Studies on photostability of butyrylated, milled wood lignin using spectroscopic analyses

Photo-stabilisation of butyrylated milled wood lignin (MWL) was investigated in this study. Chemical changes were confirmed by NMR and FT-IR spectra after butyrylation. Improvements in the photostability of MWL by butyrylation were evaluated by spectral analyses including ESR, FT-IR and UV-VIS spectra. From ESR analyses, butyrylation reduces the amount of phenoxyl free radicals of MWL after UV irradiation, which results in inhibiting the photo-oxidation of lignin followed by a significant decrease in the formation of colored chromophores. The carbonyl, carboxyl and quinonoid structures were less detected in the butyrylated MWL after UV irradiation than those of untreated MWL, and the content of degraded water-soluble materials from the photo-degradation of MWL was also reduced upon butyrylation.     

Investigation of the chemical modifications of beech wood lignin during heat treatment

Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS ¹³C NMR, ¹³C NMR, ³¹P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin.     

UV-ABC screens of luteolin derivatives compared to edelweiss extract

Pure luteolin is a remarkably heat (200°C/6 days) and UV stable UV-A screen, however, native luteolin enriched to 37% in an edelweiss extract lost its UV-A screen properties upon UV irradiation (～4MJm(-2)). This contrasting behavior led to the examination of a series of purified luteolin derivatives as UV screen candidates. 3',4',5,7-Tetralipoyloxyflavones were synthesized from luteolin (3',4',5,7-tetrahydroxyflavone) and fatty acid chlorides. These acylated semi-biomolecules show a hypsochromic shift in UV-Vis spectra of about Δλ(A→B)=58nm and absorbed in the centre of the harmful UV-B band (λ(max)=295nm). Luteolin was also hydroxyethylated with Br(CH(2))(2)OH. This substitution has no effect on the λ(max)=330nm absorption of luteolin (UV-A band). Finally the natural 4'-O-β-glucosyl-3',5,7-trihydroxyflavone was extracted from edelweiss and used as a purified natural benchmark. Glycosylated and hydroxyethylated luteolin are both UV stable. Fully acylated luteolin derivatives degrade upon UV exposure to a stable UV-C screen with a hypsochroic shift Δλ(B→C)=35nm. All in all, three molecular structures based on luteolin with sunscreen properties were found, distinguishable in: UV-A, UV-B, and UV-C filters. The natural product based UV-absorbers show promise as alternatives to synthetic molecules and nanoparticles in sunscreen products.     

Homo- and hetero-nuclear 2D NMR techniques: Umambiguous structural probes for non-cyclic benzyl aryl ethers in soluble lignin samples

A number of two-dimensional NMR experiments are evaluated with respect to their ability to provide unambiguous evidence for the presence or absence of non-cyclic benzyl aryl ether (α-O-4) structures in soluble lignin samples. The most suitable techniques, in terms of both sensitivity and structural information content were the homonuclear Hartmann-Hahn (HOHAHA) and heteronuclear multiple quantum coherence (HMQC) techniques. By spiking an acetylated Pinus radiata MWL sample with an oligomeric α-O-4 ether model compound, it was possible to determine a detection limit of <0.3 structures per 100 lignin C9 units for both the HOHAHA and HMQC techniques. From this, and other work, it can be shown that if α-O-4 structures are present in MWL samples, they are present at a level below the detection limit of these experiments. The implications of these results are discussed in terms of lignin biosynthesis and reactivity.     

Photostabilizing milled wood lignin with benzotriazoles and hindered nitroxide.

The inhibitory processes operating when a 2(-2'-hydroxyphenyl) benzotriazole-based ultraviolet absorber (UVA) and a hindered nitroxide free radical are applied to high-yield pulps were studied using milled wood lignin and filter paper as a model. Using quantitative 31P NMR it was determined that the UVA is almost completely photostable during irradiation, suggesting that its protective mechanism is based primarily on ultraviolet absorption. Furthermore, the nitroxide was found to protect the UVA from photodegradation. Analysis of irradiated lignin samples involved derivatization followed by reductive cleavage of beta-arylether groups. The phenolic-OH groups thus released were quantified using 31P NMR. The benzotriazole/nitroxide stabilizing system was found to cooperatively inhibit the cleavage of beta-arylether groups. Furthermore, this system was found to have a synergistic inhibitory effect on the formation of catechol structures. These results suggest that the synergism observed between benzotriazole-based UV screens and nitroxyl radicals on the inhibition of yellowing could be a result of their ability to slow the formation of catechol structures and beta-O-4 cleavage in addition to the possibility of a UVA-regeneration mechanism.     

