PVC - THE POISONOUS POLYMER

Polyvinyl chloride or PVC stands out as one of the most difficult plastic wastes to manage and causes serious problems for the recycling of other plastics. It comes in two forms, rigid and flexible. The more flexible form of PVC has plasticizers added such as phthalates. The flexible form is used as flooring, imitation leather, and cable insulation, but also as trays for sweets, fruit packaging, bubble foils, and other food packaging. The rigid form is mainly used in construction for water pipes, window frames, doors, and so on.

PVC has a high toxicity potential due to the relatively high content of chlorine (vinyl chloride is a class A carcinogen, toxic to the liver) in its formulation and a range of additives, including high concentrations of phthalates, and to a lesser extent lead and cadmium, which are added as stabilizers. PVC generates problems when burned in incinerators, as the chlorine content of PVC, which varies between products but can be as high as 57%, acts as a catalyst for the generation of dioxins and other UPOPs (Katami et al., 2002). Many municipal waste incinerators have a clause in the operating licence that excludes PVC as a permitted waste to try and avoid additional dioxin generation. When buried in landfills, lead, cadmium and phthalates can leach from PVC to contaminate groundwater. When burned in the open, as is the case in many developing countries, PVC (and other halogenated plastics) produce hazardous acid gases, di-oxins, and other UPOPs, especially if combined with plastics treated with brominated flame retardants .

Figure 14. Potentially recyclable polymers.

In landfills, phthalates migrate from PVC at high concentrations into the leachate and eventually into groundwater . Lead and cadmium stabilizers also present a leaching .

The high concentration of phthalates in flexible PVC has been a significant concern due to the endocrine disruption potential of phthalates. In PVC, medical equipment is a particular concern due to the exposure scenario for patients and phthalate concentrations of up to 40% by weight for intravenous medical bags and up to 80% by weight in medical tubing .

PVC has lead added as a stabilizer, but this has been found to readily leach out during use, contaminating drinking water in PVC pipes. In the EU, lead was phased out of PVC by 2015, but overseas imports may still contain lead.

PVC and its building blocks cause significant pollution and hazardous exposure during production, during use, and at its end of life. The building block for PVC’s manufacture is the production of vinyl chloride monomer (VCM). Production of VCM in China, one of the world’s largest producers of PVC, differs from most VCM production elsewhere in the world. Due to an abundance of coal and limited reserves of gas, China uses acetylene derived from coal instead of ethylene from gas to produce VCM. This coalbased manufacture of VCM combines acetylene with hydrogen chloride, and they flow through a mercuric chloride catalyst to produce VCM.19 This production process results in large quantities of mercury emissions to air, as well as mercury waste and releases. Since the early 1970s, VCM has been recognized as an occupational carcinogen (Creech and Johnson 1974).

When PVC enters the recycling system, it is imperative that it is separated from other polymers to prevent contamination of the plastic recycling output. In practice, this separation can be very difficult and expensive to carry out as plastics may arrive at the recycling facility in pieces, making identification even more challenging. When attempting to recycle PVC back into PVC by mechanical means, the problem is that PVC has many different formulations beyond simply rigid and flexible characteristics requiring varying levels of chlorine and additives. Mixing these together results in a poor quality of recyclate which is unlikely to meet the specific input needs of PVC manufacturers, and cause loss of structural integrity in the final product made from the recyclate.

When PVC is mixed with other types of polymers in a mechanical recycling process, there are similar issues and the PVC effectively ‘contaminates’ other polymers, degrading their structural properties and inhibiting production processes such as extrusion. When processing mixed polymers, the recycler is forced to heat the mixed polymers to the highest polymer melting point of the mixture. This can lead to overheating and degradation of lower melting point polymers in the mix. This is the case when PET and PVC are heated together to the higher melting point of PET, causing accelerated dehydrochlorination of the PVC.

Chemical recycling of PVC also suffers from difficulties associated with chlorine and phthalate additives. The presence of even small amounts of PVC in the input plastic stream of a pyrolysis unit leads to contamination of the output polymers by hydrochloric acid (HCl), which must be removed. Hydrochloric acid is highly corrosive and imposes severe metallurgical constraints on the process equipment of the pyrolysis unit. If the pyrolysis output is an oil or wax, even very small amounts of halogens prevent its use as fuel or feedstock .

Phthalate additives also challenge solvent processing. An example of how additives can relegate recycling unviable is the closure of the VinyLoop plant in Italy which operated since 2002 but shut down in 2018 because it could not economically separate the substantial amounts of phthalate plasticizers used in soft PVC to meet EU regulatory requirements (European Commission 2018).