基于TG-FTIR的杨木热解过程中脲醛树脂影响机理的模型物研究

热解是废弃人造板高效回收利用的方式,人造板中所含胶黏剂是其不同于生物质的主要特征。为了有效环保地利用热解技术处理废弃人造板,解明人造板热解过程中其所含脲醛树脂胶黏剂(UF)对木材热解特性的影响,深入探索UF对人造板中木材各组分的作用机制,以杨木及木材的三种主要组分(纤维素、半纤维素、木素)为研究对象,创新性地依据杨木的化学组成,以纤维素、木聚糖和木素配制成模型物,并加入UF模拟人造板的构成。利用热重红外光谱联用(TG-FTIR)分析法,对比分析了加入UF前后模型物以及杨木各主要组分的热失重特性及气相演变规律。热重及红外结果表明,UF促进了纤维素热解过程中水和羧酸类物质的生成。UF与木素结合生成热不稳定的含氮结构,释放大量氨气,并且在200～300 ℃区间内参与了木素的热解并直接影响木素热解产物的生成。由此推测,在人造板热解过程中,木材三种主要组分中与UF作用的主要成分是木素。     

黑杨受拉木纤维细胞组分及孔隙分布拉曼光谱成像数据研究

倾斜阔叶木枝干弯曲部位的上端在拉伸应力影响下通常会形成受拉木.区别于受拉伸部位下方的对应木,受拉木细胞壁通常会出现理化特性变异的现象,主要归因于细胞次生壁内侧胶质层的形成.采用透射电子显微成像技术揭示了黑杨受拉木与对应木纤维细胞壁分层结构特点,并借助532 nm共聚焦显微拉曼光谱成像(空间分辨率约为0.5μm)及图像叠...     

Proton spin-lattice relaxation time measurements of solid wood and its constituents as a function of pH: part II

The proton spin-lattice relaxation times (T1H) for isolated cuoxam lignin and fully bleached cellulose were measured as a function of pH in the solid-state. These experiments provided the opportunity to examine for possible macromolecular connectivities that may be present between lignin and carbohydrates within softwood. These studies have shown that the molecular mobilities of the isolated polymeric constituents of wood are affected by the ionization of their functional groups at different pHs. The shapes of the plots of T1H as a function of pH for the two isolated polymers were dramatically different, while those for softwood were similar. This fact provides evidence supporting the notion that in wood, lignin and carbohydrates are intimately associated with each other.     

On the morphology of cellulose nanofibrils obtained by TEMPO-mediated oxidation and mechanical treatment

The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres were assessed. Two samples were produced with the same chemical treatment (NaClO/NaBr/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation), but distinct mechanical treatment intensities during homogenization. It was shown that the nanofibrils production yield increases with the mechanical energy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-dried nanocellulose films. However, no significant differences were detected regarding the nanofibrils width as measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in size were found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulose nanofibrils suspensions as a consequence of the differences in the length distribution of both samples. The nanofibrils length of the more nanofibrillated sample was calculated based on the width measured by AFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. The DLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrils length assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. A simple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy and light scattering methods.     

一维棒状纳米纤维素及光谱性质

采用稀酸预处理纤维素浆粕,结合高压均质的物理方法,制备出一维棒状纳米纤维素.通过傅里叶红外光谱(FTIR),X射线衍射(XRD),热重分析(TGA),原子力显微镜(AFM)和透射电镜(TEM)等方法对纳米纤维素光谱性能和形貌结构进行了表征.结果表明,制得的纳米纤维素与纤维素浆粕具有相同的红外特征官能闭,但分子内氢键缔合作用被部分破坏.纳米纤维素与纤维素浆粕同属于纤维素I的晶形类型,结品度从59%提高至70%,仍保持结晶区与无定形区共存的状态.纳米纤维素的分解温度为330℃,热稳定性低于纤维素浆粕,失重温度从292℃持续至500℃,有两个明显失重阶段.纳米纤维素长度为数百纳米,宽度为数十纳米的棒状形态,易产生团聚现象.     

