Buffering Capacity of Fast-Growing Species and Curing Time of UF Resin Modified With Zinc Borate and Monoammonium Phosphate

Abstract

Problem statement: Occupying a suitable hot pressing time for particleboard fabrication seems very tricky for manufacturers of the wood-based panel. Longer or shorter pressing times can affect physical and mechanical properties of the produced particleboards and that is why extra care should be given on this matter. Longer pressing time can cause resin in a particleboard to over-cure whereas shorter pressing time can cause insufficient curing of the resin. Determination of hot pressing time is influenced by the type of filler and chemical used. The acidity or alkalinity of a filler and chemical can lengthen or shorten the time taken by the resin to cure. These parameters are usually assessed using buffering capacity test and curing time test. In this study, the two analyses were occupied to assess acidity or alkalinity of kenaf, Shorea macrophylla and Acacia mangium as well as the effect of fire retardants (zinc borate and monoammonium phosphate) to the curing rate of urea formaldehyde resin. Determine acidity or alkalinity of the wood particles through buffering capacity test. The effect of the fire retardants to the curing of Urea Formaldehyde (UF) resin was also studied. Approach: For buffering capacity test, the wood particles were extracted. Then, the extracts were separated into two parts. One part was tested with sodium hydroxide (NaOH) and another part was tested with sulphuric acid (H₂SO₄). Sodium hydroxide was added into the extracts until they reached pH 11. The other part was added with sulphuric acid until they reached pH 3. The pH value was recorded each time 5 mL chemicals added. The acidity of the plants was observed by looking at the volume of sulphuric acid needed to reduce their pH to 3, whereas alkalinity was evaluated by looking at the volume of sodium hydroxide used to increase their pH to 11. Curing times of UF resin added or not added with fire retardants were calculated in second (sec). Results: Buffering capacity study revealed that kenaf, Shorea macrophylla and Acacia mangium behaved similarly in alkali and acidic conditions. All the materials had less resistance towards acid than towards alkali. Kenaf had the greatest resistance towards alkali compared with the other two species. As an important processing parameter in particleboard fabrication, the curing time of the adhesive mixture with added fire retardants was studied in comparison with a control mixture (without fire retardant with a curing time of 140 sec). Those two fire retardants showed different effect on the curing time of the mixture. Zinc borate was found to delay the curing time by more than 100% compared with control mixture whereas, monoammonium phosphate increased the curing time by almost 60%. The curing time for control mixture (without fire retardant) was 140 sec. Conclusion: Based on the testing results, some potential modifications to improve the curing time were discussed to avoid short curing time to improve the manufacturability of the material systems.