Reduction of Formaldehyde Emission from Particleboard by Phenolated Kraft Lignin

Abstract

The aim of this study was the reduction of formaldehyde emission from particleboard by phenolated Kraft Lignin. For this purpose, the lignin was extracted from black liquor and then modified by phenolation. During the UF resin synthesis different proportions of unmodified and phenolated Kraft lignins (10, 15 and 20%) were added at pH=7 instead of the second urea. Physicochemical properties and structural changes of resins so prepared, as well as the internal bond (IB) strength and formaldehyde emission associated with the panels bonded with them were measured according to standard methods. The Fourier transform infrared (FTIR) analysis of lignin indicated that the content of O-H bonds increased in phenolated lignin while the aliphatic ethers C-O bonds decreased markedly in the modified lignin. Since both synthesis of UF resins and lignin phenolation are carried out under acid conditions, phenolation is an interesting way of modifying lignin for use in wood adhesive. The panels bonded with these resins showed significantly lower formaldehyde emission compared to commercial UF adhesives. The UF resin with 20% phenolated lignin exhibited less formaldehyde release without significant differences in internal bond strength and physicochemical properties compared to an Downloaded by [Stockholm University Library] at 01:33 25 August 2015 2 unmodified UF resin. XRD analysis results indicated that addition of phenolated lignin decreased the crystallinity of the hardened UF resins.

Effect of spent sulfite liquor on urea–formaldehyde resin performance

“…The slightly lower formaldehyde contents of the PBs produced with resins UF‐10LH‐d, UF‐10L‐a, UF‐10LH‐a, and UF‐20LH‐a, may indicate that TSSL/TSSLH may act as a formaldehyde scavenger. The capacity of technical lignins to work as formaldehyde scavengers has been reported before . This is explained, in part, by the reaction of sulfite ions, present in TSSL, with formaldehyde, producing a formaldehyde‐sulfite adduct, hydroxymethanesulfonate .…”

“…In recently published works, technical lignins, previously hydroxymethylated or phenolated, were used to replace part of the urea (15–30%), and were introduced during the resin synthesis . In general, the produced resins presented lowered free formaldehyde levels and the resulting wood composites verified the standard performance requirements.…”

Valorization of Lignin as a Sustainable Component of Structural Materials and Composites: Advances from 2011 to 2019

“…Conversely, Younesi-Kordkheili et al reported diminishing formaldehyde emission in urea-formaldehyde resin modified with phenolated lignin. Interestingly, even 10% modified lignin incorporation into a resin can lead to a significant decrease in free formaldehyde content (0.26%) compared to the control (0.40%) [35]. The foregoing examples are summarized in Table 2.…”

Green Binders for Wood Adhesives

“…In the same study, further improvement of physical and mechanical properties was obtained by adding nanoclay to the LUG resin. Lignin was modified by phenol and used in UF resins [110]. It was demonstrated that the formaldehyde emission from wood panels, bonded with modified lignin-UF resin, was lower compared with commercial UF adhesives.…”