One-component polyurethane adhesives in timber engineering applications: A review

Wood is an attractive, versatile, and sustainable construction material with excellent strength to weight ratio and a lower carbon footprint than other construction materials. One of the most important requirements in manufacturing engineered wood products (EWPs) and efficiently applying timber resources is achieving durable and mechanically stable bonds. Various types of adhesives have been used to produce wood products, and recently the application of one-component polyurethane (1C PUR) adhesives has obtained an increased market share in the EWPs industry because of its advantages like being formaldehyde-free, bonding of wood at high-moisture content, curing at ambient temperatures, and invisible glue line. 1C PUR adhesives have been used in bonding softwoods, hardwoods, preservative-treated, acetylated, and heat-treated wood. However, some drawbacks exist, such as their creep, especially temperature-dependent creep, thus also their behavior in fire, this being due to the intrinsic chemical structure of most, but not all, 1C PUR adhesives. Moreover, 1C PUR adhesives show good performance in bonding wood to dissimilar materials such as fiber-reinforced polymer (FRP). In case of the need for bonding high-density woods, woods with high extractive contents, or specific characteristics requirements, applying primers can improve the bondline quality. This paper explores the characteristics of 1C PUR adhesive, examines recent studies on their application, and offers a thorough analysis of the impact of manufacturing factors, bonding options, and 1C PUR adhesives performance in the EWPs industry.