Synthesis of hydrogels of cellulose acetate (AC) cross-linked with 3,3?,4,4? benzophenonetetracarboxylic dianhydride (BTDA) : characterization and adsorption physicochemical study.

Este trabalho descreve as s?nteses de hidrog?is superabsorventes a base de acetato de celulose (AC), com grau de substitui??o 2.5, reticulado com dianidrido 3, 3?, 4, 4? benzofenona tetracarbox?lico (BTDA). As caracteriza??es das mat?rias primas foram realizadas por an?lises t?rmicas (TG/DTG) e espectroscopia na regi?o do infravermelho (FTIR). O grau de substitui??o do acetato de celulose foi determinado por via ?mida. A confirma??o da rea??o de esterifica??o foi poss?vel a partir da t?cnica de FTIR, espectroscopia UV-vis e an?lises t?rmicas (TG/DTG). A presen?a de poros no novo material foi analisada por microscopia eletr?nica de varredura (MEV) e porosimetria (BET). A influ?ncia da concentra??o de dianidrido no meio reacional foi investigada, bem como a influ?ncia do aumento no grau de reticula??o no comportamento t?rmico do material. Foram obtidas isotermas de absor??o de ?gua em diferentes temperaturas para os hidrog?is com diferentes graus de reticula??o. Os coeficientes de difus?o dos g?is foram determinados, juntamente com a energia de ativa??o para o processo de inchamento usando a equa??o de Arrhenius. A entalpia de mistura do sistema gel-?gua foi determinada pela medida da quantidade m?xima de ?gua absorvida no equil?brio a diferentes temperaturas, empregando a equa??o de Gibbs/Helmholtz.This work describes the synthesis of hydrogels of cellulose acetate (AC), with a nominal degree of substitution DS = 2.5, cross-linked with 3,3?,4,4? benzophenonetetracarboxylic dianhydride (BTDA). The raw materials were characterized by thermal analysis (TG/DTG) and by Fourier transform infrared spectroscopy (FTIR). DS of cellulose acetate was determined by titration with a known amount of standard NaOH solution. Hydrogels of BTDA were synthesized with 0.5, 0.75 and 1.0 mol of BTDA/mol of AC. FTIR proved to be a suitable method to monitor the course of reactions and the progress of purification. UV-vis spectroscopy and analysis confirmed the esterification of the free hydroxyl groups. Surface modification of AC structure after the cross-linking reaction was analyzed by Scanning Electron Microscope (SEM) and density and porosity of the hydrogels were determined by BET. The influence of the concentration of dianhydride on the time necessary for formation of the gel was investigated. The influence from the increase in the degree of cross-linking on the thermal behavior of the material was also documented. Water absorption isotherms were obtained for hydrogels with different reticulating agents and reticulation degrees at different temperatures. The Arrhenius equation was used to determine the diffusion coefficient of the different hydrogels at distinct temperatures and the threshold energy for the swelling process. The enthalpy of mixture was determined through the measurement of the maximum quantity of water absorbed at equilibrium at different temperatures, with the Gibbs/Helmholtz equation

Monodisperse lignin fractions as standards in size-exclusion analysis Comparison with polystyrene standards

The difficulty of preparing monodisperse lignin fractions on a large scale is a limiting factor in many applications. The present paper addresses this problem by examining the properties and size-exclusion behavior of lignin isolated by the acetosolv pulping process from post-extraction crushed sugarcane bagasse. The isolated lignin was subjected to a solvent pretreatment, followed by preparative gel permeation chromatography fractionation. The fractions were analyzed by high-performance size-exclusion chromatography (HPSEC) and these samples showed a great decrease in polydispersity, compared to the original acetosolv lignin. Several fractions of very low polydispersity, close to unity, were employed as calibration curve standards in HPSEC analysis. This original analytical approach allowed calibration with these lignin fractions to be compared with the polystyrene standards that are universally employed for lignin molecular mass determination. This led to a noteworthy result, namely that the lignin fractions and polystyrene standards showed very similar behavior over a large range of molecular masses in a typical HPSEC analysis of acetosolv lignin. (C) 2009 Elsevier B.V. All rights reserved

Caracterização anatômica da fibra de bambu (Bambusa vulgaris) visando sua utilização em compósitos poliméricos.

