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

No Thumbnail Available

Access rights

openAccess

URL

Journal Title

Journal ISSN

Volume Title

A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

Date

2020-02-01

Major/Subject

Mcode

Degree programme

Language

en

Pages

Series

Holzforschung

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.

Description

Keywords

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

Other note

Citation

Lourençon, T V, Alakurtti, S, Virtanen, T, Jääskeläinen, A S, Liitiä, T, Hughes, M, Magalhães, W L E, Muniz, G I B & Tamminen, T 2020, ' Phenol-formaldehyde resins with suitable bonding strength synthesized from "less-reactive" hardwood lignin fractions ', Holzforschung, vol. 74, no. 2, pp. 175–183 . https://doi.org/10.1515/hf-2018-0203