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Open AccessArticle

Effect of NaOH Treatment on the Flexural Modulus of Hemp Core Reinforced Composites and on the Intrinsic Flexural Moduli of the Fibers

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LEPAMAP Research Group, University of Girona, Maria Aurèlia Capmany, 61, 17003 Girona, Spain
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Design, Development and Product Innovation, Department of Organization, Business, University of Girona, Maria Aurèlia Capmany, 61, 17003 Girona, Spain
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Advanced Biomaterials and Nanotechnology, Department of Chemical Engineering, University of Girona, Maria Aurèlia Capmany, 61, 17003 Girona, Spain
4
Department of Industrial and Materials Science, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden
5
Sustainable Industrial Processes, University of Girona, Maria Aurèlia Capmany, 61, 17003 Girona, Spain
*
Authors to whom correspondence should be addressed.
Polymers 2020, 12(6), 1428; https://doi.org/10.3390/polym12061428
Received: 19 May 2020 / Revised: 18 June 2020 / Accepted: 19 June 2020 / Published: 26 June 2020
(This article belongs to the Special Issue Cellulose Polymer Composites)
This paper describes the potential of using hemp core waste in the composite industry. These lignocellulosic residues can be used to produce environmentally friendly and economically viable composites and improve the overall value chain of hemp production. To this purpose, hemp core residues were alkaline treated at different NaOH concentrations and then mechanically defibrated. Hemp core fibers were mixed with polypropylene and injection molded to obtain testing specimens. The effect of sodium hydroxide on the flexural modulus of composites was studied from macro and micro mechanical viewpoints. Results showed remarkable improvements in the flexural modulus due to the presence of hemp core fibers in the composites. At a 50 wt % of reinforcement content, increments around 239%, 250% and 257% were obtained for composites containing fibers treated at a 5, 7.5 and 10 wt % of NaOH, respectively. These results were comparable to those of wood composites, displaying the potential of hemp core residues. The intrinsic flexural modulus of the hemp core fibers was computed by means of micromechanical analysis and was calculated using the ratios between a fiber flexural modulus factor and a fiber tensile modulus factor. The results agreed with those obtained by using models such as Hirsch and Tsai–Pagano. Other micromechanical parameters were studied to fully understand the contribution of the phases. The relationship between the fibers’ intrinsic flexural and Young’s moduli was studied, and the differences between properties were attributed to stress distribution and materials’ anisotropy. View Full-Text
Keywords: hemp core; intrinsic flexural modulus; composites; chemical treatment; polypropylene hemp core; intrinsic flexural modulus; composites; chemical treatment; polypropylene
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MDPI and ACS Style

Serra-Parareda, F.; Espinach, F.X.; Pelach, M.À.; Méndez, J.A.; Vilaseca, F.; Tarrés, Q. Effect of NaOH Treatment on the Flexural Modulus of Hemp Core Reinforced Composites and on the Intrinsic Flexural Moduli of the Fibers. Polymers 2020, 12, 1428.

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