Modified pine needles as a formaldehyde scavenger for urea-formaldehyde resin in plywood production

The aim of the present work was to investigate whether it is possible to use ground pine needles as formaldehyde-scavenging filler for urea-formaldehyde resin in the production of plywood. The scope of the research included determinations of both optimal amount of introduced filler and the effect of its modification (silanization, hydrothermal and alkaline treatments). Properties of adhesives such as viscosity, gel time and pH were investigated and their morphology was assessed using scanning electron microscopy. The manufactured plywood panels were tested in terms of their wet shear strength, tendency to delamination in varying conditions and formaldehyde emission. It was found that the addition of pine needles lowers the pH and reduces gel time of the adhesive. Moreover, it was shown that despite the significant reduction in formaldehyde emission, the addition of non-modified needles causes a decrease in bonding quality of plywood. Based on the results, 10 parts by weight of needles per 100 parts by weight of resin can be considered as an optimal loading. The use of ground needles modified hydrothermally and with silane allows to minimize the negative effect on the strength of glue lines and leads to further reduction of formaldehyde emission. Therefore, it can be concluded that pine needle powder has strong potential for the application as a formaldehyde-scavenging filler for urea-formaldehyde adhesive in plywood production.