Abstract:

Objective Biodegradable poly(butylene succinate) (PBS) fibers possess a wool-like handle, yet the suitable intrinsic viscosity range and corresponding melt-spinning parameters have not been thoroughly elucidated. This research aims to establish the relationship between PBS intrinsic viscosity and spinnability, and to evaluate the influence of intrinsic viscosity and draw ratio on the evolution of fiber aggregation state characteristics, specifically fiber orientation and crystalline structure.

Method In this study, PBS partially oriented yarns (POY) were firstly prepared by melt spinning and using PBS with different intrinsic viscosities, and then the as-prepared POY was subjected to different multiples of thermal drawing to obtain drawn-twist (POY-DT). The influence of intrinsic viscosity and draw ratio on PBS fiber mechanical performance was subsequently studied, and the fiber orientation and crystalline structure were analysed by sound velocity measurement and X-Ray diffraction (XRD).

Results The results demonstrated that high-viscosity PBS facilitates higher spinning speeds, but suffers significant viscosity reduction, for instance, PBS-4 had an intrinsic viscosity of 1.99 dL/g but showed a decrease of 0.51 dL/g due to the high melt spinning temperatures, leading to reduced fiber mechanical properties. It is worth noting that partially branched PBS with low-viscosity (1.53 dL/g) enabled high-speed spinning of POY at 2 700 m/min while maintaining a breaking strength of 1.74 cN/dtex, and it showed a faster crystallization rate than linear PBS, demonstrating that partial branching facilitated a balance between high melt strength and rapid crystallization rate in PBS. The tensile strength of POY was proportional to the spinning speed, exhibiting a near-linear relationship. Higher POY spinning speeds significantly enhanced the mechanical properties of the resulting POY-DT. When the POY spinning speed was lower than 2 000 m/min, the tensile strength of POY-DT with maximum draw ratio was only 1.41 cN/dtex; however, its tensile strength values could improve significantly from1.34 cN/dtex to 2.91 cN/dtex when the spinning speed increased from 1 500 m/min to 2 700 m/min. Moreover, as the orientation of PBS fibers increased with higher draw ratios, the orientation factor (f_s) increased from 0.50 (POY) to 0.73 (POY-DT) with a 2.30 draw ratio. Fibers with higher intrinsic viscosity exhibited lower sonic velocity values, and low-viscosity PBS favored fiber orientation, whereas branching presented an adverse effect on it. Analysis of the crystalline structure evolution during fiber processing revealed that drawing would induce the fiber crystallization. During the spinning process, the grain size of (020) crystal plane was decreased from 15.00 nm to 10.80 nm, indicating that crystallite size underwent gradual refinement and the crystal structure progressively perfected. Meanwhile, the crystallinity increased from 48.09% in the undrawn as-spun fiber to 78. 91% after a 2.00 draw ratio.

Conclusion This study investigated the spinnability of PBS with different intrinsic viscosities, discussed the variation of fiber mechanical properties with spinning speed and thermal draw ratio, and focuses on the evolution of the aggregation structure throughout the entire fiber formation process. The research clarified that the high-viscosity PBS could facilitate higher spinning speeds, however a significant viscosity reduction would occur in the meantime, which indicates that high-viscosity PBS was not needed when synthesis PBS fiber via melt spinning. Instead, partially branched PBS with lower viscosity show a promise prospect due to its high melt strength and rapid crystallization rate. POY spinning speeds has a significantly positive promotion on the mechanical properties of the POY-DT. The fiber aggregation state characteristics is affected by the PBS fiber intrinsic viscosity and draw ratio, which is, lower intrinsic viscosity brings a higher fiber orientation, and higher draw ratio brings a higher crystallinity. The findings provide a theoretical basis for raw material selection and spinning process optimization in the industrial production of PBS fibers.

Key words: poly(butylene succinate), melt spinning, intrinsic viscosity, spinning technology, pre-oriented yarn, draw yarn, aggregate structure