Elisabete Frollini

An efficient, one‐pot acylation of cellulose under homogeneous reaction conditions

Cellulose samples from cotton linters, sisal, and sugar cane bagasse have been successively acylated (acetate, propionate, butyrate, and acetate/butyrate) under homogeneous reaction conditions, in LiCl/N,N-dimethylacetamide (DMAC), by the following procedure: (i) cellulose and LiCl are heated under reduced pressure, at 110°C; (ii) cellulose is dissolved in LiCl/DMAC by heating at 155°C, followed by cooling to 40°C; (iii) the solubilized polymer is acylated at 60°C for 18 h. Attractive features of this one-pot procedure include: easy control and high reproducibility of the degree of substitution; elimination of base catalyst; negligible degradation of the natural polymer; and recovery/recycling of high purity DMAC and acid anhydride. Reaction conditions employed for the present celluloses are different from those previously used for Avicel PH 101 microcrystalline cellulose because their fibrous nature, higher indices of crystallinity and higher molecular weights retard their dissolution and decrease their rates of acylation by acid anhydrides.

Biobased composites from glyoxal-phenolic resins and sisal fibers.

Lignocellulosic materials can significantly contribute to the development of biobased composites. In this work, glyoxal-phenolic resins for composites were prepared using glyoxal, which is a dialdehyde obtained from several natural resources. The resins were characterized by (1)H, (13)C, 2D, and (31)P NMR spectroscopies. Resorcinol (10%) was used as an accelerator for curing the glyoxal-phenol resins in order to obtain the thermosets. The impact-strength measurement showed that regardless of the cure cycle used, the reinforcement of thermosets by 30% (w/w) sisal fibers improved the impact strength by one order of magnitude. Curing with cycle 1 (150 degrees C) induced a high diffusion coefficient for water absorption in composites, due to less interaction between the sisal fibers and water. The composites cured with cycle 2 (180 degrees C) had less glyoxal resin coverage of the cellulosic fibers, as observed by images of the fractured interface observed by SEM. This study shows that biobased composites with good properties can be prepared using a high proportion of materials obtained from natural resources.

Some aspects of acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicell PH101) was successfully acylated under homogeneous solution conditions by the following procedure: 2.0 g of cellulose were stirred with 75 mL of N,N-dimethylacetamide for 1 h at 150°C, 3.5 g of LiCl were added, the temperature was raised to 170°C, ca. 18.5 mL of the solvent were distilled and the suspension was cooled to room temperature and stirred overnight. The temperature of the clear cellulose solution was raised to 110°C, kept at that temperature for 1 h, an acid anhydride was added and the solution stirred at 110°C for additional 4 h. Acetates, propionates, butyrates, and acetate/propionate mixed ester were prepared with excellent control of the degree of substitution, DS, 1 to 3 for acetates, 2 and 3 for propionates and butyrates, and 3 for acetate/propionate. The degree of polymerization of cellulose is negligibly affected under these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit shows a preference for the C6 position.

Application of the solvent dimethyl sulfoxide/tetrabutyl-ammonium fluoride trihydrate as reaction medium for the homogeneous acylation of Sisal cellulose

Two types of Sisal cellulose were studied as starting material for homogeneous acylation in the solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF). The native Sisal cellulose investigated contains 14% hemicellulose (mainly composed of xylose) as confirmed by 13C-NMR spectroscopy in DMSO-d6/TBAF and HPLC analysis after complete polymer degradation. Alkali treatment of Sisal cellulose decreases the amount of hemicellulose, the degree of polymerization and the crystallinity. Both Sisal cellulose samples can be dissolved in DMSO/TBAF after treatment at elevated temperature. GPC measurements showed high aggregation in the solution. Different homogeneous acylation reactions using carboxylic acid anhydrides and vinyl esters were carried out, showing a pronounced tendency of the anhydride towards hydrolysis in the solvent. This disadvantage can be diminished by decreasing the amount of the salt hydrate (TBAF trihydrate) or by a distillative removal of the majority of water. A strong interaction of the polymer with the water in the solvent was observed.

Polyelectrolytes from polysaccharides: selective oxidation of guar gum- a revisited reaction

The aim of this work was to study the properties of the carboxylated polyelectrolyte obtained from guar gum. The C-6 alcohol functions of galactose units side chains were oxidized first by GO-ase to aldehyde groups and then to carboxylic groups by halogen oxidation. The enzymic oxidation step was followed by the Dische method, by viscosity and light scattering measurements. With regard to previous reports, some changes were introduced in the two-step reaction, in order to prevent polymer degradation. Several characteristics of the carboxylated polyelectrolyte have been studied, such as molecular weight distribution, degree of substitution, viscosity, intrinsic viscosity determined by the isoionic method, radius of gyration, charge parameter and apparent intrinsic persistence length. The charged macromolecule formed from native guar showed all the typical characteristics of a polyelectrolyte. The viscometry results indicate that carboxylated guar has a much higher viscosity in low salt content than the native polymer, which improves its thickening properties.

