Reactive toughening of urea–formaldehyde resin with poly(vinyl alcohol) by formation of interpenetrating networks

Abstract

A series of urea–formaldehyde/poly(vinyl alcohol) (UF/PVA) blends were prepared via in situ polymerization. During the synthesis process, intra‐ and intermolecular acetalization of PVA occurred, along with the addition and condensation reactions between urea and formaldehyde, resulting in the formation of UF/PVA interpenetrating networks. With the increase of PVA content, the curing temperature shifted to higher temperatures and the activation energy (E) increased, suggesting that it was more difficult for the blends to cure. UF/PVA blends showed high storage modulus and only one broad tan δ peak, indicating that the stiffness was enhanced and the phase separation was limited at the chain segmental level. By the introduction of PVA, the elongation at break, impact strength, KIC value, and roughness of the fracture surface increased obviously, while the tensile strength can still maintain at a high level. Due to the forced compatibilization of the two components, homogeneous interpenetrating UF/PVA networks can form and thus the toughness of the blends was enhanced. POLYM. ENG. SCI., 58:2031–2038, 2018. © 2018 Society of Plastics Engineers