Gheorghe Asachi Technical University of Iasi, no. 67, Dimitrie Mangeron Bd., 700050 Iasi, Romania.
Appl Spectrosc. 2013 Jun;67(6):606-13. doi: 10.1366/12-06628.
The weathering of acrylic films and acrylic-coated lime wood (Tillia cordata Mill.) were examined using Fourier transform infrared (FT-IR) and two-dimensional infrared correlation spectroscopy. The obtained results showed chemical changes induced by exposure to weathering conditions, in both films and coated wood. The observed spectral changes of the acrylic films refer to the absorption band assigned to the C-O stretching, which progressively decreases with increasing exposure time. In the spectra of treated wood samples the main signal indicating the advance of oxidation during the photodegradation exposure is the gradual increase and broadening of the band in the carbonyl region. This is due to the formation of the non-hydrogen bonded aliphatic carboxylic acids and γ-lactone structures in the acrylic resin and of the nonconjugated ketones, carboxyl groups, and lactones in wood. As a consequence, the increase of the 1734 cm(-1) band is due to the degradation of lignin from wood surface. These observations are also supported by the decreased intensities of the bands at 1598 and 1505 cm(-1), assigned to C=C of aromatic skeletal (lignin). The relative intensity of the characteristic aromatic lignin band at 1505 cm(-1) decreases up to 25% of its original value after weathering, being less than half of the value obtained for uncoated wood. Two-dimensional infrared (2D IR) correlation spectroscopy was used to identify the sequence of the modifications of the different stretching vibrations bands under the weathering conditions, the method allowing the prediction of the order of degradation reactions. The acrylic resin degradation starts with the formation of radicals by abstraction of the tertiary hydrogen atoms of the methyl acrylate units and the α-CH3 groups from the ethyl methacrylate units. The subsequent decomposition and oxidation led to the formation of alcohol groups, hydroperoxides, ketones, and/or carboxylic acid groups. The 2D IR correlation spectra of weathered impregnated wood also revealed the elimination of low molecular weight compounds following the degradation of lignin and carbohydrates components from wood.
采用傅里叶变换红外（FT-IR）和二维红外相关光谱法研究了丙烯酸薄膜和丙烯酸涂层石灰木（Tilia cordata Mill.）的风化情况。研究结果表明，暴露在风化条件下会引起薄膜和涂层木材的化学变化。观察到的丙烯酸薄膜光谱变化与分配给 C-O 伸缩的吸收带有关，该吸收带随着暴露时间的增加而逐渐减小。在处理过的木材样品的光谱中，指示光降解暴露过程中氧化进展的主要信号是羰基区域中带的逐渐增加和变宽。这是由于在丙烯酸树脂中形成了非氢键合的脂肪族羧酸和γ-内酯结构，以及在木材中非共轭酮、羧基和内酯。因此，1734 cm(-1) 带的增加是由于木材表面木质素的降解。这些观察结果也得到了在 1598 和 1505 cm(-1) 处分配给芳族骨架（木质素）的 C=C 带强度降低的支持。在风化后，特征芳族木质素带在 1505 cm(-1) 处的相对强度下降到其原始值的 25%，不到未涂层木材的一半。二维红外（2D IR）相关光谱法用于识别在风化条件下不同伸缩振动带的修饰顺序，该方法允许预测降解反应的顺序。丙烯酸树脂的降解始于通过从甲基丙烯酸酯单元和乙基甲基丙烯酸酯单元的α-CH3 基团中提取叔氢原子形成自由基。随后的分解和氧化导致醇基团、过氧化物、酮和/或羧酸基团的形成。风化浸渍木材的 2D IR 相关光谱也揭示了在木质素和碳水化合物成分从木材中降解后，低分子量化合物的消除。
