Structure and properties of thermotropic liquid crystal polymer and poly(ethylene 2,6-naphthalate) blend fibers

Background: The melt blending of thermotropic liquid crystal polymers (TLCPs) using conventional thermoplastics has attracted much attention due to the improved strength and tensile modulus of the resulting polymer composites. Moreover, because of their low melt viscosity, the addition of small amounts of TLCPs can reduce the melt viscosity of polymer blends, thereby enhancing the processability. Results: In this study, TLCP/poly(ethylene 2,6-naphthalate) (PEN) blend fibers were prepared by melt blending and melt spinning to improve fiber performance and processability. The relation between the structure and the mechanical properties of TLCF/PEN blend fibers and the effect of annealing on these properties were also investigated. The mechanical properties of the blend fibers were improved by increasing the spinning speed and by adding TLCP. These properties of the blend fibers were also improved by annealing. The tensile strength of TLCP5/PEN spun at a spinning speed of 2.0km h^-1 and annealed at 235°C for 2h was about three times higher than that of TLCP5/PEN spun at a spinning speed of 0.5km h^-1. The double melting behavior observed in the annealed fibers depended on the annealing temperature and time. Conclusion: The improvement of the mechanical properties of the blend fibers with spinning speed, by adding TLCP and by annealing was attributed to an increase in crystallite size, an increase in the degree of crystallinity and an improvement in crystal perfection. The double melting behavior was influenced by the distribution in lamella thickness that occurred because of a melt-reorganization process during differential scanning calorimetry scans.