Polyester chips include several key parameters, which are essential for assessing and controlling the quality of the material. These parameters typically include: IV, COOH group, melting point, DEG, coloration, TiO2, iron, ash, moisture and irregular chips.
The following, we will elaborate on the specific meanings of each parameter.
1. Intrinsic Viscosity
The intrinsic viscosity of fiber-grade polyester chips is typically 0.645. Intrinsic viscosity is an industrial measurement used to determine the molecular weight of polyester. Measuring intrinsic viscosity not only provides an accurate assessment of polyester quality but also serves as an important basis for establishing spinning process conditions. If the intrinsic viscosity is too low, indicating a lower molecular weight, the stretching process during spinning becomes difficult, and the polyester may even be non-spinnable, leading to breakage. Conversely, if the viscosity is too high, the high stretching stress during stretching can hinder the orientation of the large polymer molecules. Therefore, intrinsic viscosity affects the stability of spinning operation, the uniformity of filament yarns, and the evenness of dyeing. Ensuring stable intrinsic viscosity is of great help in improving the quality of spinning.
2. COOH Group Content
The COOH group content is also an important parameter for measuring polyester production. In general, the source of terminal carboxyl groups mainly comes from unreacted TPA or degradation products. In theory, fully reacted polyester should have zero terminal carboxyl groups. However, due to various factors, the terminal carboxyl content of polyester chips varies significantly under different process conditions. The national standard specifies the range of terminal carboxyl groups as M ± 4, where M ranges from 18 to 36, providing a relatively loose criterion. Generally, in terms of process conditions, DuPont facilities have higher terminal carboxyl content, while those in the China National Textile Academy also have great products.
3. Melting Point
The melting point of polyester refers to the temperature at which the crystalline solid material transitions into a liquid state upon heating. It reflects the purity of the polyester to some extent. Pure polyester is partially crystalline and has a melting point around 265°C. However, in actual production, impurities are present in polyester due to various side reactions. Additionally, defects in polymer crystallization and variations in crystallinity affect the melting point of polyester. The melting point of practical polyester is below 265°C, and the melting temperature range is not necessarily a single point but a certain range. According to the national standard, the melting point range is specified between 252°C and 262°C.
4. Diethylene Glycol (DEG)
Diethylene glycol content is an important indicator to measure the extent of etherification side reactions during production. Experimental results show that an increase in DEG content can lower the melting or softening point of polyester. However, it also negatively affects heat resistance, oxidation resistance, and light resistance. Under the same dyeing conditions, an increase in DEG content deepens the dyeing of polyester fibers and improves color yield. Due to the impact of DEG content on the positive and negative aspects of polyester and its subsequent processing, the control of DEG content varies under different production process conditions. DuPont processes have relatively higher control values, while China National Textile Academy processes have lower control values. Manufacturers generally agree that the absolute value of DEG content is not the main aspect; stability of the content is more important to minimize color variations in the resulting fibers. However, for applications such as magnetic tapes and video tapes, a lower DEG content is desired to increase fatigue resistance during usage.
5. Coloration
The coloration of polyester is a comprehensive indicator influenced not only by external factors such as PTA, colorants, and catalysts but also by the polyester production process itself. Both external coloration and inherent quality-related yellowing can cause yellowing of the fibers, affecting their appearance. Degradation or metallic catalyst ion-induced coloration can lead to decreased viscosity during spinning, resulting in production fluctuations. The “b” value in coloration reflects the blue-yellow hue of polyester chips. A smaller “b” value indicates a bluer shade, while a higher value indicates more yellow. The “L” value reflects the grayscale of the chips, with higher values representing brighter chips and lower values indicating grayer ones.
6. Titanium Dioxide (TiO2) Content
The addition of TiO2 as a colorant in polyester products is determined based on customer requirements. Generally, transparent chips have a TiO2 content less than 0.12%, while semi-transparent chips range from 0.12% to 0.5%. The specific content for the company falls within the range of 0.28% to 0.3%.
7. Iron Content
Iron content is also an indicator of polyester products and is typically derived from PTA, EG, catalysts, and colorants. If the levels of these impurities are not properly controlled, it indicates corrosion within the polyester process. Higher iron content is associated with increased ash content, which can negatively impact the color and quality of the fibers.
8. Ash Content
Ash content in polyester refers to the inorganic impurities present, including those derived from inorganic impurities in PTA and EG raw materials, residues from catalysts, impurities introduced during TiO2 grinding, and contaminants from the outer packaging during PTA feeding. he level of ash content not only affects the lifespan of filters in the production process and the stability of production but also impacts the usage cycle of melt filters in spinning equipment. Blockage of components and disruptions in spinning production can occur when ash content is severe, leading to an increase in yarn breakage.
9. Moisture Content
Moisture content in chips refers to the physically bound water adhering to the surface. The moisture content is influenced by factors such as chip drying level, storage time, air humidity, and environmental stability. The moisture content of chips not only affects the raw material consumption for users but also has implications for spinning production.
10. Powder and Irregular Chips
Powder refers to the debris that can pass through a 20-mesh sieve, while irregular chips are particles with larger geometrical dimensions. Both powder and irregular chips not only impact the appearance of chips but also affect consumption and production efficiency. Excessive powder can agglomerate during drying, causing material blockages. Larger-sized particles require more time and energy during the drying process. Therefore, it is essential to have chips with uniform particle size and minimal presence of powder.
By carefully interpreting these indicators, we can truly grasp their significance and how they impact our product’s performance. This deep understanding is essential for tailoring our products effectively. Examining these indicators individually helps us better comprehend the specific aspects that demand special consideration during the product’s actual usage. As a result, we can optimize the product’s performance and quality to the highest standard. Therefore, to enhance performance and address any issues, it’s vital that we closely monitor these indicators, ensuring our product excels across various application scenarios.
