毛竹与樟子松木材孔隙结构的比较

【目的】竹木材料孔隙结构特征是影响材料性能的重要因素。通过定量表征与直观观察相结合方式探索竹木材料内部孔隙结构特征。通过对比分析,建立竹木材料内部孔隙结构与组织构造的对应关系,分析竹木材料内部孔隙结构差异,研究孔隙结构对材料性能的影响。【方法】以毛竹和樟子松木材为试验材料,采用压汞法对材料的孔隙率、孔体积、孔径分布、比表面积等参数进行定量测试,分析材料的孔隙结构特征。采用扫描电镜对材料的组织结构(毛竹:导管、筛管、薄壁细胞和纹孔等部位。樟子松:管胞、射线薄壁细胞、纹孔等部位)进行观察,确定各组织结构所构成孔隙的孔径范围。【结果】孔隙率(毛竹47.58%、樟子松67.16%)及汞压入量(毛竹0.633 mL/g、樟子松1.596 mL/g)测试结果表明毛竹内部孔体积显著低于樟子松。总孔面积(毛竹82.04 m²/g、樟子松18.16 m²/g)及中孔孔径(毛竹33.8 nm、樟子松445.0 nm)对比结果表明毛竹中大部分孔隙集中在孔径较小区域(32.4 nm左右),而樟子松木材中孔隙孔径主要集中在226.7、7 082.3 nm左右,造成毛竹孔面积显著高于樟子松木材。结合扫描电镜观察结果可知,毛竹中孔径11.3～100 μm范围内孔隙主要对应导管、基本组织中的薄壁细胞及纤维细胞。而835.0 nm左右孔隙对应基本组织及纤维细胞上纹孔。樟子松木材中孔径20 μm左右孔隙对应樟子松木材管胞; 而7 082.3 nm左右孔隙则对应具缘纹孔的纹孔口和射线薄壁细胞。此外,毛竹和樟子松木材中孔径小于1 μm的孔隙结构(毛竹中32.4 nm左右,樟子松木材中226.7、749.9 nm左右)主要位于具缘纹孔塞缘及细胞壁上。【结论】采用压汞法和扫描电镜观察方法可以实现对毛竹及樟子松木材孔隙结构的表征分析,有助于分析竹木材料性能差异产生的原因。然而,在通过压汞测试材料孔隙结构参数时,受墨水瓶孔效应影响,部分孔径较大的孔隙被认为是小孔,影响测试结果的准确性。因此,后续研究应考虑竹木材料的孔隙形态,从而实现对竹木材料孔隙结构的全面准确表征。

Compare of porous structure of moso bamboo and Pinus sylvestris L. lumber

【Objective】 In naturally porous materials such as bamboo and wood, pore structure is an important factor that affects the properties. The present study utilized mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM)to quantitatively characterize and visually inspect the pore structure of bamboo and wood materials. The porous structures of bamboo and wood materials were compared and analyzed, and the pore structure was correlated with the bamboo/wood microstructure. 【Method】Moso bamboo(Phyllostachys heteyocycla cv. Pubescens)and Pinus sylvestris L. lumber were used as the experimental materials. The MIP method involved the quantitative testing of parameters, including porosity, cumulative pore volume, pore diameter distribution and specific pore areas, to identify the characteristics of the pore structure. The SEM method was a direct visual inspection of the microstructures(moso bamboo: vessels, parenchyma cells, fiber cells, pits, et al.; P. sylvestris L.: tracheids, ray parenchyma cells, pits, et al.). The pore diameter ranges found in the microstructure of both materials can also be obtained from SEM. 【Results】 Porosity(moso bamboo: 47.58%, P. sylvestris L.: 67.16%)and cumulative intrusion(moso bamboo: 0.633 mL/g, P. sylvestris L.:1.596 mL/g)indicated that the pore volume in moso bamboo was much lower than P. sylvestris L. lumber, and the comparison of pore area(moso bamboo: 82.04 m²/g, P. sylvestris L.: 18.16 m²/g)and median pore diameter(moso bamboo: 33.8 nm, P. sylvestris L.: 445.0 nm)indicated that the pore diameter in moso bamboo was relatively small(approximately 32.4 nm)while pore diameter in P. sylvestris L. lumber was larger(mainly 226.7 nm or 7 082.3 nm). The correlation of the MIP and SEM results revealed that the pores with diameter of 11.3-100 μm in moso bamboo corresponded to vessels, parenchyma cells and fiber cells in ground tissue, and the pores with diameter of approximately 835.0 nm mainly corresponded to the pits in fiber cells in ground tissue. The pores with diameter of approximately 20 μm corresponded to the tracheids of P. sylvestris L. lumber, while the pores with diameter of approximately 7 082.3 nm corresponded to the aperture of boarded pits and ray parenchyma cells. Additionally, pores with diameters below 1 μm were mainly located in the margo of boarded pits and cell walls. 【Conclusion】 MIP and SEM were effective for the characterization of pore structure in both moso bamboo and P. sylvestris L. lumber. The test methods permitted the analysis of the causes of different properties of bamboo and wood materials. However, when the MIP method was used to test the pore diameter distribution, some large pores were regarded as small pores because of the bottle neck effect; therefore, the accuracy of the test result was affected. Thus, pore morphology must be considered to produce a comprehensive and accurate characterization of the pore structure in bamboo and wood materials.