270 research outputs found
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
Chemical composition of different morphological parts from ‘Dwarf Cavendish’ banana plant and their potential as a non-wood renewable source of natural products
The study on chemical composition and structure of components from different morphological parts of ‘Dwarf Cavendish’ banana
plant (petioles/midrib, leaf blades, floral stalk, leaf sheaths and rachis) have been carried out aiming to evaluate their potential as
eventual raw materials for the chemical processing. Macromolecular components were analysed using solid-state NMR, ATR-FTIR
and wet chemistry methods. Mineral components were assessed by ICP analysis of ashes obtained after raw material calcinations.
It was verified that chemical composition of the studied fractions of banana plant varies significantly. The major extremes were
found in the contents of cellulose (37.3% in leaf sheaths and only 15.7% in floral stalk), starch (26.3 in floral stalk and 0.4% in
petioles/midrib), lignin (24.3% in leaf blades and 10.5% in rachis) and lipophilic extractives (5.8% in leaf blades and 1.2% in
petioles/midrib). All morphologic parts of banana plant contained considerable amounts of ashes (from 11.6 to 26.8%) composed
mainly by potassium, calcium and silicium salts. The hemicelluloses in banana plant are proposed to be mainly glucuronoxylan and
xyloglucan (from 5.5% in floral stalk to 21.5% in petioles/midrib). Rather significant amount of proteins was found in leaf blades
(8.3%). Lignin analysis revealed that it is of HGS type with H:G:S proportion ranged of (5–17):(18–54):(35–71). The significant
variation of lignin structure among the different morphological parts of banana plant was highlighted. Results of this study allowed
some propositions about possible applications of banana plant residues as non-wood renewable source of natural products.info:eu-repo/semantics/publishedVersio
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
Steryl glucosides from banana plant Musa acuminata Colla var cavendish
The chemical composition of the dichloromethane extracts of several vegetal fractions of banana plant, Musa acuminata Colla
var cavendish have been studied by GC–MS. Several bioactive steryl glucosides, namely campesteryl 3- -d-glucopyranoside,
stigmasteryl 3- -d-glucopyranoside and sitosteryl 3- -d-glucopyranoside were identified as the major components of the ex tracts, accounting for 838.4–1824.3 mg/kg of the plant fractions dry weight. The high abundance of these compounds might be
an important contribution to the valorization of banana plant agricultural residues.info:eu-repo/semantics/publishedVersio
Polyoxometalates as mediators in the laccase catalyzed delignification
The polyoxometalate (POM)-laccase catalytic system was applied for the first time to aerobic delignification of kraft pulps at moderate (40-60 degreesC) temperatures. Laccase was found to readily catalyze the re-oxidation of different kinds of polyoxometalates, including those, which cannot be re-oxidized by dioxygen even at high temperatures (PMo11V1, SiW11V1. etc.). This allows a sequence of catalytic redox cycles similar to that in the laccase-mediator system (LMS) where electrons are transferred from the substrate (lignin) via POM and laccase to oxygen. Results obtained showed that the POM-laccase system could decrease kappa number of eucalypt kraft pulp from 13.7 to 8.5 though the reaction rate is relatively slow. Among different POM used, SiW11V showed the best results. The effect of the process variables on the delignification was studied. The best results in delignification of eucalypt pulp were obtained at 60 degreesC, oxygen pressure of 5 bar, pH 6.3, SiW11V concentration of 4.2 mM and laccase concentration of 0.65 U/ml. The reaction temperature appears to be one of the crucial factors in the achievement of a delignification rate acceptable for practical application. (C) 2001 Elsevier Science B.V. All rights reserved
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/
New polyoxometalate-functionalized cellulosic fibre/silica hybrids for environmental applications
Cellulosic fibre/silica hybrid materials functionalized with Keggin-type polyoxometalates ([PV2Mo10O40]52, [PVMo11O40]42, ([PMo12O40]32 or [PW12O40]32) were prepared by a sol–gel method at room temperature. The novel materials are composed of ca. 56 wt% of polysaccharides, ca. 37 wt% of propylamine-modified silica, 2 wt% of polyoxometalate, and 5% of hydration water. The silica network of these hybrids exhibits relatively high degree of condensation being distributed mainly on the surface of the cellulosic fibres as a dense film. The functionalization of silica with polyoxometalates via electrostatic interactions with protonated propylamino groups of modified silica was unambiguously confirmed. Despite their high silica content cellulose/silica hybrids retained basic cellulosic pulp properties—supramolecular and fibrous structure, porosity, relatively low density, etc. The novel bio-based material functionalized with 2% of [PVMo11O40]42 shows particularly high activity towards the oxidation of volatile organic compounds (VOCs) present in urban air thus anticipating future environmental applications.publishe
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