Ultrasound-Assisted Surface-Modification of Wood Particulates for Improved Wood/Plastic Composites

The combined effects of alkali and ultrasound treatment of wood flour on the mechanical properties of polypropylene-based wood/plastic composites (WPCs) were examined. FT-IR measurements confirmed that the alkali treatment removed both hemicellulose and lignin from the wood, and there was an increase in the number of hydroxyl groups on the cellulose surface. This process was promoted by ultrasound treatment. Mechanical testing of injection-molded WPC samples revealed that alkali treatment improved both composite strength and modulus when polypropylene grafted with maleic acid was used as a coupling agent. The strength increase is due to improved adhesion between the fiber and matrix, while improved modulus is due to the removal of lignin and hemicellulose that are not as stiff as cellulose. Polarized optical microscopy showed the presence of well-defined polymer crystals on the surface of the modified wood, and this is also responsible for the improved mechanical properties. It is conclusively demonstrated that the combination of chemical treatment of wood and ultrasound assistance is more effective in improving the mechanical properties of the composites than the use of chemical treatment alone.     

A Review of Infrared Spectra from Wood and Wood Components Following Treatment with Liquid Ammonia and Solvated Electrons in Liquid Ammonia

ABSTRACT

The chemical changes that occur in wood and wood components (cellulose, holocellulose and lignin) following treatment with liquid ammonia and solvated electrons (e^? _s,) in liquid ammonia have been investigated using FTIR spectroscopy.

When ammonia penetrates into a wood structure, all carboxylate groups will react with ammonia to form ammonium salts, aldehydic and ketonic groups will follow a similar reaction to produce imines, and ester groups will react to forni amides.

After treatment with (e^? _s) in liquid ammonia, wood samples show diminished absorption around 15 13 cm^?1, a position corresponding to aromatic groups, and diminished absorption peaks associated with aldehydic, ketonic, and ester groups.

The overall changes in the IR spectra of cellulose in liquid ammonia and (e^? _s) in liquid ammonia are not dramatic. The IR spectra of the isolated holocellulose after treatment with (e^? _s) in liquid ammonia have intensities and band shape similar to those of cellulose. The isolated lignin behaves in a manner similar to wood, in that the liquid ammonia causes some decrease in the intensities of absorptions associated with C-O and C=O bands, and increase in strength of the amide functional group at 1600 cm^?1. The resulting extracts of wood, following treatment with (e^? _s) in liquid ammonia, appear to loose their “aromaticity”.

Because wood has long been used, and still is used extensively as an important constructional material, the changes in mechanical characteristics caused by the action of various reducing agents appears to have been an important area of scientific interest. The following review focuses on the chemical changes in the functional groups of the surface moieties of wood when treated with a reducing agent, such as (e^? _s + NH_3liq), using infrared spectroscopy.     

NMR spectroscopy applied to the Cultural Heritage: a preliminary study on ancient wood characterisation

High and low resolution solid state NMR methods have been applied to characterise a few samples of ancient wood. In an ancient larch wood sample, by applying ¹H low resolution NMR methods as a function of the temperature, the average pore size and its distribution have been determined. In addition, high resolution NMR techniques have allowed addressing of the question of the proximity of water pools to cellulose and lignin. In particular, a model can be hypothesized in which water pools are surrounded by thin layers of amorphous cellulose and/or lignin while the crystalline domains of cellulose surround the layers of amorphous cellulose. Preliminary results obtained using a fully non invasive and portable NMR unilateral relaxometer, the Eureka-Mouse10 (EM10), are reported. This instrumentation is shown to be perfectly suitable for characterizing degradation in ancient wood samples. PACS 76.60 k     

Use of Infrared Microspectroscopy in Plant Growth and Development

Abstract

Infrared microspectroscopy (IMS) has emerged as a key technique for the study of plant growth and development. The combination of IMS and synchrotron radiation has enabled researchers to analyze plant development at a cellular level. The spatial distribution of functional groups in plant tissue can be determined by the “chemical imaging” ability of IMS. Attenuated total reflectance (ATR) and polarized IR spectroscopies in combination with IMS makes sampling rapid and easy, providing direct analysis in situ. This review covers applications of IMS to study cell wall architecture and the major cell wall components: lignin, cellulose, and polysaccharides; applications for agricultural and feed products; and changes to plant structure due to biotic and abiotic stressors.     

