Characterisation of Textile and Oleaginous Flax Fibrous and Shives Material as Potential Reinforcement for Polymer Composites

In recent years, the use of flax fibres to replace glass fibres as reinforcement in polymer composites has gained popularity due to an increasing environmental concern and requirement for developing sustainable materials. Many works deal with the properties of flax fibres cultivated for textile applications, which are today used for polymer reinforcement. As fibrous material from oleaginous flax varieties and shives is available in large quantities and not promoted, its use in composites shall be further developed in the forthcoming years. Croatia and Slovenia mainly grow oleaginous flax, where after the seed collecting, most of the stems remain unused, the major portion being burned in fields, creating environmental pollution, or being disposed by ploughing. Therefore, the aim of this study was to characterise and compare the properties of shives and technical fibres extracted from flax Linum usitatissimum L., a textile variety planted in Croatia and from the Slovenian autochthonous oleaginous variety from Bela Krajina, to be used as potential reinforcement in polymer composites. The flax stems of the textile variety were subjected to water retting for 72 hours and the flax stems of the oleaginous variety were dew retted for four weeks. Dried retted stems were passed through a mechanical process of breaking and scotching, followed by heckling and combing, where the shives and fibres were separated into four groups according to their length. The characterisation of the fibrous material of both varieties was studied according to the results of optical and scanning electron microscopy, moisture regain, fibre length, linear density and tensile strength, and according to the results of Fourier transform infrared spectroscopy and thermogravimetric analysis. Based on the analysis results, it was concluded that the properties of investigated textile and oleaginous flax fibrous material were comparable, as were the properties of tested fibre length groups within the same variety; that flax fibres from textile and oleaginous varieties have adequate morphological and mechanical properties, and thermal stability for reinforcing polymer matrix composites; and that flax shives are more appropriate for fillers in plastics with a lower reinforcing role. As the type of fibre reinforcement (short fibres, roving/yarns, nonwoven or woven fabrics) is very important for polymer composite properties, based on the obtained results, fibres can be selected for specific purposes.