Investigation of structure of milled wood and dioxane lignins of Populus nigra and Cupressus sempervirens using the DFRC method

In this study, derivatisation followed by reductive cleavage (DFRC) were used to investigate milled wood lignin (MWL) and dioxane lignin (DL) structures of Populus nigra and Cupressus sempervirens. After the DFRC reactions, the constituents obtained from these two kinds of lignin were recognised structurally using several chromatographic and spectral methods such as ¹³C NMR, GC-MS, and GPC. Comparative results showed that the dominant structural components of the two kinds of lignin are obtained from the cleavage of ??-O-4 bonds. The main component of DL and MWL of P. nigra is 4-hydroxy-3,5-dimethoxy-1-phenyl-??-hydroxypropene (syringyl structures). Also, some guaiacyl structures were observed. The dominant component identified in both lignins of C. sempervirens is 4-hydroxy-3-methoxy-1-phenyl-??-hydroxypropene (guaiacyl structures). The cleavage method has a good performance for both P. nigra and C. sempervirens and the results obtained are in good agreement with previously published data.     

Identifying acetylated lignin units in non-wood fibers using pyrolysis-gas chromatography/mass spectrometry

A series of non-wood plant fibers, namely kenaf, jute, sisal and abaca, have been analyzed upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of the whole material. The pyrolysis products mainly arise from the carbohydrate and lignin moieties of the fibers. The lignin-derived phenols belonged to the p-hydroxyphenylpropanoid (H), guaiacylpropanoid (G) and syringylpropanoid (S) structures, and showed a high S/G ratio of between 2.0 and 5.4, the highest corresponding to kenaf. Among the lignin-derived phenols released, small amounts of sinapyl and coniferyl acetates (in both cis- and trans-forms) were identified for the first time upon Py-GC/MS of lignocellulosic materials. Acetylation of the sinapyl and coniferyl alcohols was at the gamma-position of the side chain. The release of these alcohols derived from intact acetylated lignin units upon pyrolysis seems to indicate that the native lignin in the fibers selected for this study is at least partially acetylated. Sinapyl (and coniferyl) acetates have recently been suggested to be authentic lignin precursors involved in the polymerization of lignin along with the normal sinapyl and coniferyl alcohols. Py-GC/MS will offer a convenient and rapid tool for analyzing naturally acetylated lignins, as well as to screen plant materials for the presence of acetylated units in lignin.     

Photochemical stability of poly(vinyl pyrrolidone) in the presence of collagen

The photochemical stability of poly(vinyl pyrrolidone) (PVP) in the presence of 1%, 3% and 5% of collagen has been studied by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TG) and derivative thermogravimetry (DTG). Surface properties have been studied by contact angle measurements. PVP samples and samples containing 1%, 3% and 5% of collagen were irradiated with UV light of wavelength λ = 254 nm in air for up to 24 h. The amount of gel created during UV irradiation was estimated.PVP in the presence of 1%, 3% and 5% of collagen is less stable both thermally and photochemically. Collagen enhances photochemical processes leading to crosslinking of PVP. The contact angle measurements and values of surface free energy showed that the wettability of PVP films was changed by the addition of collagen and by UV irradiation. The increase of polarity of samples indicates an efficient photooxidation on the surface upon UV irradiation.     

耐紫外光老化CO2共聚物的合成与性能

CO₂基塑料(PPC)是通过CO₂与环氧丙烷共聚所得的生物降解高分子,由于PPC的耐紫外老化性能较差,随紫外线的照射不仅PPC的相对分子质量快速下降,且其拉伸强度和断裂伸长率等力学性能也迅速降低,而农用地膜长期处于紫外线照射的环境中,因此亟待改善PPC的耐紫外老化性能。 本文设计合成了含紫外吸收基团的单体2-羟基-4(2,3-环氧丙氧基)二苯甲酮(HEB),与CO₂和环氧丙烷进行三元共聚制备了耐紫外光老化的CO₂共聚物(PPCH)。 在保证PPCH相对分子质量不低于5.0×10⁴的前提下,PPCH中HEB单元的摩尔分数最高可达0.32%,相应地其玻璃化转变温度(T_g)和起始热分解温度(T_d-5%)分别为26.7和216.9 ℃,拉伸强度达到30.97 MPa。 普通PPC经过240 h的紫外辐照后,其数均相对分子质量下降了67.8%,相应地其拉伸强度和断裂伸长率分别下降了10.1%和40.1%。 即使PPCH中的HEB摩尔分数仅为0.06%,经过240 h辐照后其数均相对分子质量仅下降了6.2%,相应地其拉伸强度和断裂伸长率也仅分别下降了1.7%和13.3%,证明PPCH具有较强的耐紫外老化性能,原因在于其主链含有HEB单元,对紫外光具有较好的吸收性能。 PPCH的紫外吸收性能随HEB单元在聚合物中含量的增加而增强,因此随着共聚物中引入的HEB单元含量增加,PPCH的相对分子质量和力学性能的保持率均得到了大幅度提高。 另一方面,对PPCH共聚物与相同二羟基二苯甲酮(BP)含量的PPC/BP共混物进行120 h的50 ℃热水萃取实验,PPCH显示出稳定的紫外光吸收性能,而PPC/BP共混物的紫外吸收性能随热水萃取时间的增长而快速下降,表明三元共聚反应能够有效解决普通共混物面临的小分子紫外吸收剂的外迁移问题。     

