Analyzing the influence of diols' chain length on the properties of bio‐based wood adhesive

Abstract Traditional adhesives made using urea or phenol formaldehyde are toxic to humans and the environment, and as a result, the industry is very interested in developing bio‐based adhesives. Polyurethane (PU)‐based adhesives are very attractive due to their strong bonding strength, and thermal and chemical stability. Polyols derived from petrochemicals are one of the most important constituents in PU‐based adhesives. Current trends are to find an alternative for petrochemical‐based polyols without compromising the important characteristics of adhesives. In this research, PU adhesives were prepared using soybean oil‐based polyol and isocyanate. Three different diols such as 1,2‐ethanediol (EDO), 1,4‐butanediol (BDO), and 1,6‐hexanediol (HDO) were used to study the effect of crosslinking, amount of crosslinkers (diols), and diol's chain length on the properties of bio‐based adhesives. The adhesive's lap shear strength using metallic and wood coupons was measured. The BDO‐based bio‐adhesives showed the best bonding strength compared to EDO and HDO adhesives. The mechanical strength was observed to be increasing with an increase in the amount of diols up to a certain concentration and then started decreasing. On the oakwood, the bonding strength was increased from 3 to 6.36 MPa after incorporating 10 wt% of BDO which was the highest bonding strength observed among all the other adhesives. The thermal and chemical stability of these adhesives were also studied. Structural characterization confirms no significant changes after being immersed in different solvents for 24 h. This work introduces a sustainable alternative to petroleum‐based adhesives using polyols from vegetable oil. Highlights Soybean oil‐based polyol was used for adhesives. 1,2‐Ethanediol, 1,4‐butanediol, and 1,6‐hexanediol were used as crosslinkers. The bonding strength was measured using wood and metallic coupons. The bonding strength was observed to be increasing with an increase in the amount of diols. The highest bonding strength of 6.36 MPa was observed.