Man Made Fibe Prduction

MAN MADE FIBRE PRODUCTION –

Manmade fibres can be modified at any stage during production for Ex: Addition of pigments and delustrants Immediately after production Ex: By drawing, crimping or the application of finishes

All man made fibres are produced from polymers These substances are solids at normal temperatures in the form of chips or small particles The polymers in solid form must be converted to liquid form as the polymer needs to be forced through fine holes to form filaments The Process of producing man made fibre is known as Spinning The process of converting staple fibres in to yarn is called as Spinning Therefore the process of manufacturing man made fibre is described as extrusion spinning

There are three methods of extruding man made fibres: Melt Extrusion Solvent-dry extrusion Wet extrusion The method used for each fibre depends upon the ease of Conversion of the polymer from solid to liquid state. Melt Extrusion: Polymer converted to liquid just by heating: Solvent-dry extrusion: If Polymer is getting chemically damaged by heating but it can be dissolved in a suitable solvent which later on evaporates Wet extrusion: Polymers cannot be melted by heat or dissolved In solvent which will evaporate later

Melt Extrusion: Polymer converted to liquid just by heating: Simplest process used for Polyester, Polyamide and Poly Propylene Required characteristics of fibre for melt spinning: Fibres should be thermo plastic Fibres must melt without decomposition and be stable to at least 30 degree higher than its melting point Mobility in the molten polymer is necessary to be extruded

Stages in Melt Spinning Process: Heating of the polymer Extrusion through the spinneret(50mm in diameter) having fine holes of 0.5mm diameter 1-50 holes for filament production and 1-100 holes for tows for production of staple fibres Filaments emerges out in to a stream of cool air which causes it to solidify

The solidified bundle of filaments are passed around a rotating roller (POY- Partially oriented yarn) and forwarded to a collecting roller. Extrusion rates are generally 1000meters per minute Further drawing is required for complete orientation of polymer in heat drawing method Conditioning and Spin finish( application of oil as lubricant) is given to the fibres finally after cooling to allow the fibres to absorb moisture and to create non electrostatic properties. For staple fibre production, the filaments are given a crimp and then cut in the process known as tow to top conversion mostly used by the worsted spinners

Solvent - Dry Extrusion: Solvent-dry extrusion: If Polymer is getting chemically damaged by heating but it can be dissolved in a suitable solvent which later on evaporates Least used of the major fibre production techniques The obvious limitation for this method is that it depends on the existence of volatile solvent for the polymer.

•Dissolution •Additions of pigments or delustrants •Filtration •Deaeration •Extrusion under the presence of heat • Evaporation of solvent in the presence of Nitrogen gas or hot air • Washing and Drawing •Recovery and Recycling of the Solvent for economic as well as environmental reasons Cellulose diacetate: Acetone as solvent low boiling Cellulose Tri acetate: Dichloro methane point Acrylic fibres: Dimethyl formamide: high boiling point of 157C (Poly acrylonitrile and mod acrylics) Alters the cross section of the filament

Holes in the spinneret should be widely spaced so that evaporation of solvent can be faster Solvents are expensive, flammable and explosive in reaction with air 3-6kg of solvent for 1kg of filament

Wet extrusion: Polymers cannot be melted by heat or dissolved in volatile solvent (which will evaporate later ) Polymer is dissolved in a non-volatile solvent There are two types of wet extrusion 7. Physical process and 8. Chemical regeneration and Physical process In both the processes the filaments will be extruded in to a Chemical bath or coagulation bath This is a slow process (30-80 meters) due to the less drag forces on the filaments

Physical process: • Polymer solution or dope • De aeration • Filtration • Extrusion through the spinneret immersed in to a coagulation bath • Washing • Drawing and • After treatment Spinnerets are made with precious metal alloys as it should be resistant to corrosion. The hole size is much smaller with large no. of holes like 20,000 holes in a spinneret of 7.5cm diameter

Chemical regeneration and Physical Process: Ex: Viscose Rayon: The natural polymer “Raw cellulose” cannot be dissolved in its original form. It must be dissolved and chemically changed to • Soda cellulose • Oxidisation –to reduce molecular chain lengths to suitable levels • Carbon disulphide –to form cellulose xanthate • Alkali –to dissolve Xanthate to form brown Viscous liquid known as Viscose • Filtration • Xanthate left to degrade back to cellulose • Extrusion in to a coagulating bath containing acid to nutralise