Department of Chemical Engineering, National Cheng Kung University , Tainan 701, Taiwan, Republic of China.
Biomacromolecules. 2017 Sep 11;18(9):2906-2917. doi: 10.1021/acs.biomac.7b00863. Epub 2017 Aug 30.
Through single-tube electrospinning, the biodegradable core-shell fibers of poly(3-hydroxybutyrate) (PHB) and poly(d,l-lactic acid) (PDLLA) were obtained from blend solutions with different compositions at a total polymer concentration of 7 wt %. Regardless whether PHB is the major or minor component (PHB/PDLLA = 90/10, 75/25, 50/50, and 25/75 wt. ratio), these phase-separated solutions all yielded core-shell fibers with PHB as core and PDLLA as shell. A new scenario of core-shell fiber formation was proposed on the basis of the relative magnitude of the intrinsic relaxation rate of fluids and external extension rate during electrospinning. The effects of blend compositions on the morphologies of the Taylor cone, whipping jet, and as-spun fibers were investigated. The diameters of core-shell fibers can be tailored by simply varying the PHB/PDLLA ratios. Two scaling laws describing the apparent viscosity (η) dependence of the outer fiber diameter (d) and core fiber diameter (d) were derived. That is, d ∼ η and d ∼ η. The microstructures of the as-spun fibers were determined by differential scanning calorimetry, Fourier transform infrared spectroscopy, and synchrotron wide-angle and small-angle X-ray scatterings. Results showed that the PDLLA component was in the amorphous state, and the crystallizability of PHB component remained unchanged, except the amorphous 10/90 fibers electrospun from a miscible solution state. The synergistic mechanical properties of the core-shell fibers were obtained, along with the ductile PDLLA shell enclosing the brittle PHB core. The enhanced toughness was attributed to the fragmentation of the brittle PHB core and necking fracture of the ductile PDLLA shell, which served as an effective route for energy dissipation. Compared with the neat PHB fiber, the 90/10 and 75/25 core-shell fibers possessed larger elastic moduli, which was attributed to the high PHB crystal orientation in their core sections despite the reduced PHB crystallinity. By contrast, the crystal c-axis of PHB in the 25/75 core-shell fibers was preferentially perpendicular to the fiber axis, suggesting the significant stretching of developing PHB crystals during electrospinning.
通过单管静电纺丝，从不同组成的共混溶液中获得了可生物降解的聚（3-羟基丁酸酯）（PHB）和聚（D，L-乳酸）（PDLLA）的核壳纤维，总聚合物浓度为 7wt%。无论 PHB 是主要成分还是次要成分（PHB/PDLLA=90/10、75/25、50/50 和 25/75wt.比），这些相分离溶液都生成了以 PHB 为核、PDLLA 为壳的核壳纤维。基于静电纺丝过程中流体的固有松弛率与外部拉伸速率的相对大小，提出了一种新的核壳纤维形成方案。研究了共混组成对泰勒锥、鞭动射流和纺丝纤维形态的影响。通过简单改变 PHB/PDLLA 比值，可以调整核壳纤维的直径。推导出了两个描述外纤维直径（d）和核纤维直径（d）与表观粘度（η）的关系的标度律。即，d∼η和 d∼η。通过差示扫描量热法、傅里叶变换红外光谱和同步加速器广角和小角 X 射线散射确定了纺丝纤维的微观结构。结果表明，PDLLA 组分处于无定形状态，除了从可混溶溶液状态静电纺丝的 10/90 纤维外，PHB 组分的结晶能力保持不变。核壳纤维具有协同的力学性能，韧性 PDLLA 壳包裹脆性 PHB 核。韧性的提高归因于脆性 PHB 核的碎裂和韧性 PDLLA 壳的颈缩断裂，这是能量耗散的有效途径。与纯 PHB 纤维相比，90/10 和 75/25 核壳纤维具有更大的弹性模量，这归因于其核部分 PHB 晶体的高取向度，尽管 PHB 结晶度降低。相比之下，25/75 核壳纤维中 PHB 的晶轴优先垂直于纤维轴，表明在静电纺丝过程中 PHB 晶体的显著拉伸。
