Upon tensile stress, the spiral cellulose fibrils in wood cell walls rotate like springs with decreasing microfibril angle (MFA), and the cellulose molecules elongate in the chain direction. Compression wood with high MFA and opposite wood with low MFA were comparatively studied by tensile tests combined with synchrotron radiation WAXS in the present study. FTIR spectroscopy revealed that compression wood had a higher lignin content and fewer acetyl groups. For both types of wood, the lattice spacing d increased and the MFA decreased gradually with the increase of tensile stress. At stresses beyond the yield point, cellulose lattice strain depended linearly on macroscopic stress, while the MFA depended linearly on macroscopic strain. The deformation mechanisms of compression wood and opposite wood are not essentially different but differ in their deformation behavior. Specifically, the contribution ratio of lattice strain and cellulose fibril reorientation to macroscopic strain was 0.25 and 0.53 for compression wood, and 0.40 and 0.33 for opposite wood, respectively. Due to the geometric effects of MFA, a greater contribution of cellulose fibril reorientation to the macroscopic deformation was detected in compression wood than in opposite wood.

中文翻译：

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原位WAXS研究马尾松压缩材及反材中微纤丝角度在纤维素原纤分子变形中的作用

在拉伸应力作用下，木材细胞壁中的螺旋纤维素原纤维像弹簧一样旋转，微原纤维角（MFA）逐渐减小，纤维素分子沿链方向伸长。本研究通过拉伸试验结合同步辐射WAXS对高MFA压缩木材和低MFA相反木材进行了比较研究。 FTIR 光谱显示压缩木材具有较高的木质素含量和较少的乙酰基。对于两种类型的木材，随着拉应力的增加，晶格间距d逐渐增大，而MFA逐渐减小。当应力超过屈服点时，纤维素晶格应变与宏观应力线性相关，而 MFA 与宏观应变线性相关。压缩木和相反木的变形机制没有本质上的不同，只是变形行为不同。具体而言，压缩木材的晶格应变和纤维素原纤维重新取向对宏观应变的贡献比分别为0.25和0.53，而相反木材的贡献比分别为0.40和0.33。由于 MFA 的几何效应，在压缩木材中检测到的纤维素原纤维重新定向对宏观变形的贡献比在相反木材中更大。