Polypropylene vs PVC

A brief look at some environmental issues.

There are significant intrinsic differences between polyvinyl chloride (PVC) and polypropylene (PP).

Polypropylene is one of the most neutral plastics, containing only two elements: carbon (C) and hydrogen (H).

PVC by comparison contains about 30% by weight, of the element Chlorine (Cl) in its basic structure. It is well documented that chlorine, like all halogens, is a dangerous substance in the environment.

When PVC is incinerated or present in accidental fires it produces toxic byproducts such as dioxins, chlorocarbons and hydrochloric acid. Complete combustion of PP, on the other hand, will generate only carbon dioxide and water.

PVC is intrinsically heat unstable and can even decompose during processing. PP is much more tolerant to heat; even under extreme conditions it will only decompose to lower molecular weight paraffins, which are elementally compatible with the base material.

Not only is PVC inherently dangerous in its basic form, but it also needs a large amount of lead to stabilise it. Lead is highly toxic both during the life cycle of a product and after its disposal. This is why there is neither lead nor other heavy metals used in the manufacture of PP sheet.

Polypropylene sheet is manufactured from propylene monomer, a relatively safe gas, which is a waste byproduct of the petroleum industry that used to be burned off into the atmosphere contributing to greenhouse gas emissions. As a consequence, the more polypropylene used in products helps in reducing greenhouse gas emissions.

Contrariwise, the monomer unit, which forms the building blocks of PVC, is very toxic. Stringent guidelines are in place for its proper handling as it is highly dangerous to transport and store. There have been numerous studies of the negative health effects on workers exposed to PVC monomer.

 

A further problem with flexible PVC is that the flexibility and softness must be induced by the addition of a large amount of plasticisers, usually phthalates, at concentrations of 30 - 50%. These phthalates may have carcinogenic properties or affect endocrinic activity in humans. They do this by mimicking the female hormone oestrogen, causing biological imbalances in humans as well as other species.

These plasticisers are mobile by nature, hence migratory. They leach out into the environment during long-term storage and into soil and aquifers after disposal. The 'mist', which accumulates on windscreens of cars containing PVC trim, is evidence of plasticiser migration. Other evidence of this instability may be seen where the print from a document migrates onto the PVC binder or file in which the document is stored.

It is impossible for these effects to occur in relation to polypropylene. The soft blend materials get their softness and flexibility from the actual molecular structure of the material, which is stable, rather than from any migratory additive.

Polypropylene is 100% recyclable .. PVC is not recyclable to the same extent, firstly because of its intrinsic chemical composition and also because of the additives it contains.

In summary, there is clear evidence that PP is a safer, non-toxic and environmentally friendly alternative to the obsolescent technologies that gave us plastics such as PVC.