Polyester fibres are defined as a manufactured fibre in which the fibre- forming substance is any long- chain polymer composed of at least 85% by weight of an ester of dihydric alcohol and terepthalic acid (FTC definition) (34).
Polyester staple fibres are used in several types of non- wovens , without the need for an intermediate yarn spinning operation.Polyester staple nonwovens in industrial applications are fibrefill and high loft nonwovens , needled nonwovens and felts, stitchbonded nonwovens and light – weight carded, spunlaced and wet laid fabrics . (35)
Polyester fibres have many important properties which made it suitable for geotextiles.
The strength , breaking tenacity of 4 to 7 g/d ,and abrasion resistance of polyesters are quite high, therefore strong fabrics can be made from them. (36)
Specific gravity of polyester fibres (1.38 g/cm3) is moderate, therefore fabrics made from polyesters are medium in weight
Polyester fibres have very good dimensional stability , but they may shrink at very high temperatures. (37)
4-Elasticity and resilience
The elasticity of polyester is generally good as polyester recovers well from stretching . Resilience of polyester fibres is excellent ( good recovery from wrinkling) (38).
Polyester is virtually unaffected by rain, seawater or other forms of water This is due to that moisture absorption of polyester is only 0.4% at room temperature and 65% relative humidity . Even at 95% humidity , less than 0.6% moisture is absorbed . Because of this, polyester geotextiles will not get heavy when wet , will not mildew , and will dry very quickly.
The mechanical properties of wet polyester geotextiles are the same as dry. There is no strength loss, elongation is not affected, there is no change in abrasion resistance , and there is no growth or shrinkage ( elasticity is not affected). (29)
Another property critical to geotextile performance in some applications is chemical resistance. Generally speaking , polyester geotextiles have excellent stability to many chemical classes such as salts, organic acids, organic solvents, oxidizing agents, reducing agents, gases and fuels ( petroleum).
Polyester fibres have outstanding thermal properties . They melt in the range of 478-490 0 F, crystallize at 250-265 0 F, all well above normal conditions encountered in geotextile applications . In addition , polyester fibres maintain excellent flexibility and strength at temperature below freezing. (29)
8-Resistance to microorganisms, insects, and aging.
Bacteria, mildew, and moth larvae will not attack polyesters. Age has no appreciable effect on polyester. (37)
For up to 400 hours of direct sunlight, untreated polyester will retain greater than 90 % of its strength . In the long term , the ultraviolet degradation of polyester slows down and can level out. Half the strength remains after 4000-5000 hours. (29)
Generally, because of polyester ̉s excellent chemical and physical properties , this material can be used with confidence and is the material of choice for most geotextile applications.