Abstract
Binderless particleboards were prepared without any resin adhesives from Broussonetia papyrifera trunk by hot pressing. The effects of particle size, pressing time, pressing temperature and board density on the physical and mechanical properties of binderless boards were investigated. The effects of chemical changes in Broussonetia papyrifera binderless particleboards on the board properties were investigated by chemical, spectroscopic and cellulose crystallinity analyses. The bonding performance of the latex of Broussonetia papyrifera was discussed. The results showed: (1) the smaller size of the particle, the higher internal bonding (IB) strength and lower thickness swelling (TS) of the binderless board had. The modulus of rupture (MOR), the modulus of elasticity (MOE) and the IB values of the boards increased with the increase of board density. Within a certain range, the binderless boards manufactured at higher temperature and longer pressing time had better properties. Under the optimum board manufacturing condition of 220 ℃/30 min/1.0 g/cm3, the Broussonetia papyrifera binderless board recorded a MOR 28 MPa, MOE 5.3 GPa, IB 2.74 MPa and 24 h TS of 7.4%, which met the performance requirements of Chinese national standard for heavy-duty particleboard. (2) The degradation of cellulose and hemicellulose during hot pressing resulted in decrease of cellulose and hemicellulose content and increase of extractives. Some of the degradation products form new bonding to increase the bonding strength and dimensional stability of the binderless boards. (3) The formation of pseudo-lignin and increased C–O–C and cellulose crystallinity of the boards during hot pressing contributed to high quality of the binderless boards. (4) The poplar veneers bonded with the latex of Broussonetia papyrifera had a certain bonding strength (0.6 MPa), indicating the latex played a positive role in self-bonding of the Broussonetia papyrifera particleboard.
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