Production of rayon fibres from cellulosic pulps: state of the art and current developments

The increasing demand for cellulosic fibres is continuously driven by the growing earth population and requirements of the textile industry. The annual cotton production of ca. 25 million tons is no longer enough to meet the market demands. This market gap of cellulosic fibres is progressively filled by regenerated cellulosic fibres derived from the dissolving pulp. The conventional industrial process of viscose production is far from being environmentally friendly due to the use of hazardous reagents. Alternatively, new trends in the production of regenerated fibres are related to the direct dissolution of cellulose in appropriate environmentally sound recyclable solvents, allowing high quality rayon fibres. This article reviews the sources of dissolving pulps used for the production of viscose and its quality parameters related to the performance of viscose production. The prospective cellulose regeneration processes, both commercialized and under development, are reviewed regarding current and future developments in the area.publishe

Caracterização do Engaço da Uva e Avaliação do seu Potencial como Matéria‐Prima Lenhocelulósica

Resumo O presente estudo avalia a composição química detalhada do engaço da uva de modo a encontrar novas formas para a sua valorização. O engaço da uva é um subproduto vinícola de origem lenhocelulósica, com 30-31% de celulose, 21% de hemicelulose, 17-18% de lenhina, 15-16% de taninos e cerca de 6,0% de proteínas. A análise dos monossacarídeos mostrou que, a seguir à celulose, a xilana é o segundo polissacarídeo mais abundante no engaço (ca. 12%). A celulose foi isolada pelo método Kürscher e Hoffer e foi caracterizada por difração de raios-X (DRX). Esta análise revelou a existência de uma célula unitária típica de celulose I com um elevado grau de cristalinidade (ca. 75%). Também foi possível verificar uma elevada abundância de compostos extratáveis em água (ca. 24%), atribuídos principalmente a sais inorgânicos solúveis, taninos hidrolisáveis e pectinas. A lenhina Klason foi caracterizada por espectroscopia de infravermelho e espectroscopia de ressonância magnética tendo-se verificado tratar-se de uma lenhina do tipo HGS, com predominância de unidades guaiacilo.Abstract The present study evaluates the detailed chemical composition of grape stalks to find new forms of recovery. Grape stalk is a by-product from winemaking process of lignocellulosic source with 30-31% cellulose, 21% hemicellulose, 17-18% lignin, 15-16% tannin and about 6.0% protein. Analysis of monosaccharides showed that, after cellulose, the xylan is the second most abundant polysaccharide in stalks (ca. 12%). Cellulose was isolated by the Kürscher and Hoffer method and was characterized by X-ray diffraction (XRD). This analysis revealed the existence of a typical unit cell of cellulose I with a high degree of crystallinity (ca. 75%). It was also observed a high abundance of water extractable compounds (ca. 24%), attributed to mainly soluble inorganic salts, hydrolysable tannins and pectins. Klason Lignin was characterized by infrared spectroscopy and magnetic resonance spectroscopy and it was found that this is a HGS lignin-type, predominantly with guaiacyl units

Caracterização Química do Folhelho Branco e do Folhelho Tinto Proveniente de Castas Típicas da Região do Dão

Resumo O presente trabalho avalia e compara a composição química do folhelho branco e tinto, proveniente de castas típicas da região do Dão. A análise química mostra que o folhelho é constituído essencialmente por celulose, hemiceluloses, proteínas e extratáveis em água. Os compostos solúveis em água são constituídos principalmente por açúcares monoméricos (glucose e frutose) e por uma mistura complexa de hemiceluloses. A celulose do folhelho branco e tinto foi avaliada por difração de raios-X (DRX) e verificou-se que se trata de celulose I com um grau de cristalinidade de 66,1 e 72,8%, no folhelho tinto e branco, respetivamente. O teor de celulose no folhelho branco (12,5%) é bastante inferior quando comparado com o do folhelho tinto (20,8%). Os métodos espectroscópicos, nomeadamente RMN CP/MAS de 13C, permitiram verificar a presença de material ceroso e cuticular em ambos os folhelhos. Os extratáveis em diclorometano dos folhelhos são constituídos maioritariamente por ácidos gordos e terpenos.Abstract The present study evaluates and compares the chemical composition of white and red grape skins, from grapes of the typical caste Dão region. Chemical analysis shows that grape skins are constituted essentially by cellulose, hemicelluloses, and water extractable proteins. Water-soluble compounds consist primarily of monomeric sugars (glucose and fructose) and of a complex mixture of hemicelluloses. The structure of cellulose from white and red grape skins was evaluated by X-ray diffraction (DRX) and found to be cellulose I polymorph with a crystallinity degree of 66.1 and 72.8% for red and white grape skin celluloses, respectively. The content of cellulose in white grape skins (12.5%) is significantly lower when compared to that in red grape skins (20.8%). Spectroscopic methods, as 13C CP/MAS NMR, allowed the detection of waxy material in both cuticular tissues of grape skins. Dichloromethane extracts of grape skins consist mostly of fatty and triterpenic acids

Isolation and structural characterization of the acetylated heteroxylan from sisal (Agave sisalana) and its fate during alkaline pulping and TCF/ECF bleaching.

