Structure and properties of urea-formaldehyde resin/polyurethane blend prepared via in-situ polymerization

Abstract

Urea-formaldehyde resin/polyurethane (UF/PU) blends with improved toughness were prepared via in situ polymerization. It was found that both urea and PU participated in the addition and condensation reactions with formaldehyde, and thus a soft PU segment was chemically introduced into the UF system. Due to the relatively low reactivity of PU compared with urea, both the reaction activation energy (E) and the end temperature of the cure reaction increased with an increase in PU content. The blends showed a lower modulus, but a higher T_g compared with neat UF due to the improved degree of crosslinking in the blends. The toughness of UF can be obviously improved without a remarkable decrease in strength by introducing PU, resulting from the formation of a reaction-induced microphase-separated morphology and strong chemical interactions between the UF matrix and PU. The toughening mechanism of the blend corresponded to the energy-dissipation mechanism.