Abstract
The development of biomaterials-based adhesives is one of the main research directions for the wood-based material industry. In previous research, tannin and sucrose were used as adhesive to manufacture particleboard. However, the reaction conditions need to be optimized. In this study, sulfuric acid was added to the tannin–sucrose adhesive as a catalyst to improve the curing process. Thermal analysis, insoluble mass proportion, FT-IR, and solid state 13C NMR were used to investigate the effects of sulfuric acid on the curing behavior of tannin and sucrose. Thermal analysis showed weight loss and endotherm temperature reduced from 205 and 215 to 136 and 138 °C, respectively, by adding sulfuric acid. In case of the adhesive with pH = 1.0, the insoluble mass proportion achieved 81% at 160 °C, which was higher than the reference at 220 °C. FT-IR analysis of the uncured adhesives showed that adding sulfuric acid leads to hydrolysis of sucrose; then, glucose and fructose converted to 5-hydroxymehthylfurfural (HMF) and levulinic acid. Dimethylene ether bridges were observed by FT-IR analysis of the cured adhesives. The results of solid state 13C NMR spectrum indicated that 5-HMF participated in the curing process and formed methylene bridges with the C8 position of the resorcinol A-rings of tannin, whereas dimethylene ether bridges were detected as a major chemical chain of the polymer. Lab particleboards were produced using 20 wt % resin content at 180 °C and 10 min press time; the tannin–sucrose adhesive modified with sulfuric acid to pH = 1.0 exhibited better performance than the unmodified tannin–sucrose adhesive; the properties of the boards fulfilled the requirement of Japanese Industrial Standard (JIS) A5908 type 15.
Highlights
Wood-based materials, such as particleboard, plywood, or fiberboard, are generally used in housing construction, interior decoration, and furniture manufacturing, which are frequently present in living environments [1,2]
Both separately adjusted with sulfuric acid to pH = 1.0 were used as control
The acidified sucrose showed a two-step degradation in the derivative TG (DTG) curve with two peaks at 138 and 155 ◦ C; these mass losses seem to be attributed to the pyrolysis or caramelization of sucrose in acidic conditions [25]
Summary
Wood-based materials, such as particleboard, plywood, or fiberboard, are generally used in housing construction, interior decoration, and furniture manufacturing, which are frequently present in living environments [1,2]. These materials are manufactured by bonding the wooden elements with synthetic resins such as formaldehyde-based, isocyanate-based, polyvinyl acetate. As a result of concerns about formaldehyde emissions and dependency on fossil resources, it is necessary to develop adhesives based on renewable resources, such as lignin, soybean, starch, or tannin [6,7,8,9]. The monomer of wattle tannin contains resorcinol A-rings and catechol or pyrogallol B-rings, and the free C6 or C8 sites on the
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