RESUMEN
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.
Asunto(s)
Poliestirenos , Eliminación de Residuos , Interacciones Hidrofóbicas e Hidrofílicas , Plásticos , Cemento de PolicarboxilatoRESUMEN
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.
Asunto(s)
Plásticos , Eliminación de Residuos , Glicol de Etileno , Tereftalatos Polietilenos , Cloruro de Polivinilo , Reciclaje , SonicaciónRESUMEN
This study developed a novel method, surface pretreatment using sodium hypochlorite along with flotation, to facilitate separation of waste polycarbonate from plastic mixtures for recycling. Surface pretreatment was observed that has an obviously negative effect on the floating ratio of polycarbonate and the floating ratio of poly-methyl-methacrylate, polystyrene, and polyvinylchloride was not affected in flotation, and this difference in floating ratio can be expected to separate polycarbonate from plastic mixtures. The optimum conditions obtained included sodium hypochlorite concentration of 0.05â¯M, pretreatment temperature of 70.0⯰C, pretreatment time of 60.0â¯min, frother dosage of 10.8â¯mg/L, and flotation time of 4.0â¯min. Under optimum conditions, polycarbonate was separated effectively from multiple plastic mixtures, and the purity and recovery were 99.8% and 100.0%, respectively. The major mechanism of surface pretreatment was ascertained by the aid of Fourier transform infrared, scanning electron microscope, energy dispersive spectrometer, and X-ray photoelectron spectroscopy, and the hydrophilic groups, pitting, and protuberances introduced on polycarbonate surface caused the reduced floating ratio of polycarbonate. Accordingly, this method can be expected to improve the recycling quality of waste plastics, and provides technological insights in the environmentally friendly disposal of waste plastics.
Asunto(s)
Plásticos , Eliminación de Residuos , Cemento de Policarboxilato , Reciclaje , Hipoclorito de SodioRESUMEN
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 0.1â¯M, molar ratio (S2O82-/Fe2+) 200, treatment time 10â¯min, flotation time 4â¯min, frother concentration 14.7â¯mg L-1 and airflow rate 6.8â¯mLâ¯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 0.64â¯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.
Asunto(s)
Acrilonitrilo , Eliminación de Residuos , Butadienos , Cloruro de Polivinilo , Espectroscopía Infrarroja por Transformada de Fourier , EstirenoRESUMEN
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.