Use of FT-NIR spectroscopy for on-line monitoring of formaldehyde-based resin synthesis E. Dessipri a , E. Minopoulou b , G.D. Chryssikos c , V. Gionis c , A. Paipetis c , C. Panayiotou b, * a A.C.M. Wood Chemicals, c/o Adhesives Research Institute (A.R.I.) Ltd., Sofouli 88, Kalamaria, Thessaloniki 55131, Greece b Department of Chemical Engineering, Laboratory of Physical Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece c Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Ave, Athens 11635, Greece Received 14 February 2003; received in revised form 20 March 2003; accepted 20 March 2003 Abstract A new method is being developed for the fast and reliable assessment of the pathway(s) followed during formal- dehyde-based resin synthesis, both at laboratory and industrial scale. The method is based on Fourier transform Near Infrared (FT-NIR) chemometrics. No sample manipulation is necessary and the complete evaluation can be performed on- or off-line in less than 1 min. FT-NIR chemometrics were found to be valuable in providing a fast and consistent way of monitoring directly the effects of a change of resin formulation when evaluating new procedures at laboratory scale. Similarly, during industrial production, NIR will soon become a standard tool for ensuring reproducibility and improving overall quality. Measurements are performed on-line and deviations from the standard synthesis pathway can be detected early, allowing the necessary steps to be taken in order to return to the desired pathway. Furthermore, NIR methodologies have been developed to identify and check the conformity of raw materials and final products from urea and UFC solutions to laminated paper produced by impregnation with formaldehyde-based resins. This can prove particularly useful in applications (such as in laminated paper production) where the reproducibility of production and the effects of storage are both questionable and difficult to assess. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Adhesives for wood; Chemometrics; Reaction kinetics; Methylolation; Polycondensation 1. Introduction Formaldehyde-based resins have been known for many years. However, new formulations for their syn- thesis are still being based, mostly, on trial and error experiments, mainly for two reasons. First, there are many different factors that affect, in subtle ways, the synthetic pathway, which are sometimes difficult to control and accurately reproduce. Second, even with the most elaborate equipment, there are difficulties associ- ated with the accurate analysis of the intermediate and final products. This is due to the ‘‘living’’ nature of the system and the destructive nature of the sample ma- nipulations (dilution, drying, etc.) necessary for most analyses. Furthermore, these analyses are labour inten- sive, time consuming and, therefore, rather expensive. A new method is being developed for the fast and re- liable assessment of the pathway(s) followed during formaldehyde-based resin synthesis at both laboratory and industrial scale. The method is based on Fourier transform Near Infrared (FT-NIR) chemometrics. No sample manipulation is necessary and the complete eval- uation can be performed on- or off-line in less than 1 min. * Corresponding author. Tel.: +30-2310-996249; fax: +30- 2310-996222. E-mail address: cpanayio@auth.gr (C. Panayiotou). 0014-3057/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0014-3057(03)00073-9 European Polymer Journal 39 (2003) 1533–1540 www.elsevier.com/locate/europolj