Polyvinyl chloride (PVC)

Polyvinyl chloride (PVC), often referred to simply as vinyl, is an important industrial material produced in huge quantities. It is relatively cheap, resistant to weathering, water and corrosion, inherently non-flammable and easy to form. This balance of properties and performance make it very useful in building products (floors, windows, siding, pipes), cable sheathing, automotive (artificial leather, dashboards, trim) and packaging (shrink wrap and clamshell packs). As a flexible rubber and fabric, it is used in apparel, rubber boots, bags, toys and shower curtains.

Production of PVC continues to grow, despite its many environmental downfalls. It is made with petroleum-derived ethylene and chlorine derived from rock salt, which are reacted to form vinyl chloride. This chemical is extremely toxic to people and the planet and a suspected carcinogen.

On its own, PVC is quite brittle and vulnerable to degradation with exposure to heat and light. Therefore it is blended with additives to improve its properties. There are many different types used, which allows PVC to be tailored to a wide range of applications, from rigid to flexible to highly elastic parts.

Plasticisers are added to increase flexibility and toughness. There are typically based on phthalic acid esters or phthalates with doses in the region of 20-40%, but can be more than 50%. Their function is to allow the polymer chains in the plastic to slide against one another. So adding 20% results in added toughness and durability, through to a very soft gel-like material. Over the life of the material, plasticiser will migrate to the surface and into contact with people and the environment. It is not locked into the polymer structure. Phthalates are harmful to human health and a known carcinogen and endocrine disrupter.

Stabilisers are added to PVC to aid manufacturing, acting as antioxidants, and provide durability to heat and light exposure. These are typically based on compounds of tin, cadmium (Cd), lead (Pb), barium (Ba) and zinc (Zn). Heavy metals, and their ions, can pose a health hazard. For example, all forms of lead are considered extremely toxic to humans due to their cumulative effect. Cadmium is an accumulative poison in the list of the top 10 hazardous pollutants of UN Environmental Programs. Since stabilisers are suspended in the polymer structure, they can leach out or evaporate from the material over time.

PVC is a source of dioxin, produced during the production of dichloroethane from ethylene and chlorine, a highly toxic compound that is known to be a serious and persistent environmental pollutant. While dramatic improvements have been made to the chemistry of PVC and its production, old PVC is likely to contain some hazardous substances. This makes recycling challenging, because the material may be considered hazardous waste.

On the upside (if that’s possible considering how toxic this material is), non-toxic stabilisers (such as calcium-zinc) and non-phthalate plasticisers are available for sensitive applications, such as toys, packaging and medical devices. Also, partially bio-based PVC is possible with the use of bioethylene, derived from bioethanol. As with polyethylene (PE), PVC produced from bio-based ingredients provides a drop-in replacement for petroleum PVC.