Upgrading of poly(vinyl chloride) by chemical modifications using sodium sulfide

The recycling of poly(vinyl chloride) (PVC) is one of the most important issues in the treatment of waste plastics. To improve PVC recycling, it is necessary to develop new recycling techniques, including new techniques for the dechlorination of chlorine-containing polymers. It has been established that wet dechlorination of PVC in NaOH/ethylene glycol solution is more effective than dry dechlorination. In this study, the wet process was used, and the chemical modification of PVC by nucleophilic substitution was considered for upgrading waste PVC. Chlorine was substituted in solution by several nucleophilic reagents, thus changing the properties of PVC. The reaction of PVC in Na2S/ethylene glycol solution at 170°C resulted in the formation of a mixture comprising 32% elimination and 26% substitution products. The scanning electron microscopy/energy dispersive X-ray spectroscopy mappings and elementary analysis of PVC indicated that this chlorine-substitution process led to cross-linking by sulfur.     

Selective separation of virgin and post-consumer polymers (PET and PVC) by flotation method

More and more polymer wastes are generated by industry and householders today. Recycling is an important process to reduce the amount of waste resulting from human activities. Currently, recycling technologies use relatively homogeneous polymers because hand-sorting waste is costly. Many promising technologies are being investigated for separating mixed thermoplastics, but they are still uneconomical and unreliable. At present, most waste polymers cause serious environmental problems. Burning polymers for recycling is not practiced since poisonous gases are released during the burning process. Particularly, polyvinyl chloride (PVC) materials among waste polymers generate hazardous HCl gas, dioxins containing Cl, etc., which lead to air pollution and shorten the life of the incinerator. In addition, they make other polymers difficult to recycle.Both polyethylene terephthalate (PET) and PVC have densities of 1.30–1.35 g/cm³ and cannot be separated using conventional gravity separation techniques. For this reason, polymer recycling needs new techniques. Among these techniques, froth flotation, which is also used in mineral processing, can be useful because of its low cost and simplicity.The main objective of this research is to recycle PET and PVC selectively from post-consumer polymer wastes and virgin polymers by using froth flotation. According to the results, all PVC particles were floated with 98.8% efficiency in virgin polymer separation while PET particles were obtained with 99.7% purity and 57.0% efficiency in post-consumer polymer separation.     

Hydrolyzable poly(ethylene terephthalate)

Due to the enormous annual increase in the volume of municipal solid waste, society's attention is focused on how to manage the solid waste problem. Plastic materials not only contribute a great deal to the litter problem but also create serious danger to the ecology. Every year, countless birds, sea turtles, and other marine mammals die from eating or getting entangled in plastic litter. Synthesizing degradable polymers can have a great impact on solving the problem of plastic litter. We have modified the structure of poly(ethylene terephthalate) to make it degradable in typical environmental conditions in presence of water. The change of physical properties of modified poly(ethylene terephthalate), resulting from hydrolysis, has been monitored and compared with those of pure poly(ethylene terephthalate).     

Kinetics of thermal de-chlorination of PVC under pyrolytic conditions

Although PVC-containing wastes are an important potential source of energy they are frequently disposed in landfill. In thermal treatment processes such as pyrolysis and gasification, the presence of poly(vinyl chloride) (PVC), a compound with 56.7% of chlorine, may cause problems concerned with environmental protection, as consequence of the formation of hydrochloric acid, chlorine gas and dioxins, as well as corrosion phenomena of the reactor/equipment materials. Thus, a possible solution may involve a previous removal of the chlorine from PVC containing waste through a pyrolysis process at low temperatures before the material being submitted to a subsequent thermal treatment, for energetic valorization. In this work, a kinetic model for the thermal decomposition of PVC has been developed, in view of its de-chlorination. DTA/TGA testing at different temperatures indicated a first order reaction and an activation energy of 133,800J/mol. An almost completed de-chlorination reaction was obtained at 340°C under an inert atmosphere. The resulted material is a C(n)H(n) type polymer with potential to be used in an energy recovery process. Validation test performed at laboratory scale indicate that the temperature of 340°C enables the removal of ～99.9% of the chlorine present in PVC. The chloride can be fixed in the form of an aqueous solution of HCl or calcium chloride, driving to an alternative full process with environmental benefits and reduction of the costs associated to the PCV - containing materials/wastes management.     

