Zagovor magistrskega dela
Zagovor magistrskega dela študenta Marcela Hribernika bo potekal 17.12.2020 ob 8.00 preko aplikacije MS Teams (Click here to join the meeting).
SUMMARY: Influence of the Aspect Ratio and Shape of Reinforcement Fibers on the Mechanical Properties of Polyethylene‑Cellulose Composites
This work aimed to determine how different viscose fiber properties (length, diameter, and shape) affect the mechanical properties of viscose fiber-reinforced thermoplastic composites (VFRT). The tested fiber shapes were round, rectangular, and trilobal. The round fibers used were also varied in length and diameter. Different fibers were pelletized, compounded into high-density polyethylene (HDPE), and test specimens were produced by injection molding. VFRT was characterized using a tensile test, the Charpy impact test, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Moreover, fiber lengths in VFRT were determined after each processing step. The fiber length was reduced to a stable length in the range from 0.6 mm to 1 mm during processing, dependent on their linear density and shape. Thicker and round fibers remained longer during processing than other fibers. The melting temperature of the VFRT increased with increasing fiber’s linear density. The width of the melting temperature peak was inversely correlated with VFRT mechanical results. VFRT containing round fibers with the length of 5 mm and diameter of 11.9 mm exhibited the best mechanical performance where tensile strength was increased from 20.7 MPa to 49.9 MPa, and Charpy impact strength increased from 6.6 kJ/m2 to 10.3 kJ/m2 (notched specimens) and from no break to 48.2 kJ/m2 (unnotched specimens) when compared to the neat HDPE. In terms of mechanical performance thinner and longer round fibers performed worse than the thicker ones. Rectangular and trilobal fibers performed worse than round ones, and thinner rectangular fibers were the worst overall. Theoretical tensile strength and elastic modulus of VFRT’s were calculated according to the modified rule of mixtures equations and compared to experimental values. The calculated elastic moduli were higher when compared to the experimental results since equations do not correctly take into account fiber packing properties. Tensile strength calculations were very close to actual measurements but only for the VFRT with the round fibers. For the composites with non-round fibers, the calculated tensile strength was highly overestimated, due to different packing properties in the VFRT.
Keywords:
Fibers, composite, polyethylene, fiber length, aspect ratio, fiber packing volume, tensile strength, impact strength, elastic modulus.
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