Methyl glucoside and lignosulphonate extenders for use with particleboard UF resins

Study results are presented to evaluate several carbohydrate and lignosulphonate compounds as potential extenders for application with urea-formaldehyde (UF) adhesive particleboard binders. For experimentation, two carbohydrate-based methyl glucosides, an ammonium lignosulphonate, and a sodium lignosulphonate compound were each examined at partial replacement levels: 0 percent (control), 2.5,5,10,15, and 20 percent in direct substitution of resin solids for the UF adhesive binders. These experimental treatments were conducted with both a 1.15:1 (low) and a 1.30:1 (high) formaldehyde:urea (F:U) molar ratio, face and core UF binder, respectively. The initial phase of this study focused on the effect of resin solids replacement on the rheological (absolute viscosity) and gelation properties (gel time) of the two UF adhesive binders. Subsequent efforts focused on particleboard manufacture with evaluation of mechanical performance including flexure (MOR and MOE) and internal bond (IB). Test measurements indicated only minor alteration of viscosity with the lignosulphonates while the carbohydrate extenders had a more pronounced effect on resin rheology. Gel time increased with the replacement treatment levels as an indication of reduced cure rate except for the face UF resin with the ammonium lignosulphonate extender. Resin pH was near constant at all treatment levels with the exception of the more acidic ammonium lignosulphonate extender, which increased acidity of the binder mixture. Irrespective of the specific resin extender, particleboard MOR, MOE, and IB values tended to decline at the higher resin solids substitution treatment levels. However, the experimental data indicate the higher F:U molar binder core resin was more tolerant to extender substitution with less adverse effect on observed board properties.