On the formaldehyde release of wood

Abstract

The paper addresses the role of the main components of wood cellulose, hemicellulose, and lignin as well as of wood extractives as a potential source of formaldehyde. Lignin seems to have a higher emission potential than cellulose and hemicellulose. Moreover, the results reveal that on the one hand extractives release formaldehyde and on the other hand that certain wood extractives react with formaldehyde and hence act as a formaldehyde scavenger. Formaldehyde emanates from wood at temperatures as low as 40°C. Higher temperatures increase the formaldehyde emission tremendously. Therefore, thermo-mechanical pulping enhances formaldehyde release exorbitantely. Differences in the formaldehyde emission between wood species are discussed and related to differences in their chemical composition. Formaldehydfreisetzung aus HolzDie Hauptbestandteile von Holz, Cellulose, Hemicellulose und Lignin, sowie Extraktstoffe des Holzes wurden hinsichtlich ihres mo Èglichen Beitrags zur Formaldehydabgabe untersucht. Lignin scheint ein ho Èheres Formaldehydabgabepotential aufzuweisen als Cellulose oder Hemicellulose. Die Ergebnisse zeigen, dass bestimmte Holzextraktstoffe zum einen zur Formaldehydbildung beitragen ko Ènnen und zum anderen als Formaldehydfa Ènger fungieren. Aus den untersuchten Ho Èlzern wurde Formaldehyd bereits bei Temperaturen von 40°C freigesetzt. Ho Èhere Temperaturen lassen die Formaldehydbildung stark ansteigen. Dementsprechend erho Èht der thermo-mechanische Holzaufschluû die Formaldehydabgabe der hergestellten Fasern in groûem Ausmaû. Unterschiede in der Formaldehydabgabe verschiedener Holzarten werden aufgezeigt und in Beziehung zu der chemischen Zusammensetzung gebracht.

Understanding of Formaldehyde Emissions from Solid Wood: An Overview

“…On the other hand, the degree of polymerization of cellulose seems to have no significant influence on the emission of formaldehyde; also, raising the temperature to 100 and 150 °C, the formaldehyde liberation from starch is also very low even at high reaction temperatures (Schäfer and Roffael 2000).…”

“…Wood as a natural material contains formaldehyde (Meyer and Boehme 1997;Que and Furuno 2007;Salem et al 2011b), which can be released during thermal treatment (Schäfer and Roffael 2000). Meyer and Boehme (1996) measured the FEs from oak, Douglas fir, beech, spruce, and pine, and the emission of formaldehyde ranged between 2 and 9 ppb.…”

“…The FE from solid wood increases at elevated temperatures and prolonged heating times (Schäfer and Roffael 2000), even in the absence of wood resin (Jiang et al 2002). On the other hand, the degree of polymerization of cellulose seems to have no significant influence on the emission of formaldehyde; also, raising the temperature to 100 and 150 °C, the formaldehyde liberation from starch is also very low even at high reaction temperatures (Schäfer and Roffael 2000).…”

“…Formaldehyde can be formed from the main components of wood (cellulose, hemicelluloses, and lignin) as well as from its extractives (Schäfer and Roffael 2000) to different extents depending on the boundary conditions (pH value, temperature). On the other hand, the inorganic substances in wood do not directly contribute to formaldehyde release.The FE from solid wood increases at elevated temperatures and prolonged heating times (Schäfer and Roffael 2000), even in the absence of wood resin (Jiang et al 2002). On the other hand, the degree of polymerization of cellulose seems to have no significant influence on the emission of formaldehyde; also, raising the temperature to 100 and 150 °C, the formaldehyde liberation from starch is also very low even at high reaction temperatures (Schäfer and Roffael 2000).…”

The Effects of Sealing Treatment and Wood Species on Formaldehyde Emission of Plywood

“…The first one is that formaldehyde in the adhesive interacts in a distinct way with each wood species. The formaldehyde can form compounds with the cellulose of wood under the pressing conditions (high temperature and acid medium produced by the catalyst); the second one is that formaldehyde emission is affected by the anatomy of the respective wood species, such as porosity and density (Martinez and Belanche 2000); the third one is that certain wood extractives react with formaldehyde and hence act as a formaldehyde scavenger (Schafer and Roffael 2000). However, cellulose content of different wood species is very close in value.…”