Parreño Ronaldo P, Liu Ying-Ling, Beltran Arnel B, Carandang Maricar B
Department of Chemical Engineering, De La Salle University 2401 Taft Avenue Manila 1004 Philippines
Chemicals and Energy Division, Industrial Technology Development Institute (ITDI), Department of Science and Technology (DOST) Taguig 1631 Philippines
RSC Adv. 2020 Apr 7;10(24):14198-14207. doi: 10.1039/d0ra01285h. eCollection 2020 Apr 6.
Electrospun nanofibers of polybenzoxazines (PBzs) were fabricated using an electrospinning process and crosslinked by a sequential thermal treatment. Functionalization by the direct sulfonation process followed after the post-electrospinning modification treatment. The first stage of experiment determined the effects of varying the concentration of sulfuric acid as the sulfonating agent in the sulfonation reaction under ordinary conditions. The second stage examined the mechanism and kinetics of the sulfonation reaction using only concentrated HSO at different reaction time periods of 3 h, 6 h, and 24 h. The mechanism of the sulfonation reaction with PBz nanofibers was proposed with only one sulfonic acid (-SOH) group attached to each of the repeating units since only first type substitution in the aromatic structure occurs under this condition. The kinetics of the reaction exhibited a logarithmic correlation where the rate of change in the ion exchange capacity (IEC) with the reaction time increased rapidly and then reached a plateau at the reaction time between 18 h and 24 h. Effective sulfonation was confirmed by electron spectroscopy with a characteristic peak associated with the C-S bond owing to the sulfonate group introduced onto the surface of the nanofibers. ATR-FTIR spectroscopy also confirmed these results for varying reaction times. The SEM images showed that sulfonation has no drastic effects on the morphology and microstructure of the nanofibers but a rougher surface was evident due to the wetted fibers with sulfonate groups attached to the surface. EDX spectra exhibited sulfur peaks where the concentration of sulfonate groups present in the nanofibers is directly proportional to the reaction time. From surface wettability studies, it was found that the nanofibers retained the hydrophobicity after sulfonation but the inherent surface property of PBz nanofibers was observed by changing the pH level of water to basic, which switches its surface properties to hydrophilic. The thermal stability of the sulfonated nanofibers showed almost the same behavior compared to non-sulfonated nanofibers except for the 24 h sulfonation case, which has slightly lower onset temperature of degradation.
采用静电纺丝工艺制备了聚苯并恶嗪（PBz）电纺纳米纤维，并通过连续热处理进行交联。在静电纺丝后改性处理之后，通过直接磺化工艺进行功能化。实验的第一阶段确定了在普通条件下，改变作为磺化剂的硫酸浓度对磺化反应的影响。第二阶段在不同反应时间段（3小时、6小时和24小时）仅使用浓硫酸研究磺化反应的机理和动力学。提出了PBz纳米纤维磺化反应的机理，由于在此条件下芳香结构中仅发生第一类取代，每个重复单元仅连接一个磺酸（-SOH）基团。反应动力学呈现对数相关性，其中离子交换容量（IEC）随反应时间的变化率迅速增加，然后在18小时至24小时的反应时间达到平稳状态。通过电子能谱证实了有效的磺化，由于磺酸基团引入到纳米纤维表面，出现了与C-S键相关的特征峰。衰减全反射傅里叶变换红外光谱（ATR-FTIR）也证实了不同反应时间的这些结果。扫描电子显微镜（SEM）图像显示，磺化对纳米纤维的形态和微观结构没有剧烈影响，但由于表面附着磺酸基团的纤维被润湿，表面明显更粗糙。能量色散X射线光谱（EDX）显示有硫峰，纳米纤维中存在的磺酸基团浓度与反应时间成正比。从表面润湿性研究发现，磺化后纳米纤维保留了疏水性，但通过将水的pH值变为碱性观察到PBz纳米纤维的固有表面性质发生变化，其表面性质变为亲水性。与未磺化的纳米纤维相比，磺化纳米纤维的热稳定性表现出几乎相同的行为，除了24小时磺化的情况，其降解起始温度略低。
