关键词: 涤纶工业丝, 纤维长周期, 连接分子, 初始模量, 非晶区模量

Abstract: "To investigate the influence of tie molecules (TMs) in polyester industrial yarns on the modulus and mechanical properties of the amorphous region, four types of polyester industrial yarns—low-shrinkage (LS), super-low-shrinkage (SLS), general-high-tenacity (GHT), and high-modulus low-shrinkage (HMLS)—were selected as research subjects. The crystallinity, orientation degree, and lamellar thickness of the materials were characterized using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD), birefringence analysis, and small-angle X-ray scattering (SAXS). The molecular chain mobility in the amorphous region was evaluated via dynamic mechanical analysis (DMA), and the concentration ratio of TMs was calculated using the Huang and Brown model (HB model). To address the theoretical limitations of Peterlin's volume-modulus model for fibers regarding the amorphous region modulus, the modulus of the amorphous region (723.87 MPa) was measured by assessing the local stress-strain relationship induced by swelling in the amorphous region. This revised amorphous region modulus significantly improved the accuracy of the Peterlin model in predicting the volume fraction of taut tie molecules (TTMs). The DSC and WAXD analyses revealed discrepancies in the crystallinity measurements of polyester industrial yarns, indicating the presence of a rigid amorphous phase within the industrial fibers. To investigate the influence of microstructure on the volume fraction of TMs, DMA, WAXD, and SAXS were employed. Both SAXS and DMA results confirmed a negative correlation between the TM volume fraction and the maximum loss tangent (tan δmax), suggesting that TMs enhance material rigidity by suppressing segmental motion in the amorphous regions. The volume fraction of TTMs in industrial yarns calculated by the revised Peterlin model aligned with the trend of the volume fraction of TMs calculated by the HB model. The concentration ratios of TMs in the four types of polyester industrial yarns, ranked from highest to lowest, were as follows: HMLS, GHT, LS and SLS. Tensile tests demonstrated a positive correlation between TTMs and the initial modulus of industrial yarns. The volume fraction of TTMs also showed a strong correlation with the strain response corresponding to the second modulus peak in the modulus-strain curve of industrial yarns, verifying that TTMs enhanced the coupling effect between the crystalline and amorphous regions through stress transfer. The volume fraction of TMs obtained from the HB model was higher than the predicted volume fraction of TTMs from the Peterlin model. This discrepancy might be attributed to the formation of relatively loose TMs structures by some molecular chains that spanned two different crystalline regions. Tensile tests further revealed that the initial moduli of HMLS and GHT industrial yarns were significantly higher than those of LS and SLS, and their modulus-strain curves exhibited a more sensitive response to strain at the second modulus peak. The modified Peterlin model demonstrated that the volume fraction of TTMs was proportional to the fiber modulus. The highest volume fraction of TTMs in HMLS confirmed that TMs enhanced the coupling effect between the crystalline and amorphous regions through the stress transfer mechanism, thereby improving the overall modulus. This study innovatively revises the modulus parameters of the amorphous region through experimental measurements, clarifies the pivotal role of TMs in stress transfer, and establishes quantitative relationships between the volume fraction of TMs and microstructural parameters (such as lamellar thickness and orientation degree) as well as macroscopic mechanical properties. The research findings not only provide a new perspective for analyzing the mechanical behavior of the amorphous region in semi-crystalline polymers, but also offer a theoretical foundation for the molecular design and process optimization of high-performance industrial fibers."

Key words: polyester industrial yarns, long period of fiber, tie molecules, initial modulus, amorphous region modulus