Physical properties
① Color. Polyester is generally milky white with mercerizing. For matt products, the matting agent TiO2 needs to be added before spinning. For pure white products, the brightener needs to be added. For colored yarns, pigments or dyes need to be added to the spinning melt.
② Surface and cross-sectional shape. The surface of conventional polyester is smooth, and its cross-section is nearly circular. If the special-shaped spinneret is used, it can be made into fibers with special cross-sectional shapes, such as triangular, Y-shaped, hollow and other special-shaped cross-sectional yarns.
③ Density. When polyester is completely amorphous, the density is 1.333g/cm3. It is 1.455g/cm3 when it is completely crystallized. Polyester usually has a high crystallinity and a density of 1.38~1.40g/cm3, which is similar to wool (1.32g/cm3).
④Moisture regain rate. Under standard conditions, the moisture regain of polyester is 0.4%, which is lower than that of acrylic (1%~2%) and nylon (4%). The hygroscopicity of polyester is low, so its wet strength decreases less, and the fabric has good washability; however, the static phenomenon during processing and wearing is serious, and the fabric has poor breathability and hygroscopicity.
⑤ Thermal 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 a fire, curl, and melt into beads, with black smoke and aromatic smell.
⑥ Light resistance. 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 area, so after 600h of sunlight, the strength only loses 60%, which is similar to cotton.
⑦ Electrical performance. Polyester is poorly conductive due to its low hygroscopicity. The dielectric constant in the range of -100 to +160°C is 3.0 to 3.8, making it an excellent insulator.
