Eco-friendly particleboards with low formaldehyde emission and enhanced mechanical properties produced with foamed urea-formaldehyde resins

Urea formaldehyde (UF) is the most widely used thermoset glue in the wood composite board industry. UF has formaldehyde emission, which is harmful to the environment and human health. In this study, it was aimed to ensure more efficient use of glue by foaming UF, as well as to reduce the amount of formaldehyde emission and thus to realize a cleaner production. In the UF resin foaming process, egg white (EW) and blood flour (BF) were used as foaming agents, which increased the resin volume by 4–7 times. Ammonium sulfate (AS) was used as a hardener for the UF. The UF resin and AS solid concentrations were 65% and 30%, respectively. The resins used in the production were prepared by blending UF, AS, and blowing agents using a mixer at 1000 rpm. The resin was then sprayed onto the surface of the wood chips via an air gun under 5 bar pressure. The PBs were produced as a monolayer from only a core layer (CL) of wood chips. The obtained PBs were characterized by their physical and mechanical properties and formaldehyde emissions. The morphological characterization of the foamed resins was also examined. The results showed that the foaming process had improved the mechanical properties of the PBs by about 30%; however, no significant differences were found in the physical properties of the PBs. Morphological characterization showed that the UF foaming with blow agents had proved to be successful and the resin volume had been increased 4–7 times by the foaming. Formaldehyde emissions were found to be lower (2.5–5.1 mg/100 g) than for the un-foamed resins (3.95–7.31 mg/100 g). It was concluded that PBs with good mechanical properties and low formaldehyde emission can be manufactured by using 30% less UF resin.