PSI - Issue 80

Hideaki Katogi et al. / Procedia Structural Integrity 80 (2026) 462–470 Hideaki Katogi / Structural Integrity Procedia 00 (2019) 000–000

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conducted for discussion. In addition, the fracture morphology of the biocomposite material was observed after tensile test. 2. Experimental method 2.1. Materials The reinforcement was a single flax yarn. Matrices were water dispersion-type poly(lactic acid) (PL-1005, Miyoshi Oil & Fat Co., Ltd.) and ethanol dispersion-type shellac resins (A-25, Gifu Shellac Manufacturing Co., Ltd.). Figure 1 shows the surface of a single flax yarn. The twist angle on surface of single flax yarn as reinforcement was measured by optical microscope. The twist angle on surface of single flax yarn was about 12 °. The average diameter of single flax yarn was about 170 um. 2.2. Molding method The prepreg using a single flax yarn was used for fabrication of biocomposite material. The single flax yarn aligned to longitudinal direction. The surface on a single flax yarn was supplied by water-dispersion type poly(lactic acid) and ethanol dispersion–type shellac resins for fabrication of biocomposite material. The dry process of matrix supplied single flax yarn was conducted under room temperature for prepregs using water-dispersion type poly(lactic acid) and ethanol dispersion–type shellac resins. Resin weight fractions of biocomposite materials using poly(lactic acid) and shellac resins were about 25 wt%. As a molding condition, the molding method was compression molding method. The molding pressure was about 25 kPa. The molding temperature was 180 °C. The molding time was 20 min. Specimen sizes of biocomposite materials using reinforcement and matrics was 150 mm long. Figure 2 shows specimens after molding process. 2.3. Tensile testing method and scanning electron microscope observation The tensile test of biocomposite material was conducted under constant temperature and humidity room. The environmental temperature was 20 °C. The humidity was 65 %RH. The crosshead speed was 10-100 mm/min. The testing machine was RTS-1310A (A&D Co., Ltd.). The gauge length of specimen was 100 mm. Microfracture morphologies of single flax yarn reinforced biocomposite materials were observed by scanning electron microscope after tensile tests. The scanning electron microscope was S-1140N (Hitachi High-Tech Co., Ltd.). 3. Results and discussion Figure 3 shows tensile properties of a single flax yarns at 10 mm/min and 100 mm/min. Tensile strength and Young’s modulus of a single flax yarn at 10 mm/min were about 252 MPa and about 11 GPa, respectively. Tensile strength and Young’s modulus of a single flax yarn at 100 mm/min were higher than those of a single flax yarn at 10 mm/min. The Young’s modulus of a single flax fiber was about 35 GPa [32] when the length of a single flax fiber was 20 mm. Then, the tensile strength of a single flax fiber was about 530 MPa [32]. But a single flax yarn as reinforcement has the spiral structure comparison with a single fiber structure [33, 34]. And a single flax fiber mainly consists of cellulose. So, the tensile property of a single flax yarn was affected by constituent material and spiral structure under loading speed. Figure 4 shows effect of loading speed on tensile properties of biocomposite materials using single flax yarn and biopolymers. Tensile strengths of biocomposite materials using poly(lactic acid) and shellac resins were about 58 MPa and about 46 MPa, respectively. The tensile strenth of biocomposite material using shellac resin at 100 mm/min was higher than that of biocomposite material using shellac resin at 10 mm/min. Particularly, the tensile strenth of biocomposite material using poly(lactic acid) resin 100 mm/min was greater than that of biocomposite material using poly(lactic acid) resin at 10 mm/min. Young’s moduli of biocomposite materials using poly(lactic acid) and shellac resins at 10 mm/min were about 12 GPa and about 7 GPa, respectively. The Young’s modulus of all biocomposite materials at 100 mm/min were higher than of all biocomposite materials at 10 mm/min. The tensile