Effects of nanoclay modification with transition metal ion on the performance of urea–formaldehyde resin adhesives

As a way of reducing the formaldehyde emission and improving the adhesion of urea–formaldehyde (UF) resins, this study investigated the addition effects of pristine nanoclay (PNC) or modified nanoclay (MNC) with transition metal ion (TMI) on the performance of UF resin adhesives. Instead of a conventional simple mixing (SM) of MNC with UF resin (coded as MNC-SM), this study explored adding PNC or MNC into either the alkaline (ALK) or acidic (ACD) reaction during the synthesis of UF resins, which were coded as PNC-ALK, PNC-ACD, MNC-ALK, and MNC-ACD, respectively. For the first time, we report that the MNC-ALK resins result in almost amorphous UF resins with 25% crystallinity, which consequently increases the cross-linking, and improve the adhesion strength and decrease formaldehyde emission of modified UF resins. It is believed that the intercalated or exfoliated MNCs facilitate the formation of more cross-linking in the modified UF resins, leading to a better cohesive strength.