Aziz Nourmamode

Adding value to Alfa grass (Stipa tenacissima L.) soda lignin as phenolic resins 1. Lignin characterization

Abstract Soda lignin from black liquors of Alfa grass was precipitated with hydrochloric acid at pH 2 and 4.5, and with sulfuric acid at pH 4.5. The molecular structures of the lignins were analyzed for the first time. The phenolic structures were studied using UV-visible spectroscopy and 31 P-NMR spectrometry. The lignin fragments were also analyzed by size exclusion chromatography and β- O -4 bond content was determined by thioacidolysis. The total phenolic content was found to be low for annual plant lignin, with more phenolic guaiacyl units than syringyl ones, and with a low proportion of condensed units. The phenolic syringyl elements appear to include β- O -4 bonds in large proportion in contrast with guaiacyl and p- hydroxyphenyl units.

Discoloration of α-Carbonyl-Free Lignin Model Compounds Under UV Light Exposure

Abstract A series of α-carbonyl-free lignin model compounds was prepared and adsorbed onto bleached chemical pulp. The rates of discoloration of these materials, under simulated solar light exposure, were established and compared to that of peroxide bleached methylated (alkali and dimethyl sulfate) and nonmethylated chemithermomechanical pulps. Phenolic phenylcoumarone and phenolic stilbenes were found to be the most sensitive chromophores under UV irradiation, both inducing a strong yellowing. Also, monophenolic biphenyl and biphenylmethane entities were shown to be prone to discolouration in contrast to the biphenolic and dimethylated ones. Moreover, the catechol structures which are known to be easily oxidizable into ortho quinones, display significant yellowing only when their absorption spectra are shifted above 300 nm where the light source emits. The behaviour of the phenolic stilbenes and the biphenyl catechol is reminiscent of the behaviour of CTMP. This indicates the possible involvement of such...

A study of the photobleaching and photoyellowing of paper containing lignin using fluorescence spectroscopy

Abstract The fluorescence of paper produced using high yield pulp increases on bleaching with hydrogen peroxide. The new blue fluorescent species help to offset the natural yellow colour of the paper. Irradiation of the paper in the presence of reducing agents leads to further bleaching and a further increase in fluorescence, probably as a result of the photoreduction of groups such as quinones.

An approach to understanding the mechanism of protection of bleached high-yield pulps against photoyellowing by reducing agents using the lignin model dimer: 3,4-dimethoxy-a-(2′-methoxyphenoxy)-acetophenone

Abstract The effect of reducing agents on the photodegradation of an O-methylated α-carbonyl β-O-4 lignin model dimer was studied in detail. The agents did not suppress the photodegradation but altered the photoproduct distribution to a minor extent and in an unpredictable way. Thus the reagents do not affect the primary photochemical process. However, a number of the compounds, e.g. Rongalit C and thiourea dioxide, suppressed the yellowing processes accompanying the degradation. This can be attributed to the reducing agents which alter the outcome of the photochemical processes of the oligomer produced in the reactions; indeed the reducing agents effectively photobleach the coloured products. The reducing agents which prevented photoyellowing when the β-O-4 compound was irradiated also prevented the photoyellowing of high-yield pulp, provided that the pulp was irradiated in solutions of the reducing agents. It is concluded that the reducing agents destroy peroxidic and coloured entities which contribute to the discoloration process.

Peroxyformic Acid Pulping of Eucalyptus Grandis Wood Chips and Sugar Cane Bagasse in one Stage and Characterization of the Isolated Lignins

Abstract An improvement in the peroxyformic acid process for the production of chemical pulps from Eucalyptus grandis wood chips and sugar cane bagasse is described. The pulping of these lignocellulosics was carried out in a single stage at 75°C (3 h) in order to benefit from the action of the peroxyformic acid and a subsequent formic acid reflux (110°C, 2 h), using the same liquor. Efficient distillation of the spent liquor allowed recovery of a large quantity of formic acid and phenolic lignin, the latter obtained after mild saponification, followed by precipitation in acidic media. The pulping process was completed with a 0.25M NaOH extraction of the pulp at 60°C to dissolve more lignin. Good quality unbleached pulps were obtained. Kappa numbers (KN) of 14 and 13, and intrinsic viscosities [n] of 1130 and 980 dm3. Kg−2 were obtained, respectively, for E. grandis and sugar cane bagasse. The structures of the lignin fractions were studied by size exclusion chromatography; methoxyl content analysis; eleme...

