Evolution of structures and properties of polyester fibers prepared by different processes under alkaline conditions
In order to explore the changes in the performance of polyester fibers prepared by different processes under alkaline conditions,high tenacity(HT)polyester industrial fiber and fully drawn polyester yarn(FDY)of high speed spinning were selected for artificial accelerated aging tests in alkaline conditions at 85 C.The mechanical properties of fibers were tested during the processes.Wide-angle X-ray diffraction,small-angle X-ray scattering and intrinsic viscosity were used to study the change in crystalline,lamellar structure and chemical structure of polyester fibers.The results showed that the changes in structure and properties of two polyester fibers in alkaline conditions can be divided into three stages.At the initial stage,the breaking strength and degree of orientation of the fibers first decreased significantly due to the effect of water and heat,while crystallinity remained constant.It was caused by the disorientation of amorphous orientated molecular chain segments in the frozen state,resulting in shrinkage.Then the decrease in breaking strength of fibers was slowed down,which was attributed to the breakage of amorphous molecular chains and the formation of a few new crystal structures.In the final stage of alkaline hydrolysis,the breaking strength of the fibers decreased significantly,while the crystallinity of fibers began to decline and the intrinsic viscosity reduced constantly,indicating that the breakage of amorphous molecular chain became the dominant factor.The alkaline hydrolysis reaction rate and the change degree of microstructure and mechanical property parameters of HT fibers were lower than those of FDY fibers,owing to the greater crystallinity and crystal size of HT fibers,which inhibited the erosion of water and OH.As a result,HT fibers had a better alkaline hydrolysis resistance than FDY fibers.
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