Electrodialysis for NaCl/EG solution using ion-exchange membranes

A new concept for the recycling of poly(vinyl chloride) (PVC) has been introduced, including the dehydrochlorination of PVC in ethylene glycol (EG) with NaOH as a reactant, the subsequent separation of NaCl from EG by electrodialysis, and the recovery of chlorine for the synthesis of new PVC. In this work, the separation of NaCl by electrodialysis was investigated. About 98 % of the salt were recovered from EG, with less than 10 % of the EG permeating the membranes after 5 h.     

Development of a catalytic dehalogenation (Cl,Br) process for municipal waste plastic-derived oil

Dehalogenation is a key technology in the feedstock recycling of mixed halogenated waste plastics. In this study, two different methods were used to clarify the effectiveness of our proposed catalytic dehalogenation process using various carbon composites of iron oxides and calcium carbonate as the catalyst/sorbent. The first approach (a two-step process) was to develop a process for the thermal degradation of mixed halogenated waste plastics, and also develop dehalogenation catalysts for the catalytic dehydrochlorination of organic chlorine compounds from mixed plastic-derived oil containing polyvinyl chloride (PVC) using a fixed-bed flow-type reactor. The second approach (a single-step process) was the simultaneous degradation and dehalogenation of chlorinated (PVC) and brominated (plastic containing brominated flame retardant, HIPS–Br) mixed plastics into halogen-free liquid products. We report on a catalytic dehalogenation process for the chlorinated and brominated organic compounds formed by the pyrolysis of PVC and brominated flame retardant (HIPS–Br) mixed waste plastics [(polyethylene (PE), polypropylene (PP), and polystyrene (PS)], and also other plastics. During dehydrohalogenation, the iron- and calcium-based catalysts were transformed into their corresponding halides, which are also very active in the dehydrohalogenation of organic halogenated compounds. The halogen-free plastic-derived oil (PDO) can be used as a fuel oil or feedstock in refineries.     

Degradation of PVC Containing Mixtures in the Presence of HCl Fixators

Degradation of a model polymer mixture (PVC/PS/PE) and a waste polymer mixture in the presence of HCl fixators (Red Mud, precipitated CaCO₃ and dolamite) was studied using thermal gravimetric analysis (TGA) and a cycled-spheres-reactor. The experiments in cycled-spheres reactor model were performed by stepwise pyrolysis. Liquid products and HCl from each step were collected separately. For the model polymer mixture, the precipitated CaCO₃ showed the best effect on the fixation of evolved HCl and the reduction of chlorine content in the liquid products whereas RM yielded the best result for the waste polymer mixture. In addition, using HCl fixator also affected the degradation of both types of polymer mixture, leading to the formation of more gaseous and less residue.     

Alkaline hydrolysis of PVC-coated PET fibers for simultaneous recycling of PET and PVC

Journal of Material Cycles and Waste Management - Polyvinyl chloride (PVC)-coated poly(ethylene terephthalate) (PET) woven fibers are one of the hardest-to-recycle polymeric materials. Herein we...     

Aminolysis and aminoglycolysis of waste poly(ethylene terephthalate)

This paper describes the chemical degradation of waste poly(ethylene terephthalate) (PET) with polyamines or triethanolamine, the characteristics of the products, and a search for ways to use these products. Solvolysis of the polymer ester bonds was caused by diethylenetriamine, triethylenetetramine, and their mixtures, as well as mixtures of triethylenetetramine and p-phenylenediamine or triethanolamine. Products of aminolysis or aminoglycolysis of PET obtained in reactions performed at 200–210°C (with a molar ratio of the recurrent polymer unit to amine of 1 : 2) have been characterized using nuclear magnetic resonance (NMR). Viscosity and hydroxyl number measurements have been done for PET/triethanolamine products. Substances from aminolytical reactions with polyamines were tested as hardeners for liquid epoxy resins, and the product of polymer aminoglycolysis with triethanolamine was tested as an epoxy resin hardener, e.g., for water-borne paints, and a polyol component for rigid polyurethane foams. The compositions of epoxy resin hardeners have been characterized using DSC and rheometry. Comparative analyses of the hardened epoxy materials have been done on the basis of glass temperature and mechanical properties data, as well as some specific properties of the coating materials and rigid polyurethane foams. Received: September 15, 2000 / Accepted: September 21, 2000     

Pet Waste Management by Chemical Recycling: A Review

The paper reviews the problem due to the use and disposal of synthetic polymers to the environment and its solutions; in particular poly (ethylene terphthalate). Wide spread application and non-biodegradability of the PET creates huge amounts of waste and disposal, tend to a serious problem. The most important cause for recycling and reprocessing the waste PET has arisen from the awareness and concern for environmental pollution. To manage this various methods of polymer recycling has been proposed. Among them chemical recycling, i.e. hydrolysis, methanolysis, glycolysis and aminolysis are reviewed in detail. Appropriate technology and waste disposal procedures based on the socio-economic aspect to solve this problem are suggested.     

