engleski

Effect of fiber treatment with naoh solution on mechanical properties of flax fabric/epoxy composites for marine application

Mechanical properties of flax fibers/polymer composites are one of the critical concerns regarding the acceptance of bio-composites for marine application. The properties strongly depend on adhesion between the reinforcement and the matrix. The bonding between untreated hydrophilic fibers and hydrophobic polymer matrices is insufficient leading to poor wettability. Fibers that undergo alkaline treatment are proven to exhibit improved fiber-matrix interfacial adhesion. In this study, biaxially oriented (90°) flax fibers are treated with alkaline solution with mass fractions of 2%, 5%, 10% and 15% NaOH dissolved in distilled water for 1 hour at room temperature. Flax fabric/epoxy composites are manufactured by hand lay-up. Tensile tests, flexural and apparent interlaminar shear strength tests were performed on epoxy based composites with fibers oriented at ±45°. The properties of composites reinforced with 3 plies of treated and non-treated fibers were compared to the demands declared by Croatian Ship Registry (CSR). None of the composites prepared fulfill the demands. However, the maximal loads applied to the treated composites were doubled compared to the untreated. The insufficient properties are the consequence of (i) shrinkage of fibers due to the treatment and a higher resin absorbance leading to an increase in composite thickness of nearly 60% and consequently to a reduction in fibers content and (ii) fibers were not oriented in the load direction. The results show that among treated composites, the best properties are achieved for those treated with 2 and 5 wt.% NaOH solutions. For the former the tensile and flexural moduli, tensile and flexural strength and the apparent interlaminar shear strength were 85%, 93%, 96%, 38% and 67% of the values recommended by the CSR, respectively. Improving the hand lay-up moulding and orienting the fibers in different directions, would lead to the composite acceptable for marine application.

bio-composites, flax fibers, epoxy, alkaline treatment, mechanical properties, marine application

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