Reducing formaldehyde emission from wood-based materials

In this research project with the University of Ljubljana/Slovenia, the Fraunhofer Institute for Wood Research assessed the effectiveness of formaldehyde scavengers on the reduction in formaldehyde emissions from wood-based materials bound with urea-formaldehyde resin. 

© Photo Fraunhofer WKI

Formaldehydemission (EN 717-1) von mit Harnstoffformaldehydharz gebundenem Buchenfurniersperrholz. A: ohne Formaldehydfänger, B: mit Harnstoff, C: mit Harnstoff/Tannin.

© Photo Fraunhofer WKI

Formaldehydabgabe (EN 717-3) von mit Harnstoffformaldehydharz gebundenen Spanplatten. A: ohne Formaldehydfänger, B: mit Tannin, C: mit Harnstoff/Tannin. 

© Photo Fraunhofer WKI

Formaldehydabgabe (EN 717-3) von mit Harnstoffformaldehydharz gebundenen mitteldichten Faserplatten (MDF). A: ohne Formaldehydfänger, B: mit Harnstoff, C: mit Harnstoff/Tannin.

The reduction of formaldehyde emission from wood-based materials and the products made from them has been pursued by researchers in the adhesive and wood-based materials industries for many years. The International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) declared formaldehyde as a carcinogen in 2004 and the U.S. Department of Health and Human Services followed suit in 2011. Furthermore, recommendations on room hygiene, regulative and normative developments on national and EU levels and the introduction of other assessment systems with very low formaldehyde limits have become significant challenges in the restriction of formaldehyde emissions for wood-based materials.

Germany has had a legally defined maximum of 0.1 ppm for formaldehyde emission (emission class 1, test chamber method EN 717-1) since 1986. The F**** system in Japan, the California Air Resources Board (CARB) rulings and the related IKEA specification ISO-MAT-0003 are other regulations which are also applied. The European chamber test equivalent to the CARB system phase 2 defines limits of 0.065 ppm for particleboard and 0.03 ppm for plywood. The European Panel Federation EPF agreed on a reduction of formaldehyde emission to a maximum of 0.065 ppm (test chamber method EN 717-1) in summer 2011 for CE-labelled, uncoated wood-based materials for use in the building trade (EN 13986). The recommended limit is to be implemented in European standardization. It can be assumed that legislators will also further reduce the current legal formaldehyde emission limit for all wood-based materials in future.

Wood-based materials’ formaldehyde emission depend on numerous factors such as wood species, wood preparation, recycling material, adhesive, additives, moisture content, board composition, pressing conditions, subsequent treatment and the age of the material. The most important ways to reduce formaldehyde emission from wood-based materials bound with aminoplast resin are:

• Use of low-formaldehyde or formaldehyde-free resins
• Use of modified urea-formaldehyde resins
• Optimization of the manufacturing parameters (wood species, layers of the panel, moisture, pressing conditions)
• Use of formaldehyde scavengers
• Application of a diffusion barrier
• Subsequent treatment of the material with formaldehyde-binding systems
• Storage of the wood-based materials

In a research project with the University of Ljubljana/Slovenia, the Fraunhofer Institute for Wood Research assessed the effectiveness of formaldehyde scavengers on the reduction in formaldehyde emissions from wood-based materials bound with urea-formaldehyde resin. The work concentrated strongly on the use of tannin as a formaldehyde scavenger. Tannins are polyphenolic extracts from wood and bark. These tannins, condensed from acacia bark or quebracho wood for example, can form polymer networks when they react with the formaldehyde and act as a binding agent in wood-based materials.

In these investigations, three-layer, beech veneer plywood was made using urea-formaldehyde resins. The specimens contained different formaldehyde content levels. Urea and quebracho tannin were used as formaldehyde scavengers. The plywood formaldehyde emission, measured using the test chamber method (EN 717-1), were significantly reduced by the tannin, especially in the case of the urea-formaldehyde resin which was richer in formaldehyde (Fig. 2). The formaldehyde emission were under the limit of 0.065 ppm recommended by the EPF. Emission levels similar to untreated natural wood were achieved when using urea or urea combined with tannin in the case of the low-formaldehyde urea-formaldehyde resin. The tensile shear strength of the plywood bound with low-formaldehyde urea-formaldehyde resin was improved by the use of the tannin. The formaldehyde emission from particleboards (Fig. 3) and medium density fiberboards (Fig. 4) were reduced slightly by using tannin and significantly by adding urea (Fig. 3 and 4).

Further work is being conducted to reduce the formaldehyde emission of particleboard and MDF with a particular focus on the influence of particle moisture, board composition and the pressing conditions.

For further details log on website :
https://www.wki.fraunhofer.de/en/departments/vst/profile/research-projects/formaldehyde-emission-from-wood-based-materials.html