Design and performance evaluation of triboelectrostatic separation system for the separation of PVC and PET materials using a fluidized bed tribocharger

A triboelectrostatic separation system using a fluidized-bed tribocharger for the removal of PVC material in the mixture of PVC/PET plastics was designed and evaluated as a function of tribocharger material, air flow rate, electric field strength, and the mixing ratio of two-component mixed plastics. The test system consists of the fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. PVC and PET particles can be imparted negative and positive surface charges, respectively, due to the difference in the work function values of plastics suspended in the fluidized-bed tribocharger, and can be separated by passing them through an external electric field. Experimental results show that separation efficiency is strongly dependent on the tribocharger material, electric field strength and particles mixing ratio. In the optimum conditions of 150l/m air flow rate and 2.6 kV/cm electric field strength, highly concentrated PVC (99.1%) can be recovered with a yield of more than 95% from the mixture of PVC and PET materials for a single stage of processing.     

Separation of PVC and Rubber from Covering Plastics in Communication Cable Scrap by Tribo-Charging

Abstract

Triboelectrostatic separation of PVC and rubber from covering plastics in communication cable scrap has been performed. In this work, particles charged as positive (+) and negative (?) according to the difference of work function of each material after tribo-charging can be separated through an opposite electric field. In charger material selection tests using a vertical-reciprocation charger, PVC and rubber particles in the covering plastics were charged with the opposite polarity in the charger material made of PP, HDPE, or PET. The difference of charge density (charge to mass ratio, nC/g) of the PVC and rubber was higher in the tribo-charger made of HDPE. Furthermore, in lab-scale triboelectrostatic experiments for separating the PVC and rubber, the charging efficiency of the mixed PVC and rubber increased when the air velocity was adjusted to over 8.2 m/s. The charge density, the electrode potential, and splitter position needed for the separation of the PVC were determined to be 25 nC/g, 30 kV and +2 cm, respectively. In the optimum conditions, we developed a separation technique that can separate up to 99.8% PVC grade with 95.0% of recovery from the covering plastics.     

含PVC混合塑料水热反应中的氯迁移特性

聚氯乙烯(PVC)的大量使用导致城市生活垃圾(MSW)中的氯含量相对较高。水热反应将氯尤其是有机氯高效脱除是实现垃圾无害化处理和资源化利用的前提。MSW中塑料组分复杂,有机氯主要来源于PVC,研究影响PVC水热脱氯中氯迁移特性的因素具有重要意义。选取两种型号(HB-65和S-65)的PVC和聚乙烯(PE)、聚丙烯(PP)、聚苯乙烯(PS)、丙烯腈-丁二烯-苯乙烯(ABS)作为原料,研究了PVC自身性能和水热条件对氯脱除的影响规律,考察了塑料混合水热过程中的氯迁移特征。结果表明,PVC自身性能是影响水热脱氯内在因素,水热条件如水热温度、保温时间和反应物浓度是外在因素。塑料因不同的热膨胀性在混合水热过程中存在协同效应,添加PP和ABS使PVCHB-65脱氯率分别下降了71.66%和70.96%,使PVCS-65脱氯率分别下降了19.05%和18.15%;添加PE和PS使PVCHB-65脱氯率分别下降了71.06%和43.06%,使PVCS-65脱氯率分别升高了8.20%和46.70%。     

The effect of plastic addition on coal caking properties during carbonization

The recycling process of waste plastics using coke ovens is now being studied. The effect of plastic addition on coal caking property was investigated. It was revealed that thermal decomposition products of plastics interacted with bituminous coal during carbonization in coke ovens. The effect of plastic addition on coal caking property varied with types of plastics. The addition of aliphatic polymers such as polyethylene (PE), polypropylene (PP) and poly(vinyl chloride) (PVC) had only a small effect on coal caking property and coke strength and in some cases PE addition increased coke strength. On the other hand, the addition of polystyrene (PS), poly(ethylene terephthalate) (PET) and terephtalic acid (TFA) inhibited coal expansion and fusion, decreased maximum fluidity and total dilatation, and deteriorated the coke strength. These differences were discussed from the viewpoint of the interaction between thermal decomposition products of plastics and hydrogen in coal. It was suggested that the radical formed as a result of PS or PET thermal decomposition abstracted hydrogen from coal, which resulted in the decrease in coal caking property.     

