The aim of this study is the evaluation of the effect of chemical treatment of jute fi bres on their permeability with polyester resin and determination of optimal treatment parameters. Unmodifi ed jute fabric by LENTEX, Poland and polyester resin ESTROMAL 14 were used in the experiments. NaOH and KOH water solutions (various concentration -from 1 to 15% -and treatment duration -from 0.5 to 6h), vinyl acetate, methanol, toluene diizocyanate were used for the treatment. Determination of the

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... t of the chemical treatment on fi ber-resin interaction was made in: infi ltration of resin into reinforcement structure tests and fabric absorbability tests. Three criteria: time of penetration of resin into the reinforcing fabric, fabric absorbability and the area of a part of the specimen cross-section penetrated with the resin were taken into account. The fabrics treated with 1-5% -long-time and 15% short-time NaOH and KOH water solutions showed the best results within the tested criteria. These results do not correspondent directly with the mechanical properties of cured composites manufactured on the base of the treated fabrics. Alkali-and organic treatments signifi cantly improve the mechanical performance of natural fi bres reinforced composites, but organic treatments (methanol, toluene diisocyanate) gives better improvement in mechanical properties in comparison with the alkali-treatments. The measurement methods applied in the study may be generally useful in the evaluation of the effect of chemical treatment of natural fi bres on their wettability with the liquid matrix.