Melamine can be incorporated in the synthesis of urea-formaldehyde (UF) resins to improve performance in particleboards (PB), mostly in terms of hydrolysis resistance and formaldehyde emission. In this work, melamine-fortified UF resins were synthesized using a strong acid process. The best step for melamine addition and the effect of the reaction pH on the resin characteristics and performance were evaluated. Results showed that melamine incorporation is more effective when added on the initial acidic stage. The condensation reaction pH has a significant effect on the synthesis process. A pH below 3.0 results on a very fast reaction that is difficult to control. On the other hand, with pH values above 5.0, the condensation reaction becomes excessively slow. PBs panels produced with resins synthesized with a condensation pH between 4.5 and 4.7 showed good overall performance, both in terms of internal bond strength and formaldehyde emissions.
Currently, the majority of binders used in wood particleboard (PB) manufacturing are formaldehyde-based synthetic resins. Because of the toxicity of formaldehyde, there is a strong demand for eco-friendly alternatives with similar performances and economic viability. In this work, thick spent sulfite liquor (TSSL), an industrial byproduct from sulfite pulp mills, is proposed as a binder for fully bio-based PBs. The results showed that PBs bound with TSSL present appropriate mechanical performance, which was further improved when TSSL was combined with wheat flour at an 84:16 dry weight ratio and preheated to 94 °C prior to application. For 13.2% binder content per dry wood weight, the PB internal bond strength was 0.46 N mm−2, which is above the standard requirements for PB type P2 (0.35 N mm−2). Optical microscopy showed that TSSL hinders the gelatinization of starch granules during preheating, allowing the binder mixture to maintain a low viscosity suitable for combination with wood particles and PB production.
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