Molecular Weight Discrete Distribution-Induced Orientation of High-Strength Copolyamide Fibers: Effects of Component Proportion and Molecular Weight

The mechanical properties of polymer fibers are dependent on the molecular chemical structure and condensed state structure. Effective control over these two structural parameters allows us to study the relationship between fiber structures and properties and thereafter optimizes the material performance. In this work, the copolyamides (CoPAs) are prepared by selecting polyamide 6 (PA6) as the matrix and copolymerizing with the polyamide 66 (PA66) component, and the CoPA/HwPA6 (CoPA-Hw) composites with discrete molecular weight distribution are further fabricated by adding the high-molecular-weight PA6 (HwPA6) component in the CoPA. The CoPA fibers and CoPA-Hw fibers are prepared via melt spinning, and the crystal structures and mechanical properties of the fibers are studied. The mechanical properties cannot be effectively improved by adjusting the content of the PA66 component in the CoPA molecular chains or increasing the molecular weight of the CoPA. However, the addition of the HwPA6 component can effectively inhibit the slippage of molecular chains under stress and maintain the orientation of the molecular chains during annealing. Therefore, the mechanical properties of the CoPA-Hw fibers are significantly improved, and the stress at break can reach 6.86 cN/dtex. It is expected that the molecular chain orientation of polymer materials resulting from discrete molecular weight distribution can be used to improve the mechanical properties of other polymer materials.