Triboelectrostatic separation of covering plastics in chopped waste electric wire

To develop a triboelectrostatic separation technique for covering plastics in waste electric wire, process variables such as charger material, relative humidity, air velocity, electrode potential, and splitter position have been studied. Polypropylene was found to be the most effective material for a tribo‐charger in the separation of cross‐linked polyethylene (XLPE) and polyvinyl chloride (PVC). The charge density of XLPE and PVC was increased with deceasing relative humidity and increasing air velocity in the tribo‐charger. The charge density of a 1:1 mixture of XLPE and PVC was determined to be higher than that of individual XLPE and PVC. A dominant charging mechanism in the tribo‐charger with a 1:1 mixture of XLPE and PVC seems to be the charging of a combination of particle‐particle and particle‐charger surface. However, in case of individual plastics, the charging of particle‐particle occurred. Over 98.05% PVC recovery with 99.50% grade was successfully obtained under the conditions of a splitter position of +2 cm from the center, 25 kV electrode potential and over 13 nC/g PVC charge density for the optimum triboelectrostatic separation. POLYM. ENG. SCI., 47:1975–1982, 2007. © 2007 Society of Plastics Engineers     

Catalytic degradation and dechlorination of PVC-containing mixed plastics via Al-Mg composite oxide catalysts

A alumina-magnesium composite oxide catalyst (Al-Mg) was synthesized for catalytic degradation of poly vinyl chloride (PVC) containing polymer mixtures, i.e. polypropylene (PP)/PVC, low-density polyethylene (LDPE)/PVC, polystyrene (PS)/PVC, and LDPE/PP/PS/PVC. In the catalytic degradations the Al-Mg composite oxide catalyst accelerated the rate of polymer degradation and lowered the carbon distribution of liquid products. In addition, it showed good effect on the fixation of evolved HCl and greatly decreased the chlorine content in the oil. These results suggested that the Al-Mg composite oxide catalyst can be effectively used for catalytic degradation and dechlorination of PVC-containing mixed plastics.     

Triboelectrostatic Separation of Fly Ash with Different Charging Materials

A combination of mechanical sieving and triboelectrostatic separation were used to separate fly ash. The results indicate that a simple separation of unburned carbon from fly ash is achievable at particle sizes of 74 and 44 microns. Subsequently, triboelectrostatic separations were conducted via a louvered plate separator. The results show that the final carbon content in the products, which can be as low as 1.5 % or as high as 60 % with different mineral components, can be further adjusted with the combination of sieving, louvered plate separator with a tribocharger made of different materials (copper and Teflon), and the location on the louvered plate where the fly ash particles were collected.     

Thermoplastic composites from maleic anhydride modified post-consumer plastics

In attempts to identify potential applications for refined commingled postconsumer plastics, a feedstock containing about 80% polyethylene (PE) and lesser amounts of poly(ethylene terephthalate) (PET), polystyrene (PS), polypropylene (PP), and poly(vinyl chloride) (PVC) was modified through functionalization with maleic anhydride in a co-rotating intermeshing twin-screw extruder. The modified and unmodified blends were compounded with various fillers and reinforcements such as glass fibers, mica flakes, talc, and calcium carbonate. Injection molded composites based on the modified matrix had, in general, superior mechanical and thermal properties. These findings are discussed in view of the improved adhesion resulting from reactions and/or enhanced polar interactions at phase boundaries. Several compounds prepared in this work had overall property data comparable to, or approaching those, of equivalent commercial HDPE molding compounds that are commonly used in “durable” applications.     

