热解条件对橡木组成结构与纳米压痕测试结果的影响

摘要

以阔叶材橡木为对象,研究热解过程中木材组成结构与微观力学性能的转变特征.分别使用傅里叶红外光谱技术(FTIR)、X射线衍射技术(XRD)和纳米压痕技术(NI)分析热解过程中木材化学组成成分、微纤丝结构和细胞壁微观力学性能的转变.研究结果表明,热解温度达到325℃时木材化学组成与微纤丝结构都发生了显著转变,木材化学成分中的纤维素和半纤维素已基本裂解完毕,木质素结构仍有存在,且已有碳素材料特征峰出现;对应XRD图谱分析,由于纤维素的热解,325℃时细胞壁微纤丝构造引起的衍射峰已经消失.NI研究发现热解温度达到300℃时,橡木纤维细胞壁微观力学性能变化显著,弹性模量从未热解处理的(16.6±1.39) GPa下降至(5.78±0.30)GPa.细胞壁硬度与未热解处理木材的(0.46±0.045)GPa相比,当热解温度为250℃和300℃时,硬度值略有上升,分别为(0.54±0.049)和(0.52±0.024)GPa;同时发现300℃热解后木材细胞壁弹性模量和硬度数值的分散度变小,认为是因细胞壁组成与结构变得均一化所造成.%This study selected hardwood oak as a raw material.The transition characteristics of composition,structure and micro mechanical properties of oak in pyrolysis process were investigated.The Fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD),nanoindentation (NI) were used to examine the changes of chemical compositions,structure of micro fibril and micro mechanical properties at different pyrolysis temperature respectively.The results showed that the chemical compositions and structure of micro fibril changed dramatically when the pyrolysis temperature reached 325℃.The results of FTIR examination showed that,when the pyrolysis temperature was 325℃,the cellulose and hemicellulose in wood were decomposed completely,meanwhile the lignin was still detected and some carbon materials began to appear.Corresponded to the XRD spectrum,as the cellulose decomposed completely at 325℃,the XRD peak caused by the structure of micro fibril of wood vanished.The results of NI investigation showed that the micro mechanical properties of wood cell wall changed significantly.Compared with the original oak wood,when the pyrolysis temperature reached 300℃ the elastic modulus of cell wall decreased from (16.6± 1.39) GPa to (5.78±0.30) GPa.The hardness of wood cell walls changed slightly,in contrast with the elastic modulus.The hardness of the original wood cell wall was (0.46±0.045) GPa,and when the pyrolysis temperature were 250℃ and 300℃,the hardness increased to (0.54±0.049) GPa and (0.52±0.024) GPa,respectively.The data dispersion of elastic modulus and hardness became smaller when wood was pyrolyzed at 300℃ as the composition and structure of wood cell walls became homogenization.It was concluded that,under the experimental conditions of this study,the temperature of 300-325℃ was the very significant turning point.When the pyrolysis temperature reached 300-325℃,the composition,structure and physical properties of wood would change dramatically.