Preparation And Characterization Of Nacre-inspired Wood Composite

In order to find a new way of high-valued and clean utilization of wood resource residues,soft phase and hard phase materials of nacre-inspired wood composite were determined according to the composition and structural features of shell nacre,and a multilayer nacre-inspired structure with poplar powder,poplar fiber and walnut shell granules was constructed;Through the experiment design and analysis method combining single factor test method and response surface test method,the optimum composite mass ratio of multilayer composite structure and the optimum process parameters of warm pressing process were determined.Aiming at the characteristics of strength,toughness and weather resistance of nacre-inspired wood composite prepared under the conditions of using multilayer composite structure model,optimum composite mass ratio and optimum process parameters,the changes of functional group of walnut shell granules before and after alkali treatment,and the composite powder of poplar powder,poplar fiber and walnut shell powder after alkali treatment in a given ratio and the specimen(nacre-inspired wood composite)formed by warm pressing process of the composite powder were compared and analyzed by Fourier infrared spectroscopy.The thermal stability and the crystallinity of composite powder and nacre-inspired wood composite were compared and analyzed through synchronous thermal analyzer and X-ray diffractometer.According to the microstructure and fracture mechanism of natural shell,the microstructure of nacre-inspired wood composite was analyzed through scanning electron microscopy,and the strengthening and toughening mechanism of nacre-inspired wood composite was revealed;Based on the finite element model and numerical model of damage evolution established by Abaqus and its secondary development,the failure process of nacre-inspired wood composite under three-point bending test was studied,and then the fracture morphology of the test was compared with the fracture morphology of the simulation.The main contents and innovations are as follows:(1)According to the composition and structural characteristics of artificial shell nacre,the seven-layer bionic design of wood composite is carried out.The hard phase walnut shell granules are interleaved into soft phase poplar powder to realize the single layer structure of shell nacre.Then,the four-layer single layer structure as hard phase and three-layer poplar fiber without angle as soft phase are alternately paved to obtain a multi-layer structure of artificial shell nacre.The nacre-inspired wood composite with good strength,toughness and weather resistance is successfully prepared by warm pressing,all of which realize the innovation of design and preparation method of wood composite.(2)Through the experiment design and analysis method combining single factor test method and response surface test method,the optimal composite mass ratio of "poplar powder/walnut shell granules layer " and "poplar fiber layer"(6:4),and the optimum process parameters of warm pressing process of nacre-inspired wood composite(forming temperature of 162℃,forming pressure of 77MPa and holding time of 25min)were obtained.Nacre-inspired wood composite has a static bending strength of 47.72MPa,an impact toughness of 7.13KJ·m-2 and a water absorption of 3.39%.Such good strength,toughness and weather resistance make it capable of being used in engineering environments at 200 ℃,all of which indicates that this study adds a new member to wood composite.(3)The strengthening and toughening mechanism of nacre-inspired wood composite is investigated.Fourier transform infrared spectrometer(FTIR),synchronous thermal analyzer(TG/DSC/DTG),X-ray diffractometer(XRD)and scanning electron microscopy(SEM)are utilized to analyze the nacre-inspired wood composite and its raw and auxiliary materials.It is found that treating walnut shell granules with alkali can improve the self-bonding strength of nacre-inspired wood composite,and warm pressing process can increase its crystallinity by 14.6%,compared with the composite powder of its raw and auxiliary materials.Meanwhile,the strong and tough characteristics are obtained through "crack deflection" and"crack bridging".