Highly flexible glycol-urea-formaldehyde resins

Urea-formaldehyde resins are successfully used in many contexts, but their tightly crosslinked thermoset structure impairs some applications, due to stiff and brittle behavior. In this work we show that copolymerization of urea and formaldehyde with glycols introduces linear flexible segments in the polymer structure, thus increasing the resilience and flexibility of the resin after curing. Glycols with different molecular weights (106, 200 and 400 g/mol) were incorporated in the synthesis in different amounts. The chemical and physical-mechanical properties of the resulting products were investigated in detail, namely using FTIR, C-13 RMN, GPC/SEC analysis, dynamic mechanical analysis, adhesive bond strength, and tensile-strain testing. Use of polyethyleneglycol with molecular weight 200 g/mol yielded the most promising glycol-urea-formaldehyde resin, with remarkable resilience and good adhesion properties. When used for paper impregnation, the modified resins yielded flexible and tough papers, in comparison with a conventional urea-formaldehyde resin, which produced brittle papers that fractured easily upon bending.