydroxyl groups. The effective SAP process proves that chemical recycling of waste plastic can provide a novel strategy for surface modification and flotation separation of PS and PC.

Surface Reactions in Selective Modification: The Prerequisite for Plastic Flotation

Improper disposal of waste plastic has caused much environmental pollution, but plastic recycling can reduce the amount of new and residual waste plastic in the environment through source control. Plastic flotation can separate waste plastics with similar physical and chemical properties, which suggests its promising application in plastic recycling. With the help of the different hydrophilicities waste plastic can be separated by flotation, and hydrophilization can be accomplished by surface modifications. However, no systematic studies addressing these surface reactions have been published yet, and such modifications are a prerequisite for plastic flotation. In this critical review, we not only summarize the various modification mechanisms, including physical regulation, surface oxidation, surface degradation, dechlorination, and coating, but also have reasonably added additional information for some reactions covering surface reconstruction, plastic degradation, polymer stability, wastewater treatment, soil remediation, and chemical recycling of plastic. An entirely novel concept, the "plastic gene", is also proposed to elaborate on some contradictory results. Plastic flotation with clear surface reactions may promote plastic recycling and thereby control waste plastic at the source, save energy, and reduce microplastics. We also predict challenges for clean, efficient, and practical surface modifications and plastic flotation.

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.

Flotation separation of polyethylene terephthalate from waste packaging plastics through ethylene glycol pretreatment assisted by sonication

The recycling of packaging plastics is hindered by the various plastic mixtures and their similar surface properties. Plastic separation is a key step to improve recycling efficiency of waste plastics. We proposed a simple and efficient protocol to separate polyethylene terephthalate (PET) from polycarbonate (PC), acrylonitrile-butadienestyrene copolymer (ABS), and polyvinyl chloride (PVC) by converting PET surface from hydrophobicity to hydrophilicity. PET surface was modified by potassiumhydroxide (KOH)and ethylene glycol ((CH₂OH)₂) with the aid of sonication. Contact angle, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to research the reactions on PET surface. It can be confirmed that the reaction of base-catalyzed transesterification occurs, leading to a hydrophilic PET plastic. We investigated the effects of ultrasonic power, ultrasonic time, (CH₂OH)₂ dosage, KOH dosage, flotation time, and frother concentration on the flotation separation. The flotation recovery and purity of PET are 98.8% and 100%, respectively when (CH₂OH)₂ dosage is 10 mL, KOH dosage is 2 g, ultrasonic time is 5 min, ultrasonic intensity is 160 W, flotation time is 4 min, and frother concentration is 52.7 mg/L. This study provided a novel surface modification with reliable mechanisms for the flotation of PET from plastic mixtures.

Regeneration and Recovery of Plastics

Plastics are the most essential commodities in the world and are replacing the metals, wood, glass, cements and other materials in some application areas. Plastics are easy handling, resource-saving, non-toxic with esthetically attractive. Oil and gas are the major feedstocks for plastics, besides sugar and corn as renewable feedstocks. Plastics represent a serious waste-handling problem, with only 10%–12% of the plastic waste generated worldwide being regenerated/recycled. After disposal, plastic waste takes very long time to decompose naturally and impact the environment during the degradation process. The above situation has necessitated the invention of efficient technologies for regeneration and recovery of plastics all over the world.

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

A combining technology of advanced oxidation by S₂O₈^2-/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 S₂O₈^2-/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 (S₂O₈^2-/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 S₂O₈^2-/Fe²⁺ advanced oxidation and flotation is a practical and efficient technology for separating PVC and ABS.

Separation of acrylonitrile-butadiene-styrene and polystyrene waste plastics after surface modification using potassium ferrate by froth flotation

