Michel R. Vignon

Cellulose microfibrils from potato tuber cells: Processing and characterization of starch–cellulose microfibril composites

The ultrastructure and morphology of potato (Solanum tuberosum L.) tuber cells were investigated by optical, scanning, and transmission electron microscopies. After removal of starch granules, pectins and hemicelluloses were solubilized under alkaline conditions. The alkaline insoluble residue consisted mainly of primary cell wall cellulose, which can be disintegrated under shearing to produce a homogenized microfibril suspension, as reported in a previous work.40 Composite materials were processed from this potato cellulose microfibril suspension, gelatinized potato starch as a matrix and glycerol as a plasticizer. After blending and casting, films were obtained by water evaporation. The mechanical properties and water absorption behavior of the resulting films were investigated, and differences were observed depending on the glycerol, cellulose microfibrils, and relative humidity content.

Mechanical behavior of sheets prepared from sugar beet cellulose microfibrils

The mechanical behavior of films cast from sugar beet cellulose microfibrils was investigated through tensile tests. The obtaining of these microfibrils by chemical and mechanical treatments from the raw beet pulp is described. Depending on their purification level, individualization state, and moisture content, differences in tensile modulus are observed. It is found that pectins act as a binder between the cellulose microfibrils, which tends to increase the Youngs modulus in dry atmosphere and to decrease it in moist conditions. The extraction of the cellulose microfibrils from the sugar beet cell wall and the obtainment of microfibril suspensions with partial individualization of the microfibrils by a mechanical treatment lead to the formation of a network of cellulose microfibrils within the film, which in turn increases the tensile modulus. Furthermore, the effect of the remaining pectins is compared with the effect of pectins previously removed and added to completely purified cellulosic microfibrils. As expected, once removed and so partly degraded, those pectins have nearly no influence on the mechanical properties.

Mercerization of primary wall cellulose and its implication for the conversion of Cellulose I -› Cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with 13C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.

Structural aspects in ultrathin cellulose microfibrils followed by 13C CP-MAS NMR

13C CP-MAS NMR was used to study the ultrastructural aspects of ultrathin microfibrils extracted from sugar beet pulp. Depending on the stocking condition, the cellulose microfibrils contained different amounts of the polymorphs Iα and Iβ. Structural changes were followed after a purification treatment. It was found that the crystallinity, as measured by solid-state NMR, increases as the purification proceeds. This is primarily due to the removal of non-cellulosic polysaccharides during the different treatments. This was confirmed by neutral sugar analysis. A crystallite size of 4 nm is derived from the NMR results which is in good agreement with the TEM observations. To avoid any underestimate of the microfibrils size, most of the hemicelluloses tightly bound to the cellulose microfibrils has to be removed.

Chemical and 13C N.M.R. studies on two arabinans from the inner bark of young stems of Rosa glauca

Abstract Two water-soluble arabinan fractions have been isolated from the inner bark of Rosa glauca stems. Methylation analysis and periodate oxidation revealed that the two polysaccharides have similar, highly branched structures consisting of α- L -arabinofuranose residues substituted (1→2), (1→3), and (1→5). The two arabinans differ in their degree of polymerization: 100 and 34, respectively. 13 C-N.M.R. spectroscopy has been used to distinguish between glycosidically substituted and free C-5 groups in the polymer, as well as to assign the methoxyl groups at positions 2, 3 and 5 of the methylated arabinans. The different types of linkages could also be identified. The results obtained by chemical N.M.R.-spectroscopic methods were in good agreement.

TEMPO-oxidation of cellulose: Synthesis and characterisation of polyglucuronans

A series of pseudo amorphous cellulose samples were reacted with catalytic amounts of 2,2,6,6-tetramethyl-1-piperidine oxoammonium salt (TEMPO), sodium hypochlorite and sodium bromide in water. In all samples the primary alcohol groups were selectively oxidised into carboxyl groups, and several water-soluble polyglucuronic acid sodium salts were obtained with different molecular weights. With this reaction system, the degradation of the amorphous cellulose samples may be minimized, provided the oxidation is performed at 4 °C and at constant pH 10, with controlled amounts of TEMPO and sodium hypochlorite.

Isolation, 1H and 13C NMR studies of (4-O-methyl-d-glucurono)-d-xylans from luffa fruit fibres, jute bast fibres and mucilage of quince tree seeds

Abstract The (4- O -methyl- d -glucurono)- d -xylans isolated from luffa fruit fibres ( Luffa cylindrica ), jute bast fibres ( Corchorus capsularis ) and mucilage of the seeds of the quince tree ( Cydonia oblonga ) were studied by 1 H and 13 C NMR spectroscopy. Their NMR spectra were grossly similar, but the molar proportions of d -Xyl and 4- O -Me- d -GlcA varied and were found to be, respectively, 7.5:1, 5:1 and 2:1 for luffa fibres, jute bast fibres and quince tree seeds mucilage. The mucilage extracted from the seeds of the quince tree contained cellulose microfibrils strongly associated with a glucuronoxylan possessing a very high proportion of glucuronic acid residues. In addition to 4- O -methyl- α - d -glucopyranosyluronic residues the presence of α - d -glucopyranosyluronic residues was noticed, respectively, in the molar ratio 4- O -Me- d -GlcA and- d -GlcA 9:1.

Morphological characterization of steam-exploded hemp fibers and their utilization in polypropylene-based composites

An investigation is described in which the morphology of hemp stem was examined by optical and scanning electron microscopy. We reported the results concerning steam-explosion treatment either on bast fibers impregnated with alkaline liquor or on woody hemp chenevotte samples impregnated under neutral, acidic and alkaline conditions. The influence of steam-explosion treatment parameters were followed by optic and scanning electron microscopy, chemical composition and evolution of the average (DPv) values of the purified samples. Hemp bast fibers purified by steam treatment were compounded with polypropylene (PP), either directly or after surface treatment with polypropylene-maleic anhydride co-polymer (PPMA). Polypropylene/hemp fibers composite films with various amount of fibers were prepared and their mechanical properties were improved, in particular when fibers treated with PPMA were used.

Aspects of the conformation of polyguluronate in the solid state and in solution

Abstract Evidence from X-ray diffraction and n.m.r. studies that the conformation of polyguluronate remains unchanged in the condensed and solution phases is presented. The experimental results have also been correlated with a computer modelling description of the polyguluronate chain, and preliminary results concerning the accessibility of oxygen atoms to cations are considered. The relevance of the computer modelling approach to a description of the cation binding sites in polyguluronate and the molecular interactions in alginate gel junction zones is discussed.

Attribution des signaux de résonance magnétique nucléaire-13c de disaccharides peracétylés dans la série du D-glucose

Abstract Selective, double irradiation allows the assignment of most 13 C-n.m.r. signals in a series of per- O -acetyl disaccharides composed of two D -glucose residues linked α-(1→3), β-(1→3), α-(1→4), β-(1→4), α-(1→6), β-(1→6), and α,α-(1→1). The main influences that affect the chemical shifts are discussed and the spectra of β-cellobiose octaacetate and β-maltose octaacetate are compared to those of cellulose and amylose triacetate, respectively, to show the possibilities and limitations of a disaccharide model for the interpretation of the 13 C-spectrum of a polymer.