3.8. Brightness
The brightness measurement results are presented in Fig. 9. The coloration of the biocomposite material is mostly dependent on raw fiber hue, which is a result of their chemical composition. The biocomposites reinforced with jute, the darkest of all the investigated fibers, have also shown the darkest coloration. As opposed to the brightest softwood and softwood reinforced biocomposites. The brightness parameter is important in household and furniture parts were only a bright raw composite material enables it further in-melt coloration with pigments.
4. Conclusions
This paper comprises a research study of four types of natural fibers that are most commonly used in the plastic industry. It contains thorough characteristics of fibers and their polypropylene biocomposites. Both matrix and natural lignocellulosic fibers provided the lightweight aspect of the manufactured biocomposites. Although most natural fibers have a similar chemical composition, due to the different alignment of cellulose microfibrills in a single fiber and different geometry of a fiber bundle, their mechanical properties can vary distinctively between one another.
Obtained results:
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Kenaf fibers gave outstanding strengths for their biocomposites.
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Abaca fibers gave the best improvement of impact resistance.
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Jute fibers are the most temperature stable among investigated fibers.
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Wood microfibers can provide relatively good strength at low expense.
From the results, it can be concluded that the properties of biocomposites are influenced mainly by the mechanical properties and geometry of fibers. Higher aspect ratios ensure better matrix-to-fibre stress transfer which results in better strength of the biocomposite. The heat deflection temperature is also better at higher aspect ratios of fibers. The situation is slightly different for impact strength when except for aspect ratios, thicker fibers can induce fiber pull-out effect or fracturing of their bundles can absorb impact energy, which in turn can increase the fracture toughness of a biocomposite to a greater extent. The presented differences in the physical properties of natural fiber types can be smartly used for tailoring of the properties of their thermoplastic biocomposites. Furthermore, the use of different fiber combinations in one matrix (hybrid composite) may accurately meet the requirements of particular applications.
Acknowledgements
The authors would like to express their appreciation to JELU-WERK for softwood flour and HSH Chemie, Poland for the compatibilizer of Clariant Masterbatches. The authors would also like to thank a partner company Prachtgroup for the Arburg Allrounder 270S 350-100 injection molding machine and to EKOTEX for cutting the fibers.
The study was conducted within the Polish–German project “Agro4Comp – manufacturing of micro-fibers from grain by-products for the reinforcement of thermoplastic and thermosetting composites” co-funded by the National Centre for Research and Development in Poland (NCBiR) and Bundesministerium fuer Bildung und Forschung in Germany.