Abstract Since PMDA-ODA polyimide is insoluble, its prepolymer (PMDA-ODA polyamic acid) has to be used to prepare asymmetric membranes which are then converted to polyimide using the imidization method. However, the phase inversion process of polyamic acid (PAA) in water is slow, which causes difficulties in the process of spinning PMDA-ODA hollow fiber (HF). In this paper, a variety of spinning parameters, including the PAA concentration, the content of ethanol additive, the bore fluid composition, the dope and bore flow rates, the HF take-up speed, the air gap distance, the temperature and size of coagulation bath have been adjusted to investigate their impacts on the HF cross-section morphologies. Based on our observations, the guidelines of spinning PMDA-ODA HF with regularly round inner and outer surfaces are given. That is, first, increase the phase inversion rate of the PAA dope; second, increase the residence period of the HF in the water coagulant; and third, maintain a relatively low coagulant temperature. Moreover, the viscosities, the grown rates of the precipitation and convection fronts of different PAA dopes, and the ternary phase diagram have been measured. The formation mechanism of the cross-section morphologies of the PAA HFs have been well explained using the abovementioned results.

中文翻译：

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具有规则截面形貌的PMDA-ODA中空纤维的制备及形成机理研究

摘要 由于PMDA-ODA聚酰亚胺不溶，必须使用其预聚物（PMDA-ODA聚酰胺酸）制备不对称膜，然后通过酰亚胺化方法将其转化为聚酰亚胺。然而，聚酰胺酸（PAA）在水中的转相过程缓慢，这给PMDA-ODA中空纤维（HF）的纺丝过程造成了困难。在本文中，各种纺丝参数，包括 PAA 浓度、乙醇添加剂含量、孔液成分、涂料和孔流速、HF 卷取速度、气隙距离、温度和尺寸已调整凝固浴以研究它们对 HF 横截面形态的影响。根据我们的观察，给出了旋转具有规则圆形内外表面的 PMDA-ODA HF 的指导方针。也就是说，首先，提高PAA涂料的相转化率；二是增加HF在混凝剂中的停留时间；第三，保持较低的混凝剂温度。此外，还测量了粘度、不同 PAA 涂料的沉淀和对流前沿的增长速率以及三元相图。使用上述结果已经很好地解释了 PAA HF 横截面形态的形成机制。