Viscosity. Intrinsic viscosity is an index used in industry to characterize the molecular weight of polyester. Determination of intrinsic viscosity can not only correctly evaluate the quality of polyester, but also provide an important basis of formulating spinning process conditions. Therefore, intrinsic viscosity is an important indicator for selecting textile grade PET Chips.
Carboxyl terminal content. One of the important parameters to measure polyester production. Generally speaking, the source of terminal carboxyl groups is mainly generated from uncreated PTA or after degradation. In theory, the terminal carboxyl groups of fully reacted polyester should be 0. Due to the existence of various factors, the terminal carboxyl groups of polyester chips under various process condition is very different.
Melting point. The melting point of a polyester is the temperature at which a crystalline solid substance changes from a solid to a liquid. It partly reflects the purity of polyester. Generally, pure polyester is a partially crystalline polymer with a melting point of 265℃. In actual production, there are some impurities in polyester due to various side reactions. At the same time, the defects of polymer crystals and differences in crystallinity also affect the melting point of polyester is below 265℃, and the melting point temperature isn’t a fixed value, but a certain range.
Diethylene glycol(DEG) content. Polyester diethylene glycol is an important indicator to measure the degree of etherification side reactions in the production process. From the experimental results, the increase of the content of DEG can reduce the melting point or softening point of polyester, and deteriorate the thermal oxidation resistance and light resistance. Because of the effect of DEG content on polyester and subsequent positive and negative sides, the control content is also different under each production process condition. At present, the consensus of various manufacturers on the content of DEG is that the absolute value of the content of DEG isn’t the main aspect, but the stability of the content, which can reduce the dyeing difference of the produced fibers. For the production of magnetic tapes, video tapes, the DEG content should be lower, which can increase the fatigue strength during use.
Chroma. This is a comprehensive index, which is not only affected by the outside world such as PTA, matting agent and catalyst, but also by the production process of polyester production itself. The B-value in the chromaticity reflects the blue-yellowness of the polyester chips. The smaller the B-value is, the more blue the polyester is, and the higher the yellower. The L-value reflects the grayscale of the slice. The larger the L-value, the brighter the slice, and the smaller the grayer.
Iron content is also an indicator to characterize polyester chips. Generally speaking, the source of iron is PTA, EG, catalyst and matting agent. If the iron content is high, the ash content is also high, which easily affects the color and quality of fiver.
Ash. Ash is the inorganic impurities in polyester, including inorganic impurities from PTA and EG raw materials, catalyst residues, and impurities brought in during TiO2 grinding. Another important aspect is that when bagged PTA is fed, caused by the entry of impurities in the outer bag.
Moisture. The moisture content of the slices refers to the physically bound moisture adhered to the surface of the slices. It is related to the dryness of the slices, storage time, air humidity, environmental stability and other factors. The level of slice moisture not only affects the user’s raw material consumption, but also affects the production of spinning.
Titanium dioxide content. TiO2 is added to polyester products as a matting agent, and its dosage is determined according to the needs of users.