NC State
BioResources
Chen, F., Wang, B., and Xia, X. (2020). "Effects of dilute acid activation and tannin modification on the binding mechanism of formaldehyde-free particleboards," BioRes. 15(3), 6165-6180.

Abstract

The development of a formaldehyde-free wood-based panel is a major research direction in the wood-based material industry. Previous research has demonstrated that nitric acid activated fibers and coupling agents could be utilized to manufacture formaldehyde-free medium-density fiberboards. Herein, based on the chemical characteristics of wood, nitric acid and tannin were applied in formaldehyde-free particleboard, featuring suitable mechanical properties and water absorption resistance. The results of modulus of rupture (MOR), surface bonding strength, internal bonding strength, and 2 h moisture thickness swelling (TS) of formaldehyde-free particleboard (that was synthesized at optimal conditions and satisfied the China National Standards GB/T 4897 (2015) and GB/T 17657 (2013)) are discussed. The investigation of the technological conditions on bond performance showed that when the particleboard was bonded with the conditions of 20/80 nitric acid/particles mass proportion, 50% tannin concentration, and 135 °C temperature, the MOR, surface bonding strength, inner bonding strength, and 2 h TS were better than that of the particles with urea formaldehyde resin adhesive. The synthesis mechanism was studied by both Fourier transform infrared spectroscopy and wide-angle X-ray diffraction, and the chemical composition indicated polycondensation of furfural and tannin, and hydrogen bonding of hydroxyl groups as the reaction mechanism between nitric activation and the tannin coupling agent.


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