Value-adding to cellulosic ethanol: lignin polymers.

Lignin is the most abundant aromatic polymer in nature. Due to its high amount of phenolic compounds storage, lignin is considered as an alternative source for various polymers and biomaterials production. Except for the native lignin in lignocellulose, a massive amount of technical lignin is being produced daily all over the world. However, the complex structure and low reactivity of lignin limit its further applications and currently, most of the lignin is burned for generating energy. Therefore, the depolymerization of lignin is considered one of the important challenges in lignin utilization. Methods for lignin depolymerization can be divided into thermochemical treatment, mechanical treatment, chemical catalysis, and biological treatment. Different methods for lignin depolymerization, their characteristics and products are extensively discussed in this review.

Lignin utilization: A review of lignin depolymerization from various aspects

Properties and chemical modifications of lignin: Towards lignin-based nanomaterials for biomedical applications

1 Chemical Composition of Wood and Pulps: Basic Constituents and Their Distribution.- 2 Separation and Analysis of Wood Constituents with Respect to Their Morphological Location.- 3 Carbohydrates.- 4 Lignin.- 5 Extractives.- 6 Direct Characterization of Chemical Properties of Fibers.- 7 Characterization of Pulping Liquors.- 8 Analysis of Bleach Liquors.- 9 Analysis of Papermaking Process Waters and Effluents.- 10 Analysis of Inorganic Constituents.

Analytical Methods in Wood Chemistry, Pulping and Papermaking

Microfibrillated cellulose (MFC) obtained by disintegration of bleached softwood sulphite pulp in a homogenizer, was hydrophobically modified by surface silylation with chlorodimethyl isopropylsilane (CDMIPS). The silylated MFC was characterized by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and white light interferometry (WLI). The degree of surface substitution (DSS) was determined using Si concentrations from XPS survey scans, as well as deconvoluted peaks in high-resolution C1s XPS spectra. The DSS values obtained by the two methods were found to be in good agreement. MFC with DSS between 0.6 and 1 could be dispersed in a non-flocculating manner into non-polar solvents, TEM observations showing that the material had kept its initial morphological integrity. However, when CDMIPS in excess of 5 mol CDMIPS/glucose unit in the MFC was used, partial solubilization of the MFC occurred, resulting in a drop in the observed DSS and a loss of the microfibrillar character of the material. The wetting properties of films cast from suspension of the silylated MFC were also investigated. The contact angles of water on the films increased with increasing DSS of the MFC, approaching the contact angles observed on super hydrophobic surfaces for the MFC with the highest degree of substitution. This is believed to originate from a combination of low surface energy and surface microstructure in the films.

Properties and characterization of hydrophobized microfibrillated cellulose

The effect of pH on the formation of precipitates (lignin, extractives and metals) on kraft pulp surfaces was examined by electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry and atomic force microscopy (AFM). A softwood kraft pulp slurry from an oxygen delignification stage was diluted to 3% consistency with water or an acidic Z filtrate. After heating to 70 °C the pH was lowered from 11 to 2–5, using sulphuric acid. Lignin and extractives precipitated at pH values below 6, and their amounts increased with decreasing pH. Most of the precipitated lignin was found on the pulp surface after sheet forming, whereas the main part of the precipitated extractives could be easily washed away with water. The layer of precipitated lignin was apparently thicker than the layer of extractives. AFM showed the precipitated material as a granular phase. Neither surface morphology nor surface coverage depended on the addition of Z filtrate. The amount of metals ID the pulp and on the pulp surface decreased when pH was lowered to 2. More metals, such as Ca and Mg, were detected ID the pulps as well as on the sheet surfaces when the pulp was diluted with Z filtrate. Strength and bonding properties of the pulp sheets were slightly impaired by the precipitated material. Acidification appears to be the main reason for the precipitation of both lignin and extractives on the pulp surfaces. This should be taken into account when filtrates are recycled ID the bleaching or washing of pulps.

Precipitation of lignin and extractives on kraft pulp: effect on surface chemistry, surface morphology and paper strength

In x-ray photoelectron spectroscopy (XPS), knowledge of elemental depth distributions within the first 10 nm is often essential. However, none of the conventional XPS methods can reliably discern, for example, a thin overlayer from clusters on rough surfaces. Therefore, reliable experimental data on the actual distributions of lignin and extractives on the fibre surfaces is needed, although there are numerous XPS studies on cellulosic fibres and paper. We have studied surface distributions of organic compounds on natural cellulosic fibre materials (cotton, flax and softwood pulps) with XPS, using a novel approach introduced by Tougaard. We were able to model the surface composition of rough fibre surfaces via simple spectral analysis of the O is signal. The simple spectral background analyses used show that in the case of cotton and flax, the non-cellulosic compounds cover the cellulosic fibre surface much more effectively than in softwood pulps, in spite of the smaller amount of non-cellulosic material present.

On surface distributions in natural cellulosic fibres

Different types of fines, i.e. fibrils and flakes, were separated from thermomechanical pulp (TMP) fibers and their surface chemical and morphological properties were studied and compared to those of fibers. Fines contained more extractives and lignin than fibers, both on their surface and in the bulk. Fibrillar fines were especially rich in extractives and lignin, the latter indicating that they originated from primary wall rather than from secondary wall. Flakes had large amounts of lignin on their surfaces. Fibers contained more cellulose than did fines, with 50% of their surface covered with polysaccharides. The most common extractives on the surfaces of fibers and fines were fatty acids, probably present mainly as triglycerides, and sterols and steryl esters. Fines and fibers differed in their surface morphology. Fibrillar fines were largely covered with two different types of material, interpreted as being lignin and extractives. The surfaces of flake-like fines proved to be mainly covered with granular lignin and cellulose fibrils. On the fiber surfaces, areas with different microfibrillar orientations were found. In some areas the orientation was random as in the primary cell wall layer and in some areas the orientation was parallel to the fiber axis, indicating that S 2 had been exposed during refining.

Surface chemical and morphological properties of mechanical pulp fines

Chemical characterization of mechanical pulp fines and fiber surface layers

The development of paper strength properties during chlorine dioxide ECF and alkaline peroxide TCF bleaching of kraft and soda-AQ pulps and the relation to the chemical composition of the fiber sur ...

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Papers

Precipitation of lignin and extractives on kraft pulp: effect on surface chemistry, surface morphology and paper strength

On surface distributions in natural cellulosic fibres

Surface chemical and morphological properties of mechanical pulp fines

Chemical characterization of mechanical pulp fines and fiber surface layers

Fiber surface composition and its relations to papermaking properties of soda-anthrapuinone and kraft pulps