A New Unsaturated Poly(ester-urethane) Based on Terephthalic Acid Derived from Polyethylene Terephthalate (PET) of Waste Bottles

The new unsaturated poly(ester-urethane) was synthesized by the reaction of 4,4??-methylenediphenyldiisocyanate with 4,4??-di(2,3-butenhydroxyl) terephthalate in the ratio of 1:1. 4,4??-di(2,3-butenhydroxyl) terephthalate was first prepared by reacting 2?mol of cis-2-butene-1, 4-diol with 1?mol of terephthalic acid. The terephthalic acid used was derived from the recycling of PET bottles via subjection to saponification process. The synthesized compounds were characterized by CHN analysis, FT-IR, ¹H NMR and UV?CVis spectroscopy, with consistency of results showing the presence of the new unsaturated poly(ester-urethane) II. Thermal properties of the new polymer was verified by differential scanning calorimetry and thermogravimetric analysis, whereas the mechanical properties were characterized by tensile, elongation, hardness, adhesion and impact testing. The electrical conductivity and the electrical resistance of the compound were observed with increasing applied voltage.     

Recovery of solid fuel from municipal solid waste by hydrothermal treatment using subcritical water

Hydrothermal treatments using subcritical water (HTSW) such as that at 234 °C and 3 MPa (LT condition) and 295 °C and 8 MPa (HT condition) were investigated to recover solid fuel from municipal solid waste (MSW). Printing paper, dog food (DF), wooden chopsticks, and mixed plastic film and sheets of polyethylene, polypropylene, and polystyrene were prepared as model MSW components, in which polyvinylchloride (PVC) powder and sodium chloride were used to simulate Cl sources.While more than 75% of carbon in paper, DF, and wood was recovered as char under both LT and HT conditions, plastics did not degrade under either LT or HT conditions. The heating value (HV) of obtained char was 13,886-27,544 kJ/kg and was comparable to that of brown coal and lignite. Higher formation of fixed carbon and greater oxygen dissociation during HTSW were thought to improve the HV of char.Cl atoms added as PVC powder and sodium chloride to raw material remained in char after HTSW. However, most Cl originating from PVC was found to converse into soluble Cl compounds during HTSW under the HT condition and could be removed by washing.From these results, the merit of HTSW as a method of recovering solid fuel from MSW is considered to produce char with minimal carbon loss without a drying process prior to HTSW. In addition, Cl originating from PVC decomposes into soluble Cl compound under the HT condition. The combination of HTSW under the HT condition and char washing might improve the quality of char as alternative fuel.     

Nucleophilic substitution of poly(vinyl chloride) with iminoacetic acid and n-dodecanethiol

The modification of poly(vinyl chloride) was carried out with iminodiacetic acid (IDA, C₄H₇NO₄) and iminodiacetic acid dimethylester (IDADM, C₆H₁₁NO₄), as well as with n-dodecanethiol (DT, C₁₂H₂₆S) in the presence of K₂CO₃. The reaction was carried out at different temperatures below 100 °C with dimethyl formamide (DMF) and cyclohexanone as solvents. IDA did not show any reactivity, probably due to the dipolar character of the molecule. IDADM caused the elimination of HCl, while only substitution ratios of about 3 % were observed. However, the modification of PVC with DT resulted in a substitution rate of 18 % without elimination. DT-PVC showed excellent thermal properties, comparable with those of the unmodified polymer.     

High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas–liquid fluidized bed reactor

In this research a gas–liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas–liquid fluidized bed reactor was running at 280–320 °C, where hot N₂ was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N₂ to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300 °C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1 min after melting is completed as the flow rate of N₂ gas was set around 0.47–0.85 Nm³ kg^?1 for the molten PVC. Larger N₂ flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N₂ flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas–liquid fluidized bed reactor for dechlorination.     

Depolymerization of Waste PET with Phosphoric Acid–Modified Silica Gel Under Microwave Irradiation

Chemical recycling of waste poly(ethylene terephthalate) (PET) using phosphoric acid–modified silica gel as a solid catalyst is reported. Advantageously, microwave irradiation was used to progress the depolymerization of PET. In this study, depolymerization of PET with a small amount of water is suggested as a suitable method. The depolymerized product, terephthalic acid was obtained and assigned by ¹H NMR and FT-IR spectroscopy. Finally, over 90 % conversion to terephthalic acid was achieved when waste plastic bottles were treated with the method. This results confirm the importance of the microwave power technique as a promising recycling method for plastic bottles made from PET, resulting in monomer recovery in addition to substantial energy saving.     

