Abstract:

Objective Poly (butylene succinate) (PBS) is a synthetic biodegradable polymer and silk sericin is a natural biodegradable polymer. PBS fiber can be prepared by melt spinning process, which is applied in textile industry as raw material. Silk sericin can be used as moisturizer in skincare and textile industries. To improve the skin-friendliness of PBS fiber, PBS and silk sericin was mixed by melt blending, then the blend fiber was prepared by melt spinning process.
Method After vacuum drying at 80 ℃ for 4 h, the PBS and silk sericin were melt blended using an internal mixer at the rotation rate of 60 r/min for 25 min. The mixing temperature of the PBS/silk sericin blends was set to 140 ℃, and the weight ratio of PBS/silk sericin is shown in Tab. 1. After that, the PBS/silk sericin blend fibers were spun through a single-screw extruder at 160 ℃. Then, the fiber was cooled in a water bath at room temperature. The extrusion speed was 1.95 g/min, the drawing speed was 3.60 m/min, and the draw ratio was 4.
Results The scanning electron microscopy (SEM) of the cross-section of the PBS/silk sericin blend fiber is shown in Fig. 1. The rough cross-section of PBS/silk sericin blend fiber indicates poor compatibility between PBS and silk sericin. There were small voids on the cross-section of the blend fibers, the number of voids would increase with the rise of silk sericin mass fraction. The XRD pattern of PBS/silk sericin blend fiber is shown in Fig. 3 and the crystallinity of PBS is listed in Tab. 2. With the increase of silk sericin mass fraction, the crystallinity of the blend fiber decreases. It seems that the crystallization process of PBS was obstructed by the dispersion of silk sericin in the fiber. The mechanical property of PBS/silk sericin blend fiber is shown in Fig. 4. Tensile strength and elongation at break of the blend fiber decrease when the silk sericin mass fraction increases, and the elongation at break of PBS fiber is 212.1%. However, for the blend fiber when the mass fraction of silk sericin became 15%, the elongation at break of was only 8.9%, this value meets the requirement of textile requirement. Hence, the overlarge elongation at break of PBS fiber can be reduced with the existence of silk sericin. The saturated moisture regains of the PBS/silk sericin blend fibers is shown in Fig. 6. It can be found that the saturated moisture regain of the blend fiber is improved with the increase of silk sericin mass fraction. For the blend fiber when the silk sericin mass fraction is 15%, the saturated moisture regain is 3.90%. This value is similar to the saturated moisture regain of polyamide 6 fiber (saturated moisture regain is 3.95%) with good hydrophilic property. The improved saturated moisture regain of the blend fiber is not only related to the hydrophilic group of silk sericin, but also associated with the increase of amorphous region area in the blend fiber. The weight loss rate of PBS/silk sericin blend fibers after soil burial test is shown in Fig. 7. The weight loss rate of the blend fiber after 6 weeks during the soil burial test is up to 53.6%. When silk sericin is degraded by microorganisms firstly, the specific surface area increases, which is beneficial to the contact between PBS and microorganisms. Then, the degradation rate of PBS is also accelerated.
Conclusion In this research, the PBS/silk sericin blend fibers were prepared by melt spinning method. The effect of PBS/silk sericin weight ratio on the morphology, mechanical strength and biodegradability was studied. The main findings are as follows,the small voids can be found on the cross-section of the PBS/silk sericin blend fibers, which is related to the weak interface force between PBS and silk sericin. For the PBS/silk sericin blend fiber when the mass fraction of silk sericin is 15%, the elongation at break is 8.9%, the saturated moisture regain is 3.90%. By contrast, the elongation at break of PBS fiber is 212.1%, the saturated moisture regain is 2.26%. The existence of silk sericin not only reduces the overlarge elongation at break of PBS fiber, but also improves the hydrophilic property. For the PBS/silk sericin blend fiber when the mass fraction of silk sericin is 15%, the weight loss rate after 6 weeks during the soil burial test is up to 53.6%. The biodegradability of PBS/silk sericin blend fiber of PBS is better than that of PBS fiber. Hence, the PBS/silk sericin blend fiber degrades quickly after use.

Key words: poly(butylene succinate), silk sericin, blend fiber, hygroscopicity, biodegradability