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Copolymerization of UF Resins with Dimethylurea for Improving Storage Stability without Impairing Adhesive Performance

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EuroResinas-Indústrias Químicas, 7520 Sines, Portugal
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ARCP—Associação Rede de Competência em Polímeros, 4200 Porto, Portugal
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DEMad—Instituto Politécnico de Viseu, 3504 Viseu, Portugal
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LEPABE—Faculdade de Engenharia da Universidade do Porto, 4200 Porto, Portugal
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Author to whom correspondence should be addressed.
Materials 2018, 11(6), 1032; https://doi.org/10.3390/ma11061032
Received: 16 May 2018 / Revised: 30 May 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
Urea-formaldehyde (UF) resins are the most used resins in the wood industry due to high reactivity and low price. However, their reduced stability during storage is a drawback, imposing strict limits in terms of allowable shipping distances and storage times. This instability, manifested by viscosity increase that renders the resin unusable, occurs due to the progress of condensation reactions between the polymeric species present in the liquid medium. In order to achieve a stable resin formulation, dimethylurea (DMeU) was selected for being less reactive than urea. Dimethylurea is shown to co-polymerize with the UF polymer during the acidic synthesis condensation step. However, during storage it behaves like an end group blocker, due to its lower reactivity at basic pH. By adding 1.25% DMeU, it was possible to obtain a formulation that remained with stable viscosity during two-month storage at 40 °C. The reference UF resin remained stable only for eight days in these conditions. Wood particleboards produced with modified resins showed internal bond strengths of about 0.5 N·mm−2, similar to the fresh reference UF resin, even when the resins were used after the two-month storage period. Formaldehyde content values were below the limit for E1 class, ≤8 mg/100 g oven dry board (EN 13986). View Full-Text
Keywords: urea-formaldehyde resins; storage stability; copolymerization; dimethylurea urea-formaldehyde resins; storage stability; copolymerization; dimethylurea
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MDPI and ACS Style

Pereira, P.; Pereira, J.; Paiva, N.T.; Ferra, J.M.; Martins, J.M.; Carvalho, L.H.; Magalhães, F.D. Copolymerization of UF Resins with Dimethylurea for Improving Storage Stability without Impairing Adhesive Performance. Materials 2018, 11, 1032.

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