O desenvolvimento de materiais compósitos utilizando fibras vegetais como reforço é crescente e vêm conquistando novos segmentos de mercado, pois as fibras vegetais apresentam baixo custo, biodegradabilidade, menor densidade e boas propriedades mecânicas, físicas e térmicas adequadas às aplicações industriais. Este trabalho apresenta os resultados de recentes pesquisas sobre a fibra de Bambusa vulgaris realizadas no laboratório de anatomia da madeira da Universidade Federal de Lavras, onde foram avaliadas suas dimensões e relações entre elas, bem como o ângulo de micro fibrila. O principal objetivo deste estudo é mostrar que estes materiais não convencionais podem apresentar propriedades semelhantes e/ou superiores a outros materiais que tradicionalmente vem sendo empregados na produção de compósitos. Os resultados da pesquisa mostraram que os valores de ângulo de micro fibrila (11,54º), comprimento (2.299,47 μm), diâmetro da fibra (13,93 μm), diâmetro do lume (3,81 μm), relação comprimento/largura (172,53) e espessura da parede celular (5,06 μm) poderão maximizar as propriedades mecânicas dos compósitos onde forem utilizadas tornando-os mais resistentes e mais leves em comparação com outras fibras.The development of composite materials using vegetable fibers as reinforcement is increasing and comes conquering new market segments, because the vegetable fibers have low cost, biodegradability, lower density and good mechanical properties, physical and thermal suitable to industrial applications. This paper presents the results of recent research about the fiber of Bambusa vulgaris performed in the laboratory of wood anatomy of the Federal University of Lavras, where were evaluated their dimensions and relations between them, as well as the micro fibril angle. The main objective of this study is to show that these unconventional materials may have similar properties and/or superior to other materials that traditionally come being employed in the production of composite materials. The results of the research has shown that the values of angle of micro fibril angle (11.54º), length (2,299.47 μm), fiber diameter (13.93 μm), lumen diameter (3.81 μm), length/width ratio (172.53) and cell wall thickness (5.06 μm) will be able to maximize the mechanical properties of composites where they will be used becoming then stronger and lighter compared with other fibers

Pulpa de bambú tratada con NaOH y dianhídrido benzofenona tetracarboxílico como refuerzo de nuevos materiales poliméricos.

Bamboo admittedly and engineering material widely used for buildings in several countries. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. The aim of this work was esterify the refined pulp of bamboo came from kraft industrial pulping, previously treated with sodium hydroxid and organic solvents for the production of less hydrophilic materials. In order to verify the occurrence of reaction, assays of spectroscopy in the region of IV, thermogravimetry, elementary analysis and water absorption were performed. After the reaction, the infrared spectra presented bands related to the ester and carboxylic acid groups, evidencing the exchange of OH groups for ester groups. This test also shows a decrease in the absorbance ratio due to the presence of ester group causing a reduction in the crystallinity index of the sample. These results were proven by the gain in the value of carbon content after the elementary analysis. In the water absorption test, the pulp modified with dianhydride showed the lowest level as compared to other samples. The thermogravimetric analysis also showed a decrease in initial temperature of pulp degradation, as well as decrease in the moisture, facts that proved the efficiency in the modification using dianhidrido BTDA.El objetivo de este trabajo fue esterificar pulpa refinada procedente de bambú industrial kraft, pre-tratados con hidróxido de sodio y disolventes orgánicos para producir materiales menos hidrofílicos. Con el fin de verificar la aparición de reacción de esterificación, espectroscopia infrarroja, análisis termogravimétrica, análisis elemental y absorción de agua fueron realizadas. Después de la reacción, el espectro infrarrojo mostró bandas relacionadas con los grupos éster y grupos de ácido carboxílico, que muestra el intercambio de grupos OH por grupos éster. Esta pruebla también mostró una proporción reducida de la absorbancia debido a la presencia del grupo éster causando una reducción en el índice de cristalinidad de la muestra. Estos resultados se corroboraron por un aumento en la cantidad de contenido de carbono después del análisis elemental. En la prueba de absorción de agua, la pulpa modificada con dianhídrido mostro el nivel más bajo en comparación con otras muestras. El análisis termogravimétrica mostró también una reducción en la temperatura de inicio de la degradación de pulpa refinada, así como una disminución en el contenido de humedad, los eventos que demostraron La eficacia de la modificación utilizando BTDA dianhídrido