Pyrolysis kinetics of waste PVC pipe.

The pyrolysis kinetics of waste PVC pipe was investigated with a thermal gravimetric analysis system at heating rates of 5, 10, and 30 degrees C/min in a nitrogen atmosphere. Freeman-Carroll method was employed to evaluate kinetic parameters. Two dominant peaks were observed on derivative gravimetric curves, hypothetically suggesting a two-stage apparent reaction model. The first-stage reaction was likely to be represented by stoichiometric reaction to yield volatiles (mainly HCl) and intermediates. The second-stage reaction might be described by thermal degradation of intermediates competitively into gas, liquid, and solid by-products. Quasi-isothermal operations were introduced to verify the reaction types of the first and second reaction. The generation reaction of intermediates achieved at lower temperatures was carried out independently with their decomposition reaction at higher temperatures. The effects of additives on the pyrolysis kinetics of waste PVC pipe seem to be significant, especially on the first-stage reaction. The first-stage reaction was retarded. A merged peak at low temperatures was observed on the derivative thermogravimetry (DTG) curve instead of two peaks usually observed for that of pure PVC resin. The first peak on the DTG curve of pure PVC resin may shift more, resulting in the complete overlap of two peaks. The quantity of evolved HCl was likely to decrease because of interaction of metal components of stabilizers with either HCl or active chlorine atom or both. The final residual fraction increased as a result of pyrolysis of organic forms of additives to yield extra char. On the other hand, the second-stage reaction kinetics demonstrates a similar pattern to that of pure PVC resin, implying that the effects of additives may be less significant in comparison with that at the first-stage reaction.     

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.     

Vinyl 2010 — nearing the target date

For almost 10 years, Vinyl 2010 has provided original approaches to technical, environmental, and political problems relating to poly(vinyl chloride) (PVC) material cycles and waste management. On the one hand, PVC has outstanding qualities in a wide range of applications; on the other hand, concerns about potential impacts attributed to production, additives, and waste management led to calls for PVC-specific regulations and mandatory substitution in certain applications. Considering the entire life cycle of PVC products, the industry proposed a comprehensive set of measures rendering production cleaner, eliminating controversial additives, and promoting responsible management of waste, favoring recycling. Vinyl 2010 can now be regarded as a highly successful example of applying voluntary commitments instead of the more usual command and control approach from regulatory authorities.     

Evaluation of Poly(ethylene-terephthalate) Products of Chemical Recycling by Differential Scanning Calorimetry

Poly (ethylene-terephthalate), (PET) bottles waste was chemically recycled by glycolysis and hydrolysis. The depolymerization processes were carried out in different time intervals from 5 to 360 min, in two different molar ratios of PET/EG, 1:5 and 1:18 and at different temperatures. The PET glycolysis leads to formation of bis(2-hydroxy-ethyl)terephthalate (BHET) monomer and PET oligomers with hydroxyl and carboxyl end groups while PET hydrolysis is followed by formation of monomers terephthalic acid (TPA) and ethylene glycol (EG). Fractions of monomers and oligomers were further characterized by FTIR spectroscopy and by differential scanning calorimetry (DSC). The results show that DSC is successful method to describe the different structures of oligomers formed during chemical recycling of PET.     

Chemical Recycling of PET Waste with Multifunctional Pentaerythrytol in the Melt State

Chemical recycling of poly(ethylene terephthalate) PET waste in the melt state through alcoholysis with multifunctional alcohol—pentaerythrytol (PENTE)—was performed in a internal mixer Haake Rheomix 600, at 250 °C, 60 rpm, for 10 min, in presence of zinc acetate. The following PET:PENTE molar ratios 1:0; 1:0.16; 1:0.48 and 1:3.4 were studied. The chemical structure of the end-products was characterized by FT-IR. Thermal properties and X-ray diffractograms were also assessed. The esterification and alcoholysis reactions took place and were dependent on the molar ratio. The first one is dominant in compositions rich in PET leading to the formation of star-branching copolymer. The second one brings about the PET oligomerization and an oligoester named herein bis(tri-hydroxylneopentyl) terephthalate (BTHNPT) was obtained. The end-products have potential application as asphalt additive or adhesive.