Renewable Resources as Reinforcement of Polymeric Matrices: Composites Based on Phenolic Thermosets and Chemically Modified Sisal Fibers

Abstract

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.

Sisal chemically modified with lignins: Correlation between fibers and phenolic composites properties

“…However, when sisal fibers are used as reinforcement in the preparation of phenolic matrix composites, as used in this work, the problem of lack of adhesion is minimized by some degree of interaction between the sisal fibers and the phenolic matrix. This interaction results from the presence of polar groups in the chemical structure of the phenolic matrix, clearly an advantage of this matrix over other hydrophobic matrices [13]. The phenolic matrices are obtained from phenolic rings that can react with aldehydes, such as formaldehyde, resulting in condensation products, that is, phenolic prepolymers, a well-known fact.…”

The surface properties of cellulose and lignocellulosic materials assessed by inverse gas chromatography: a review

“…However, the chemical changes occurring at the fibers surface during bleaching cannot be disregarded. Megiatto et al (2007) chemically modified sisal fibers by ClO 2 or dichromate oxidation and reaction with furfuryl alcohol (FA) or polyfurfuryl alcohol (PFA) and determined the dispersive component of the surface energy and the acid-base character of the surface. The c s d value greatly increased with the modifications from 21 mJ m -2 (untreated fibers) up to 63-70 mJ m -2 (at 30°C).…”

Ionized‐Air‐Treated Curaua Fibers as Reinforcement for Phenolic Matrices

“…The test was carried out as described elsewhere, [9] in accordance with ASTM (American Society for Testing and Materials) D570, which describes several types of tests. Three specimens (76 Â 26 Â 5 mm 3 ) of every sample were submerged in distilled water at 25 8C.…”

“…Furthermore, phenolic matrices have hydroxyl polar groups, similar to those on the surface of lignocellulosic fibers, which can improve the adhesion at fiber-matrix interface. Considering such phenolic matrix characteristics, this material was selected for our studies on composites reinforced with several lignocellulosic fibers as sugarcane bagasse, [6] jute, [7] sisal, [8,9] and coconut. [10] In the present work, a lignocellulosic fiber obtained from a species that grows in the Amazon region was used, that is, the Ananas erictifolius, which belongs to the Bromeliaceae family and is commonly known as curaua.…”

“…This goal can be accomplished by introducing modifications in the fiber and/or matrix. [1,9,12] In a previous work, curaua fibers were chemically modified by first oxidizing with chlorine dioxide, followed by grafting furfuryl alcohol, which is a chemical obtained from a renewable source. The wettability of the fibers by the resins was improved, but as they were partially degraded by the chemical treatment, the impact strength of the composites reinforced with these fibers decreased.…”