关键词: 聚酯工业丝, 共聚型, 阻燃, 力学性能

Abstract: Polyester industrial yarns are widely used in the fields of safety belts, rubber reinforcement materials, geotextile, and cables due to their excellent dimensional stability, weather resistance, and mechanical properties. However, the flammability of the polyester limits its further application. With excellent flame-retardant durability, the copolymerized flame-retardant polyester is the ideal method for the flame-retardant modification of polyester industrial yarns. In the process of high-temperature melt spinning, how to restrain the thermal degradation of high molecular weight copolyesters and ensure the appropriate liquidity of melt is the key technology to prepare the copolymerized flame-retardant polyester industrial yarns. Based on the rheological behavior of high molecular weight flame-retardant copolyesters during spinning and melting, the corresponding spinning process was designed, the thermal degradation degree of copolyesters during spinning and forming was determined, and the process parameters were optimized. Polyester industrial yarns with good mechanical properties, flame-retardant properties, and durability were prepared. 
The rheological properties of high molecular weight flame-retardant copolyesters at different temperatures were tested by the rotating rheometer. The spinning processing temperature range was defined according to appropriate melt fluidity and stable spinning pressure requirements. At the same time, the thermal degradation of copolyesters was quantified at different spinning temperatures to optimize the melt-spinning process. Then, the thermal drawing processes such as temperature and ratio were designed to improve the mechanical properties of the fibers. The mechanical and flame-retardant properties of the industrial yarns were measured by means of tensile and combustion tests. In addition, X-ray diffraction and sonic orientation equipment were used to analyze and test the crystal and orientation of the fibers. It is found that compared with pure PET, the viscosity of copolyesters melt is lower and the temperature sensitivity is more obvious. When the temperature is between 275 °C and 285 ℃, the melt viscosity is similar to that of pure PET spinning temperature. The pressure fluctuation of the spinning pack in this temperature range is small, which is conducive to avoiding excessive adjustment of spinning parameters in the production process. The process was further optimized by choosing a lower spinning temperature (about 285 ℃). The melt viscosity had little influence on spinning pressure and the thermal degradation degree was low (the viscosity dropped to 11.5%). Finally, by multistage hot drawing process, the breaking strength of the flame-retardant industrial yarns prepared by the primary fiber can reach 6.75 cN/dtex, the limit oxygen index (LOI) can reach 31% and the flame-retardant durability is outstanding, which meets the requirements of flame-retardant and mechanical properties of flame-retardant polyester industrial yarns. The results of microstructure analysis show that the copolymerization unit reduces the number of pure polyester chain segments and results in a short length of near-end pure polyester chain segments, which makes it difficult to embed in the lattice and further leads to the decrease of crystallinity and the low orientation of the amorphous chain segment, and the decline of mechanical properties of flame retardant fibers.
Based on the rheological properties and degradation behavior of high molecular weight flame-retardant copolyesters, the key technical factors of processing and molding were studied. The melt spinning process was designed, the drawing parameters were optimized, and the relationship between structural characteristics and mechanical properties of the prepared flame-retardant copolyesters was analyzed. On this basis, the flame-retardant polyester industrial yarns with good mechanical properties and excellent flame-retardant properties and outstanding flame-retardant durability were prepared, which greatly expanded the application of polyester industrial yarns and had certain guiding significance for the development and application of flame-retardant polyester industrial yarns.

Key words: polyester industrial yarns, copolymerized, flame retardant, mechanical properties