1. Physical Properties

① Color. Polyester is typically milky white with a silky sheen. To produce matte products, a TiO2 desiccant is added before spinning. For pure white products, a whitening agent is required. To create colored fibers, pigments or dyes are added to the spinning melt.

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

③ Density. Polyester has a density of 1.333g/cm3 in its completely amorphous state and 1.455g/cm3 when fully crystalline. Polyester typically exhibits a high degree of crystallinity, with a density ranging from 1.38 to 1.40g/cm3, which is similar to wool (1.32g/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, resulting in minimal decrease in wet strength and good wash-and-wear fabric properties; however, static phenomena are severe during processing and wearing, and the fabric has poor breathability and moisture absorption.

⑤ Thermal properties. The softening point of polyester is T230-240°C, the melting point Tm is T255-265°C, and the decomposition point is approximately T300°C. Polyester can burn in fire, curl, and melt into beads, emitting black smoke and a fragrant odor.

⑥ Lightfastness. Its lightfastness is only slightly inferior to acrylic. The lightfastness of polyester is related to its molecular structure; polyester has a strong absorption band only in the 315nm light wave range, so after 600 hours of sunlight exposure, its strength loss is only 60%, which is comparable to cotton.

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

2. Mechanical Properties

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

② Moderate extension, 20% to 50%.

③ High modulus. In large varieties of synthetic fibers, the initial modulus of polyester can reach up to 14~17 GPa, making the fabric dimensionally stable, non-deforming, and retaining its pleats for a long time.

④ Excellent elasticity. Its elasticity 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 second only to nylon and exceeds other synthetic fibers, with nearly identical wear resistance.

3. Chemical Stability. The chemical stability of polyester mainly depends on the molecular chain structure. Besides poor resistance to alkalis, polyester exhibits excellent properties against other reagents.

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

②Alkali Resistance. Due to the ester groups on the polyester macromolecules being easily hydrolyzed by alkali, the fiber can be damaged when exposed to concentrated alkali at room temperature or dilute alkali at high temperatures. Only under low temperatures does the fiber exhibit stability with dilute or weak alkali.

③ Solvent Resistance. Polyester exhibits strong resistance to general non-polar organic solvents, even showing 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 does not degrade. Under heated conditions, polyester can dissolve in phenol, xylenol, o-dichlorophenol, benzyl alcohol, nitrobenzene, etc.

Benzene and phenol in mixtures with carbon tetrachloride, chloroform, toluene, and other solvents.

4. Resistance to Microorganisms. Polyester is resistant to microbial action, unaffected by pests such as moths and mold. There is no need to prevent moth infestation when storing polyester clothing, making fabric preservation easier.