This work develops a simple and practical process for separation of acrylonitrile-butadienestyrene (ABS) and polystyrene (PS) waste plastics by froth flotation after surface modification using potassium ferrate. ABS plastics containing brominated flame retardants (BFRs) can release hazardous emissions during the process of disposal. Moreover, ABS and PS are typical styrene plastics with similar properties, posing severe restrictions on their separation for recycling. Thus, potassium ferrate modification was investigated and found to decrease selectively the floatability of ABS, providing available process for separation of ABS and PS. Contact angle measurements, FT-IR, XPS and SEM characterization analysis confirmed that potassium ferrate modification can induce the desired changes in the surface properties of ABS. With consideration to separation of ABS and PS, the optimum conditions are potassium ferrate concentration 0.15 M/L, modification time 15 min, temperature 60 °C, stirring rate 200 rpm, frother concentration 14.50 mg/L and flotation time 2 min. Under optimum conditions, separation of ABS and PS with different mixing ratios was accomplished with a recovery and purity of 98.60% and 98.62% respectively. Moreover, reusing of potassium ferrate solution is feasible, further eliminating emissions and cost of this process. Consequently, surface modification using potassium ferrate can be applied for facilitating flotation separation of ABS and PS waste plastics.

Evaluation of ground calcite/water heavy media cyclone suspensions for production of residual plastic concentrates

Viable recycled residual plastic (RP) product(s) must be of sufficient quality to be reusable as a plastic or source of hydrocarbons or fuel. The varied composition and large volumes of such wastes usually requires a low cost, high through-put recycling method(s) to eliminate contaminants. Cyclone separation of plastics by density is proposed as a potential method of achieving separations of specific types of plastics. Three ground calcite separation medias of different grain size distributions were tested in a cylindrical cyclone to evaluate density separations at 1.09, 1.18 and 1.27 g/cm³. The differences in separation recoveries obtained with these medias by density offsets produced due to displacement of separation media solid particles within the cyclone caused by centrifugal settling is evaluated. The separation density at which 50% of the material of that density is recovered was found to increase from 0.010 to 0.026 g/cm³ as the separation media density increased from 1.09 to 1.27 g/cm³. All separation medias were found to have significantly low Ep₉₅values of 0.012-0.033 g/cm³. It is also demonstrated that the presence of an excess content of <10 µm calcite media particles (>75%) resulted in reduced separation efficiencies. It is shown that the optimum separations were achieved when the media density offset was 0.03-0.04 g/cm³. It is shown that effective heavy media cyclone separations of RP denser than 1.0 g/cm³ can produce three sets of mixed plastics containing: PS and ABS/SAN at densities of >1.0-1.09 g/cm³; PC, PMMA at a density of 1.09-1.18 g/cm³; and PVC and PET at a density of >1.27 g/cm³.

Separation of plastics by froth flotation. The role of size, shape and density of the particles

Over the last few years, new methods for plastic separation in mining have been developed. Froth flotation is one of these techniques, which is based on hydrophobicity differences between particles. Unlike minerals, most of the plastics are naturally hydrophobic, thus requiring the addition of chemicals that promote the selective wettability of one of its components, for a flotation separation. The floatability of six granulated post-consumer plastic - Polystyrene (PS), Polymethyl methacrylate (PMMA), Polyethylene Terephthalate (PET-S, PET-D) and Polyvinyl Chloride (PVC-M, PVC-D) - in the presence of tannic acid (wetting agent), and the performance of the flotation separation of five bi-component plastic mixtures - PS/PMMA, PS/PET-S, PS/PET-D, PS/PVC-M and PS/PVC-D - were evaluated. Moreover, the effect of the contact angle, density, size and shape of the particles was also analysed. Results showed that all plastics were naturally hydrophobic, with PS exhibiting the highest floatability. The contact angle and the flotation recovery of six plastics decreased with increasing tannic acid concentration, occurring depression of plastics at very low concentrations. Floatability differed also with the size and shape of plastic particles. For regular-shaped plastics (PS, PMMA and PVC-D) floatability decreased with the increase of particle size, while for lamellar-shaped particles (PET-D) floatability was slightly greater for coarser particles. Thus, plastic particles with small size, lamellar shape and low density present a greater floatability. The quality of separation varied with the mixture type, depending not only on the plastics hydrophobicity, but also on the size, density and shape of the particles, i.e. the particle weight. Flotation separation of plastics can be enhanced by differences in hydrophobicity. In addition, flotation separation improves if the most hydrophobic plastic, that floats, has a lamellar shape and lower density and if the most hydrophilic plastic, that sinks, has a regular shape and higher density. The results obtained show that froth flotation is a potential method for plastics separation, in particular for plastics with particle size greater than 2.0mm.