Ramie (Boehmeria nivea (L.) Gaud.) and Spanish Broom (Spartium junceum L.)fibres for composite materials: agronomical aspects, morphology and mechanical properties

The agronomic characteristics of Ramie and Spanish Broom were investigated for seven years in the pedoclimatic conditions of Central Italy. The chemic al, physical and mechanical properties of these fibres were also examined i n order to evaluate the feasibility to use them in composite materials. Res ults demonstrate that Ramie grown in the temperate environment can be harve sted three times a year. The yield of green Ramie plants per annum was almo st 10 000 g m(-2). The fresh Ramie plant is composed, by weight, of 30% gre en leaves and 70% green stems. The yield dry fibre is almost 3% of the gree n stems, giving a total yield of 200 g m(-2). Spanish Broom can reach a fre sh biomass yield of 4000 g m(-2) per annum, represented by 53% of long slen der terete green branches which constitutes the economic products. The dry yield per annum was about 1800 g m(-2) with a dry branchlets yield of 900 g m(-2). Ramie and Spanish Broom cortical fibres are multiple elementary fib res (ultimates) arranged in bundles. In Ramie, the elementary fibres are bo und by gums and pectins, while in Spanish Broom they are bound together by lignin. Both species showed a thick secondary cell wall indicating a high c ellulose content. Ramie ultimate fibres are flattened and irregular in shap e, while those of Spanish Broom are more regular in shape. The diameter of the ultimates varies from 10 to 25 mu m in Ramie, while the Spanish Broom u ltimates ranges from 5 to 10 mu m; the diameter of the whole bundle is abou t 50 mu m for both species. Ramie fibre showed a content of lignin, pentosa ns and extractives lower than Spanish Broom. Both fibres had a high content of cellulose which, on the base of X-ray analysis, was evaluated to be in excess of 70%. Ramie and Spanish Broom fibres had tensile strength of 950 M Pa and 700 MPa, respectively. The elastic moduli were approximate to 65 and approximate to 20 GPa, respectively, which well compare with the modulus o f E-glass fibres (70-90 GPa). The strength of the fibre-matrix interface wa s measured using the single filament fragmentation technique and an epoxy r esin as the polymer matrix. Values for carbon and glass fibres in the same resin were also measured for comparison. The interface strength for the veg etable fibres was higher than that of carbon and glass, likely due to a mec hanical lock mechanism. These values confirm both fibres as potential repla cement for man made fibres in composite materials. (C) 2000 Elsevier Scienc e B.V. All rights reserved.