马尾松木材褐腐降解的红外光谱研究

用傅立叶变换红外光谱(FTIR)研究了马尾松木材被茯苓褐腐菌降解过程中化学成分的变化。测量了木质素和综纤维素的相关红外吸收峰的峰高比值,用湿化学方法测定了未褐腐和不同褐腐时间木材的Klason木质素含量和综纤维素含量,分析了红外吸收峰峰高比值与Klason木质素含量和综纤维素含量的相关性。褐腐15周内,1736和1372cm-1处归属于综纤维素的吸收峰强度逐渐减弱,1510和1225cm-1处归属于木质素的吸收峰强度逐渐增强;但褐腐15周后,1736和1372cm-1处的吸收强度却开始略微增强,1510和1225cm-1处吸收强度略微下降。I1510/I1736,I1510/I1372,I1225/I1736和I1225/I1372与Klason木质素和综纤维素含量之间均存在非常好的线性相关,R2为0.96～0.99。I1736/I1510和I1372/I1510与综纤维素含量之间存在高度线性相关,R2=0.96。结果说明用红外光谱技术可以对木材褐腐过程中的综纤维素含量和Klason木质素含量进行准确分析。     

利用X射线衍射技术与红外光谱分析真菌侵蚀的木材

为了弄清真菌侵蚀木材的微细结晶构造与主成分官能团的变化,利用X射线衍射技术和红外光谱研究了分别经过黄孢原毛平革菌(PC)和棉腐卧孔菌(PP)侵蚀不同时间后毛白杨木材的结晶度、晶胞内层间距、晶粒宽度和主成分官能团的变化情况。结果表明：(1)PC与PP的侵蚀对木材纤维素结晶区的晶格构造没有影响,纤维素结晶区衍射2θ角和层间距基本保持不变,但纤维素结晶度和晶粒宽度随侵蚀时间增加而呈减小的趋势,并且受PP侵蚀的要比受PC侵蚀的明显,表明PP侵蚀对纤维素的破坏程度要大于PC侵蚀;(2)半纤维素在侵蚀过程中其木聚糖被不同程度的降解,使得产物中羰基含量增加,PC与PP对半纤维素的降解效果与纤维素几近相同;(3)木质素受PC侵蚀后苯环被氧化裂解生成链烃,而受PP侵蚀的变化不明显。     

δ2H, δ13C and δ18O from whole wood, α-cellulose and lignin methoxyl groups in Pinus sylvestris: a multi-parameter approach

Novel tree ring parameters – δ¹³C and δ²H from methoxyl groups – have been developed to reconstruct palaeoclimate. Tests with δ¹³C and δ¹⁸O derived from whole wood and cellulose samples, however, indicated differences in the isotopic composition and climate signal, depending on the extracted wood component. We assess this signal dependency by analysing (i) δ¹³C and δ¹⁸O from whole wood and cellulose and (ii) δ¹³C and δ²H from methoxyl groups, using Pinus sylvestris L. growing near Altenkirchen (Germany). Results indicate significant correlations among the time series derived from whole wood, cellulose, and lignin methoxyl groups. Compared with the whole wood samples, δ¹³C from methoxyl groups showed a different and overall lower response to climate parameters. On the other hand, δ²H from methoxyl groups showed high correlations with temperature and was also correlated with ring width, indicating its potential as a temperature proxy. Isotope time series with the highest correlation with climatic parameter were: (i) whole wood and cellulose δ¹³C with growing season precipitation and summer temperature; (ii) methoxyl groups with spring precipitation; (iii) whole wood and cellulose δ¹⁸O correlates with annual evapotranspiration and water balance; and (iv) methoxyl group δ²H with spring temperatures. These findings reveal that multiple climate elements can be reconstructed from different wood components and that whole wood proxies perform comparably to cellulose time series.     

INFRARED AND RAMAN SPECTROSCOPY IN PAPER AND PULP ANALYSIS

Infrared and Raman spectroscopy are essential analytical tools for the structural analysis of paper and pulp chemistry. The studies of cellulose, hemicellulose, lignin, thermal- and photo-induced oxidation; cross-linking; and various chemical treatments of pulp and paper products are all made possible using these forms of molecular spectroscopy. In this review, containing 70 references, a broad range of applications into pulp and paper materials, components, and processes is described from recent and classic research over predominantly the past 20 years.     

New Approaches to Cellulose Microfibril Isolation from Musaceae Agro-Industrial Residues

In this work, Musaceae isolated vascular bundles from rachis agro-industrial residues were evaluated as a potential source of cellulose microfibrils. For vascular bundle isolation, a biological retting was used. For cellulose microfibril isolation, two different alkaline treatments (sodium hydroxide or potassium hydroxide combined with bleaching and acid steps) were used in conjunction with a mechanical process. Cellulose microfibrils using both alkaline processes were successfully isolated, and the presence of non-cellulosic components, especially lignin and some hemicellulose as arabinose and galactose were reduced. In spite of an important amount of oxides being removed during the biological retting, XRF analysis revealed that calcium minerals were still present in the vascular bundles, and they can affect the cellulose microfibril isolation. AFM micrographs of isolated samples revealed cellulose microfibril bundles, and their presence can be associated with non-cellulosic components still present in the samples. Thermal analysis showed that when potassium hydroxide was used, a higher reduction of lignin was observed. Nevertheless, X-ray diffractions indicated no change in the crystallization pattern of cellulose I had occurred due to the isolation process used.     

