Nucleator induced highly oriented crystalline structure of poly(lactic acid) fiber enables superior intrinsic piezoelectric and antibacterial effect

Abstract

Due to the continuous worldwide threats from infectious diseases, exploring novel antibacterial materials based on renewable, biodegradable and biocompatible polymers, like poly(lactic acid) (PLA), is essential for the development of advanced personal protective equipment, but the incorporation of a large amount of inorganic piezoelectric nanoparticles to endow it with a piezoelectric antibacterial effect deteriorated the unique properties of PLA. In this work, a self-assembling hydrazide nucleator (HNA) was introduced into PLA through melt blending, while PLA–HNA fibers were prepared by melt spinning–hot drawing dual processes, and further knitted into a plain fabric. The incorporation of HNA improved the spinnability/uniformity of the fibers, and promoted the formation of a highly oriented crystalline structure of fibers under a high draw ratio (DR), exhibiting a higher degree of crystallinity/orientation in both crystalline and amorphous regions than neat PLA fiber. With increasing DR, the shish-kebab crystallinity of the fibers changed to fibrillar crystallinity, forming compact microfibrillar structures along the drawing direction, and the tensile strength and modulus increased remarkably, reaching as high as 645.27 MPa and 8.87 GPa at a DR of 6. Meanwhile the open-circuit voltage (V_pp), short-circuit current (I_sc), and piezoelectric sensitivity increased with DR, and compared with PLA fiber, incorporating HNA improved the piezoelectricity of the fiber significantly with high cycling stability. The knitted fabric with twisted and tightly interweaved fibers exhibited a much enhanced piezoelectric response, generating V_pp and I_sc signals of 9.17 V and 210 nA, respectively. Moreover, both the PLA–HNA fiber and fabric inhibited E. coli bacteria almost completely by ultrasonic coculture with V_pp signals of 89.3 and 95.8 mV, respectively, reaching an inhibition rate of more than 99%, exhibiting an excellent intrinsic piezoelectric and antibacterial effect, and showing promising potential as personal protective equipment.