The increasing environmental awareness, growing global waste problems and continuously rising high crude oil prices have motivated governments all over the world to increase the legislative pressure. This in turn promotes researchers, industries and farmers to develop the concepts of environmental sustainability and reconsider renewable resources. Renewable resources from agricultural or forestry products form a basis for new industrial products or alternative energy sources, such as hemp fibre. Hemp fibres have long been valued for their high strength and long fibre length, and used extensively in the fabrication of ropes and sails, as well as for paper and textiles. Hemp fibres consist of different hierarchical microstructures, whereby microfibrils serve as basic units.
The microfibrils are embedded in a matrix of hemicelluloses and form the different cell wall layers of an elementary fibre, which generally has a large average diameter ranging from 10 to 50 m.The elementary fibres are bonded together with pectin’s and small amounts of lignin framing the next level of microstructure, i.e. technical fibres, with a diameters ranging from 50 to 100 m . These filaments are fixed together with a pectin-lignin matrix to form fibre bundles in the cortex of plant stems. Thus, bast fibres are bundles of individual strands of fibres held to-gether by a pectin-lignin interface. The fibres of never dried hemp contain numerous de-formations. All these deformations appear where there is a change in microfibril direction and a distorsion of the fibrils. The deformations can be seen under polarized light, but the largest of them also could be dis-cerned without polarisers.
The deformation of fibres can affect the strain distribution in elementary fibre, leading to localized strain concentrations , and hence reduce both compressive strength and tensile strength , which was also proved by a finite element modeling of the tensile behaviour of single flax and hemp fibre. The fibres in the matrix may break at the point with deformations , and the concentration of stresses around the deformation could act as the site of initiation of fibre-matrix debonding as well as for the formation of micro-cracks in the matrix which contribute to global fracture of composite. Limited work conducted on the breaking behaviour of wood pulp, cotton , and flaxalso indicated that the break behaviour of the primary and secondary cell wall of the flax fibres was different from that of wood and cotton . The primary cell wall generally breaks in a brittle manner, whereas the secondary cell wall, bridged by fibrils, splits relatively easily along the length direction. The experience has highlighted that it is not possible to use or appropriate to compare data available from different investigations reported in the literatures.
Microstructural defects, fibre abstraction and processing are all yet to be studied. This pa-per is an attempt to characterize the surface and reveal the failure mechanism of elementary hemp fibres. Systematic and improved methodologies and advanced technologies have been developed to investigate the microfibril angles of elementary hemp fibres and the crystallinity of hemp fibres. The surface of hemp fibres after tensile loading and fracture of fibres after breaking were also observed carefully to characterize the surface and reveal the failure mechanism of elementary hemp fibres. This paper is the first of a series of papers from an intensive research programme aiming at a better understanding of natural fibre resources and the develop-ment of their high strength composites for applications in various industrial sectors. The purpose of this article is two-fold. First, we advocate the use of mathematical models to characterize the learning process for researchers interested in exploring the effects of marijuana on learning and memory. While articles contain the results of statistical tests, to our knowledge no previous article has promoted the use of mathematical models to characterize potential learning and memory effects either on marijuana or other plant based products purporting to improve memory.
Mathematical models have much to recommend them for the study of marijuana and other plant based products. Such models can easily summarize large amounts of data, direct research, stimulate the development of theory, and guide therapeutic intervention. They can also be used to test claims made by advocates of plant based products that such products improve learning and memory.Second, we advocate the use of the first order system transfer function. We have used this model in a wide variety of studies ranging from the assessment of memory in drug addicts and alcoholics to the detection of memory impairment in individuals suffering from either Type-2 diabetes mellitus or multiples clerosis. The model has also been applied to both the child and adult versions of the California Verbal Learning Test .