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(ii) Polyester fabrics maintain their smooth appearance / creases well throughout the working day thus maintaining the smart and confidant appearance of the wearer. Polyester fabrics do not get crumpled even if the person wearing sleeps in them.
(iii) Dyes and prints on polyester fabrics are fast to repeated washings / dry cleanings and do not fade over years of use..
(iv) Polyester fabrics do not shrink or lose their shape on long usage. And
(v) Polyester offers a wide range of speciality fibres - and the list is growing.
1.3 Polyester has its share of disadvantages too. The major drawbacks are:
(i) It generates static charge - particularly in dry weather. This charge attracts dirt and dust, which fortunately are not held tenaciously.
(ii) If proper precautions have not been taken, polyester fabrics could generate pills in places where repeated rubbings take place.
(iii) Polyester's very low moisture absorbency can lead to considerable discomfort to the wearer particularly in hot, humid atmosphere and if the wearer is doing a vigorous physical activity, the RH at skin level then could go well above 80 - 85%. A wearer is comfortable only if RH at skin level is held below 50 % and
(iv) White polyester tends to turn 'yellow' after long exposure to bright sun light.
1.4 Speciality polyester fibres are essentially modified polyester fibres and have at least one property which fully covers one of polyester's disadvantage e.g. Antistatic or conducting fibres do not generate static charge, anti pill fibres produce pill free fabrics, moisture management fibres carry perspiration out very fast thereby maintains RH at skin level at a comfortable level and Optically Bright or White fibres ensure very slow yellowing of the white fabrics. Apart from these, there are several other specialities like flame retardant, anti bacterial, UV Block etc, which give some very special property to the fabrics made - and what is important is that all the fabrics from speciality polyester fibre do have all the good properties of the standard polyester fabrics.
1.5 Several methods are used to make speciality fibres. These are:
(i) Adding a specific chemical / compound during polymerization. Thus the special property conferred is permanent, fast to any number of washes / dry cleanings, as the specific chemical becomes an integral part of the fibre. Examples are: Flame retardant fibre wherein a derivative of phosphoric acid is added and anti bacterial / anti fungal fibres where another additive is added.
(ii) Alterations to polymer quality - like lowering of Intrisic Viscocity (IV) for making antipill fibres
(iii) Making changes in the manufacturing process - examples are micro denier fibres and sewing thread fibres.
(iv) Modifying the cross section of the fibre - examples are single and multiple hollow, trilobal, triangular, pentalobal, octalobal, flat, kidney shaped and dog bone shaped fibres. There are also serreated fibres and in plus sign shape and
(v) Addition of a suitable colorant like carbon black and pigments. To give dope dyed fibres in black and over 60 shades covering the full range of a rainbow. Black, of course, is the most popular fibre in this range.
1.6 Only a few polyester fibre manufacturers offer a range of specialities. Some of these are: Toray, Teijin and Unitika from Japan, Saehan in Korea, Nan Ya Plastics of Taiwan, Penfibre from Malaysia, Thai Teijin in Thailand, Sasa of Turkey, Hoechst in Germany and Wellman from USA. Information on quantities of Speciality Fibres made is not easily available.
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