The heteroxylan from sisal, an O-acetyl-(4-O-methylglucurono)xylan with a molecular weight (Mw) of 18 kDa, was isolated by extraction of peracetic holocellulose with Me2SO and thoroughly characterized by wet chemistry, and NMR spectroscopy. The heteroxylan backbone is composed of (1→4)-linked β-D-xylopyranosyl units (Xylp) partially ramified with terminal (1→2)-linked 4-O-methyl-α-D-glucuronosyl (MeGlcpA) and a small proportion of α-D-glucuronosyl (GlcpA) residues. Roughly 61mol% of Xylp residues are acetylated (DS =0.70). During soda/AQ pulping, GlcpA and MeGlcA are partially removed or converted to 4-deoxy-β-L-threo-hex-4-enopyranosyluronic acid (HexA), though notable proportion of GlcpA maintained intact. The major part of acetyl groups was hydrolyzed during pulping. It was proposed that the predominantly low molecular weight xylan fraction was removed from pulp during bleaching. The profiles of uronosyl residues in xylans from TCF and ECF bleached sisal pulps were rather different.This study has been supported by the Spanish MEC (Project AGL2005-01748) and EU Contract NMP2-CT-2006-26456. We thank CELESA (Tortosa, Spain) for providing the samples. G.M. thanks the Spanish Ministry of Education for a FPI fellowship.Peer reviewe

Integrated utilization of grape skins from white grape pomaces

An approach for the integrated utilization of grape skins from white grape pomaces has been proposed. This consists of consecutive or simultaneous extraction of grape skins with neutral organic solvent and water under reflux. Organic extract is a valuable raw material for the isolation of oleanolic acid. The aqueous extract (ca 50%, w/w) is composed of essentially hexoses and suitable for the high yield (till 51%) bioethanol production at a maximum specific cell growth rate (μmax) of 0.29 h−1. The remained extracted grape skins are the complex of structural polysaccharides embedded into cutinous matrix. Extracted grape skins were shown to be a prospective raw material for the production of low-density boards (d ≤ 0.40) for insulation needs. The boards produced from grape skins and bind of 8% urea–formaldehyde resin revealed reasonable tensile strength (0.4 MPa) and a low thermal conductivity (0.09–0.12 W (m K)−1) over a wide range of temperatures (40–200 °C).info:eu-repo/semantics/publishedVersio

Structural characterization of lignin from Grape Stalks (Vitis vinifera L.)

The chemical structure of lignin from grape stalks, an abundant waste of winemaking, has been studied. The dioxane lignin was isolated from extractive- and protein-free grape stalks (Vitis vinifera L.) by modified acidolytic procedure and submitted to a structural analysis by wet chemistry (nitrobenzene and permanganate oxidation (PO)) and spectroscopic techniques. The results obtained suggest that grape stalk lignin is an HGS type with molar proportions of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units of 3:71:26. Structural analysis by 1H and 13C NMR spectroscopy and PO indicates the predominance of β-O-4′ structures (39% mol) in grape stalk lignin together with moderate amounts of β-5′, β-β, β-1′, 5-5′, and 4-O-5′ structures. NMR studies also revealed that grape lignin should be structurally associated with tannins. The condensation degree of grape stalks lignin is higher than that of conventional wood lignins and lignins from other agricultural residues.N/

Assessment of chromophores in chemically treated and aged wood by Uv-Vis diffuse reflectance spectroscopy

The optical properties and degradation of fir wood treated by different inorganic salts, which are components of waterborne wood preservatives, were studied before and after wet-thermal accelerated ageing (T=85 °C, RH=65%, for 30 days) using UV-Vis diffuse reflectance spectroscopy. The colour of all impregnated samples was due to the same chromophoric structures, thus revealing that the primary reactions leading to colour changes are essentially very similar. These chemically treated as well as standard (non-treated, unaged) and reference (treated only with distilled water, unaged/aged) samples have a significant absorption band at 358 nm, along with a shoulder near 265 nm of various intensity. The broad band at higher wavelength is attributed to the chromophoric structures derived especially from lignin, i.e. quinones, stilbenes, charge transfer complexes causing a bathochromic shift and other conjugated carbonyl structures. Coniferaldehyde is also a major contributor to this absorption. The band at 265 nm belongs to chromophores arising predominantly from carbohydrate degradation products, i.e. furan derivatives, quinone-type derivatives, catechol structures. Catechol structures (colourless) form coloured complexes with transition metal cations (Cu2+, Fe3+) or are oxidized to form highly coloured benzoquinone structures. Alkaline solutions of borax cause the reduction of conjugated and non-conjugated carbonyls and the degradation of coniferaldehyde. Generally, after ageing, the samples show higher absorptions in the visible region of the spectra in comparison with the unaged ones, which explains their yellowing and loss of brightness after the action of elevated temperature and moisture

