Curing characterization of tannin-hexamine adhesive by automated bonding evaluation system, dielectric analysis, and dynamic mechanical analysis

Abstract

The characterization of the curing process allows the determination of the optimal pressing parameters, which is essential for the economical production of wood-based composites. In this study, an automated bonding evaluation system (ABES), dielectric analysis (DEA), and dynamic mechanical analysis (DMA) were used to determine the curing parameters of biobased pine tannin-hexamine adhesive at five temperatures ranging from 75 to 175 °C. This study aimed to compare the three above methods and to find correlations between them. All methods showed the same trend of the curing process, which became faster with increasing temperature. Due to various heating rates among the different methods, the curves representing the degree of cure were shifted to the left for the period in which nearly isothermal conditions were reached. It was determined that these methods could be mutually comparable. The ABES was regarded as the reference method; the DEA was regarded as a method that overestimates the curing process and that describes the beginning of the curing process more precisely; and the DMA method was regarded as a method that underestimates the curing process and that describes the end of the curing process more precisely. Linear trend lines were found between the observed methods.

Curing Kinetics of Tannin and Lignin Biobased Adhesives Determined by DSC and ABES

“…The density of the prepared adhesive was determined to 1.04 g/cm³, and solid content to 35.6%. This adhesive was presented in detail in our previous study [9].…”

“…In recent years, the most interesting research attempts have been in the preparation of lignin non-isocyanate polyurethane (NIPU) adhesives [7,8]. Our previous research investigated curing characterisation by ABES, DMA, and DEA on a tannin-hexamine adhesive [9,10] and developed a new organosolv lignin NIPU adhesive [11].…”

“…Wood absorbs water from the adhesive and thus accelerates the mechanical curing. The presence of wood and its pH nature can also interfere with the chemical curing of the adhesives [9].…”

“…In this research, the curing process of one perspective tannin and one new lignin-based adhesive mixtures were examined with ABES and DSC methodologies. These tannin and lignin-based adhesives were investigated as part of the ERA Net project WooBAdh and represent the continuation of our previous work [9,11]. Since the ABES method directly measures the adhesive bond strength, it was used as a reference.…”