Constructing Bone-Mimicking High-Performance Structured Poly(lactic acid) by an Elongational Flow Field and Facile Annealing Process

Abstract

Poly(lactic acid) (PLA) as one of the most promising biodegradable polymers is being tremendously restricted in large-scale applications by the notorious toughness, ductility, and heat distortion resistance. Manufacturing PLA with excellent toughness, considerable ductility, balanced strength, and great heat distortion resistance simultaneously is still a great challenge. Natural structural materials usually possess excellent strength and toughness by elaborately constructed sophisticated hierarchical architectures, however, completely reproducing natural structural materials' architecture have evidenced to be difficult. Inspired by the hierarchical construction of the compact bone, an innovational method with an intensive and continuous elongational flow field and facile annealing process was developed to create bonemimicking structured PLA at an industrial scale. The bone-mimicking structured PLA with unique and novel hierarchical architectures of interlocked 3D network lamellae and large extended-chain lamellae connecting the regular lamellae was constructed by in situ formed oriented thermoplastic poly(ether)urethane nanofibers (TNFs) acting as "collagen fibers", orderly staggered PLA lamellae behaving as "hydroxyapatite (HA) nanocrystals", and the tenacious interface functioning as a "soft protein" adhesive layer. Attributed to the unique structure, it possesses super toughness (90.3 KJ/m 2 ), high stiffness (2.15 GPa), balanced strength (52.6 MPa), and notable heat distortion resistance (holding at 163 °C for 1 h) simultaneously. These excellent performances of the structured PLA provide it with immense potential applications in both structural and bio-engineering materials fields such as artificial bones and tissue scaffolds.

Phase transformation and dielectric properties of polyvinylidene fluoride/organic‐montmorillonite nanocomposites fabricated under elongational flow field

“…Initially, the strong tensile stress stemming from the compression effect of convergence flow path forces large aggregated OMMT layers to separate to stacks of silicate tactoids. In the meanwhile, the tensile stress also facilitates the disentanglement and the orientation of PVDF chains, which are more conducive to the diffusion of chains 20,29 . PVDF chains and OMMT tactoids accumulate large amounts of energy in the compression process of convergence region, which is converted into the strong motion energy of molecular chains and OMMT in the form of the tensile stress when entering the divergent region.…”

“…At present, the plasticizing equipment based on elongational flow field has been gradually applied to the processing of high viscosity polymers, such as, ultrahigh molecular weight polyethylene (UHMWPE), 18 binary‐phase incompatible polymers 19,20 and nano‐paricle or nano‐fiber based composites 21,22 . Some researchers established theoretical models for the influence of processing flow field on mixing dispersion in the compounding process of polymer nanocomposites 23,24 .…”

Recent Advances in Elongational Flow Dominated Polymer Processing Technologies

“…Poly-L-lactic acid (PLA) as a biodegradable and biocompatible polymer, has attracted intensive attentions of researchers. Simple and effective methods to improve the crystallization of the PLA matrix for further mechanical-strength enhancements were proposed [ 43 , 44 , 45 , 46 ].…”

“…With an optimized TPU content of 25 wt%, an impact strength of 73.5 kJ m −2 was achieved. Further study demonstrated that the interfacial relaxation through the plastic deformation of PLA/TPU matrix endowed a better absorption and dissipation of fracture energy after an annealing process [ 45 ]. Thus, reaching a balanced toughness of 90.3 kJ m −2 and a stiffness of ~2.15 GPa.…”

“…The improved compatibility between PLA and in-situ fiberized components due to both the increased contacted area [ 47 , 48 ] and the on-fiber nucleating effect [ 44 , 45 ]. And the synergetic enhancement induced by the elongational flow dominated plasticizing and conveying process might be further expanded in other polymer composites.…”