The physical properties of polyester chips are closely related to their quality. Except for intrinsic viscosity (IV), what are other important physical properties of polyester chips?
Intrinsic Viscosity (IV)
Generally speaking, the IV for textile-grade PET chips is 0.645. The viscosity is used to characterize the molecular weight of the polymer in industry. IV measurement can not only correctly evaluate the quality of polyester, but also formulate spinning process conditions. If IV is too low, the molecular weight will be small. Then stretching will be very difficult during the spinning process. What’s worse, yarn will be lack spinnability and even prone to breakage. On the other hand, the high IV brings large tensile stress during stretching. To sum up, the intrinsic viscosity has an impact on the spinning stability, filament evenness, and dyeing uniformity. Therefore, ensuring IV stability is of great help to improve the quality of spinning.
The -COOH content is also an important parameter to measure polyester quality. Generally speaking, the source of terminal carboxyl groups mainly comes from the unreacted PTA or the material after degradation. In theory, the COOH content should be zero in the fully reacted polyester. But actually, due to the existence of various factors, COOH content is very different under various process conditions. The national standard is M±4, and the M value is from 18 to 36, which is a very loose index. Generally speaking, in terms of process conditions, the DuPont device has a high-end carboxyl group content, while the China Textile Institute process has a lower one.
The melting point of polyester is the temperature at which a crystalline solid substance changes from solid to liquid. It reflects the purity of polyester to a certain extent. Generally speaking, pure polyester is a partially crystalline polymer with a melting point of 265℃. In actual production, due to various side reactions, there are some impurities in the polyester. At the same time, the defects of the polymer crystal and the difference in crystallinity will also affect the melting point of the polyester. The actual melting point of the polyester is below 265°C, and the melting point temperature range is not a fixed value, but a certain range.
The national standard of melting point is between 252°C and 262°C.
Polyester diethylene glycol is an important indicator to measure the degree of etherification side reaction in the production process. According to the test results, the increase of DEG content brings a decrease in melting point or softening point and worsen thermal oxidation resistance and light resistance. Under the same dyeing conditions, the increase of DEG content can deepen the dyeing of polyester fibers and increase the coloring rate. Because of the influence of DEG content on polyester and subsequent positive and negative sides, the control content is also different under various production process conditions. Correspondingly, the DuPont process control value is higher, and the China Textile Institute process control value is lower. Nearly all the manufacturers think that the main point is not the absolute value of the DEG content but the stability of the content. The stable content is very important to reduce the poor dyeing issue in fiber production. But for the production of tapes, videotapes, and other purposes, the DEG content should be lower, which can increase the anti-fatigue strength during use.
The color value of polyester is a comprehensive index, which is affected by PTA, matting agents, catalysts, and the production process. Whether it is the influence of external chromaticity or the yellowing problem caused by the inherent quality, it will make the fiber yellow and affect the appearance of the fiber, especially the yellowing or graying color value caused by degradation or metal catalyst ions. This color problem makes it easy to increase the viscosity drop during the spinning process and then brings fluctuations in the spinning production. The b value in the chromaticity reflects the blue-yellowness of the polyester chip. The smaller the b value, the more blue the polyester color, and the higher the yellower. The L value reflects the grayscale of the chips. The larger the L value, the brighter the slice, and the smaller the grayer.
TiO2 is added as a delustering agent to polyester products, and its dosage is determined according to the needs of users. Generally speaking, the content of bright chips is less than 0.12%, and the content of semi-dull slices is generally between 0.12% and 0.5%. More information about TiO2 used in polyester, please click https://www.polyestermfg.com/what-is-application-of-tio2-in-polyester/
Iron content is also an indicator to characterize polyester products. Generally speaking, the source of Fe is PTA, EG, catalysts, and matting agents. However, when Fe content exceeds the standard one, it indicates that there is corrosion in the polyester device. And when the iron content is high, the ash content is also high, which easily affects the color and quality of the fibers.
Ash is the inorganic impurities in polyester, including that derived from PTA and EG, catalyst residues, impurities from TiO2 grinding, and PTA packages.
The level of ash content not only affects the service life of the filter in the device and production stability but also affects the life cycle of the melt filter in the spinning device. What’s worse, it may clog the components, affect the continuity of spinning production, and cause the yarn to break.
The moisture content refers to the water adhered to the surface of chips. The content is closely related to dryness, storage time, air humidity, environmental stability, and other factors. The content affects not only the raw material consumption but also the production of spinning.
Powder and Abnormal Chip Content
Powder refers to crumbs that can pass through a 20-mesh sieve, and special-shaped chips are particles with excessively large geometric dimensions. Whether it is powder or abnormal slices, it will affect the appearance and consumption during the production process. When there is much powder, it will stick during drying and cause blockage. Oversized particles will consume more time and energy when drying.
Hope the above Physical Properties of Polyester Chips could help you to have a better understanding of them. And any need from your side, please contact us.