Photodegradation of lignin : a photochemical study of phenolic coniferyl alcohol lignin model molecules

A better understanding of the involvement of coniferyl alcohol structures in the yellowing of high-yield pulps exposed to daylight was approached by studying the photophysics and the photochemistry of coniferyl alcohol (1) and two phenolic lignin models (2 and 3) incorporating a 3-hydroxy-l-propenyl residue and a biphcnyl structure. Their photochemical reactivity was examined in both liquid (CH2C12 and tBuOMc) and solid media (adsorbed on filter paper and incorporated in 2-hydroxypropylcellulose (HPC) films). The influence of oxygen during the irradiation was also investigated. In solution we observe efficient photolysis of the models 1, 2 and 3 yielding essentially the photoisomers and in large amount a complex mixture of oligomcrs which include coloured substances. The expected aldehydes 4,5, 6 and 6a have not been detected. The structure and titration (GC-MS analysis) of the non-oligomeric photoproducts indicate that addition of water on the double bond (provided by the formation of a conjugated quinonc methide) and elimination of formaldehyde are important processes of the photodegradative steps. Phenoxy radicals generated by direct photolysis of the phenols appear to be the main source of the oligomers. Thioacidolysis of the latter shows a large proportion of quinoid structure which might partly account for the colour of the irradiated solutions. Irradiation of the models adsorbed on filter paper shows rapid consumption of the starting materials and reticulation of the coloured photoproducts with the cellulosic framework. Irradiation of the models included in HPC indicates a loss of aromatic structure at 285 nm and a yellowing of the films. These results are reminiscent to those obtained in the photochemistry of 2-methoxyhydroquinone and confirm the role played by the phenolic groups which are photolysed when the aromatic π system is able to absorb above 300 nm.

A Study of the Photoyellowing of Paper Made from Bleached CTMP

Abstract The photoyellowing of papers produced from bleached CTMP is retarded when these papers are irradiated in aqueous solutions containing reducing agents such as Rongalit C and Blankit D. Papers impregnated with the reducing agents showed some photostability when irradiated in the dry state but not when irradiated in aqueous solution. The reducing agents present in these papers also failed to significantly retard the photoyellowing under natural lighting conditions and under simulated solar irradiation. It is concluded that the migratability of the reducing agents is important if photoprotection is to be achieved and that the latter is caused by the reagents bleaching the yellow photodegradation products as well as destroying prodegradent species such as hydroperoxides.

Attempts to photostabilize paper made from high-yield pulp by application of UV screens and control of pH

Paper made from bleached chemithermomechanical pulp (CTMP) was treated with UV absorbers, e.g. 2,4-dihydroxybenzophenone and a 2-(2-hydroxyphenyl)benzotriazole derivative (Tinuvin 1130) to reduce the tendency of the paper to undergo photoyellowing. Whilst some of the UV absorbers offer some protection, their effect can be enhanced by use in conjunction with a reducing agent (sodium hypophosphite) and by lowering the pH of the paper by application of potassium dihydrogen phosphate. The best effect was obtained by using Tinuvin 1130 in combination with both a reducing agent and potassium dihydrogen phosphate. The use of hindered phenols in both the presence and absence of thiols offered little protection to the paper.

Photodelignification of Eucalyptus grandis organosolv chemical pulp

Abstract Efficient delignification of Eucalyptus grandis organosolv pulp was achieved. The process, which was chlorine and sulphur free, removed 88% of the lignin (kappa number (KN) 65 to 8) with moderate viscosity loss ( η = 19 cP to 12 cP). The best sequence involved three photochemical stages in alkaline medium (NaOH) at 85°C. The first stage involved oxygen treatment; this was followed by the action of excited singlet oxygen produced by methylene blue (4 × 10 −5 mol l −1 ). The last stage, using hydrogen peroxide (6% relative to the weight of oven dried pulp (odp)), was the most efficient, the structure of the lignin having been prepared by the first two stages. The mechanism of the overall process remains unknown.

Synthesis and complexation properties of two new curcuminoid molecules bearing a diphenylmethane linkage

Abstract Bis-curcuminoids 3 and 4 , bearing a diphenylmethane bridge for both compounds and a crown ether chain adapted to complex Li + for compound 4 , were synthesized and characterized by mass and NMR spectroscopies. By their preorganized geometry, they represent a new class of curcuminoids able to complex transition metal cations. Their absorption spectra in DMF by comparison with those of curcumin 1 and dimethylcurcumin 2 have shown that the phenolate forms in the two halves are in interaction in compound 3 and are independent in compound 4 . Complexation studies have revealed a poor selectivity of curcuminoids for transition metals. Nevertheless complexation of Cu (II), studied by UV–visible absorption spectroscopy, has shown subtle differences between curcumin 1 and bis-curcuminoid 3 . These observations were supported by quantum mechanic calculations to establish the most probable structures of non- and complexed compounds.