Slovenian Faculty of Mechanical Engineering, University of Maribor Researcher,
Mr. Dr. Silvo Hribernik, carries out scientific work in the field of Mechanical and morphological analysis of hemp fibres: towards selection of suitable hemp varieties for textile and biocomposite applications. Dr. Hribernik, will presented his excellent results at this year's WORLD HEMP CONGRESS 2018.
Silvo Hribernik is a Scientific Associate at the Faculty of Mechanical Engineering, University of Maribor. He finished his graduate study in 2005 in the field of eco-textile engineering and doctoral study in 2010 in the field of textile technology, both conducted at the Faculty of Mechanical Engineering in Maribor, Slovenia. During this time he also performed research work as a visiting scientist at Institute of Chemistry in Ljubljana and at the Fraunhofer Institute in Potsdam, Germany. Main area of his research is development of fibre-based functional materials with implementation of nanotechnology and is comprised of several research interests; study of materials’ structure; synthesis of nano-particles, with special attention to magnetic and conductive particles; study and development of coating and adsorption processes.
Presented study presents the results of fibre procurement from different hemp varieties, targeting the isolation of single fibres rather than fibrous agglomerates. Single or elementary fibres possess a variety of favourable properties which can be exploited in different applications, while at the same time present a platform for functionalization and as such act as building blocks for new materials.
In order to separate fibres from the whole plant, several processes were employed, i.e. enzymatic and chemical scouring, as well as mechanical retting. Pectin that connects bast fibres in hemp stalk is necessary to isolate single fibres; pectins are a structural polysaccharide contained in the primary cell wall and their decomposition is usually achieved by enzyme action. Enzymes themselves are biocatalysts, which, when conditions of appropriate temperature, oxygen concentration and suitable pH are met, degrade various species in low-molecular water-soluble fractions, while enzymes do not transform during those processes. Analysis of tensile properties and fineness of hemp fibres was conducted according to standardised methods for the determination of mechanical properties of single fibres and linear density; SIST EN ISO 5079:1999 and SIST EN ISO 1973:1999, respectively. Breaking force and elongation at break were determined using dynamometer where fibres are mounted with a specified pretension between two clamps and stretched until rupture. All samples were conditioned prior analysis, i.e. stored and analysed at 20°C and 65% relative humidity. Morphological examination of hemp fibres was performed with an electron scanning microscope.
Morphology of enzymatically-treated fibres showed a wide variety of structural features within one single variety, let alone when different varieties were compared; mechanical defibrillation which followed enzyme treatment did not result in complete separation of fibres and removal of lignin. In order to achieve more efficient fibre separation and removal of lignin, two factors which contribute to dimensionally and topographically more homogenous fibres, chemical post-treatment was performed after the enzymatic scouring. Analogous to visual investigation, mechanical analysis of enzyme-treated hemp bast fibres also shows a wide scattering of measured values of tensile properties; correlating these results with observed fibre morphology, the inhomogeneity of fibre agglomerate diameters was recognised as on one of the main factors influencinf the fibre fineness and their behaviour during tensile tests. Introduction of additional chemical treatment procedure, as mentioned above, greatly improved the repeatability and reliability of the mechanical testing. In addition to results of mechanical and morphological investigation of different hemp species, possible applications of hemp fibres will be presented, ranging from more traditional usage in textile sector to advanced applications in medicine and biocomposite development.
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