Effects of heat treatments and cross‐linking on the crystal structure and torsional properties of polyester fibers

Abstract

Artificial muscles have attracted great attention as actuators and coiled and twisted monofilament actuators are considered the most promising ones. In the present work, the torsional properties of poly(hexamethylene adipamide) (PA66), poly(ethylene terephthalate) (PET), and high‐strength PET (HTPET) monofilaments were investigated. Furthermore, cross‐linked PET (CPET) monofilaments were melt‐spun by adding 1 wt% of 2‐dimethoxy‐2‐phenylacetophenone (ultraviolet (UV) initiator) and triallyl iso‐cyanurate (cross‐linking agent) in PET chips under UV radiation. The HTPET monofilaments had the highest torsional modulus of 1.1 GPa followed by the PET (0.8 GPa) and PA66 (0.6 GPa) monofilaments. Subsequently, the HTPET monofilaments were subjected to heat treatments under tension. When the heat treatment time was 10 min, the mechanical properties of the HTPET monofilaments also tended to first increase and then decrease with the rise of heat treatment temperature. The molecular arrangement and crystal structure of the HTPET monofilaments were gradually improved with the prolongation of tension heat treatment. The tensile strength and initial modulus of the HTPET monofilaments were 871.4 MPa and 15.8 GPa, respectively. The mechanical properties of the CPET monofilaments first increased and then decreased with the increase of the drawing ratio. When the drawing ratio was 10, the CPET monofilament had a tensile strength of 717.2 MPa, an initial modulus of 16.7 GPa, and a maximum torsional modulus of 1.3 GPa. Therefore, both heat treatment and cross‐linking increased the mechanical strength of the PET monofilaments. CPET and HTPET are possible to be used as artificial muscles.