Characterisation of thermally modified wood: molecular reasons for wood performance improvement
Characterisation of thermally modified wood: molecular reasons for wood performance improvement
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DOI：
10.1007/s001070050287
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发表时间：
1998-05-01
期刊：
影响因子：
--
通讯作者：
Militz, H
中科院分区：
文献类型：
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作者：
Tjeerdsma, BF;Boonstra, M;Militz, H
通过固相CP-MAS 13 C-NMR研究了木材的相对温和的热处理，根据两个步骤的过程，导致改善的尺寸稳定性和改善的木材性能，以在分子水平上理解所报道的改进的原因。所描述的所有情况似乎都是木材化学中已知的反应的结果。这些是从半纤维素释放的乙酸的形成，其进一步催化碳水化合物裂解，导致碳水化合物的聚合度降低。酸催化的降解导致甲醛、糠醛和其它醛的形成以及在C α和O 4处的一些木质素裂解，并且据信导致从木质素单元C γ产生一些醛，所有这些都发生在第一反应步骤中。木质素通过裂解的带正电荷的苄型C α形成一些亚甲基桥的自缩合大概已经在该第一阶段开始发生。一些木质素单元的芳环上的自由反应位点的数量的增加已经发生在这一阶段，但继续进入下一个。在第二个处理步骤中，木质素的自动缩合的完成被认为是通过形成连接芳环的亚甲基桥来发生的。芳核位点通过脱甲氧基和通过裂解的带正电荷的苄型C α释放。在第一步阶段中形成的一些醛基与木质素芳核位点发生反应，通过亚甲基桥连接芳环，这些反应的程度是温和的，但它们导致交联的增加，从而改善木材的尺寸稳定性和降低木材的吸湿性。
Relatively mild thermal treatments of wood according to a two step process which leads to improved dimensional stability and improved timber performance were investigated by solid phase CP-MAS 13C-NMR to understand at molecular level the reasons for the improvements reported. All the occurrences described appear to be the consequence of reactions which are known in wood chemistry. These are the formation of acetic acid liberated from the hemicelluloses, which further catalyses carbohydrates cleavage, causing a reduction of degree of polymerisation of the carbohydrates. Acid catalysed degradation results in the formation of formaldehyde, furfural and other aldehydes as well as some lignin cleavage at C alpha and O4 and believed to cause some aldehyde production from lignin units C gamma, all occurring in the first reaction step. Lignin autocondensation through the cleaved, positively charged benzylic C alpha to form some methylene bridges presumably starts already to occur in this first phase. The increase in the number of free reactive sites on the aromatic ring of some lignin units already occurs in this phase but continues into the next.In the second treatment step completion of the autocondensation of lignin is believed to occur through the formation of methylene bridges connecting aromatic rings. The aromatic nuclei sites are released by demethoxylation and through the cleaved, positively charged benzylic C alpha. Reactions of some of the aldehyde groups formed in the first step phase occur with lignin aromatic nuclei sites to connect aromatic rings through methylene bridges.The extent of these reactions is mild, but nonetheless they lead to an increase in cross-linking with consequent improvement in dimensional stability and decreased hygroscopicity of wood.