Polyesters are those fibers containing a minimum of 85th of a polymeric organic compound of a substituted aromatic carboxylic acid together with, however not restricted to, terephthalic acid and p-hydroxybenzoic acid. the most important polyester in commerce is polyethylene terephthalate, an ester fashioned by step growth polymerization of terephthalic acid and therefore the diol ethylene glycol. Poly-1,4- cyclo hexylene dimethylene terephthalate is that the polyester of additional restricted usage and is made through the step growth polymerization of terephthalic acid with the additional complex glycol 1,4-cyclohexylenedimethanol. The polyester fibers all have similar properties, are extremely resilient and immune to wrinkling, possess high sturdiness and dimensional stability, and are resistant to chemical and environmental attack.
 |
Fig 1: Structure of Polyethylene terephthalate polyester |
Polyethylene terephthalate polyester is that the leading synthetic fiber in production volume and owes its quality to its skillfulness alone or as a blended fiber in textile structures. Once the term "polyester" is employed, it refers to the present generic kind. it's used extensively in woven and knitted apparel, home furnishings, and industrial applications. Modification of the molecular structure of the fiber through texturizing and or chemical finishing extends its quality in numerous applications.
 |
Fig 2: |
1. Structural Properties
Polyethylene terephthalate (Fig. 1) is made through step-growth polymerization of terephthalic acid or dimethyl terephthalate with ethylene glycol at 250°-300°C within the presence of a catalyst to a DP of 100-250.
The resultant polymer is isolated by cooling and solidification and dried. Polyester fibers are melt-spun from the copolymer at 250°-300°C, followed by fiber orientation, and stretching. The polyester molecular chains are fairly stiff and rigid as a result of the presence of periodic phenylene groups on the chain. The polyester molecules among the fiber tend to pack gently and control along by van der Waals forces. The polyesters are extremely crystalline unless comonomers are introduced to disrupt the regularity of the molecular chains. Polyester fibers are typically smooth and rodlike with round or trilobal cross sections (Fig. 2).
2. Physical Properties
Polyester from polyethylene terephthalate is an especially strong fiber with a tenacity of 3-9 g/d (27-81 g/tex). The elongation at break of the fiber varies from 15 August 1945 to 500th looking on the degree of orientation and nature of crystalline structure among the fiber. The fiber shows moderate (80%-95%) recovery from low elongations (2%-10%). The fiber is comparatively stiff and possesses excellent resiliency and recovery from bending deformation. The fiber features a relative density of 1.38. The fiber is kind of hydrophobic; with wet regain of 0.1%-0.4% underneath normal conditions and one.0% at 2I °C and 100% RH. it's swollen or dissolved by phenols, chioroacetic acid, or sure chlorinated hydrocarbons at elevated temperatures. The fiber exhibits moderate heat conductivity and has high resistivity, resulting in depth static charge buildup. On heating, the fiber softens within the 210°-250°C vary with fiber shrinkage and melts at 250°-255°C.
3. Chemical Properties
Polyethylene terephthalate polyester is extremely resistant to chemical attack by acid, bases, oxidizing and reducing agents, and is only attacked by hot concentrated acids and bases. Biological agents don't attack the fiber. On exposure to sunlight, the fiber slowly undergoes oxidative attack without color modification with an accompanying slow loss in strength. The fiber melts at regarding 250°C with only restricted decomposition.
4. Polyester End-Use Properties
Polyester has the following properties:
1. The staple is the most common form because filaments tend to crush and not recover.
2. Polyester possesses good strength and durability characteristics but exhibits moderate to poor recovery from stretching.
3. Polyester's durability is better than wool.
4. Its abrasion resistance is good.
5. It has a LOI of 21.
6. It is a moderately flammable fiber that bums on contact with a flame, but melts drips and shrinks away from the flame.
7. Static build up occurs.
8. The fiber is hydrophobic and nonabsorbent without chemical modification.
9. Due to its hydrophobicity and high crystallinity, polyester is difficult to dye and special dyes and dyeing techniques must be used.
10. When dyed, polyester generally exhibits excellent colorfastness properties.
11. Oily soil is retained unless treated with appropriate soil-release agents.
12. It has excellent resistance to most household chemicals and is resistant to sunlight-induced oxidative damage.
13. It has a bright translucent appearance unless a delusterant has been added to the fiber.
14. Polyester is often made from recycled materials.
15. Stain resistance is good.
No comments:
Post a Comment