Phenol-urea-formaldehyde resin co-polymer synthesis and its influence on Elaeis palm trunk plywood mechanical performance evaluated by 13C NMR and MALDI-TOF mass spectrometry

This study evaluated a new method of producing phenol-urea-formaldehyde (PUF) adhesives formulated differently under actual in-situ resin synthesis conditions. This was carried out by co-polymerizing urea formaldehyde (UF) resin with phenol-formaldehyde resin in the core layer of low molecular weight (LMW) phenol-formaldehyde (PF) resin treated Elaeis palm trunk veneers during the gluing process of Elaeis palm plywood. Matrix assisted laser desorption Ionization time of flight (MALDI-TOF) mass spectrometry (MS) illustrated and confirmed a series number of the phenol-urea co-condensates repeating unit in the prepared PUF resins which corroborated well with its mechanical properties (modulus of elasticity and modulus of rupture), bonding quality (dry test and weather boil proof or WBP test) and physical properties. A series of PF, UF and PUF resins oligomers forming repeating units up to 1833 Da were identified. Besides that, the solid state (13)Carbon nuclear magnetic resonance (NMR) interpretation identified that the signal at 44-45 ppm and 54-55 ppm corresponding to methylene bridges were co-condensated in between phenol and urea in the PUF resin system. The C-13 NMR investigation showed that the synthesis process of PUF resin contained no free formaldehyde elements. Furthermore, the proportion of urea and methylolureas in the mixture to synthesis PUF resin were sufficient and incorporated well into the formulation by reacting with LMWPF units to form co-condensed methylene bridges. This study showed a new and useful method to synthesize PUF resin during the gluing process of manufactured Elaeis palm plywood which can also enhance the performance of Elaeis palm plywood panels for structural instead of utility grade applications. (C) 2015 Elsevier Ltd. All rights reserved.