Impact of alkaline–acid and strongly acid process on the synthesis of urea–formaldehyde resins and derived composites: a comparison study

  • C. Gonçalves
  • J. Pereira
  • M. Almeida
  • N. T. Paiva
  • J. M. Ferra
  • J. M. Martins
  • F. D. Magalhães
  • A. Barros-Timmons
  • L. H. CarvalhoEmail author


This paper presents the impact of different processes for producing urea–formaldehyde resins and their roles on the physico-mechanical properties and the formaldehyde emission of the resulting particleboards. Five resins were produced: four via the alkaline–acid process (Resin A to D) and one using the strongly acid process (Resin E). The differences between the syntheses are mainly related to different formaldehyde/urea molar ratios during the synthesis, temperatures, and the number of urea load addition. The molecular weight distribution of the resins was monitored by gel permeation chromatography/size exclusion chromatography and the unreacted oligomers were followed by high-performance liquid chromatography. The shear strength of adhesive joints was evaluated using automated bonding evaluation system. Particleboards produced with these resins were analyzed according to the usual standards for mechanical tests and formaldehyde emission. The resins differ in some characteristics, namely percentage of unreacted oligomers, chemical composition, viscosity, and reactivity. At a pressing time of 120 s, the internal bond of the particleboards was similar for all the resins produced using the alkaline–acid process (≈ 0.60 N mm−2) but differed from that obtained using the strongly acid process (≈ 0.40 N mm−2). However, formaldehyde emissions were apparently independent of the synthesis process.



Carolina Gonçalves thanks ENGIQ-Doctoral Programme in Refining, Petrochemical and Chemical Engineering (PDERPQ); FCT and EuroResinas-Indústrias Químicas for the PhD grant PD/BDE/114352/2016. This work was financially supported by: project UID/EQU/00511/2019-Laboratory for Process Engineering, Environment, Biotechnology and Energy-LEPABE funded by national funds through FCT/MCTES (PIDDAC); and within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement and 2GAR project under PT2020.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.LEPABE-Faculdade de EngenhariaUniversidade do PortoPortoPortugal
  2. 2.ARCP-Associação Rede de Competência em PolímerosPortoPortugal
  3. 3.EuroResinas-Indústrias Químicas SASinesPortugal
  4. 4.DEMad-Wood Engineering DepartmentInstituto Politécnico de ViseuViseuPortugal
  5. 5.CICECO-Aveiro Institute of Materials and Departamento de QuímicaUniversidade de AveiroAveiroPortugal

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