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Tannin–phenolic polymers prepared using tannin, a macromolecule obtained from natural sources, were used in the preparation of composites reinforced with coir fibers. The composites based on tannin–phenolic polymers (50% (w/w) of tannin as substitute of the phenol) were prepared using the coir fibers as reinforcement (30–70% (w/w), 3.0–6.0 cm, randomly distributed). The Izod impact strength of the composites showed an improvement in this property due to the incorporation of coir fibers in the tannin–phenolic matrices. The SEM images showed excellent adhesion at the fiber/matrix interface. The coir fiber had bundles regularly spaced, which enhanced the diffusion of the resin into the fiber. In addition, the high lignin content of this fiber results in a high concentration of aromatic rings, which increased the compatibility with the matrix. The values of the diffusion coefficient of water, determined using Fick's laws, show that there was no correlation between the fiber percentage and the water diffusion. The DMTA curves showed that the storage moduli of the composites reinforced with coir fibers were considerably higher than that of the thermoset, and the increase in the proportion of fibers led to a proportional increase in the storage moduli of these materials. The biobased composites obtained have potential for non-structural applications, such as in the internal parts of automotives vehicles. To our knowledge, this is the first study on this kind of biobased composites.

A new chemical modification of sugar cane bagasse fibers for phenolic thermoset composites is presented. It consists in creating quinones in the lignin portions of fiber and react them with furfuryl alcohol to create a coating around the fiber more compatible with the phenolic resins used to prepare polymeric matrix. Sodium periodate was used in suitable conditions to oxidize mainly phenolic syringyl and guaiacy units of the lignin polymer to create quinones, which were characterized by UV-visible diffuse reflectance spectroscopy by comparison with model compounds. The reactivity of furfuryl alcohol (FA) with fibers was greatly enhanced after they were oxidized: 13% weight percent gain compared to 2% without oxidation. Chemical analysis of unmodified and FA-modified fibers have shown an important degradation of hemicellulose and a slight one of cellulose which almost maintains its crystallinity. A 25% decrease of strength and length properties of the fibers after FA chemical treatment was measured by dynamic mechanical analysis. The lignin-like proportion of the fiber was greatly enchanced after the FA-treatment. This was confirmed by thermal analysis, DSC, and TGA experiments, on unmodified and FA-modified fibers. SEM analysis of the fibers and of phenolic composites with modified fibers have confirned the FA grafting and shown a better comptability at the interface between the chemically modified fibers and the phenolic matrix. Nevertheless, the chemical treatment of the fibers decreased the impact strength of the composite, which could be caused by the fiber damage suffered during the chemical modification and for the more intense adhesion at the interface, wich in some cases decrease somewhat the impact strength.