Characterization of poly(vinyl acetate)/sugar cane bagasse lignin blends and their photochemical degradation

The acetone-soluble lignin fraction (ASLF) of sugar cane bagasse, from a sugar and alcohol factory residue, was obtained after extraction with formic acid and used to prepare blends with poly(vinyl acetate) (PVAc) by casting. PVAc and ASLF/PVAc blends were irradiated with ultraviolet light (Hg lamp). Blend formation and the irradiation effects were examined through thermal analysis (TG and DSC), scanning electron microscopy, and atomic force microscopy. The DSC results show PVAc glass transition temperature (T _g) shifts because of both, irradiation and ASLF incorporation. Non-irradiated pure PVAc presented a smooth surface, while after UV irradiation, light surface spots are observed. ASLF/PVAc 10/90 and 5/95 blends did not exhibit differences before and after UV irradiation, suggesting that lignin protects PVAc from photochemical degradation.     

Photoluminescent behavior of poly(3‐hexylthiophene) derivatives with a high azobenzene content in the side chains

A series of polythiophene derivatives with substantially higher azobenzene contents in the side chains were prepared via copolymerization of 3‐hexylthiophene with four different types of 4‐((4‐(phenyl)azo)phenoxy)alkyl‐3‐thienylacetate. The alkyl spacers with different lengths, i.e. butyl, hexyl, octyl and undecyl groups were used between the azobenzene group and the thiophene ring. The compositions, structures and thermal properties of these polythiophene derivatives were characterized. The structural dependence of photoluminescent emission, photochromic behavior of these copolymers were systematically studied and compared with poly(3‐hexylthiophene). The results show that the azobenzene substitution renders the polythiophene some interesting optical properties that can be modulated by UV light irradiation. In the azobenzene modified polythiophene, the intensity of photoluminescent emission associated with the conjugated polythiophene main chain was found to decrease significantly upon UV irradiation. The finding suggests that the photo‐induced trans‐cis isomerization of the azobenzene pendant groups has a significant effect on photoluminescent emission, particularly when short spacers are used between azobenzene groups and the main chain. However, the effect becomes less prominent when longer spacers are used between the azobenzene group and the main chain. Furthermore, UV irradiation of the copolymers also resulted in an increase in intensity and broadening of bandwidth for the absorption peak associated with the polythiophene backbones. Again the magnitude of intensity changes upon UV irradiation were found to be dependent on the spacer length between the azobenzene group and polythiophene main chain. Copyright © 2005 John Wiley & Sons, Ltd.     

Microwave-assisted photo-Fenton decomposition of chlorfenvinphos and cypermethrin in residual water

The coupling of microwave radiation with photo-Fenton reaction for wastewater treatment was evaluated. This strategy was performed in a focused microwave digestion oven with open vessels. Ultraviolet radiation was obtained from microwave lamps (MWL) activated by microwave radiation. The operational conditions were established considering the extent of degradation of chlorfenviphos and cypermethrin used for bovine ticks (Boophilus michoplus) control. The results were based on residual carbon content, always comparing the procedures in the presence or absence of UV radiation. The combination of MWL and Fenton reaction degraded pesticide residues efficiently (>98%) in about 4 min.     

紫外光照射下ZnO超微粒子表面上的光反应

由于半导体超微粒子具有独特的尺寸量子化效应和表面效应^[1~6],它在利用太阳能光催化降解有机污染物,有机光合成及光电转化等领域中有着极其广泛的应用.目前,大量的工作集中在超微颗粒表面上有机物的光反应过程的研究^[7].     

Surface modification of polystyrene by photoinitiated introduction of cyano groups

The surface of polystyrene was modified by the introduction of CN groups. This was achieved by irradiating the polymer with UV light (254 nm) in the presence of gaseous cyanogen bromide (BrCN). X-ray photoelectron spectroscopy (XPS) and FTIR analysis showed that after irradiation both Br and CN groups were covalently bound to the polymer surface. Quantitative XPS analysis revealed that upon prolonged irradiation every second monomer unit at the surface was modified with a CN group. It was demonstrated that photochemical techniques can be employed to attach specific functional groups onto polymer surfaces.     

