Characterization of Curing and Bonding of Wood with Adhesive Mixtures of Liquefied Wood and Hexamethylenediamine

Abstract

Various crosslinking agents can be added to the formulations of natural-based adhesives for wood bonding in order to achieve better durability and higher strength of the formed joints. In the present study, the effect of hexamethylenediamine (HMDA) addition on the performance of liquefied wood (LW) adhesive for wood bonding is investigated. Differential scanning calorimetry showed the improved thermal stability and crosslinking of the LW adhesive with HMDA. The intensified presence of amide linkages (C-N bonds) was found in LW+HMDA with attenuated total reflection Fourier transform infrared spectroscopy. Analysis of the bonded joints using an automated bonding evaluation system showed that a higher press temperature resulted in stronger bonds for both types of adhesives. Moreover, the addition of HMDA to LW adhesive improved the bond strength of the joints and accelerated the crosslinking of the adhesive. However, with a tensile shear strength of (6.76 ± 2.16) N × mm −2 (for LW) and (6.89 ± 2.10) N × mm −2 (for LW+HMDA), both adhesives were found to be unsuitable for interior non-structural use. In addition, the acidity of LW resulted in relatively high wood failure (70%) in the adhesive joints tested. Improved crosslinking of LW with HMDA was reflected in improved resistance of LW+HMDA adhesive joints to water degradation. In conclusion, HMDA is a promising additive for improving the adhesive performance of LW adhesives.