Effect of Annealing on the Thermal and Mechanical Properties of PLLA Spin Draw Yarns

열처리 조건이 PLLA SDY 섬유의 열적 특성 및 물성에 미치는 영향

Poly(L-lactic acid) (PLLA) filament fibers were prepared by one-step melt spinning process with spin drawing and the effects of the annealing at $100^{\circ}C$ and $120^{\circ}C$ on their thermal and mechanical properties were investigated by using a differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), and universal testing machine (UTM). The glass transition temperature ($T_g$) of the PLLA spin draw yarn (SDY) fibers increased with increasing annealing time while the melting temperature ($T_m$) remained unaffected. The birefringence increased with increasing time at both $100^{\circ}C$ and $120^{\circ}C$, indicating the enhanced orientation of the polymers in the fiber. The tenacity of the fibers increased to almost double, while the elongation at break decreased to almost half by 5 minutes annealing at both $100^{\circ}C$ and $120^{\circ}C$. However, annealing time of more than 5 minutes did not affect the tenacity and elongation at break. The boiling water shrinkage (BWS) decreased continuously with increasing time, the increment was larger for the annealing at $120^{\circ}C$ than that at $100^{\circ}C$. A BWS of less than 3% was obtained by annealing at $120^{\circ}C$ for 30 minutes.