INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Effects of Absorption Distilled and Artificial Sea Water and Fiber Orientation on Dielectric Behaviour Properties of Vinyl-Ester Sisal Fiber
Autor/es:
A.N.FRAGA, J.C.DOUMECQ, A.VAZQUEZ
Lugar:
Rio de Janeiro, Brasil
Reunión:
Congreso; 4th International Conference of Science and Technology of Composite Materials, COMAT 2007; 2007
Resumen:
Gravimetric and dielectric measurement has been used to monitor distilled water and artificial sea water uptake in vinyl-ester matrix and sisal composites. Results showed that the amount of water absorbed is independent of fiber directionality within the composite and also of the salinity of the water where samples were submerged. Dielectric constant values resulted greater for samples immersed in artificial sea water than for samples in distilled water, due to the increase of conductivity because of the presence of salt ions. The behaviour of  the dielectric dissipation factor (tan ¥ä) was the opposite in this case, responding directly to the variation in conductivity. The effect of fiber directionality in electric properties was studied with sisal fiber vinyl-ester composite samples of similar thickness. The dielectric constant was measured for 90¨¬, where samples were cut in such a way to place fibers perpendicular to the electric field and for 0¨¬, with fibers parallel to the field, founding that dielectric constant is greater for 90¨¬, where contact surface between the fiber and the electrode is greater than for 0¨¬ composites. Results showed that the dielectric constant of vinyl-ester polymer is lower than its composite based on sisal fibers. Changes in dielectric permittivity and tan ¥ä were measured at different frequencies, first with matrix alone samples, then with composite dry samples, then at different instances of the water absorption process.  It was found that the dielectric permittivity of the matrix and that of the composite decreases as the frequency increases, independently of the fiber orientation in the composite.  A model describing the increase in permittivity with water absorption in the frequency range of 400 Hz to 1 MHz for composite polymer was proposed. Then, a method for calculation of water absorption from changes in the permittivity has been proposed and verified experimentally.