DOI 10.1007/s00107-005-0048-x KURZORIGINALIA · BRIEF ORIGINALS Holz als Roh- und Werkstoff (2005) 63: 477–478 Aldo Ballerini · A. Despres · Antonio Pizzi Non-toxic, zero emission tannin-glyoxal adhesives for wood panels Published online: 3 November 2005  Springer-Verlag 2005 Abstract In this study different tannin-glyoxal glue mixes for particleboard were studied. Gel times at 100 ◦ C of 45% water solutions of commercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with re- spectively 8% paraformaldehyde and 9% glyoxal were done at different pHs. Duplicate one layer laboratory particleboards were prepared by adding 12% total resin solids of adhesives composed of commercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with paraformaldehyde, or glyoxal or polymeric 4,4’ di- phenylmethanne diisocianate (pMDI), respectively. It was found that tannin-glyoxal panels which do not contain formaldehyde and with an emission equal to that of unbounded wood can be obtained by the use of glyoxal as hardener. 1 Introduction Tannin adhesives have been used extensively in several coun- tries in the Southern Hemisphere and are starting now to be used industrially in Japan and there is also interest for their use in Europe. The quest to decrease or completely eliminate formal- dehyde emission from wood panels bonded with adhesives, alt- hough not really necessary in polyflavonoid tannin adhesives due to their already low emission (as for most phenolic resins), has nonetheless promoted some research to further improve their formaldehyde emission. As part of the quest for zero formal- dehyde emission adhesives, tannin adhesives based on tannin autocondensation (Pizzi et al. 1995), on hexamine as hardener (Pizzi et al. 1994, Pizzi et al. 1995, Pizzi et al. 1996, Pizzi et al. 1998, Pichelin et al. 1999) and on nitroparaffins as hardeners (Trosa and Pizzi 2001) have already been proposed and some of these technologies are now already in commercial use. Glyoxal is a non-volatile, reactive aldehyde which is qualified as non- A. Ballerini (✉) Dept. of Wood Engineering, University of B´ ıo-B´ ıo, Concepci´ on, Chile E-mail: aballeri@ubiobio.cl A. Despres · A. Pizzi ENSTIB, University of Nancy 1, Epinal, France toxic with a LD 50 > 7000 mg/kg body weight and is as such a prime candidate for use as a hardener for exterior grade tannin adhesives. In this study different tannin-glyoxal adhesives were studied. 2 Materials and Methods Gel times at 100 ◦ C of 45% water solutions of commercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with 8% paraformaldehyde and 9% glyoxal respectively were done at the different pHs shown in Fig. 1. Duplicate one layer laboratory particleboard of 350 × 350 × 14 mm dimensions were prepared by adding 12% total resin solids of adhesives composed of com- mercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with paraformaldehyde, or glyoxal or polymeric 4,4’ diphenyl- methane diisocianate (pMDI) respectively according to the re- lative percentages by weight shown in Table 1. The percentage moisture content of the resinated particles was of 20%–22%. Total pressing time was 7.5 minutes and the press cycle was 2 mi- nutes from panel contact to maximum pressure of 3.5 MPa and holding, followed by a descending pressing cycle of 2.5 minu- tes at 1.6 MPa and 3 minutes at 0.8 MPa, at 190 ◦ C–195 ◦ C press Fig. 1 Comparison of gel times as a function of pH of pine tannin + 8% paraformaldehyde and of pine tannin + 9% glyoxal Abb. 1 Vergleich der Gelierzeiten in Abhängigkeit vom pH für Kieferntan- nin mit 8% Paraformaldehyd sowie für Kieferntannin mit 9% Glyoxal.