Production and mechanical characterization of reinforced zinc oxide nanoparticle-coated silk waste bio-composites

There has been an increasing trend of using natural fibre reinforcements as an alternative to manmade fibre reinforcements for engineered composite applications. Natural fibres are alternative composite reinforcement materials due to their biodegradability, inexpensiveness, abundance and excellent physical properties. This study aims at analysing the mechanical properties of the fabricated bio-composite from polyester resin reinforced with silk waste fabric. The specific objectives of this work are to characterise physical and mechanical properties of silk waste fabric, fabricate a bio-composite from silk waste fabric treated with zinc oxide nanoparticles and polyester resin and to analyse the static mechanical properties (tensile, flexural and impact). The silk waste fabric is characterized and the composite fabricated using hand lay-up technique and a mould with dimensions 360 × 210 × 4 mm. Central composite design is used in the design of experiments, and the fibre weight fraction was varied from 11 to 25%. Treatment with nanoparticles is done by soaking silk waste fabric in a 6% concentration of zinc oxide nanoparticles and 1% citric acid. A sonicator uses to evenly distribute the nanoparticles in the solvent, and the fabric is coated using the pad dry cure method. The fabricated composites are cured at room temperature for 24 h under consolidated pressure of 2.65 kN/m². The mechanical properties of the composites are determined using D790, D638 and D6110 ASTM standards, whereas the morphology is investigated using a scanning electron microscope. The areal density of the silk waste fabric is 76 g/m², and its tensile strength was 16.80 MPa. The tensile, flexural and impact strengths of uncoated composites are 27.92 MPa, 52.13 MPa and 32.17 kJ/m²_, respectively. The flexural and tensile strengths of the coated bio-composites increase with increasing fibre weight fraction up to peak values of 32.23 MPa and 53.47 MPa, respectively. Bio-composites produced with silk waste fabric treated with nanoparticles had slightly better strengths (tensile 32.23 MPa and flexural 53.47 MPa) compared to bio-composites with non-treated silk waste fabric (tensile 27.92 MPa and flexural 52.13 MPa). The static mechanical properties attained in this study reveal that these bio-composites may be used for non-structural applications for instance partitioning walls and ceiling boards. The study recommended future research studies on increasing the number of plies beyond six with different fabric weave designs of twill, satin, sateen and warp rib and use of thermal evaporation as a coating technique of nanoparticles onto silk waste fabric to establish their effect on mechanical and thermal properties and morphology.