Valorization of an industrial organosolv–sugarcane bagasse lignin: Characterization and use as a matrix in biobased composites reinforced with sisal fibers

In the present study, the main focus was the characterization and application of the by‐product lignin isolated through an industrial organosolv acid hydrolysis process from sugarcane bagasse, aiming at the production of bioethanol. The sugarcane lignin was characterized and used to prepare phenolic‐type resins. The analysis confirmed that the industrial sugarcane lignin is of HGS type, with a high proportion of the less substituted aromatic ring p‐hydroxyphenyl units, which favors further reaction with formaldehyde. The lignin–formaldehyde resins were used to produce biobased composites reinforced with different proportions of randomly distributed sisal fibers. The presence of lignin moieties in both the fiber and matrix increases their mutual affinity, as confirmed by SEM images, which showed good adhesion at the biocomposite fiber/matrix interface. This in turn allowed good load transference from the matrix to the fiber, leading to biobased composites with good impact strength (near 500 J m−1 for a 40 wt% sisal fiber‐reinforced composite). The study demonstrates that sugarcane bagasse lignin obtained from a bioethanol plant can be used without excessive purification in the preparation of lignocellulosic fiber‐reinforced biobased composites displaying high mechanical properties. Biotechnol. Bioeng. 2010;107:612–621.

Resistência ao Impacto e Outras Propriedades de Compósitos Lignocelulósicos: Matrizes Termofixas Fenólicas Reforçadas com Fibras de Bagaço de Cana-de-açúcar

Phenolic and lignophenolic (40% sugarcane bagasse lignin/phenol w/w) pre-polymers were synthesized to produce thermoset matrices composites, using sugarcane bagasse as reinforcing agent. This lignocellulosic material was modified by chemical and/or physical methods (alkali treatment, esterification, ionized air). Sugarcane bagasse showed a small improvement in impact strength for both phenolic and lignophenolic matrices. The surface treatment methods improved dispersion as well as adhesion between the resins, phenolic and lignophenolic, and lignocellulosic fibers, but only the composites treated with ionized air exhibited better impact strength results. Concerning the water uptake, for the phenolic composites it was observed that the one reinforced with fibers treated with 8 % NaOH presented a smaller water uptake. For the lignophenolic composites, that reinforced with fibers esterified during 24 hr, using succinic anhydride, presented the lower water uptake.

Sugar Cane Bagasse Lignin in Resol-Type Resin: Alternative Application for Ligninphenol-Formaldehyde Resins

Abstract Lignin can be recovered from sugar cane bagasse, which is widely available in Brazil as a residue from sugar mills. Many reports can be found in the literature on the partial replacement of phenol by lignin in phenolic-type resins, but normally only their application as an adhesive is considered. This work is part of a study intended to look for other uses for lignin-phenol resins; for instance, in molded materials. Resols were prepared with the partial replacement of phenol by organosolv sugar cane bagasse lignin (10, 20, 40, 100% w/w), and the pre-polymers were characterized by TGA and DSC. The cure reaction was performed in a mold in a process monitored by infrared spectroscopy. The resins obtained were characterized by TGA, DSC, and DMTA. TGA and DSC results revealed that endothermic and exothermic steps are probably involved in the cure reaction. From infrared results it can be inferred that lignin is really incorporated to the phenol polymer chain, where it acts as a chain extender. DMTA an...

Thermal conductivity of polymers by hot-wire method

The hot-wire standard technique, mostly used for ceramic materials, was adapted to determine the thermal conductivity of nylon 6,6, polypropylene, poly(vinyl chloride), and poly(methyl methacrylate). The results obtained showed that the hot-wire standard technique can be used with accuracy and reproducibility to measure the thermal conductivity of polymers. In the second stage, to verify the effect of the use of a lignin (a “macromonomer”) in the thermal conductivity of phenolic resins, this technique was applied to phenol-formaldehyde and phenol–lignin–formaldehyde resins.

Plastics and Composites from Lignophenols

Alkali and ionized air treated and untreated lignocellulosic fibers, such as sisal, jute and curaua, were used to reinforce phenolic and lignophenolic matrix materials. The results favor sisal fiber for its excellent performance as a reinforcing agent of phenolic and lignophenolic matrices, increasing the impact strength up to 35 fold in relation to that obtained with thermoset composites. The use of lignin as a partial substitute for phenol in closed cell lignophenolic foams reduces the thermal conductivity and allows classifying the lignophenolic foam as a thermal isolating structural foam.