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In the hemp industry, retting is considered as an upstream processing treatment that facilitates the decortication of fibres in the central woody part of the stem. This treatment is currently carried out empirically in the fields, and leads to variability in the color, (micro)structure and intrinsic properties (thermal properties) of hemp fibers. The present study aims to compare unretted and retted hemp fibres harvested at the end of flowering. The results show that retting induces a change in the color of fibres from light green to dark gray due to the activity of the microbial community at the stem surface. A separation of the fibre bundles into elementary fibres occurs with the degradation of the cementing compounds present in the middle lamella. The cellulose and its crystallinity degree increased from 68 to 75 % and 85 to 89 %, respectively, with a removal of non-cellulosic materials, which leads to an improvement of the thermal stability for the retted fibres. [ABSTRACT FROM AUTHOR]

The raw earth is a natural material originating from the slow decomposition of rocks and stones. It can be used as a construction material as cob, daub, wattle, adobe, moulded bricks, rammed earth or compressed earth blocks. The use of a specific technique depends on the vernacular habits and also on the climate to which the building will be submitted or on the intrinsic properties of the earth. In this paper, we study the thermal and mechanical properties of compressed earth blocks (CEB) made of raw earth from Benin. In order to improve the mechanical properties of this brittle material, especially the tensile stress, kenaf fibers are incorporated into the mix. To determine the influence of the fibers on the various properties of CEB, the fiber content and the fiber length was varied. The results show a strong influence of these parameters on the porosity and as a consequence on the thermal and mechanical properties (compressive and tensile strengths). The increase in the porosity of the material yields a decrease in the mechanical strengths whatever the fiber content, except for long fibers. This seems to demonstrate combined effects of the porosity decrease and of the resistance to traction efforts due to the fibers. The addition of fibers also induces a decrease in the thermal conductivity of the material mainly due to the increase in the porosity. [ABSTRACT FROM AUTHOR]

The laser filament winding of preimpregnated thermoplastic tapes requires a multiphysical analysis, leading to the control of transformation parameters. Such an analysis is generally carried out by considering the raw material, the tape, as a "standard material". Consequently, conclusions can be biased due to the material variability, which presents at least a natural variability, at worst local or repeated defects. Therefore, in the present work, the subject under study is the thermal behavior of the tape, independently of the manufacturing conditions. The detected thermal irregularities are then put into perspective with the irregularities of the material, such as thickness variations or porosities. [ABSTRACT FROM AUTHOR]