Synthesis of a boron modified phenolic resin
doi: 10.5028/jatm.2010.02027610

Aparecida M. Kawamoto
Instituto de Aeronáutica e Espaço
São José dos Campos - Brazil
aparecidamkawamoto@hotmail.com

Luiz Cláudio Pardini*
Instituto de Aeronáutica e Espaço
São José dos Campos - Brazil
pardini@iae.cta.br

Milton Faria Diniz
Instituto de Aeronáutica e Espaço
São José dos Campos - Brazil
miltond@iae.cta.br

Vera Lúcia Lourenço
Instituto de Aeronáutica e Espaço
São José dos Campos - Brazil
vlucia@iae.cta.br

Marta Ferreira K. Takahashi
Instituto de Aeronáutica e Espaço
São José dos Campos - Brazil
martat@iae.cta.br

*author for correspondence

Abstract:

Phenolic resin has long been used as matrix for composites mainly because of its flame retardant behavior and high char yield after pyrolysis, which results in a self supporting structure. The addition of ceramic powders, such as SiC and B4C, as fillers to the phenolic resin, results in better thermo-oxidative stability, but as drawbacks, it has poor homogeneity, adhesion and processing difficulties during molding of the composites. The addition of single elements, such as boron, silicon and phosphorus in the main backbone of the thermo-set resin is a new strategy to obtain special high performance resins, which results in higher mechanical properties, avoiding the drawbacks of simply adding fillers, which results in enhanced thermo-oxidative stability compared to conventional phenol-formaldehyde resins. Therefore, the product can have several applications, including the use as ablative thermal protection for thermo-structural composites. This work describes the preparation of a boron-modified phenolic resin (BPR) using salicyl alcohol and boric acid. The reaction was performed in refluxing toluene for a period of four hours, which produced a very high viscosity amber resin in 90% yield.The final structure of the compound, the boric acid double, substituted at the hydroxyl group of the aromatic ring, was determined with the help of the Infrared Spectroscopy, ¹H-NMR, TGA-DSC and boron elemental analysis. The absorption band of the group B-O at 1349 cm ˉ¹ can be visualized at the FT-IR spectrum. ¹H-NMR spectra showed peaks at 4.97-5.04 ppm and 3.60-3.90 ppm assigned to belong to CH2OH groups from the alcohol. The elemental analysis was also performed for boron determination.The product has also been tested in carbon and silicon fibers composite for the use in thermal structure. The results of the tests showed composites with superior mechanical properties when compared with the conventional phenolic resin.

Keywords:

Phenolic resin, Boron, Thermal protection, Oxidizing agents.

J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.2, pp. 169-182, May-Aug., 2010
Received: 14/06/10
Accepted: 28/06/10