An interesting point was raised at the recent 5th European Wood-Based Panel Symposium by Professor Marutzky. He said that if urea and melamine formaldehyde resins were banned for use in WBPs, then the industry as we know it would cease to exist because there are insufficient quantities of alternative adhesives. This may be true now, but what about the future? Could another adhesive dominate the WBP industry as the aminoplasts have? To do so it would have to perform as well as, or better than, the aminoplasts and come from renewable resources. Such adhesives have existed for a long time, with many based on tannins, proteins and starches. Of these, the tannins have achieved most success, being used to make plywoods and particleboards commercially, either as pure adhesive or as an additive to a synthetic adhesive. Tannins are a complex group of phenolic compounds concentrated in the bark of many trees. There are two types: hydrolysable and condensed. The hydrolysable tannins are not used for adhesives as they tend to have lower molecular weights and lower reactivity to formaldehyde. Condensable tannins on the other hand, react readily with formaldehyde. Flavonoids are the monomers of condensed tannins. The four structures (above) represent the monomer units thought to be most relevant to the adhesives industry. If we disregard the technological difficulties of using tannin-based adhesives - inconsistency, mechanical characteristics, colour, etc - and assume these can be overcome, could tannin-based adhesives replace aminoplasts? According to the FAO, world production of WBPs in 2005 was 231.5 million m³. Assuming an adhesive content of 8%, the quantity required is around 18.5 million tons, 90% of which are aminoplasts. So, around 16 million tons of tannin per year would be needed to replace aminoplasts. The FAO also states that the world produced 3,490 million tons of roundwood in 2005. Assuming that 30% of the trees could yield some useful bark, that the bark represents 15% of log volume, and that a supreme effort is made to harvest the bark, resulting in, say, 50% being available for processing, then 78 million tons of bark would be available. The condensable tannin content of bark varies widely, but, assuming an extraction level of 10%, then almost eight million tons of tannin would be available for adhesives. Even with the rather generous assumptions used above, the quantity of tannin is insufficient. This shows that demonstration of the viability of an adhesive must also be supported by sufficient volumes. Tannin based adhesives and those based on other renewable molecules do have a future, but, the transition is not going to be quick and will demand long-term planning at the governmental level. Questions? Email: mark.irle@ecolesuperieuredubois.com