Lignin, extracted from sugarcane bagasse by the organosolv process, was used as a partial substitute of phenol (40 w/w) in resole phenolic matrices. Short sugarcane fibers were used as reinforcement in these polymeric matrices to obtain fiber-reinforced composites. Thermoset polymers (phenolic and lignophenolic) and related composites were obtained by compression molding and characterized by mechanical tests such as impact, differential mechanical thermoanalysis (DMTA), and hardness tests. The impact test showed an improvement in the impact strength when sugarcane bagasse was used. The inner part of the fractured samples was analyzed by scanning electron microscopy (SEM), and the results indicated adhesion between fibers and matrix, because the fibers are not set free, suggesting they suffered a break during the impact test. The modification of fiber surface (mercerization and esterification) did not lead to an improvement in impact strength. The results as a whole showed that it is feasible to replace part of phenol by lignin in phenolic matrices without loss of properties.

Carbon fiber reinforced composites (CFRC) have been used in aeronautical industry in the manufacture of different aircraft components that must attend tight mechanical requirements. This paper shows a study involving mechanical (flexural, shear, tensile and compressive tests) and morphological characterizations of four different laminates based on 2 epoxy resin systems (8552 and F584) and 2 carbon fiber fabric reinforcements (Plain Weave (PW) and Eight Harness Satin (8HS)). All laminates were obtained by handing lay-up of prepregs plies (0°/90°) and consolidation in an autoclave following an appropriate curing cycle with vacuum and pressure. The results show that the F584-epoxy matrix laminates present better mechanical properties in the tensile and compressive tests than 8552 composites. It is also observed that PW laminates for both matrices show better flexural and interlaminar shear properties.

Summary: The study and development of polymeric composite materials, especially using lignocellulosic fibers, have received increasing attention. This is interesting from the environmental and economical viewpoints as lignocellulosic fibers are obtained from renewable resources. This work aims to contribute to reduce the dependency on materials from nonrenewable sources, by utilizing natural fibers (sisal) as reinforcing agents and lignin (a polyphenolic macromolecule obtained from lignocellulosic materials) to partially substitute phenol in a phenol‐formaldehyde resin. Besides, it was intended to evaluate how modifications applied on sisal fibers influence their properties and those of the composites reinforced with them, mainly thermal properties. Sisal fibers were modified by either (i) mercerization (NaOH 10%), (ii) esterification (succinic anhydride), or (iii) ionized air treatment (discharge current of 5 mA). Composites were made by mould compression, of various sisal fibers in combination with either phenol‐formaldehyde or lignin‐phenol‐formaldehyde resins. Sisal fibers and composites were characterized by thermogravimetry (TG) and DSC to establish their thermal stability. Scanning electron microscopy (SEM) was used to investigate the morphology of unmodified and modified surface sisal fibers as well as the fractured composites surface. Dynamic mechanical thermoanalysis (DMTA) was used to examine the influence of temperature on the composite mechanical properties. The results obtained for sisal fiber‐reinforced phenolic and lignophenolic composites showed that the use of lignin as a partial substitute of phenol in phenolic resins in applications different from the traditional ones, as for instance in other than adhesives is feasible.Micrograph of the impact fracture surface of phenolic composite reinforced with mercerized sisal fiber (500 X).magnified imageMicrograph of the impact fracture surface of phenolic composite reinforced with mercerized sisal fiber (500 X).