真空热处理人工林落叶松木材吸湿性变化机理研究

热处理是一种环境友好型的木材改性方法,可提高木材的耐腐性和尺寸稳定性。研究以落叶松木材为试验材料,在处理温度200 ℃的条件下,对其进行了不同时间的真空热处理。利用动态水蒸气吸附(DVS)对热处理前后木材吸湿性的变化进行了表征,通过傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和X射线衍射(XRD)分析了热处理前后木材化学组分和结构变化,通过化学变化分析阐明了热处理木材吸湿性变化的作用机制。结果表明：真空热处理落叶松木材的平衡含水率降低,热处理木材的平衡含水率随热处理时间的延长呈逐渐下降的趋势。结合红外光谱和光电子能谱发现,热处理后木材纤维素和半纤维素等化学成分发生降解,木质素发生交联缩合反应,使得吸湿性基团含量减少,碳元素与氧元素含量发生变化,氧碳比降低,从C原子的结合形式来看,热处理材的C1含量增加,C2和C3含量降低,这些化学变化使得热处理材的吸湿性降低。此外,真空热处理未破坏木材的结晶结构,木材的相对结晶度随真空热处理时间的延长而增大,结晶度的增大减少了纤维素分子链上吸水性基团的数量,从而降低了木材的吸湿性。     

Effect of cellulose–lignin interactions on char structural changes during fast pyrolysis at 100–350 °C

This study investigates the cellulose–lignin interactions during fast pyrolysis at 100–350 °C for better understanding fundamental pyrolysis mechanism of lignocellulosic biomass. The results show that co-pyrolysis of cellulose and lignin (with a mass ratio of 1:1) at temperatures < 300 °C leads to a char yield lower than the calculated char yield based on the addition of individual cellulose and lignin pyrolysis. The difference between the experimental and calculated char yields increases with temperature, from ～2% 150 °C to ～6% at 250 °C. Such differences in char yields provide direct evidences on the existence of cellulose–lignin interactions during co-pyrolysis of cellulose and lignin. At temperatures below 300 °C, the reductions in both lignin functional groups and sugar structures within the char indicate that co-pyrolysis of cellulose and lignin enhances the release of volatiles from both cellulose and lignin. Such an observation could be attributed to two possible reasons: (1) the stabilization of lignin-derived reactive species by cellulose-derived reaction intermediates as hydrogen donors, and (2) the thermal ejection of cellulose-derived species due to micro-explosion of liquid intermediates from lignin. In contrast, at temperatures ≥ 300 °C, co-pyrolysis of cellulose and lignin increases char yields, i.e., with the difference between the experimental and calculated char yields increasing from ～1% at 300 °C to ～8% at 350 °C. The results indicate that the cellulose-derived volatiles are difficult to diffuse through the lignin-derived liquid intermediates into the vapor phase, leading to increased char formation from co-pyrolysis of cellulose and lignin as temperature increases. Such an observation is further supported by the increased retention of cellulose functional groups in the char from co-pyrolysis of cellulose and lignin.     

Fibre matrix adhesion of natural fibres cotton,flax and hemp in polymeric matrices analyzed with the single fibre fragmentation test

In this research the adhesion and the resulting interfacial shear strength (IFFS) between the natural fibres flax, hemp and cotton and the polymer matrices polypropylene with coupling agent (MAPP) and polylactide acid (PLA) was surveyed with the single fibre fragmentation test (SFFT). The adhesion between MAPP and the fibres was good enough to produce fragments, whereas the adhesion between PLA and flax was too weak to transmit enough tension for fibre cracks which is clearly visible on SEM-photographs. Comparing the IFFS values of the fibres in MAPP with an equal fibre diameter shows that the IFFS value of flax is highest with 7.09 N/mm² followed by hemp 6.13 N/mm². The IFFS of cotton is a lot smaller (0.664 N/mm²). The critical fragmentation or fragmentation length of the bast fibres flax (3.16 mm) and hemp (3.20 mm) in MAPP is smaller than the critical fragmentation length of cotton (5.03 mm). The adhesion between the lignocellulosic fibres and MAPP is much better than between the lignin and pectin free cellulose fibre and MAPP. Possible reasons for this — the surface structure of the cotton fibre and its different chemical composition being made up of only cellulose, hemi-cellulose and wax with no pectin or lignin present — are discussed.     

