Saving marine resources
Every year, seven lakh tons of fishing nets enter marine ecosystems worldwide. These nets are either lost or intentionally discarded in adverse weather conditions to reduce weight. The nets drift around and whales, propellers and rudders often get entangled in them. As fishnets are not easily degraded, they survive for several years in the marine ecosystem, polluting the sea and endangering marine life.
Michael Raj from the Stella Mary’s College of Engineering, Azhikal and researchers from the University College of Engineering and the St. Xavier’s Catholic College of Engineering, Nagercoil thought of reusing discarded nets as a substitute for fibreglass to build boats.
They collected fishnets from the sea, washed off the salts and sun-dried them. For the experiments, they used multifilament fishnets of three different mesh sizes: 16, 32 and 60 millimeters.
They combined the fish nets with fibreglass in different combinations and made composite specimens with unsaturated polyester as matrix, methyl ethyl ketone peroxide as catalyst and cobalt naphthenate as accelerator.
They prepared ten such composite specimens with a different number of layers each, different fishnet mesh sizes and varying amounts of fibreglass. And they tested tensile strength, impact resistance, flexural strength, modulus and elongation at break.
The team found that fishnet composites have high flexural strength – the tendency of a material to bend without deformation. The composites also have good fibre matrix interfacial adhesion which strengthened the material and bonded well with it. The researchers found that smaller mesh size gave more fishnet fibre, improving stress transfer. When mesh size increases, interfacial adhesion decreases. Therefore, flexural strength, interfacial adhesion and modulus depend on mesh size.
The team also noted higher tensile strength and elastic modulus in fibreglass composites than in fishnet fibre. However fishnet fibre composites have more impact resistance, essential to withstand turbulent waves during adverse conditions at sea.
From the results of their experiments, the team conclude that the partial substitution of fibreglass with 16 millimeter mesh size fishnet fibre produces composites with better mechanical properties than fibreglass alone.
Partially substituting fibreglass with fishnet in composites for making boats can save costs, says Michael Raj, Stella Mary’s College of Engineering, Azhikal.
Recycling abandoned fishnets can help reduce pollution and make marine resources more sustainable, says Vinod Kumar, University College of Engineering, Nagercoil.
Boat makers can now save money and make more durable boats.
SHIPS AND OFFSHORE STRUCTURES, 14 (4): 412-419 (2019)
Siranjothi K, MSSRF