Pretreatment of man-made fibres
Synthetic fibres are usually free from natural impurities but they contain secondary impurities being added during spinning, weaving and knitting processes. These include sizing agents, spin finishes, sighting colours, lubricants, etc. The sizing agents are usually easily removed from synthetic fibres at the desizing stage since these agents are either water-soluble or self-emulsifiable compositions. Therefore the scouring of man-made fibres is easier than natural fibres and most of the impurities mentioned can be removed by mild alkaline conditions in the presence of a surfactant.
Scouring conditions for synthetic fibres:
- Polyester: Scouring can be carried out with alkali (NaOH, etc.) or anionic surfactant depending on impurities.
- Nylon: The scouring conditions are commonly mild alkaline with presence of non-ionic surfactants.
- Acrylic (PAN): Acrylic fibres are sensitive to alkaline conditions; therefore strong alkalis are usually avoided for scouring.
- Viscose: These fibres can be scoured by non-ionic or ionic surfactant and they should be rinsed in less tension as they have poor wet strength.
Bleaching conditions:
- Polyester (PET): Sodium chlorite in acidic pH is preferred for PET bleaching.
- Nylon: Sodium chlorite is the most appropriate bleaching agent for nylon. Nylon should be bleached in acidic conditions due to its sensitivity to basic pH.
- Acrylic (PAN): Acrylic can be bleached with sodium chlorite in acidic pH.
- Viscose: Bleaching with NaOCL or H2O2 can be carried out.
Heat-setting:
Heat-setting is a heat treatment applied for fabrics made of synthetic thermoplastic fibres. During all of the processes from fibre to dyed fabric, the material is subjected to different tensions having resulted in sorted stress within the fibre. If the stresses are not relieved, they will cause an irregular fabric appearance and dimensional instability. Excellent dimension stability and good crease-proof properties will be obtained by this heat treatment followed by cooling at the required fibre dimension. This treatment affects (reduces) the dye-ability of fibres thereby it is extremely important to apply heat-setting uniformly and fabric must be treated in precisely controlled temperature and moisture conditions. This heat-treatment is carried out by passing fabrics through a heating zone for specified temperature (160-170°C) and time (15-50sec) depending on fibre type, fabric density and previous heat story of the fibres.
Stenter is the machine used for heat-setting.
Flexible line for coating and printing
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This resource was developed as part of an Erasmus+ project, funded with support from the European Commission under grant agreement 2016-1-SE01-KA203-22064.
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- The University of Borås, Sweden
- The University of the Highlands and Islands, Scotland
- The University of Alcalá, Spain
- Digital Connections, Scotland
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