Recent developments in the performance of micro/nanoparticle-modified urea-formaldehyde resins used as wood-based composite binders: A review

Urea-formaldehyde resins (UFs) for adhesives have attracted particular interest among other thermosetting polymers applied in the broad area of wood panels technology. UFs are the most common thermoset resins, typical of adhesives formed through polycondensation reactions, extensively applied in the wood-based composites industry. Formaldehyde emission (FE) in UF resins-bonded wood panel products is one of the main drawbacks of UFs resins. The increasing demand for eco-friendly products requires a compelling drive towards the promotion of nano-particles science. Using various types of nanoparticles with their interesting properties due to their large surface area and, occasionally, high aspect ratios can improve the resin's desired properties. Nevertheless, various features of nano-enhanced UFs resins, including the type of nanomaterials, their structure, and performance, which determine the compatibility between UF resins and nanomaterials, should be investigated to guarantee high effectiveness. This critical review, for the first time, emphasizes the importance of recent progress to improve the target properties of UF resins such as mechanical properties, thermal and curing behavior, and formaldehyde emission in the presence of nanoparticles. These and different aspects of such engineered resins are discussed, as well as evaluating their future perspectives. Using nanoparticles in liquid UF polycondensates has the potential to significantly lower environmental and health hazards. This article will also summarize the emerging new nanotechnology features for developing and adapting eco-friendly UF-bonded composites.