Estudo da modificação superficial de fibras de sisal com ligninas, e sua utilização em matrizes cimentícias.

Abstract

The objective of this work is to evaluate different treatments of sisal vegetable fibers for use in cementitious matrix composites. The treatments consist of impregnating superficially fibers of sisal (S) with lignin organossolv (LO), lignin organossolv + glutaraldehyde (LOG), lignin kraft (LK) and lignin kraft + glutaraldehyde (LKG), aiming to reduce the porosity and increase or maintenance in the mechanical properties of the fibers. After treatment, the fibers presented a significant reduction of the absorption of water and did not obtain significant changes in the mechanical properties when compared with the natural fiber (SNAT). By scanning electron microscopy, SLOG, SLO, SLKG and SLK presented a rough appearance, with lignin deposited on the surface of the fibers, evidencing that the treatment with impregnation at the beginning occurred. By Fourier transform infrared spectroscopy with attenuated total reflection technique also verified the impregnation of lignin in the fibers SLOG, SLO, SLKG and SLK. By thermogravimetric analysis, it observed that the impregnation treatment delayed the thermal degradation of the treated fibers when compared to the untreated fibers. To evaluate the performance in the cement mixture Cement Plates (CP) with fibers treated (CP-SLOG, CP-SLO, CP-SLKG and CP-SLK) and without treatment (CP-SNAT) were made. With the exception of CP-SNAT, all plates did not statistically show differences in absorption and porosity indexes. Analyzing the mechanical properties, the CP-SNAT showed a significant increase in the rupture module, elasticity module and toughness from 28 to 180 days, probably due to the process of carbonation of the matrix. CP-SLK showed a significant increase in the modulus of elasticity from 28 to 180 days and CP-SLO presented a significant increase in the toughness from 28 to 180 days. By scanning electron microscopy done at 180 days, it observed that the section of the fibers immersed in the cementitious plates showed no degradation, indicating that the impregnation of lignin acted as protective agent of the fibers. Regardless of the type of lignin used in the impregnation, it concluded that the presence of glutaraldehyde is dispensable for treatment.