Investigation on thermal and chemical properties of bio-adhesive based on tannin and lignosulfonate

In recent years, there has been a great demand to replace fossil materials with environmentally friendly and sustainable ones. One of these materials is the adhesives that are usually produced from fossil sources and are commonly used in wood products. Formaldehyde-based resins are the most common commercial crosslinker used in the wood industry, which is considered one of the biggest sources of environmental pollution in cases based on wood products and endangers human health. Therefore, research on natural adhesives based on lignin and tannin is currently increasing, and today many efforts are underway to replace natural adhesives with synthetic adhesives. In this research, an adhesive was prepared from tannin and lignosulfonate as an environmentally friendly raw material. Furfural and polyethyleneimine, siricin, and glutaraldehyde were used as crosslinkers. Initially, the raw materials were mixed with furfural crosslinker, and then other binders were added in different proportions and mixed at 80°C for half an hour. By mixing these materials, 12 types of different adhesive compounds were prepared. These compounds were subjected to FT-IR spectroscopy to identify the functional groups and to check the thermal properties of different adhesive treatments such as TGA and DSC analysis. The results showed that compounds containing polyethyleneimine had good resistance to thermal degradation, and furfural also improved the characteristics of the adhesives. The combination of raw materials, furfural, polyethyleneimine, and sericin showed the most stability in the TGA test. In fact, the presence of more crosslinkers led to an increase in the thermal stability of the adhesives due to the presence of functional groups and the increase in the density of resin joints.