傅里叶变换红外光谱研究拉伸过程中应压木主要化学组分的响应规律

Chemical Construction Changes of Compression Wood Main Components in Longitudinal Tension by the FTIR Analysis

应压木的适应性生长导致了针叶树木材化学性质发生变化,其中微纤丝角的变大主要引起木材主要化学组分变形机制发生了变化,影响其力学性质。以马尾松应压木和正常材为研究对象,通过傅里叶变换红外光谱对比研究应压木和正常材在拉伸过程中木材主要化学组分官能团的变化规律差异,对研究应压木力学性能变化的分子响应机制具有重要意义。结果表明:应压木的微纤丝角为35.17°±2.30°,而正常材为15.15°±1.61°;应压木和正常材的顺纹抗拉强度分别为(45.37±3.41)和(109.75±11.87) MPa,弹性模量分别为(18.10±0.76)和(70.95±6.60) MPa,但应压木的屈服变形大于正常材,破坏点的应变值约为正常材的3倍。傅里叶变换红外光谱结果表明:应压木和正常材纤维素中糖苷键C-O-C(1 161 cm^-1)和纤维素分子内氢键O(3)H…O(5)(3 348 cm^-1)的红外吸收特征峰波数都随拉伸应变发生线性变化。其中,应压木中纤维素的糖苷键C-O-C向低波数偏移量为-1.52 cm^-1·dε^-1,而正常材的苷键偏移量为-2.15 cm^-1·dε^-1;应压木中纤维素分子链内氢键O(3)H…O(5)的波数向高波数偏移量为4.62 cm^-1·dε^-1,而正常材纤维素分子链内氢键偏移量为2.76 cm^-1·dε^-1。应压木纤维素的糖苷键向低波数的偏移量、纤维素分子链内氢键向高波数的偏移量均小于正常材,但两者木质素和半纤维素特征官能团的红外吸收特征峰波数没有明显偏移。根据应压木和正常材拉伸过程中的主要化学组分响应规律,纤维素依然作为应压木在拉伸过程中的承载物质,而基体的主要作用是应力传递;但微纤丝排列重新取向;与正常材相比,应压木中较大的微纤丝角会导致纤维素分子链长度方向的变形较小,但微纤丝与基体之间的剪切变形会较大。这也导致了应压木在拉伸过程中会发生较大的屈服变形,破坏点的应变大于正常材。

The adaptive growth of compression wood(CW)leads to the changes of chemical properties of coniferous wood,which the change of microfibril angle(MFA)affects the wood mechanical properties and macromolecular deformation.In this paper,the Fourier transform infrared spectroscopy(FTIR)was explored together with mechanical loading as a means of studying the molecular responses to the loading of Masson pine CW and normal wood(NW).It is of great significance to study the molecular biological mechanism of the mechanical properties changes of the CW.The results indicated that the MFA,tensile strength along grain and modulus of elasticity of the CW were 35.17°±2.30°,(45.37±3.41)and(18.10±0.76)MPa,respectively,and were 15.15°±1.61°,(109.75±11.87)and(70.95±6.60)MPa of the NW.What is more,the strain at the break-point of the CW was three times than that of the NW.The FTIR results indicated that the wavenumber shifts of the FTIR bands at 1161 and 3348 cm-1 showed an approximately linear relationship with strain.The C—O—C of cellulose at 1161 cm^-1 band shifted to lower wavenumber with tensile strain increase,and shift rate was 2.15 and 1.52 cm^-1·dε-1 for the CW and NW,respectively.Furthermore,the O(3)H…O(5)of cellulose intramolecular 3348 cm^-1 bands shifted to higher wavenumber,and shift rate was 4.62 and 2.76 cm^-1·dε^-1 of the CW and NW,respectively.The shift rates of 1161 and 3348 cm-1 bands of NW were more than that of CW.However,the characteristic peaks of lignin and hemicellulose were shown not to be affected.The above results indicate that the cellulose mainly provides the strength of the wood and the matrix of hemicellulose and lignin is benefited to load transform between cellulose microfibrils.Compared with the NW,the larger orientation of microfiber of the CW leads to smaller tension deformation along the direction of cellulose molecular chain,but the larger of shear deformation between microfibrils and matrix.This also leads to a large yield deformation in the tensile process of the CW,and the strain of the failure point is greater than the NW.