1. Physical Properties

① Color. Polyester is typically milky white with a silky sheen. To produce matte products, a light-diffusing agent, TiO2, must be added before spinning. For pure white products, a whitening agent is required. And for colored filaments, pigments or dyes are added to the spinning melt.

② Surface and cross-sectional shapes. Conventional polyester has a smooth surface and a nearly circular cross-section. By using special-shaped spinnerets, fibers with unique cross-sectional shapes can be produced, such as triangular, Y-shaped, and hollow sections.

Polyester has a density of 1.333 g/cm3 in its completely amorphous state and 1.455 g/cm3 in its fully crystalline state. Polyester typically has a high degree of crystallinity, with a density ranging from 1.38 to 1.40 g/cm3, similar to wool (1.32 g/cm3).

④ Resin moisture regain rate. The standard moisture regain rate of polyester is 0.4%, lower than acrylic (1%~2%) and nylon (4%). Polyester has low hygroscopicity, so its wet strength decreases less, making the fabric easy to wash and wear; however, static electricity is severe during processing and wearing, resulting in poor fabric breathability and moisture absorption.

⑤ Thermal Properties. Polyester has a softening point T of 230-240°C, a melting point Tm of 255-265°C, and a decomposition point T of approximately 300°C. It can burn in fire, curl, and melt into beads, emitting black smoke and a fragrant aroma.

⑥ Lightfastness. Its lightfastness ranks second only to acrylic. The lightfastness of polyester is related to its molecular structure, as polyester has a strong absorption band only in the 315nm light wavelength region, resulting in a strength loss of only 60% after 600 hours of sunlight exposure, which is similar to cotton.

⑦ Electrical Properties. Due to its low moisture absorption,涤纶has poor conductivity. Its dielectric constant ranges from 3.0 to 3.8 within the temperature range of -100 to +160℃, making it an excellent insulator.

2. Mechanical Properties

High strength. Dry state strength ranges from 4 to 7 cN/dex, while it decreases in the wet state.

② Moderate in extension, ranging from 20% to 50%.

③ High Modulus. Among large varieties of synthetic fibers, polyester boasts a high initial modulus, which can reach up to 14~17 GPa. This characteristic ensures the dimensional stability of polyester fabrics, preventing deformation and maintaining their shape, as well as long-lasting pleats.

④ Excellent elasticity. Its resilience is close to wool, and it can almost fully recover after stretching by 5% and removing the load. Therefore, polyester fabrics have better wrinkle resistance than other fiber fabrics.

⑤ Abrasion resistance. Its abrasion resistance is only second to nylon and exceeds other synthetic fibers, with nearly identical abrasion resistance.

3. Chemical Stability. The chemical stability of polyester mainly depends on the molecular chain structure. Apart from poor alkaline resistance, polyester exhibits excellent resistance to other reagents.

① Acid resistance. Polyester is stable against acids, especially organic acids. Its strength is unaffected after being soaked in a 5% hydrochloric acid solution at 100℃ for 24 hours or in a 70% sulfuric acid solution at 40℃ for 72 hours. However, it cannot resist the prolonged action of concentrated nitric acid or sulfuric acid at room temperature.

②Alkali Resistance. Due to the ease of hydrolysis of the ester groups on the polyester macromolecules under alkaline action, the fibers can be damaged when exposed to concentrated alkali at room temperature or dilute alkali at high temperatures. Only under low temperatures are they relatively stable with dilute or weak alkali.

③ Solvent Resistance. Polyester exhibits strong resistance to general non-polar organic solvents, and even shows robust resistance to polar organic solvents at room temperature. For instance, when immersed in acetone, chloroform, toluene, trichloroethylene, and carbon tetrachloride for 24 hours at room temperature, the fiber strength remains unaffected. Under heated conditions, polyester can dissolve in mixtures such as phenol, cresol, ortho-dichlorophenol, benzyl alcohol, nitrobenzene, and mixtures of phenol with tetrachloroethylene, chloroform, or toluene.

4. Resistance to Microorganisms.涤纶 is resistant to microbial action, making it immune to pests and mold. Storing polyester clothing does not require pest prevention, and fabric preservation is relatively easy.