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首页> 外文期刊>Journal of Applied Polymer Science >Correlation of C-13-NMR analysis with fungal decay tests of polymeric structural wood constituents. I. Basidiomycetes
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Correlation of C-13-NMR analysis with fungal decay tests of polymeric structural wood constituents. I. Basidiomycetes

机译：C-13-NMR分析与聚合物结构木材成分的真菌衰减测试的相关性。 I.担子菌

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摘要

Heat treatment at relatively high temperatures (from 150 to 260 degrees C is an effective method to improve the durability of wood. This study investigates the reasons for the decay resistance of heat-treated and nontreated wood with respect to the polymeric structural constituents by solid-state cross-polarization/magic-angle spinning (CP-MAS) C-13-NMR analysis before and after exposure to brown rot and white rot fungi. An industrial two-stage heat-treatment method under relatively mild conditions (< 200 degrees C) has been used to treat the samples. Brown rot fungi attack polymeric carbohydrates of nontreated Scots pine sapwood at C4, resulting in cleavage and eventually depolymerization of cellulose and hemicelluloses. The attack at the carbohydrate C6, which has never been observed before, is remarkable because the C6-CH2OH group has no covalent structural function but acts in fixing the three-dimensional carbohydrate configuration just by secondary forces. The -CH,OH group carries -OH, which forms some of the strongest hydrogen bonds in the structure of the crystalline native cellulose. It is suggested that the fungus tries to cleave this group to open the cellulose crystalline structure into an amorphous structure to decrease its water repellency to facilitate enzymatic cellulose degradation. Considerable degradation of the hemicelluloses occurs during brown rot fungal exposure, whereas in general the attack on lignin is rather limited, being mainly demethoxylation. However, Gloeophyllum trabeum is an active brown rot fungus in the (partial) degradation of lignin because there is some indication of ring opening of the aromatic ring of lignin during fungal exposure. Aromatic ring opening has also been observed after exposure to Coriolus versicolor, a white rot fungus. The demethoxylation of lignin and some attack on wood carbohydrates are also characteristic of the attack of this white rot fungus. The CP-MAS C-13-NMR spectra of heat-treated Norway spruce reveal similarities but also clear differences after fungal exposure in comparison with non-treated Scots pine sapwood. Brown rot fungi seem to have a preference to attack the carbohydrates of heat-treated wood at C4 and especially C1, cleaving the skeleton of cellulose and glucomannans. In untreated Scots pine sapwood, this attack mainly occurs at C4, the nonreducing end of the glucose unit. An attack on the out-of-the-ring alcoholic group -CH2,OH of the carbohydrates of heat-treated Norway spruce is less obvious than that in untreated Scots pine. The attack on C3/C5 of the carbohydrates is remarkable, indicating ring opening of the glucose units, which has not been observed in nontreated Scots pine sapwood. Lignin degradation is limited to demethoxylation, and low or no aromatic ring opening is observed, even after C. versicolor exposure. (c) 2006 Wiley Periodicals, Inc.
机译：在相对较高的温度（150至260摄氏度）下进行热处理是提高木材耐久性的有效方法。本研究调查了经过热处理的和未经处理的木材相对于固结聚合物结构成分的耐腐烂性的原因。状态交叉极化/魔角旋转（CP-MAS）暴露于褐腐和白腐真菌之前和之后的C-13-NMR分析。在相对温和的条件下（<200摄氏度）的工业两阶段热处理方法）已被用于处理样品。褐腐真菌在C4处攻击未经处理的苏格兰松材边材的聚合碳水化合物，导致纤维素和半纤维素裂解并最终解聚。在C6处的碳水化合物受到的攻击是前所未有的因为C6-CH2OH基团没有共价结构功能，但仅通过次级作用力就能固定三维碳水化合物构型。 -OH，在晶体天然纤维素的结构中形成一些最强的氢键。建议真菌试图裂解该基团以将纤维素晶体结构打开为无定形结构以降低其疏水性以促进酶促纤维素降解。在褐腐真菌暴露期间，半纤维素发生相当大的降解，而通常对木质素的攻击相当有限，主要是脱甲氧基化。然而，由于在真菌暴露过程中存在木质素芳香环开环的某些迹象，因此，球根菌是木质素的（部分）降解中的一种活性褐腐真菌。暴露于白色腐霉菌Coriolus versicolor后，还观察到芳香环的打开。木质素的脱甲氧基化和对木材碳水化合物的一些侵蚀也是这种白腐真菌侵蚀的特征。与未经处理的苏格兰松木边材相比，经热处理的挪威云杉的CP-MAS C-13-NMR光谱显示出相似性，但在真菌暴露后也存在明显差异。褐腐真菌似乎更喜欢在C4尤其是C1侵蚀热处理木材的碳水化合物，从而裂解纤维素和葡甘露聚糖的骨架。在未经处理的苏格兰松材中，这种攻击主要发生在葡萄糖单元的非还原端C4。与未经处理的苏格兰松树相比，对经过热处理的挪威云杉的碳水化合物中环外醇基-CH2，OH的攻击不那么明显。碳水化合物对C3 / C5的攻击非常明显，表明葡萄糖单元的开环，这在未经处理的苏格兰松木边材中尚未观察到。木质素的降解仅限于脱甲氧基化，即使在暴露于杂色衣藻后，也观察不到低或无芳族开环。 （c）2006年Wiley Periodicals，Inc.

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