Neste trabalho, fibras lignocelulósicas de diferentes fontes (bananeira e coco) foram utilizadas como agentes de reforço na preparação de compósitos de matriz fenólica e lignofenólica. O fenol, utilizado na formulação da matriz, foi substituído parcial e totalmente por lignina, extraída do bagaço de cana de açúcar por processo Organosolve, na preparação dos termorrígidos lignofenólicos. Os polímeros foram moldados sob compressão e aquecimento controlados. Para caracterização das fibras lignocelulósicas, além da análise da composição, foram utilizadas as seguintes técnicas: difração de raios-X, cromatografia gasosa inversa (IGC), espectroscopia na região de infravermelho (IV), calorimetria exploratória diferencial (DSC), termogravimetria (TG), microscopia eletrônica de varredura (MEV), resistência à tração. Os pré-polímeros (fenólicos e lignofenólicos) foram caracterizados via cromatografia de exclusão por tamanho (SEC), IV, DSC, TG. Os compósitos obtidos foram caracterizados através de ensaios de impacto Izod, análise dinâmico-mecânica (DMA), absorção de água, DSC, TG. Os resultados revelaram que: a substituição total do fenol por lignina é viável; das duas fibras utilizadas como reforço, fibras de coco e banana (não tratadas, ou tratadas com solução alcalina ou ar ionizado), estas últimas apresentaram melhores resultados como reforço de matriz fenólica, possivelmente devido ao mais alto teor de celulose, que é o componente das fibras lignocelulósicas presente nos domínios cristalinos, e que, portanto, exerce a maior influência sobre as propriedades mecânicas destas, e conseqüentemente sobre a ação como reforço em compósitos; em se tratando de compósitos lignofenólicos, principalmente naquele em que fenol foi totalmente substituído por lignina, embora a fibra de coco não tenha boas propriedades mecânicas devido ao baixo teor de celulose, o alto teor de lignina presente neste fibra passou a corresponder a propriedade importantíssima, pois aumentou consideravelmente a afinidade fibra/matriz (também com alto teor de estruturas típicas de lignina). A intensificação das interações na interface possivelmente facilitou a transferência de carga da matriz para a fibra durante o impacto, levando ao material com mais alta resistência ao impacto, dentre os considerados no presente trabalho. Os resultados de absorção de água no geral foram importantes, pois além de indicar a afinidade do material por água, trouxeram também, dentre outras, informações sobre a interface fibra/matriz. No caso dos compósitos preparados a partir de pré-polímeros em que fenol foi totalmente substituído por lignina, os testes de absorção de água também foram importantes no sentido de indicar o melhor processo a ser utilizado na preparação dos pré-polímeros, sendo os resultados condizentes com aqueles obtidos via ensaio de impacto. Deve-se destacar o fato de ter sido possível preparar um compósito com boas propriedades, em que lignina foi usada como macromonômero na preparação da matriz polimérica, sendo esta reforçada com fibras vegetais, ou seja, obteve-se um compósito a partir de alta porcentagem de material oriundo de fontes renováveis In this work, lignocellulosic fibers from different sources (banana tree and coconut) were used as reinforcing agents in the preparation of phenolic and lignophenolic matrix composites. The phenol used in the matrix formulation was substituted both partially and totally by lignin, extracted from sugarcane bagasse by organosolv process, in the preparation of the lignophenolic thermosets. The composites were molded under controlled pressure and heating. Besides composition analysis, the following techniques were used to characterize the lignocellulosic fibers: X-ray diffraction, inverse gas chromatography (IGC), infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetry (TG), scanning electron microscopy (SEM), and tensile strength. The prepolymers (phenolic and lignophenolic) were characterized by size exclusion chromatography (SEC), IR, DSC, and TG. The composites obtained were characterized by Izod impact strength, dynamic mechanical analysis (DMA), water absorption, DSC, and TG. The results revealed that: -the total substitution of phenol by lignin is viable; - from the two reinforcing fibers used (banana tree and coconut, both treated and untreated with alkaline solution and ionized air), the former presented the best results as a phenolic matrix reinforcement, possibly due to their larger cellulose content, which is the component of the lignocellulosic fibers present in the crystalline domains. This has a greater influence on the mechanical properties of the fibers, and consequently on their action as composite reinforcement; -concerning the lignophenolic composites, mainly those in which phenol was completely substituted with lignin, although the coconut fibers do not have good mechanical properties due to their low cellulose content, their high lignin content contributed to a very important property, that is, a considerable increase in the affinity between the fiber and the matrix, which also has a high content of typical lignin structures. The intensity of the interactions at the interface may have made the load transfer from the matrix to the fiber during impact easier, resulting in a material with the highest impact strength, when compared to others prepared in the present study; -the water absorption results were generally important as besides information on the affinity of the material for water, they also gave further information on the fiber/matrix interface. In the case of composites prepared from prepolymers whose phenol was totally substituted by lignin, the water absorption tests were also important to indicate the best prepolymer preparation process, which was in agreement with impact assay results. It is important to highlight the fact that it is was possible to prepare a composite with good properties using lignin as a macromonomer in the preparation of a polymeric matrix reinforced with natural fibers, that is to say, with a high percentage of material derived from renewable sources

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.