Biobased composites from tannin–phenolic polymers reinforced with coir fibers

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.