Fishing and Gear Technology

Unit 2 - Fishing gear materials

2.3.Synthetic fibre
The development of synthetic fibres was started around 1920 by H. Staudinger, a winner of Nobel Prize for chemistry in 1953. He found that all fibrous material consists of chain of molecules in which a great number of equal simple units are linked together. Synthetic fibres are man made fibre manufactured by chemical synthesis of simple substance like phenol, benzene, acetylene, prussic acid. Depending on the type of polymerization, 4 different groups of compounds can be identified.

• Poly condensation: Water is eliminated. eg. Polyamide (PA), Poly ester (PES), Terrylene, etc.
• Polymeric compound: water is not eliminated. Polyvinyl chloride (PVC), Polyvinyl Alcohol (PVA), Polyvinylidin Alcohol (PVAA).
• Mixed polymers: These are formed by co-polymerisation of mixture of vinylidene and vinyl alcohol. PVD, Polyamolidine chloride.
• Poly additive compound

Physical properties:

• Density: It is the mass per unit when and is expressed (g/cm3). Fibres with low density like PE(0.96), PP (0.91) float in water and hence hold more weight. Low density material gives more length/weight and vice versa. This property of the material is significant in construction of certain gear like purse seine. The sinking speed of the gear increase with the increase in the density of the material.
• Breaking strength: This is the maximum force applied to a specimen causing it to rapture or break. It is expressed in kg and special equipment known as Breaking strength testers/Dynometer are used for determining is expressed in terms of tenacity and tensile strength.
• Tenacity: It is the Breaking strength per unit denier and Tenacity = Breaking loading / Total density
• Tensile strength: It is the Breaking strength per unit area and expressed as kg/mm2.In wet condition PA & PVAA loose breaking strength and PES, PE and PP remain unaffected.
• Elastic property: Elasticity is a property of a material by virtue of which it tends to recover its original length and shape after removal of the stress.
• Extensibility: This is the property of a material to undergo extension/elongation under the influence of a force.
• Water absorption: This is the property of netting material to absorb water when it is immersed in water and expressed as % of dry weight. Natural fibres absorb more water where as synthetic materials do not absorb water.
• Shrinkage: This is the reduction in length of a material due to wetting. Shrinkage is not a major problem in synthetic fibres.
• Abrasion resistance: This is the resistance of a material to wear off any part when rubbed against any surface. The abrasion resistance of vegetable fibre is comparatively less. Staple fibre show lower resistance to abrasion than continuous fibres.
• Sinking speed: This is the speed at which material sinks through the water. It is important in purse seine.
• Visibility: It is the property of the netting material to be seen in water during operation. This property is relevant for gears like gill net. Veg. fibre is more visible than synthetic fibres. Mono filament is almost invisible as it as transparent.
• Melting point: This is the property of heat resistance of the material. The melting point and shrinking are important factors while dying the fibres. PA & PES are more heat resistant than PE & PP.
• Weather resistance: This is the property of the materials to with stand the effect of sun light, rain, wind, smoke and gases and other atmospheric element. Natural materials are more resistant than synthetic. The rate of deterioration is measured in terms of breaking strength.