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Author(s): Jorge Martins
Cristina Coelho
João Pereira
João Ferra
Luísa Carvalho
Title: Strategies to reduce formaldehyde emissions from wood-based panels: impact on physico-mechanical properties and machinability (Cap. 8)
Issue Date: 2017
Abstract: Formaldehyde is a common organic compound used as raw-material in several industrial applications, namely in urea-formaldehyde (UF), melamine-ureaformaldehyde (MUF) and phenol-formaldehyde resin (PF) production. These resins have been used in the manufacture of wood-based panels for decades, playing a central role within their production and properties. Since the reclassification of formaldehyde as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC) in 2004, several efforts have been made by industry to reduce formaldehyde in wood-based panels. New product classes based on formaldehyde emission emerged and different world regions have established their own classifications, reference methods, and standards, for example CARB in California, F**** in Japan, and E1Plus in Europe. Reduction in the F/U molar ratio has been a strategy adopted in the last decades to decrease formaldehyde emission. However, this reduction decreases the reactivity of UF resins. Another strategy is the use of scavengers. Natural or bio-based substances such as pozzolan, tannins, charcoal, starch, chitosan, and chemical compounds such as as primary and secondary amines, sodium sulfites, borax, and ammonium phosphates have been tested. Commercial formaldehyde scavengers are available on the market, usually based on amino compounds, polyalcohols, and other compounds. However, in certain cases they penalize physico-mechanical properties and have adverse effects such as discoloration of wood and formaldehyde reemission. Furthermore, the abrasive characteristics of formaldehyde scavengers could affect the machinability of wood-based panels. It is known that substances such as starch, added as fillers to the resin in plywood production, increase tool wear. In this chapter, a review of several formaldehyde test methods and release classes, as well as a comparison of results obtained at our laboratory (chamber, gas analysis, desiccators, and perforator methods) for particleboard produced with low formaldehyde emission (UF and MUF) resins are presented. An overview of the use of formaldehyde scavengers in wood-based panels is presented, as well as the latest development achieved by our team. The performance of several scavengers, namely sodium metabisulfite, ammonium bisulfite, and urea, is assessed through the resulting physico-mechanical properties and formaldehyde emission (perforator, desiccators, and gas analysis). The tested scavengers showed distinct performances under different emission testing conditions,whichwere interpreted in terms of the stability of the formed chemical compounds. The impact of the addition of formaldehyde scavengers on machinability is also addressed in a few case studies.
Source: Wood Composites: Materials Manufacturing and Engineering
Document Type: Capítulo ou Parte de Livro
Rights: restrictedAccess
Appears in Collections:FEUP - Capítulo ou Parte de Livro

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