Wood mechanical properties and their correlation with microstructure in Chinese fir clones

Abstract

Mechanical testing, microscopic image analysis, and X-ray diffraction were used to study the mechanical properties and their correlation with microstructure in three 20-year-old Chinese fir clones (Kailin 24, Kaihua 13, and Kaihua 3). The Chinese fir clones featured a modulus of rupture (MOR) of 52–59 MPa, a modulus of elasticity (MOE) of 10–11 GPa, and a compressive strength parallel to the grain of 31–34 MPa. Kaihua 13 and Kailin 24 had similar mechanical properties and were superior to Kaihua 3 among the tree clones. Radial variation indicated that their outerwood (rings 9–18) had better mechanical properties than their corewood (rings 3–7). Kaihua 13 with better mechanical properties had a larger ratio of cell wall to lumen than Kaihua 3 and Kailin 24. Outerwood with better mechanical properties also had a larger ratio of cell wall to lumen and a smaller microfibril angle compared to corewood with poor mechanical properties. Linear regression analysis also shows that for various clones and different radial positions in the same clone, anatomical structure parameters such as average cell wall thickness and the ratio of cell wall to lumen were positively correlated to their mechanical properties, while the microfibril angle was negatively correlated to mechanical properties. The two factors synergistically influence the mechanical properties of wood.