Effect of spent sulfite liquor on urea–formaldehyde resin performance

Abstract

Combination of urea-formaldehyde (UF) resins with technical lignins has been often reported in the literature. However, the actual implications of this approach have not been effectively addressed yet. In this work, unmodified thick spent sulfite liquor (TSSL) and hydroxymethylated TSSL (TSSLH) were incorporated in a standard UF resin in different amounts (10 and 20%) and at different stages. When 10% of TSSLH was incorporated after the synthesis, the produced particleboards performed equivalently to when 90% of UF resin was used. In all other cases tested, combining UF resin with TSSL/TSSLH actually led to lower internal bond strengths. The results evidence that addition of TSSL or TSSLH does not have a beneficial effect on UF bonding performance.

Lignosulfonates as Fire Retardants in Wood Flour-Based Particleboards

“…As a consequence, LD behaves as an inert or deteriorating agent towards the UF resin. A similar effect was reported for another urea-formaldehyde system modified with lignosulfo-nates [39]. Conversely, an improvement in mechanical performances was recorded for the WF95-APP5 composite, which was modified with APP.…”

Lignosulphonates as an Alternative to Non-Renewable Binders in Wood-Based Materials

“…Nevertheless, these resins include formaldehyde which is a known carcinogenic. Nowadays, concerns about formaldehyde emissions and the sustainability of the used raw materials and final products are reducing the popularity of formaldehyde-based synthetic resins for wood-based panels [ 23 , 68 , 92 ]. Thus, formaldehyde-free systems which combine LS with polyethylenimine, furfuryl alcohol, polymeric isocyanate, chitosan, tannins, glyoxal, and wheat flour have been proposed [ 70 , 78 , 84 , 93 , 94 , 95 ].…”

“…The produced UF resins were reported by some works to display increased cold adhesion to wood particles and higher storage times. On the other hand, the resultant particleboards had improved mechanical properties, as well as lower formaldehyde emissions [ 92 ].…”

“…The authors concluded that unmodified or hydroxymethylated TSSL acted as either inert or detrimental compounds in the performance of the UF resin, depending on the TSSL modification and incorporation stage. However, incorporation of unmodified or hydroxymethylated TSSL during the synthesis led to lower condensation times of the resins, lowering production costs [ 92 ].…”

“…Bekhta and coworkers also reported this effect. Thus, the sulfite and bisulfite ions in the sulphite liquor create a buffer system, therefore increasing the amount of acid needed to change the pH and slowing down resin cure [ 92 , 97 ]. This factor alongside the presence of ashes and sugars may significantly increase gel time [ 92 ].…”