Technically Speaking: Measuring formaldehyde | 49
FORMALDEHYDE MEASURING
Dr Morwenna Spear of Bangor University’s BioComposites Centre looks at the question of formaldehyde and how we measure it
W
e might expect that everyone in the wood-panels industry is aware of
formaldehyde as a challenge to be kept at bay. Colleagues in mills may be always watching for new resins, new scavengers, clever adjustments to press conditions or other approaches to stay one step ahead of the game. Indeed, the industry has made enormous progress over the decades to reduce levels to a tolerable or even acceptable level. For this issue’s Technically Speaking I thought it high time to take a refresher and consider what formaldehyde is, and how we measure it. Then, because formaldehyde is such a complex but intriguing topic, I soon discovered we might need a couple of issues to cover all the angles! Here we’ll start with the formaldehyde content, which is different from the formaldehyde emissions (see next issue). Formaldehyde is a small organic compound
(HCHO) that is an integral component of several of the resins that are used in wood- based panels. Especially urea formaldehyde – the most commonly used option, but also melamine urea formaldehyde resins, phenol formaldehyde and others like phenol resorcinol formaldehyde.
In all of these resins, the formaldehyde is fully chemically reacted with the other ingredient (e.g. the urea or the phenol). A covalent bond forms, and the thermosetting resin is made. But the reaction is sometimes incomplete, as there may be more formaldehyde present than the other component to react with it (or sometimes vice versa).
The ratio is one of the main options in tuning UF resin manufacture. This could lead to a small amount of free formaldehyde (that’s not bonded) which can evaporate from the board. Usually this occurs pretty quickly after pressing is complete – while the panel is hot. Formaldehyde is a gas, and its rapid migration out of solids like wood panels leads to it being terms a volatile organic compound (VOC). Like many other VOCs, we need to be careful with how much is present in the atmosphere for people to inhale.
But for some of the resins I named
above a second process may happen, called hydrolysis. This involves small amounts of
Formaldehyde emissions from wood-based panels are a big focus point. Photo: Shutterstock
www.wbpionline.com | Summer 2026 | WBPI
water (from the atmosphere) which are able to react with the chemical bonds in the UF resin and undo the covalent linkage. This process happens slowly, and at low levels. It can go on for years after manufacture. This is why formaldehyde emissions (see next issue) need to be considered, not just the free formaldehyde at the end of manufacturing. Such values are low but are also the most relevant for the customer – as they relate to the atmosphere when the board is in use somewhere. However, for the manufacturer, seeking
to understand the board quality, and how well the resin cured, the formaldehyde content (sometimes called Total Extractable Formaldehyde, TEF) is useful. There’s a European standard for this (EN 120) and it uses solvent to remove every possible molecule of formaldehyde that’s not firmly chemically bonded into the resin. Small cubes are cut from the test panel and boiled in toluene for 2 hours. The vapours are cycled through water in a special type of glassware called a perforator. The
formaldehyde which starts in the toluene migrates into a second solution which is used for the next step in the analysis. This water solution with formaldehyde in it is handled quantitatively and a standard sized sample taken for acetylacetone reaction. After reacting, the test sample gains a slight straw yellow colour (if the formaldehyde content is strong) and this is measured using a UV spectrometer.
The results from the test sample panels are
compared with values for calibration solutions of known concentrations to get a precise value for the panel. At the end we have a quantity of formaldehyde in milligrams per 100g of dry board. These values are useful to the manufacturer (especially the team making and adjusting the resin, but also the quality control team), but don’t necessarily relate directly to the emissions the board will give in service. For example, they may not show the benefit of the scavenger (which helps trap and retain formaldehyde slowing release into the atmosphere). We’ll look at the tests that relate to formaldehyde emissions next time
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