polyester.lec

Polyester Overview

  • Polyester is a synthetic fiber widely used in the textile industry

  • Focus on manufacturing methods, properties, and applications

Polyester Fiber Development

  • Developed post-Nylon by researchers at Imperial Chemical Industries (ICI)

  • Dacron® polyester first produced in the U.S. by Dupont in 1953

  • Derived from esters formed from alcohol and acid, specifically polyethylene terephthalate (PET)

Types of Polyester

  • Poly(ethylene naphthalate) (PEN)

  • Poly(butylene terephthalate) (PBT)

  • Poly(trimethylene terephthalate) (PTT)

  • Poly(ethylene terephthalate) (PET): The most prevalent type

Manufacturing Process

  • Raw materials: glycol and terephthalic acid

  • Variations in processing methods depending on polyester types

Polymerization

  • Major polyester: PET, formed from terephthalic acid and ethylene glycol

  • Condensation polymerization is key; dimethyl terephthalate is often used

  • Process includes extruding material into ribbon and cutting into chips

Spinning and Drawing Processes

  • Chips must be dried before melting

  • Melt spinning process extrudes melted polymer through spinnerets

  • Staple Fiber Production:

    • Group filaments and heat/draw them to orient molecular structure and reduce shrinkage

    • Crimping and drying are essential

  • Filament Yarn Production:

    • Continuous fibers may undergo texturing or twisting for strength

Fiber Morphology

  • Macro Structure: Fine, translucent fibers, lengths determined by the yarn package

  • Micro Structure: Lacks identifiable features, resembles glass when magnified

Polyester Polymer Characteristics

  • Linear structure based on PET

  • Degree of polymerization ranges from about 115 to 140

  • Involves polar and non-polar groups, held by van der Waals and weak hydrogen bonds

Physical Properties

  • Tenacity: Generally strong; unaffected by moisture

  • Elastic-Plastic Nature: Stiff, resists wrinkling due to crystalline structure

  • Hygroscopic Nature: Low moisture regain (0.2% to 0.8%); oleophilic, attracting oils and greases

Thermal Properties

  • Melting point similar to Nylon (480 to 550˚F)

  • Thermoplasticity: Can be molded when heated, retains shapes post-cooling

  • Higher second-order transition temperature aids in retaining heat sets

Chemical Properties

  • Acid Resistance: Esters resist acid hydrolysis, maintaining clarity during use

  • Alkali Hydrolysis: Limited to the fiber's surface during washing, sustaining whiteness

  • Sunlight Resistance: Good resistance to UV due to benzene rings in the polymer

Environmental and Mechanical Properties

  • Resistance to Microorganisms: Mildew and moth larvae do not affect polyester

  • Strength: Generally strong, breaking tenacity ranges from 4 to 9.5 g/d

  • Dimensional Stability: Excellent if heat-set; low moisture regain prevents shrinkage

Dyeing Properties

  • Difficult for dyes to penetrate crystalline structure; requires disperse dyes

  • Disperse dyes have good light-fastness and wash-fastness

Applications of Polyester

  • Versatile use in apparel, home furnishings, and industrial products

  • Common in curtains, bedding, outdoor gear, and insulation

  • Applications extend to safety equipment, ropes, and textiles for construction

  • Increasingly used in carpets, though Nylon still preferred for specific applications