| Broussonetia papyrifera is one of the commonly fast-growing tree with a wide distribution range and excellent fiber quality in China.The binderless board is a new product with strong vitality and development prospects in the field of wood-based panels due to its being harmless to the environment and human’s health.In recent years,using Broussonetia papyrifera wood to prepare wood-based panel has become a new research topic.In this study,the characteristics of Broussonetia papyrifera wood was analyzed,and binderless particleboards were manufactured from Broussonetia papyrifera trunk without any resins by conventional hot pressing.The effects of pressing conditions(particle size,board density,pressing time and pressing temperature)on the board’s properties were investigated.Meanwhile,the bonding mechanism of binderless boards was studied.Afterwards,sucrose and citric acid were added to the Broussonetia papyrifera wood particles to prepare enhanced-performance binderless particleboards.The main research content and results are as follows:(1)Based on analyzing the fiber morphology and chemical composition of Broussonetia papyrifera wood.The results showed that:the Broussonetia papyrifera wood fiber was belong to medium size.The holocellulose,α-cellulose,hemicellulose,lignin,hot water extractive and alcohol-benzene extractive contents of Broussonetia papyrifera wood were 81.2%,50.45%,30.75%,19.28%,3.34%and 1.47%,respectively.The contents of cellulose,hemicellulose of Broussonetia papyrifera wood were belonging to above average in hardwood,and the content of extractive is far lower than that of hardwood.In addition,the components in Broussonetia papyrifera latex mainly contained starch grains,polysaccharides and organic acids.The chemical components of latex and high hemicellulose content of Broussonetia papyrifera wood were beneficial for preparing binderless board.(2)Based on investigating the effects of different manufacturing condition on board properties.It was found that the smaller size of the particle,the better the performance of the binderless board had.The properties of the boards increased with the increase of board density(0.8-1.1 g/cm3).Within a range of temperature(180-220℃)and time(15-30 min),the binderless boards manufactured at higher temperature and longer pressing time had better properties.Under the optimum board manufacturing conditions of 220℃,30 min,1.0 g/cm3,the binderless board recorded a MOR 28 MPa,MOE 5.3 GPa,IB 2.74 MPa and 24 h TS of 7.4%,respectively,which met the performance requirements of Chinese national standard for heavy-duty particleboard(20 MPa,3.1 GPa,0.6 MPa and 16%).(3)The self-bonding mechanism of Broussonetia papyrifera wood binderless particleboards was explored.The results showed that with the increase of hot-pressing temperature,the content of cellulose and hemicellulose decreased,but the content of lignin(including pseudo-lignin),hot water and alcohol-benzene extractive increased.The binder and pseudo-lignin generated from hemicellulose degradation and the cross-linking reaction between pseudo-lignin and carbohydrates resulted in improving the performance of binderless board.FTIR and XPS analysis showed that the number of C-O-C increased with the increase of pressing temperature,which contributed to increasing the bonding strength and dimensional stability of the binderless boards.XRD analysis showed that the relative crystallinity of cellulose of binderless board increased with the increase of pressing temperature,the performances of the binderless board were improved with the increase of the crystallinity.It was found that the latex of Broussonetia papyrifera had a bonding strength(0.6 MPa),indicating the latex played a positive role in self-bonding of the Broussonetia papyrifera wood particleboard.(4)Enhanced-performance Broussonetia papyrifera wood binderless particleboards were prepared successfully from the smaller size(less than 10 mesh)Broussonetia papyrifera wood particles and adding additives(citric acid and sucrose).With the increase of the content of additives(0%,2%,5%,10%),the performance of binderless boards were significantly improved.Under the optimum board manufacturing condition of 220℃,30 min,1.0 g/cm3 and the additive content of 10%,the enhanced-performance binderless board recorded a MOR 36 MPa,MOE 6.5 GPa,IB 4.32 MPa and 24 h TS of 1.8%,respectively.All the properties far exceeded the performance requirements of Chinese national standard for heavy-duty particleboard.In addition,with the increase of additive content,the amount of C-O-C and C=O of the binderless boards increased,as well the relative crystallinity of cellulose of the binderless boards also increased,all of the above changes contributed to improving the performance of the binderless board. |
