关键词: 激光烧蚀技术, 木基复合材料, 胶合界面, 微观结构

Abstract: [Objective] In order to put forward a simple and feasible preparation method for detecting the microstructure of wood-based composites, the effect of laser ablation sampling on the surface morphology and microstructure of wood/adhesive interphase were investigated in this paper.[Method] Cryptomeria fortunei/urea-formaldehyde resin(UF) interphase and Cryptomeria fortunei/polyvinyl acetate(PVAc) interphase were chosen as experimental samples. Conventional microtoming method and laser ablation method were used to process the samples, and the surface morphology and microstructure of the treated samples were observed by scanning electronic microscopy.[Result] For conventional microtoming method, burrs and scratches were observed on the sample surface due to mechanical cutting, and the wood cells deformed and even broken. Moreover, the bondline of wood/UF bonding sample was fractured, and the tracheids near the bondline were broken, which was not conductive to investigate both the morphology of bondine and the combination between adhesive and wood cell walls. Although the bondline in wood/PVAc bonding sample was tore, it had less influence on the observation and analysis of interphase microstructure. For laser ablation method, several sputtering traces resulted from small wood or adhesive particles were observed on the sample surface, especially in adhesive region and latewood area. In addition to the scratch defect, laser ablation method can also lead the fracture of parts of the earlywood tracheids positioned a certain distance from bondline, and some of the broken cell walls were left in lumens. However, these defects did not affect the observation of microstructure of wood/adhesive interphase, including the distribution of adhesive in wood cells, the morphology of bondine, the interfacial compatibility between adhesive and wood cell walls and so on. Laser ablation method was suitable for investigating the variation of micro defects in wood/adhesive interphase under different pressures.Results showed that the number and size of both holes in the UF bondline and gaps between adhesive and wood cell walls gradually reduced with the increase of pressure. When the pressure came to 1.2 MPa, slight cracks appeared in wood cell walls and regions between adhesive and wood cell walls.[Conclusion] Comparing with conventional microtoming method, laser ablation method shows its advantages in sample preparation, since the sample needs no preprocessing treatment, and there is no requirement for the sample size. The processing time for samples with larger size and higher density would be longer. The laser ablation method with wide applicability is helpful in studying the microstructure of bonding interphase for wood-based composites.

Key words: laser ablation technique, wood-based composites, bonding interphase, microstructure