废弃塑料的回收利用

论述了目前废弃塑料回收利用方面的发展现状,介绍了聚丙烯、聚乙烯、聚对苯二甲酸乙二醇酯、聚氯乙烯、聚苯乙烯等废弃塑料的回收利用方法,以实现保护人类健康和减少环境污染和资源循环使用的目的。     

Recycling polymeric wastes by means of pyrolysis

Different polymeric wastes, which include materials from the automobile industry, such as tyres, automobile shredder residues (ASR) and sheet moulding compound (SMC), and materials from municipal solid wastes (MSW), such as cardboard, tetrabrik and plastics (LDPE, PP, PS, PET and PVC), pure and mixed, have been pyrolysed in a 3.5 dm³ autoclave at 500 °C for 30 min in a nitrogen atmosphere. The amount and characteristics of the solid, liquids and gases obtained are presented. The suitability of the different materials for the pyrolysis recycling process is discussed. It is concluded that pyrolysis is a very promising technique for recycling tyres, SMC, one type of ASR (heavy ASR), and LDPE, PP and PS, either pure or mixed; with all of them valuable solid, liquid and gaseous products are obtained in pyrolysis. On the contrary, light ASR, tetrabrik and cardboard do not yield valuable products in the pyrolysis process and therefore their recycling by pyrolysis is not of interest, except as a way of volume reduction. PET and PVC turned out to be troublesome in the pyrolysis experiments; for a proper study of their recycling by pyrolysis other operating conditions and installations are required. © 2002 Society of Chemical Industry     

Laser‐induced plasma spectroscopy for plastic identification

The goal of this work was instant identification of post‐consumer plastics by laser induced plasma spectrometry (LIPS). LIP spectra from plastics in a 200–800 nm spectral window were compared with reference spectral libraries stored in a computer. The libraries consisted of representative spectra from different groups of recycled plastic samples. The plasma emission spectra of polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were studied. Simple statistical correlation methods including linear and rank correlations were used. The probabilities of correct identification ranged from 0.8 to 1 with values close to unity for most of the polymers studied.     

汽车破碎残余物中PVC处理技术进展

汽车破碎残余物(Automobile Shredder Residues,ASR)通常定义为报废汽车(End-of-Life Vehicles,ELVs)经去污、拆解、破碎,除去金属后产生的残渣。包含塑料、橡胶、涂料、泡沫、纤维、金属等几十种物质的碎片和粉末,其中塑料最具有回收价值。ASR中含量最多的四种塑料是聚乙烯(PE)、聚丙烯(PP)、聚氯乙稀(PVC)、聚氨酯(PU)。在ASR的回收过程中,特别是热解和汽化,PVC中Cl的存在将严重影响ASR的回收。文章简要概述了ASR的特性以及国内外PVC的分离及脱氯技术研究进展。     

Recycling of commingled plastics by cellulosic reinforcement

In this article, a model study was conducted on the effect of combining cellulose on the properties of virgin and/or recycled commingled plastics with a simulated waste‐plastics fraction composed of high‐density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and poly(vinyl chloride) (PVC) (PE/PP/PS/PVC = 7/1/1/1 by weight ratio). The compatibilizing effect of maleic anhydride‐grafted styrene–ethylene/butylene–styrene block copolymer (SEBS‐g‐MAH) for the cellulose‐reinforced commingled blends was also investigated. Commingled blends were prepared in a table kneader internal mixer. Mechanical properties were measured by using a universal testing machine. Thermal stability was measured by a thermogravimetric analyzer. It was found that the addition of more than 12.5% cellulose into the commingled blends was effective to enhance the mechanical properties of the virgin and recycled blends. The thermal stability as well as the mechanical properties of the commingled blends were much improved by the reactive blending of cellulose with the commingled blends by peroxide and maleic anhydride. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1531–1538, 1999     

Optimization of froth flotation procedure for poly(ethylene terephthalate) recycling industry

This article addresses the separation of polyethylene terephthalate (PET) from ternary blends with polyvinyl chloride (PVC) and polystyrene (PS) by froth flotation. The experimental work was carried out with representative samples from post‐consumer waste packages collected at drop‐off‐points. Previous to froth flotation, PET selective wetting was achieved by alkaline treatment followed by surfactant adsorption. For this purpose, an aqueous solution of NaOH and an industrial detergent commonly used for waste plastic washing were tested as alkaline treatment, and calcium lignosulphonate and Hostaphat were tested as surfactants. An enriched product with 98.9% grade in PET and only 0.6% in PVC was recovered in the nonfloated product. The PET recovery in this product was 97% while ～96% of PVC and 91% of PS were recovered in the floated product. An analytical method was developed for the quantification of the waste plastic composition. The method was based on the selective dissolution of the plastics in the mixture. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

