Catalytic influence of wood on the hardening behavior of formaldehyde-based resin adhesives used for wood-based panels

Abstract

The aim of this work was to monitor the hardening behavior of two different ureaformaldehyde (UF) resins and to investigate the possible catalytic effect of cold water extractives of different wood species on the hardening characteristic. A pure UF resin and a melamine-modified UF resin were used for this investigation. For the experiments, ammonium chloride, ammonium sulphate, acetic acid and oxalic acid at different addition levels were used as hardeners. The gel times determined at three temperatures, the pH drop of the resins after the hardener addition, the buffering behavior and changes in the complex viscosity η * with time, as well as the development of the bond strength were chosen as parameters for characterizing the systems both with and without wood extractives. As expected, the buffering capacity of the melamine fortified resin was found to be much greater than for the pure UF resin. The gel times of the investigated resins were strongly dependent on the applied temperature, decreasing steeply at higher temperatures. Based on these data the apparent activation energies for various hardener additions have been calculated. The complex viscosity and the development of the internal bond strength indicated that cold water wood extractives had little or no effect on the curing progress of the resins.

Properties of High-Density Fiberboard Bonded with Urea–Formaldehyde Resin and Ammonium Lignosulfonate as a Bio-Based Additive

“…With the addition of ALS, the curing temperature increased regardless of the addition level, which indicates lower reactivity [ 120 ]. According to the literature, the curing peak of different lignin types of resins varies between 130 and 150 °C [ 121 , 122 ]. Our results are slightly lower due to UF and due to the hydrophilicity of this lignin type and the slightly retarding effect on curing of adhesive [ 123 , 124 ].…”

The Effect of the Beech Wood Steaming Condensate on Curing Behaviour of Urea-formaldehyde Adhesive

“…Some earlier studies have also shown that wood extractives strongly affect the gel time of UF resins (Albriton and Short 1979; Popović et al 2013) which is strongly dependent on the pH and the buffer capacity of wood extracts for a de ned temperature (Johns and Naizi 1980). Stefke and Dunky (2006) have noticed only a slightly retarding effect of cold-water wood extractives on the curing of UF adhesive. More detailed information concerning the kinetic analysis of UF adhesive curing was obtained by the differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods (Xing et al 2005, Gao et al 2008).…”

Use of Agave durangensis Bagasse Fibers in the Production of Wood-Based Medium Density Fiberboard (MDF)

“…The aforementioned is in agreement with the results obtained by Park et al [45], who reported that high alkalinity fibers retarded the curing of UF in MDF. According to Stefke and Dunky [46], the condensation reactions of UF resin take place during the hardening process causing a cross-linked condition and The decrease in mechanical properties of MDF30 panels may be due to the presence of small particles in the ADBF and the minimal contact between them [33]. The pH of the ADBF is another factor that could reduce the mechanical strength of the panels.…”

“…The aforementioned is in agreement with the results obtained by Park et al [45], who reported that high alkalinity fibers retarded the curing of UF in MDF. According to Stefke and Dunky [46], the condensation reactions of UF resin take place during the hardening process causing a cross-linked condition and thus developing the internal bond between the fibers. UF preferably needs a low pH for the above to take place.…”