Cationization of eucalyptus kraft lignoboost lignin: preparation, properties, and potential applications

Current changes toward a more biobased economy have recently created tremendous renewed interest in using lignin as a valuable source for chemicals and materials. Here, we present a facile cationization approach aiming to impart kraft lignin water-solubility, with similar good features as lignosulfonates. Eucalyptus globulus kraft lignin obtained from a paper mill black liquor by applying the LignoBoost process was used as the substrate. Its reaction with 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTAC) in an aqueous alkaline medium was studied to assess the impact of different reaction conditions (temperature, time, educt concentration, molar CHPTAC-to-lignin ratio) on the degree of cationization. It has been shown that at pH 13, 10 wt % lignin content, 70 °C, and 3 h reaction time, a CHPTAC-to-lignin minimum molar ratio of 1.3 is required to obtain fully water-soluble products. Elemental analysis (4.2% N), size-exclusion chromatography (M w 2180 Da), and quantitative 13C NMR spectroscopy of the product obtained at this limit reactant concentration suggest introduction of 1.2 quaternary ammonium groups per C9 unit and substitution of 75% of the initially available phenolic OH groups. The possible contribution of benzylic hydroxyls to the introduction of quaternary ammonium moieties through a quinone methide mechanism has been proposed. Since both molecular characteristics and degree of substitution, and hence solubility or count of surface charge, of colloidal particles can be adjusted within a wide range, cationic kraft lignins are promising materials for a wide range of applications, as exemplarily demonstrated for flocculation of anionic dyes.publishe

Kinetics of Eucalypt Lignosulfonate Oxidation to Aromatic Aldehydes by Oxygen in Alkaline Medium

The oxidation kinetics of lignosulfonates (LS) from acidic magnesium-based sulfite pulping of Eucalyptus globulus wood with oxygen under alkaline conditions was studied. The analysis of oxidation products in the reaction system O(2)/NaOH revealed a predominance of aromatic aldehydes (vanillin and syringic aldehyde) though small amounts of vanillic and syringic acids and acetophenone/phenylacetaldehyde derivatives have also been detected. The rate constant of syringic aldehyde formation was roughly twice of that for vanillin. The effective activation energies for the oxidation of LS to aromatic aldehydes (ca. 60-70 kJ/mol) were rather different to those found for the formation of aromatic acids (ca. 110 kJ/mol) indicating different mechanisms involved in the rate-determining reaction step. The addition of catalyst (copper salt, 20% w/w) promoted the LS oxidation with increments of aromatic aldehyde yields by 25-50%. The maximum yields of syringic aldehyde and vanillin upon LS oxidation were 16.1 and 4.5%, respectively (150 degrees C, 20 min, P(O2) = 10 bar, 0.9 M NaOH solution). The highly negative effect of concomitant sugars in sulfite liquor to the yield of aromatic aldehydes was highlighted

Structural characterization of polysaccharides isolated from grape stalks of Vitis vinifera L.

The main structural polysaccharides of grape stalks are cellulose, heteroxylan, and glucan. Cellulose contributes 30.3% of grape stalk matter and has an unusually high degree of the crystallinity (75.4%). Among hemicelluloses, xylan was the most abundant one, contributing ∼12% to the weight. The heteroxylan was isolated from the corresponding peracetic holocellulose by DMSO extraction followed by precipitation in ethanol. The Mw of heteroxylan (19.0kDa) was assessed by size exclusion chromatography (SEC) and the structure was inferred by methanolysis and methylation linkage analysis, as well as 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. The heteroxylan is a partially acetylated (DS=0.49) glucuronoxylan possessing the main backbone composed by β-(1→4)-linked d-xylopyranosyl units ramified with α-(1→2)-linked 4-O-methyl-α-d-glucuronosyl residues (MeGlcpA) at a molar ratio 25:1. The isolated heteroxylan contained concomitant β-glucan (ca. 15%), whose structure was elucidated by methylation linkage analysis and by NMR spectroscopy. The results obtained revealed mixed β-(1→3; 1→4)-d-glucan with a molar ratio of β-(1→3)- to β-(1→4)-linked glucopyranosyl units of 1:2.info:eu-repo/semantics/publishedVersio