PTA process has the advantages of low raw material consumption and short reaction time, and has become the main process and preferred technical route of polyester since 1980s. Large production lines are continuous production processes, and semi-continuous and intermittent production processes are suitable for small and medium-sized production devices. The uses of polyester now include fibers, various containers, packaging materials, films, films, engineering plastics and other fields.
Test index
1, viscosity
The intrinsic viscosity of fiber-grade polyester chips is generally 0.645, which is used to characterize the molecular weight of polyester in industry. The determination of intrinsic viscosity can not only correctly evaluate the quality of polyester, but also provide an important basis for formulating spinning process conditions. The intrinsic viscosity is too low, and the molecular weight of polyester is small, so it is difficult to stretch or even spinnable during spinning, and it is easy to break.
If the viscosity is too high, the tensile stress will be too high and the macromolecules will not be well oriented. Therefore, the intrinsic viscosity has an influence on the running stability of spinning, the evenness of filament and the uniformity of dyeing. Therefore, ensuring the stability of intrinsic viscosity is of great help to improve spinning quality.
2. Content of carboxyl end groups
The carboxyl-terminated content is also an important parameter to measure the polyester yield. Generally speaking, the source of carboxyl-terminated groups is mainly unreacted PTA or after degradation. Theoretically, the carboxyl end group of fully reacted polyester should be zero.
In fact, due to various factors, the content of carboxyl-terminated groups in polyester chips varies greatly under various technological conditions. The range of carboxyl groups in the national standard is m 4, and the value range of m is 18 to 36, which is a very loose index. Generally speaking, in terms of process conditions, the carboxyl group content of DuPont factory is high, while that of China Textile Institute is low.
3. Melting point
The melting point of polyester is the temperature at which a crystalline solid substance changes from solid to liquid when heated to a certain temperature, which reflects the purity of polyester to some 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 polyester, and the melting point of polyester is also affected by polymer crystallization defects and crystallinity differences everywhere. The melting point of actual polyester is below 265℃, and the melting point temperature range is not necessarily a certain point, but a certain range. The melting point in the national standard is between 252℃ and 262℃.
4. diethylene glycol
Polyester diethylene glycol is an important index to measure the degree of etherification side reaction in production process. From the experimental results, the content of diethylene glycol increased. It will reduce the melting point or softening point of polyester, and make the thermal oxidation resistance and light resistance worse. Under the same dyeing conditions, the increase of diethylene glycol content can deepen the dyeing of polyester fiber and improve the dye uptake.
It is precisely because of the influence of DEG content on polyester and the subsequent positive and negative sides that the control content is different under various production process conditions, and the corresponding DuPont process control value is higher and the China Textile Institute process control value is lower.
In front of manufacturers, the basic understanding of diethylene glycol content is that the absolute value of diethylene glycol content is not the main aspect, but the stability of content is very important to reduce the dyeing difference of produced fibers. However, when it is used to produce magnetic tapes, video tapes and other purposes, the DEG content should be low, which can increase the fatigue strength during use.
5. Sexuality
The chromaticity of polyester is a comprehensive index, which is influenced not only by external factors such as PTA, matting agent and catalyst, but also by the production process of polyester itself.
No matter the influence of external chromaticity or the yellowing of polyester caused by internal quality, the chromaticity of fiber will turn yellow, which will affect the appearance of fiber, especially the yellowing and graying of chromaticity caused by degradation or metal catalyst ions, which will easily increase the viscosity drop during spinning and cause fluctuations in spinning production.
The B value in chromaticity reflects the blue-yellow degree of polyester chips. The smaller the B value, the bluer the polyester color, and the higher the B value, the yellower the polyester color. The l value reflects the gray level of the slice. The greater the L value, the brighter the slice, and the smaller the slice, the grayer it is.
6, titanium dioxide content
Titanium dioxide is added to polyester products as matting agent, and its dosage depends on the needs of users. Generally speaking, the content of glossy chips is less than 0. 12%, semi-dull chips are generally between 0.12 and 0.5%, and the content of our company is between 0.28 and 0.3%.
7. Iron content
Iron content is also an index to characterize polyester products. Generally speaking, the sources of iron are PTA, EG, catalyst and matting agent. But when these contents are certain, it means that the polyester plant has been corroded. If the iron content is high, the ash content will be high, which will easily affect the color and quality of the fiber.
8. Ashes
Ash is an inorganic impurity in polyester, including inorganic impurities from PTA and EG raw materials, catalyst residue and impurities brought in by TiO2 _ 2 grinding. Another important aspect is that impurities in the outer bag enter when the bagged PTA is fed.
Ash not only affects the service life and production stability of the filter in the device, but also affects the service life of the melt filter in the spinning device, blocking parts, seriously affecting the continuity of spinning production, resulting in an increase in broken wires.
9. Moisture
The moisture content of slices refers to the physical combined moisture adhered to the surface of slices, and the moisture content of slices is related to factors such as drying degree, storage time, air humidity and environmental stability. The moisture content of slices not only affects the raw material consumption of users. It also affects spinning production.
10, abnormal section of powder
Chip powder refers to the crumbs that can pass through the 20-mesh sample sieve, and special-shaped chips refer to the particles with oversized geometric dimensions of polyester chips. Whether it is powder or irregular slices, it will not only affect the appearance of slices, but also affect the consumption and production of manufacturers. If there is too much powder, it will stick to the material when drying, which will cause material blockage. The oversized particles will consume more time and energy when drying, so it is required to slice evenly and have fewer particles.