Condensed tannin resins extracted from Pinus radiata bark as a support matrix in carbon nanofiber-reinforced polymers

Condensed tannins extracted from the Pinus radiata bark (PRTs) were used as a replacement for phenol in the synthesis of resol-type phenolic resins (FRs) and tested as polymer matrix in carbon nanofiber (CNF)-reinforced composite materials. The PRTs used herein contained a phenol and lignin content of 31 (Eq/L) and 35 (%w/w), respectively. The molecular weights of these polyphenols indicated the presence of 16 flavonoid units. Tannin resins were synthesized, and their characteristics were compared with those of the synthesized FRs using a formaldehyde/phenol ratio of (1.6/1.0), which has the highest total solids content. The results showed that the gel time and useful life of the resins decreased with the addition of the tannins, while there was no significant variation in the degradation temperature with varying FR contents. The mechanical properties of the CNF-reinforced composite materials were determined by DMA, and the results showed an increase of 1000 MPa, due to the better distribution of the fibers in the matrix. The modulus (E') in the reinforced composite materials with tannin resins was 2322 MPa and 1803 MPa without tannins, while modulus E¨ for composite materials doubled for resins with tannins. Tannins improved the dispersion of CNTs and the matrix-filled interface.