Abstract
The curing behavior of lignin-based phenol-formaldehyde (LPF) resin with different contents of nano-crystalline cellulose (NCC) was studied by differential scanning calorimetry (DSC) at different heating rates (5, 10 and 20°C/min) and the bonding property was evaluated by the wet shear strength and wood failure of two-ply plywood panels after soaking in water (48 hours at room temperature and followed by 1-hour boiling). The test results indicated that the NCC content had little influence on the peak temperature, activation energy and the total heat of reaction of LPF resin at 5 and 10°C/min. But at 20°C/min, LPF0.00% (LPF resin without NCC) showed the highest total heat of reaction, while LPF0.25% (LPF resin containing 0.25% NCC content) and LPF0.50% (LPF resin containing 0.50% NCC content) gave the lowest value. The wet shear strength was affected by the NCC content to a certain extent. With regard to the results of one-way analysis of variance, the bonding quality could be improved by NCC and the optimum NCC content ranged from 0.25% to 0.50%. The wood failure was also affected by the NCC content, but the trend with respect to NCC content was not clear.
Highlights
Lignin is one of the three main components of wood, and its content in hardwoods is usually in the range of 18 to 25%, whereas it varies between 25% and 35% in softwoods [1]
The curing behavior of lignin-based PF resin with different nano-crystalline cellulose (NCC) contents was studied by a high-pressure differential scanning calorimetry (DSC) at heating rates of 5, 10 and 20 ̊C/min
The results indicated that DSC curves for all resins had only one peak, and the values of the peak temperatures were close
Summary
Lignin is one of the three main components of wood, and its content in hardwoods is usually in the range of 18 to 25%, whereas it varies between 25% and 35% in softwoods [1]. Because lignin contains phenolic compounds, it has been used to partially substitute phenol in the manufacturing of phenol-formaldehyde resins for wood composites products. Because of the low reactivity of lignin with formaldehyde, several researchers tried to replace phenol with lignin for phenolic resin development in past few decades, but have not reached commercial applications yet. To produce more reactive phenolic precursors, lignin can be modified prior to resin synthesis. Lignin-based phenolic resins were synthesized and investigated using various percentages of lignin replacement for phenol. The bonding property was evaluated through mechanical testing of oriented strandboard (OSB) or plywood manufactured with lignin-based phenolic resins [3]-[18]
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