Propriedades mecânicas de compósitos poliéster/juta: efeitos de tratamentos superficiais, envelhecimento térmico e absorção de água.

Abstract

This work deals with the mechanical properties of polyester matrix composites reinforced by hessian cloths as a function of fiber content, thermal exposure time, fiber drying previous to composite lamination and fiber surface treatment. The water adsorption of these composites as a function of the above parameters was also evaluated. The results show that the composites mechanical properties depend on fiber content. Increases of up to 20% in tensile strength and 108% in modulus were obtained for composites reinforced by 4 plyes of hessian cloths (50% w/w of jute). The elongation at break, albeit not varying significantly, tended to slightly increase with fiber content. Drying of the cloths prior to lamination significantly increased the strength and modulus of all composites investigated. The isocyanate pre-polymer surface treatment was the most effective among the two treatments employed on the hessian cloths, however, the increases obtained for the composite's performance were not significant. Best mechanical properties were obtained by composites reinforced with surface treated cloths dried just before lamination. All composites under investigation, despite their reinforcement having been surface treated and/or previously dried or not, exhibited the same behavior during thermal exposure, i.e.: a) tensile strength decreased within the first 10 days of exposure and leveled off at longer times; b) the modulus was not affected or tended to increase with thermal aging and c) elongation at break decreased with thermal exposure. The composites reinforced by pre-dried hessian cloths absorbed less water than those reinforced by non-dried cloths. The lowest effective diffusion coefficients, and therefore, the lowest water sorption rate was obtained for composites reinforced by isocyanate modified, pre-dried cloths. Sorption kinetics was adequately described by a diffusional model and, in all cases, correlation coefficients better than 0.99 were obtained.