Correlation between processing parameters and microstructure of electrospun poly(D,L-lactic acid) nanofibers
Correlation between processing parameters and microstructure of electrospun poly(D,L-lactic acid) nanofibers
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DOI：
10.1016/j.polymer.2009.10.025
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发表时间：
2009-11-27
期刊：
影响因子：
4.6
通讯作者：
Jhang, Hao Jhe
中科院分区：
文献类型：
--
作者：
Wang, Chi;Chien, Huan-Sheng;Jhang, Hao Jhe
使用二甲基甲酰胺作为溶剂，通过用于控制溶液温度范围为25至104 ℃的加热夹套进行具有各种浓度的聚（D，L-乳酸）（PDLLA，D-丙交酯含量：10%）溶液的静电纺丝。此外，还使用了红外线发射器，将周围温度控制在110摄氏度左右。研究了溶液性质和工艺参数对锥形/射流/纤维形态的影响，并采用偏光FTIR、WAXD和DSC对静电纺丝纤维的内部结构进行了表征。在给定溶液中存在足够的缠结密度是成功获得不含珠粒的均匀纤维的重要要求。比粘度（eta（sp））与PDLLA体积分数（phi（v））的对数-对数图为制备纤维状静电纺丝产品时确定缠结浓度（c（e））提供了有用的指导。eta（sp）的phi（v）依赖性从稀溶液的类似于phi（1.1）（v）的eta（sp）变化到具有缠结链的溶液的类似于phi（4.7）（v）的eta（sp）。从缠结的初始浓度，测定的c（e）类似于10重量%，这与通过2 M（e）/M-w的简单关系理论预测的相当一致，其中M-e和M-w分别是熔体缠结之间的分子量和PDLLA的平均分子量。然而，为了获得不含珠粒的均匀PDLLA纤维，对于具有足够网络强度的缠结溶液需要类似于1.9c（e）的最小浓度，以防止喷射搅打期间的毛细管不稳定性。射流直径（d（j））和纤维直径（d（f））与零剪切粘度（eta（o））的双对数图表明，本溶液存在两个标度律，即d（j）与eta相似（0.07）（o）和d（f）类似于eta（0.45）（o）对于给定的解，d（j）和d（f）之间的密切关系被导出为d（f）类似于d（j）（0.61），而与所应用的工艺变量的变化无关。高温静电纺丝由于eta（o）的降低而产生小直径的纤维，但由于溶剂蒸发的增强，当溶液温度高于56 ℃时，这种影响逐渐减弱。-0.063，而与所应用的静电纺丝条件无关。这表明在纳米纤维中没有形成优先链取向。然而，在DSC单元中以10 ° C/min的速率加热时，在97 ° C下发生快速结晶，随后分别以121和148 ° C为中心的两个分离良好的熔融吸热。WARD和FTIR结果显示仅存在α型晶体。这些独特的功能是由于在静电纺丝过程中发生的相分离，中断了沿沿着纤维在喷射拉伸过程中的链取向，并产生更多的反式-反式构象与更延长的链结构，容易促进在后加热过程中的冷结晶。(C)2009爱思唯尔有限公司保留所有权利。
Using dimethyl formamide as the solvent, electrospinning of poly(D,L-lactic acid) (PDLLA, D-lactide content:10%) solutions with various concentrations was performed by means of a heating jacket for controlling the solution temperature range from 25 to 104 degrees C. In addition, an IR emitter was used to control the surrounding temperature at similar to 110 degrees C. The effects of solution properties and processing variables on the morphologies of the cone/jet/fiber were investigated, and the internal structure of the electrospun fibers was characterized using polarized FTIR, WAXD and DSC. A sufficient entanglement density existing in a given solution was an important requirement for successfully obtaining uniform fibers without beads. The log-log plot of specific viscosity (eta(sp)) versus PDLLA volume fraction (phi(v)) provided us with a useful guideline to determine the entanglement concentration (c(e)) for preparing fiber-shaped electrospun products. The phi(v)-dependence of eta(sp) varied from eta(sp) similar to phi(1.1)(v) for a dilute solution to eta(sp) similar to phi(4.7)(v) for a solution possessing entangled chains. From the incipient concentration of entanglements, the determined c(e) was similar to 10 wt%, which was in fair agreement with what was predicted theoretically by a simple relation of 2M(e)/M-w where M-e and M-w were the molecular weight between melt entanglements and the average molecular weight of PDLLA, respectively. To obtain uniform PDLLA fibers without beads, however, a minimum concentration of similar to 1.9c(e) was required for the entangled solutions possessing sufficient network strength to prohibit the capillary instability during jet whipping. The log-log plots of the jet diameter (d(j)) and fiber diameter (d(f)) versus zero shear viscosity (eta(o)) showed two scaling laws existing for the present solution, that is, d(j) similar to eta(0.07)(o) and d(f) similar to eta(0.45)(o) For a given solution, an intimate relation between d(j) and d(f) was derived to be d(f) similar to d(j)(0.61), regardless of the variations of processing variables applied. High-temperature electrospinning produced small diameter fibers because of the reduction of eta(o), but the effect was gradually diminished for solution temperatures higher than 56 degrees C owing to the enhanced solvent evaporation.The as-spun nanofibers of this thermally slow-crystallizing PDLLA species were amorphous, and the Hermans orientation function calculated from the polarized FTIR results was ca. -0.063 regardless of the electrospinning conditions applied. This suggests that there was no preferential chain orientation developed in the nanofibers. In the heating in a DSC cell at a rate of 10 degrees C/min, however, rapid crystallization took place at 97 degrees C, followed by two well-separated melting endotherms centered at 121 and 148 degrees C, respectively. WARD and FTIR results exhibited the exclusive presence of alpha-form crystals. These unique features were attributed to the occurrence of phase separation during electrospinning, which interrupted the chain orientation along the fiber during jet stretching, and yielded more trans-trans conformers with more extended chain structure to readily facilitate the cold crystallization during post-heating. (C) 2009 Elsevier Ltd. All rights reserved.