| In this paper, we studied the preparation of nanocrystalline cellulose(NCC), and analyzed its characters with SEM and XRD. Then we researched NCC reinforcing mechanism on adhesive by nanoindentation, including mechanical properties variation of adhesive, the bondline character of adhesive reinforced with NCC and the creep properties of adhesive reinforced with NCC. Furthermore, the thermo-properties of adhesives(PF, UF and soybean glue) reinforced with NCC were analyzed, and also being verified by the improvement in properties of wood-based panel. The main conclusions are as following.(1) Poplar NCC prepared by 2,2,6,6-tetrathylpiperidine/Na Cl O/Na Br were microfibril bonds mostly, has extradinary high aspect ratio and rank in order evenly, keeping crystalline region preferably. Most of them partly reached nano scale. In this reaction, TEMPO and Na Br was catalyzer, keeping their amount constant in the end. Carboxylate dominated in the surface, and there was no oxide in crystalline region. The swtichgrass CNC prepared by acid was rodlike and has high aspect ratio. Its crystallinity index was 69% and was not a 100% ideal crystal. The NCC size prepared by enzyme was in the range of 100nm-300 nm, reaching the standard of NCC in wdith. And there was no variation on chemical group, explaining that the enzyme processing only changed the cellulose morphology and size, without destroying the chemical structure of cellulose. The cellulose enzyme mainly affected on the amorphous region, improving the crystallinity index.(2) The hardness(H) and elastic modulus(Er) of adhesive were tested and analyzed by nanoindetation. We concluded that the Er and hardness of PF resin with NCC addition were higher than control PF resin. Thereinto, among all these samples, PF resin with 3% CNC addition has the highest Er, 56% higher than the control sample. NFC added one has high reinforcing effect in the fibril direction, and the MFC added sample has least satisfying reinforcing effect.(3) Add different types of NCC(MFC, NFC and CNC) to PF resin and glued wood sample with them in certain temperature and pressure condition. Compared with control sample, NFC-added sample has prominent improvement on Er and hardness, nearly twice as control ones. And MFC reinforcing PF resin has high micro-mechanical properties in the bondline and areas nearby. In wood-UF samples, the addition of NFC made the Er and H in increasing tendency on the interface of wood and UF resin. The Er of 1% and 2%NFC added samples increased from 12.1GPa to 14.8GPa and 17.4GPa separately on the cellwall of interface. The internal bonding(IB) of 3% NFC-added PB was much higher than controlones, nearly 1.3 times.(4) The creep property variation of control PF resin and resin with three kinds of NCC(MFC, NFC and CNC) were investigated by nanoindentation. Thus we found among all the samples, the cured PF resin has the lowest strength, and the pure wood one was next. Among the three kinds of samples with NCC addition, in the same load the wood-resin sample with NFC addition has the least deformation, and the least unrecoverable deformation after unloading, the next was MFC-added wood-resin sample and then CNC-added wood-resin sample. From creep curve, we can see in 5 minutes the MFC-added wood-resin sample has the least interface deformation under constant load, the next was CNC-added wood-resin sample and then NFC-added wood-resin sample.(5) The DSC analysis showed 3% NFC addition improved the curing temperature of PF and UF resin in the same heating rate, and with 3% NFC added, the curing activate energy was obviously lower than control PF and UF resin. In soybean glue DMA curves, we concluded the unfolding of soybean glue was a cooperative transformation in company with endothermic phenomenon in the ranfe of 50。C ~200。C. In soybean glue DMA curve, adding 1% NCC, the storage modulus E/ increased and the dissipation factor tand decreased, illustrating poplar NCC improved the deformation and heat resistance of soybean glue plywood. |
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