Phenol-formaldehyde resins with suitable bonding strength synthesized from "less-reactive" hardwood lignin fractions

Tainise V. Lourençon (Corresponding Author), Sami Alakurtti, Tommi Virtanen, Anna Stiina Jääskeläinen, Tiina Liitiä, Mark Hughes, Washington L.E. Magalhães, Graciela I.B. Muniz, Tarja Tamminen (Corresponding Author)

Research output: Contribution to journalArticleScientificpeer-review

3 Citations (Scopus)

Abstract

The substitution of phenol by lignin in phenol-formaldehyde (PF) resins is one of the most promising end uses of lignin valorization. Lignin from grasses and softwood has been the focus of the studies in this field as they present a higher number of theoretical reactive sites for resin synthesis. Herein we examined the composition and chemical reactivity of "less-reactive" hardwood lignin fractions and their performance in PF resins, synthesized by substituting 50 wt% of the phenol with lignin. Before resin synthesis, the samples were hydroxymethylated and the maximum formaldehyde consumption was recorded. By doing so, we observed that hardwood fractions consumed formaldehyde close to the theoretical calculation, whereas the reference softwood lignin consumed only about of the theoretical value. In the resin synthesis, we added formaldehyde to the formulation according to the measured maximum formaldehyde consumption. Thus, low values of free formaldehyde in lignin-PF (LPF) resins were achieved (<0.23%). Moreover, the resin bonding strength displayed similar performance irrespective of whether the LPF resins were made with softwood or hardwood lignin (range of 3.4-4.8 N mm-2 at 150°C and 45-480 s of press time). Furthermore, we concluded that hardwood kraft lignins present no disadvantage compared to softwood lignins in PF resin applications, which have significant practical implications.

Original languageEnglish
Pages (from-to)175-183
Number of pages9
JournalHolzforschung
Volume74
Issue number2
Early online date24 May 2019
DOIs
Publication statusPublished - 1 Feb 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • formaldehyde consumption
  • kraft
  • phenolic resins
  • reactive sites
  • technical lignin

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