Dynamic mechanical behavior of vinylester matrix composites reinforced by Luffa cylindrica modified fibers.

Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix

Dimensional stability of Bambusa vulgaris for the production of GLB and furniture.

The objective of this study was to determine the dimensional stability of Bambusa vulgaris, analyzing the technical viability of its use by industries of GLB (glued laminated bamboo) and furniture. The variations occurred in the dimensions of the specimens after immersion in water and dried on a stove were investigated. The assessment of quality was performed through the anisotropy of shrinkage and swelling, volumetric shrinkage and swelling, basic density and water absorption of 2-year-old samples made in the form of slivers. The bamboo presented lower values of shrinkage and swelling anisotropy for the basal region. The mean total value of volumetric shrinkage for the studied regions was stable, and was therefore classified as medium shrinkage. Because the mean values of basic density were lower than 0.5 g/cm3 in all the regions, the species was classified as a light material. The present study also showed that the increase of basic density was related to a decrease on the rates of water absorption. These results point to the great potential use of such species on the sector of GLB and furniture

Synthesis and characterization of hydrogels from cellulose acetate byesterification crosslinking with EDTA dianhydride.

Hydrogels were prepared from cellulose acetate with a degree substitution (DS) 2.5 dissolved indimethylformamide by esterification crosslinking with Ethylenediaminetetraacetic dianhydride (EDTAD)catalyzed by triethylamine. Subsequent conversion of the unreacted carboxyl groups to sodium carbox-ylates by the addition of aqueous NaHCO3was performed to enhance the water affinity of the gels. Theabsorbency of the products was strongly dependent on the amount of EDTAD that was esterified to cellu-lose acetate, and the highest absorbency was observed for the hydrogel composed of approximately 0.36molecules of EDTAD per repeat unit of cellulose acetate. The hydrogels were synthesized with differentdegrees of crosslinking and were analyzed by IR spectral (FTIR), near infrared (NIR), thermogravimetryanalysis (TG and DTG), and crosslink density evaluation by Flory-Rehner theory. The hydrogels have syn-thesized with molar ratios EDTAD/OH groups: [1/1], [1/2], and [0.1/1]. The capacity for water absorbencywas studied and compared with the water absorbency of the CA

Obtenção e caracterização de blendas de asfalto CAP 20, modificado com poliestireno reciclado, resíduos de pneu e lignina organossolve

O presente trabalho trata da obtenção e caracterização de blendas envolvendo matrizes asfálticas (CAP 20), em misturas com poliestireno reciclável (PS), pó de pneu (PPN) e lignina organossolve (LIG). Quando se adicionam polímeros à matriz asfáltica, pretende-se, principalmente, aumentar a impermeabilidade, impedindo a deterioração pela água, diminuir a fragilidade a baixas temperaturas e diminuir o desgaste por abrasão. As propriedades físicas, incluindo índice de penetração, ponto de amolecimento e índice de susceptibilidade térmica do CAP 20 modificado, foram analisadas e comparadas com o CAP 20 não modificado. Os resultados obtidos mostram que a adição de PPN, PS e LIG afeta as propriedades mecânicas das blendas formadas com o CAP 20, diminuindo os índices de penetração e aumentando os pontos de amolecimento de uma maneira geral