Not so long ago, if the term VOC was mentioned, one's thoughts may have turned to a highly decorated war hero, a well paid American executive or you may have thought that someone was offering you an Advocaat or even a halfway decent brandy. The stark reality of the 21st Century however demands that this acronym be recognised as the somewhat disconcerting 'Volatile Organic Compound'.
Volatile Organic Compounds means organic materials that will form a vapour in air under the range of environmental conditions in which we live. Organic compounds means compounds (or chemicals) that use carbon as their basic building block and most jurisdictions have accepted that volatile means compounds that have a boiling point of less than 250°C at normal temperature and pressure. But all is not so simple as it might appear!
VOC listing (especially in America) is subject to political lobbying and there are many exemptions that simply defy logic. One can legitimately, in America, have a paint full of exempt solvents (even the very ominous sounding chloro-fluoro compound known as Parachlorobenzofluoride) yet still claim it to be VOC free.
Closer to home, the Australian Paint Approvals Scheme (APAS) exempts acetone - clearly a hazardous organic compound - yet includes ammonia, which, by definition is not organic!
Waterborne paints may include small amounts of VOCs as exipients in some of the raw materials used but the major deliberate use of VOCs is confined to two areas - coalescing agents and open time additives.
Although there are some exceptions to this rule, waterborne paints are generally made from somewhat hard polymers (to achieve film toughness), which are temporarily softened (to improve film formation) by the addition of a small percentage of volatile organic coalescing solvents. The most successful (both technically and commercially) of these coalescing solvents had a quoted boiling point of 246°C - clearly then a VOC.
The world's major supplier of this material recently changed its test method for determining boiling points and, lo and behold, it came out at 251°C - not a VOC! They have been able to convince the European Parliament and APAS as to the veracity of their results so that the material is no longer seen as a VOC. Because of this, VOC levels in many paints have dropped by about half at the stroke of a pen.
The drying rate of waterborne paints is dominated by weather conditions and generally needs slowing down to achieve good flow and to maintain a 'wet edge'. The additive of choice here is propylene glycol, a bland material that is used in medicines (both topical and oral), in a wide range of cosmetics and toiletries, and in foods, such as ice cream. It is defined as a VOC (as is this scribe's drug of choice - ethyl alcohol - active ingredient of wine and other spirituous liquors).
In a test in an environmental chamber designed to model the L.A. Basin, degradation products were found from propylene glycol, which were designated hazardous air pollutants. Although this has no known relevance outside the L.A. Basin (and dubious relevance even there) in the absence of other data, propylene glycol is damned as a polluting VOC.
There are games manufacturers can play with both coalescing and open time additives using slightly higher boiling homologues to improve their stated VOC level to further confuse an already confusing subject. In a gentler, more co-operative era, the New Zealand Paint Manufacturers Association agreed to help all members who were genuinely trying to reduce the toxicity of their products. It was agreed however, that trying to score marketing points by playing a VOC numbers comparison game was inappropriate in this confusing and hard to measure area.
This scribe should quietly retreat from the rat-race to the countryside but there I would be face to face (not literally) with all of the VOC belching cows and, even worse, those deadly pine forests spewing out their daily tonnes and tonnes of pinene (et al) VOCs. Is there no escape...?
The Resene architect's memo section provides technical information on a variety of topics relating to paints, finishes and coatings.