农业生物质与塑料共热解技术进展

共热解技术是将多种原料通过热化学方法转化为清洁能源的重要手段。本文综述了以农业生物质为主要原料与塑料(聚丙烯PP、高密度聚乙烯HDPE、低密度聚乙烯LDPE、聚氯乙烯PVC、聚苯乙烯PS、聚对苯二甲酸乙二醇酯PET等)共热解技术的发展现状和研究进展。分析农业生物质与塑料共热解的动力学模型以及各组分之间的协同效应,阐述农业生物质与塑料的共热解机理;总结了温度、升温速率、滞留时间、原料混配比等因素对共热解协同作用的影响规律;探究生物质与塑料共热解固、液、气三相产物特性及分布规律,总结共热解技术优势及存在问题,展望未来发展方向,可为生物质与塑料共热解制备高附加值产品提供参考,同时也为农业生物质和农膜处理问题提供新方法、新思路。     

纳米塑料研制进展(续)

综述了纳米塑料（包括PE、PP、PVC、PET、PBT、PA）的研制、性能、应用和展望。     

Co-pyrolysis characteristics of typical components of waste plastics in a falling film pyrolysis reactor

Waste plastics mainly come from MSW and usually exist in the form of mixed plastics. During the co-pyrolysis process of mixed plastics, various plastic components have different physicochemical properties and reaction mechanisms. Considering the high viscosity and low thermal conductivity of molten plastics, a falling film pyrolysis reactor was selected to explore the rapid co-pyrolysis process of typical plastic components (PP, PE and PS). The oil and gas yields and the compositions of pyrolysis products of the three components under different ratios at pyrolysis temperatures were analyzed to explore the co-pyrolysis characteristics of PP, PE, and PS. The study is of great significance to the recycling of waste plastics.     

木/塑发泡材料研究现状及其发展趋势

总结了国内外学者在木／塑发泡材料方面的研究工作。分别从制备方法（物理发泡法和化学发泡法）、工艺过程、发泡效果影响因素及发泡材料性能改性等方面介绍了聚氯乙烯类、聚烯烃类及聚苯乙烯类木／塑发泡材料，认为它们是一类具有优良性能以及可回收、无污染等特点的新材料。     

基于翅片式摩擦桶的车用聚合物粒子荷电及静电分离探索

对摩擦桶式荷电器中车用聚合物粒子的荷电情况进行了初步探究，基于法拉第桶测定了聚丙烯（PP）、聚氨酯（PU）、聚酰胺（PA）、聚乙烯（PE）、聚氯乙烯（PVC）和丙烯腈?丁二烯?苯乙烯（ABS）6种车用聚合物粒子在摩擦桶式荷电器下的摩擦荷电序列，并以ABS和PA为例，验证了其在不同摩擦桶式荷电器转速（n）和荷电时间（t）下的荷电规律，确定了ABS和 PA的最佳静电分选参数。结果表明，聚合物粒子荷电量（Q）与n和t呈正比关系；各车用聚合物粒子的摩擦荷电序列为（-）PE→ABS→PVC→PU→聚甲基丙烯酸甲酯（PMMA）→PP→PA（+）；ABS和PA的最优分选参数为n=20 r/min、t=1 min，此时两者分离纯度分别达到94.18 %和99.86 %，回收率分别为88.4 %和75.3 %，总回收率为90.15 %。     

废旧塑料回收中的共混技术应用

通过对废旧塑料回收方法的分析 ,提出了在物理回收中应用共混技术 ,可以提高产品性能和产品附加值 ,降低成本。并着重探讨了塑料回收中PVC/CPE、PS/SBS、PP/LDPE、PVC/PE/CPE等体系的共混方法。