Molecular Structure and Tensile Mechanical Properties of Birch Enzymatic Lignin
To compensate for the lack of tensile strength-related data on wood pseudo in-situ lignin,this study combines ball milling,weak alkaline pretreatment,and enzymatic methods to extract three types of birch(Betula platyphylla)wood lignin:dual-enzyme lignin(DEL),alkaline-treated triple-enzyme lignin(ATEL),and dual-alkaline-treated dual-enzyme lignin(ADEL).Subsequently,the molecular purity,molecular structure,tensile strength,elastic modulus,Poisson's ratio,and shear modulus of the isolated lignin were tested.The results show that the purities of DEL,ATEL,and ADEL were 48.2%,99.29%,and 97.79%,respectively.ATEL and ADEL cause minimal chemical degradation of in-situ lignin in birch,exhibiting typical infrared spectroscopic features of hardwood lignin,including representative linkage types such as β-O-4 and β-β bonds,making them suitable for use as pseudo in-situ lignin.At 5%water content,the tensile strengths of DEL,ATEL,and ADEL were 17.14,5.38,and 5.62 MPa respectively;the elastic modulus were 7.97,6.36,and 6.23 GPa respectively;the Poisson's ratios were 0.31,0.34,and 0.34 respectively;the calculated shear modulus were 3.04,2.39,and 2.33 GPa respectively.DEL contains a large amount of cellulose and hemicellulose,resulting in higher tensile mechanical properties.ATEL and ADEL test data can be used to evaluate the tensile mechanical properties of in-situ birch lignin.
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