木材胶合界面微观结构样品制备新方法--激光烧蚀技术

Novel Sample Preparation Methodology of Wood/Adhesive Interphase for Microstructure Study——Laser Ablation Technique

【目的】分析激光烧蚀技术对木材胶合界面样品表面及微观结构的影响,为木基复合材料样品微观结构检测等相关领域研究提供一种简单可行的样品制备方法。【方法】以柳杉木材/脲醛树脂(UF)胶合界面和柳杉木材/聚醋酸乙烯酯(PVAc)胶合界面为研究对象,采用切片制样和激光烧蚀2种方法对样品进行处理,利用扫描电镜观察处理后的样品表面及微观结构。【结果】切片制样过程中的机械切割使得样品表面出现毛刺和刀痕,细胞形态发生变化甚至破碎。柳杉/UF样品胶层发生断裂,并且胶层附近的管胞出现破碎现象,既不利于观察胶层形态,也不利于检测胶黏剂与木材细胞壁之间的结合。柳杉/PVAc样品胶层有撕扯现象,但对于观察和分析界面结构的影响程度不大。激光烧蚀样品表面出现一些木材或胶黏剂小颗粒溅射的痕迹,尤其以胶黏剂区域和晚材区域较为明显。除划痕缺陷外,激光烧蚀还会导致部分离胶层一定距离的早材管胞破碎且有碎屑残留在细胞腔内,但这些缺陷并不影响胶合界面微观结构的观察,如胶黏剂在木材细胞中的分布、胶层区域的形貌以及胶黏剂与细胞壁之间的界面相容性等。激光烧蚀方法还适用于研究不同压力下胶合界面微观缺陷的变化规律,随着压力增加,柳杉/UF胶合界面上的胶层孔洞以及胶黏剂与木材细胞壁之间的缝隙数量逐渐减少,尺寸逐渐减小,但当压力增至1.2 MPa时,木材细胞壁开始出现细微裂纹,胶黏剂与细胞壁之间也开始出现裂隙。【结论】与切片制样方法相比,激光烧蚀方法不需任何预处理,并且对样品尺寸没有限制,所耗时长与样品尺寸及其密度呈正比,适用性广,可为其他木基复合材料胶合界面微观结构的研究提供技术支持。

【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 regionand 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 to1. 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.