Moisture Absorption Behavior of Wood/Plastic Composites Made with Ultrasound-Assisted Alkali-Treated Wood Particulates

The combined effects of alkali and ultrasound treatment of wood flour on the moisture absorption behavior of polypropylene-based wood/plastic composites (WPCs) were examined. FT-IR measurements confirmed that the alkali treatment removed both hemicellulose and lignin from the wood, and there was an increase in the number of hydroxyl groups on the cellulose surface. This process was promoted by ultrasound treatment. Particle size analysis of treated wood fibers revealed that alkali treatment reduced the particle size slightly, and the particle size was further reduced by the assistance of ultrasound. Moisture absorption measurements revealed the interplay between the presence of relative amounts of cellulose, hemicellulose and lignin in the wood and the amount of coupling agent added. It was found that appropriate alkali treatment and an optimum amount of added coupling agent could simultaneously improve composite mechanical properties and reduce both the rate and the maximum amount of moisture absorbed. Further improvements require preferential removal of hemicellulose from the wood and conditions that promote covalent bonding between the coupling agent and the wood reinforcement.     

近红外光谱法快速测定毛竹Klason木质素的含量

研究了用近红外漫反射光谱法对毛竹Klason木质素含量的快速预测。选取了代表不同竹龄、不同高度和横向不同位置的54个竹材粉末样品,用常规实验室方法测定了54个样品的Klason木质素含量,用近红外光谱仪漫反射方式在350～2500 nm范围内采集相应样品的光谱,利用多变量统计分析软件建立样品木质素含量和光谱数据之间的相关性模型。结果表明,对原始光谱进行二阶导数预处理后,选择1 011～1675 nm和1930～2488 nm波长区间,用偏最小二乘法(PLS1)和完全交互验证方式建立了的校正模型和预测模型的相关系数分别为0.99,和0.97,校正标准误差SEC＝0.36％,预测标准误差SEP=0.59％,说明毛竹Klason木质素含量和近红外光谱之间存在非常好的相关性,用近红外光谱技术可以实现对竹材样品中Klason木质素含量的快速预测。     

基于近红外光谱技术的紫外光老化落叶松木材表面材色变化的定性和定量研究

自然光中的紫外光在木材表面产生复杂的光化学反应,是木材在自然环境中老化降解速度最快,反应最强的化学过程。基于近红外光谱(NIRs)技术探讨了落叶松表面材色在340 nm波长紫外光照射条件下的老化状况。不同时间(180,540,900,1 080 h)试材弦切面经紫外光人工老化后,测量木材表面材色色度学指数,并采集NIRs信息。由NIRs二阶导数及其差谱图反映的信息,定性分析和讨论了木材表面化学组分基团的变化;定量建立基于偏最小二乘法(PLS)结合留一交叉验证的木材表面材色预测模型。结果表明：(1) 随着人工老化时间延长,木材表面明度值L*降低,红绿指数a*与黄蓝指数b*出现先增加后缓慢降低的趋势,表明发色基团的形成随着紫外光照射时间的延长而减少,在辐射时间540 h达到最大值,此外,色差值ΔE*与紫外光照射时间成正相关。(2) NIRs二阶导数在6 996,6 773以及6 287 cm-1等分别反映木材中纤维素非结晶区、半结晶区和结晶区的光谱吸光度随着老化时间的延长而增加,而5 986 cm-1反映木质素特征性谱带吸收峰随着紫外光老化时间的延长而降低,表明木质素出现降解。通过紫外光照射1 080 h与对照材的差谱分析发现,纤维素和半纤维素基团的特征峰差谱值为正,表明紫外光辐射后木材表面的纤维素和半纤维素相对含量增加,而木质素基团特征峰差谱值为负,表明经紫外光辐射后,木质素的降解导致其相对含量减少。这些结果与色度值测量结果相一致。(3) 基于NIRs建立的紫外光照射落叶松表面材色预测模型中,L*交叉验证模型决定系数(R2)为0.949,相对分析误差(RPD)为4.42;a*交叉验证模型R2是0.928,RPD是3.73;b*的交叉验证模型R2是0.831,RPD为2.43,建立的材色预测模型满足预测要求。