1.   Physical properties
① color.   Polyester is generally milky white with mercerization.   To produce matte products, it is necessary to add matting agent TiO2 before spinning.   To produce pure white products, it is necessary to add whitening agent.   To produce colored silk, it is necessary to add pigments or dyes to the spinning melt.
② surface and cross-sectional shape.   Regular polyester has a smooth surface and a nearly circular cross-section.   If special-shaped spinnerets are used, fibers with special cross-section shapes can be made, such as triangular, Y-shaped, hollow and other special-shaped cross-section filaments.
③ density.   When polyester is completely amorphous, its density is 1.333g/cm3.   When fully crystallized, it is 1.455g/cm3.   Generally, polyester has a high degree of crystallinity, and its density is 1.38~1.40g/cm3, which is similar to wool (1.32g/cm3).
④Moisture regain.   Under standard conditions, the moisture regain of polyester is 0.4%, which is lower than that of acrylic (1%~2%) and nylon (4%).   Polyester has low hygroscopicity, so its wet strength decreases less, and the fabric has good washability and wearability;   but the electrostatic phenomenon is serious during processing and wearing, and the fabric has poor air permeability and hygroscopicity.
⑤Thermal performance.   The softening point T of polyester is 230-240°C, the melting point Tm is 255-265°C, and the decomposition point T is about 300°C.   Polyester can burn in fire, curl up, and melt into beads, with black smoke and fragrance.
⑥Lightfastness.   Its light resistance is second only to acrylic.   The light resistance of polyester is related to its molecular structure.   Polyester only has a strong absorption band in the 315nm light wave region, so its strength only loses 60% after 600 hours of sunlight exposure, which is similar to cotton.
⑦ electrical properties.   Due to its low hygroscopicity, polyester has poor electrical conductivity, and its dielectric constant is 3.0~3.8 in the range of -100~+160°C, making it an excellent insulator.
2.   Mechanical properties
① High strength.   The dry state strength is 4~7cN/dex, and the wet state decreases.
② moderate elongation, 20% to 50%.
③ High modulus.   Among the large varieties of synthetic fibers, the initial modulus of polyester and its value can be as high as 14~17GPa, which makes the polyester fabric dimensionally stable, no deformation, no aliasing, and long-lasting pleats.
④ Good resilience.   Its elasticity is close to that of wool, and when it is stretched by 5%, it can recover almost completely after unloading.   Therefore, the wrinkle resistance of polyester fabric is better than that of other fabrics.
⑤ wear resistance.   Its wear resistance is second only to nylon, but surpasses other synthetic fibers, and its wear resistance is almost the same.
3.   Chemical stability.   The chemical stability of polyester mainly depends on the molecular chain structure.   In addition to poor alkali resistance, polyester has excellent resistance to other reagents.
①Acid resistance.   Polyester is very stable to acids (especially organic acids).   After soaking in a hydrochloric acid solution with a mass fraction of 5% at 100°C for 24 hours, or at 40°C for 72 hours in a sulfuric acid solution with a mass fraction of 70%, its strength There is no loss, but it cannot resist the long-term action of concentrated nitric acid or concentrated sulfuric acid at room temperature.
② Alkali resistance.   Because the ester group on the polyester macromolecule is easily hydrolyzed by alkali.   The fiber can be damaged by the action of concentrated alkali at room temperature and dilute alkali at high temperature, but it is relatively stable to dilute alkali or weak alkali at low temperature.
③Solvent resistance.   Polyester has strong resistance to general non-polar organic solvents, even to polar organic solvents at room temperature.   For example, soaking in acetone, chloroform, toluene, trichlorethylene, carbon tetrachloride for 24 hours at room temperature will not reduce the fiber strength.   In the heated state, polyester is soluble in phenol, xylenol, o-dichlorophenol, benzyl alcohol, nitric acid
Benzene and phenol-carbon tetrachloride, phenol-chloroform, phenol-toluene and other mixed solvents.
4.   Microbial resistance.   Polyester is resistant to microorganisms and is not affected by moths and molds.   It is not necessary to protect polyester clothes from moths, and the fabric is easier to preserve.