Effect of UV irradiation on the physico-chemical properties of iron crosslinked collagen

Collagen is the main component of connective tissue and finds immense applications as a biomaterial. In this study, effect of UV irradiation on collagen crosslinked with iron has been carried out. The physical and optical properties of crosslinked collagen affected by UV irradiation were analyzed using electrospectral and fluorescence studies. The electronic spectral studies showed that the photoproducts formed on UV radiation decrease in the presence of iron. Circular dichroic studies revealed that the conformational changes brought about in the protein due to UV irradiation have been reduced owing to the crosslinking with iron. However, prolonged irradiation does bring about conformational changes to the protein.     

Enzymatic degradation of Lignin-Carbohydrate complex (part I)

Initial steps in an early metabolic pathway of biodegradation of lignin by white-rot fungus are very important for application of biotechnology to the utilization of biomass; for example, enzymatic pretreatment for ethanol production from plant resources and biological pulping. Lignins in woody plants exist as giant high molecular weight compounds bounded with carbohydrates, mainly hemicelluloses at middle lamella and in secondary cell wall, and show resistance against the invasion of general microorganisms other than wood-rotting fungi and also against enzymatic digestion of cellulose. We assumed that white-rot fungi first attack the lignin-carbohydrate complex (LCC) and then decompose to some degree into oligomers of lignin and hemicellulose by an unknown enzymatic reaction. The study began with a screening of the fungus, which grew well on the LCC medium. LCCs were prepared from wood meal ofPicea jezoensis that had been extracted MWL, by the method of Koshijima (1). Six fungi (2) that grew well on the media containing decayed lignin were inoculated on agar media of LCC. After 3 d cultivation, the fungiGanoderma sp. andPoria subacida showed most growth on the medium. Crude enzyme preparations were made from decayed wood meal media with each fungus. Chromatographic detection of decomposed compounds from LCC, which is soluble in hot water, by each enzyme and Meicelase fromTricoderma viride, suggest that the wood-rotting fungus may contain another enzyme able to liberate a phenolic compound from LCC besides the enzymes ofTricoderma viride.     

Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm⁻¹ with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.     

Association behaviour of lignins and lignin model compounds studied by multidetector size-exclusion chromatography

SEC elution curves of spruce milled wood lignin (MWL) and guaiacyl lignin polymer models (G-DHPs) in N,N-dimethylformamide (DMF) exhibited a bimodal elution profile. Light scattering measurements indicated that these elution profiles were due to association effects between the molecules. This became apparent from the determination of high molar masses in the range 10(5)-10(8) g/mol. To study this effect, MWL and DHP were fractionated by precipitation in tetrahydrofuran (THF). The THF-insoluble fractions were found to be the fractions corresponding to the apparent high molar mass part of the DMF elution profiles. The THF-soluble fractions proved to be the less-associated fractions, with lower apparent molecular mass. The individual fractions proved to be rather stable in DMF. Accordingly, the bimodal elution profiles of the starting materials were not the result of an equilibrium between associated and molecular dispersed molecules but of different structures exhibiting a specific and stable association pattern. The different fractions were further characterised by SEC in THF after acetylation to determine molar masses in molecular disperse solutions.     

Effects of ultraviolet irradiation on melanogenesis from tyrosine, Dopa and dopamine: a matrix-assisted laser desorption/ionization mass spectrometric study

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry experiments were applied to study the influence of ultraviolet (UV) irradiation in melanogenesis. Samples were prepared starting from three different precursors, tyrosine, Dopa and dopamine, in the presence or absence of tyrosinase, the enzyme responsible for the synthesis of melanin. Enzymatic reactions were carried out for 10, 30, 60 and 120 min under UV irradiation at 365 nm, and aliquots were then immediately ultrafiltered and lyophilized. Samples obtained by irradiation of tyrosine solution revealed the formation of 5,6-dihydroxyindole (DHI) oligomers up to pentamers at 120 min; the reaction kinetics were markedly enhanced in the presence of tyrosinase. In the case of Dopa, UV irradiation favored melanogenesis only in the presence of the enzyme; in this case, many reaction pathways were activated, originating various oligomeric species of Dopa, DHI and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Conversely, when dopamine was used as tyrosinase substrate under UV light, mechanisms of melanogenesis different from those generated by simple enzymatic reaction without irradiation were not activated, as the same oligomeric species were present.