Ge Jia-wen, Liu Shao-xuan, Zhang Cheng-feng, Li Qin, Xia Jin-ming, Xu Yi-zhuang, Wu Jin-guang
College of Pharmacy, Henan University, Kaifeng 471003, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2012 Jan;32(1):118-22.
In the present work, we prepared nylon 6 crystals via crystallization of nylon from phosphoric acid by using the vapors of ammonium hydroxide as a precipitation regent. Both XRD and FTIR results demonstrate that the obtained nylon 6 sample exhibit characteristic peaks of nylon 6 in gamma form. In addition, treatment of nylon 6 in boiling water for half an hour followed by FTIR and XRD characterization shows that the obtained nylon 6 sample is in gamma form rather than in meta-stable b form. DSC characterization indicates that the nylon 6 sample exhibits two melting peaks (213 and 220 degrees C) when the sample is heated at a heating rate of 10 degrees C x min(-1). The reason for this phenomenon is that the nylon 6 sample has different lamellar thickness. To investigate the thermal behavior of the nylon 6 sample, the sample underwent the following thermal treatment procedure. First, the sample was heated to a pre-set temperature (T(s)) and kept at that temperature for an hour. Subsequently, the sample was cooled down to 100 degrees C at a cooling rate of 1 degrees C x min(-1), and then cooled down to room temperature at a cooling rate of 10 degrees C x min(-1). The treated samples were characterized by FTIR and DSC method. Experimental results show that the treated nylon 6 samples exhibit different crystalline behavior. When T. ranges from 130 to 160 degrees C, no significant changes were observed. When T(s) is 170 degrees C, a small fraction nylon 6 crystals is destroyed and recrystallized into thin lamellae in a form. As a result, a pre-melting peak appears in DSC result. The pre-melting peak moves to higher temperature and its peak area increases significantly upon increasing T(s) from 170 to 198 degrees C. When T(s) amounts to 200 degrees C, the pre-melting peak and the melting peaks 213 degrees C merge into one melting peak and two melting peaks are observed at 212 and 220 degrees C in the DSC results. FTIR spectra indicate that significant amount of crystalline nylon 6 in a form appears but the majority of crystalline phase of the sample is still gamma phase. As T(s) increases from 200 to 209 degrees C, the melting peak at lower temperature moves to higher temperature with increasing its peak area. On the other hand, the melting peak at 220 degrees C decreases in intensity but does not show any peak shift. As T(s) reaches 209 degrees C, the two melting peaks merge into one peak and FTIR results demonstrate that nylon 6 in a form becomes dominate phase in the sample. In the whole heat-treatment process, the gamma phase nylon 6 sample began to transform to a phase at the heat-treatment temperature of 170 degrees C, which is far below the melting point of the original sample (221 degrees C). This is different from the results reported in the literature, which state that gamma phase nylon 6 will not transform to alpha-phase until nylon is melt.
在本工作中，我们通过使用氢氧化铵蒸汽作为沉淀剂，使尼龙在磷酸中结晶来制备尼龙6晶体。XRD和FTIR结果均表明，所获得的尼龙6样品呈现出γ型尼龙6的特征峰。此外，将尼龙6在沸水中处理半小时，随后进行FTIR和XRD表征，结果表明所获得的尼龙6样品为γ型而非亚稳态的β型。DSC表征表明，当样品以10℃×min⁻¹的升温速率加热时，尼龙6样品呈现出两个熔点峰（213℃和220℃）。出现这种现象的原因是尼龙6样品具有不同的片晶厚度。为了研究尼龙6样品的热行为，该样品经历了以下热处理过程。首先，将样品加热至预设温度（T(s)）并在该温度下保持一小时。随后，将样品以1℃×min⁻¹的冷却速率冷却至100℃，然后以10℃×min⁻¹的冷却速率冷却至室温。通过FTIR和DSC方法对处理后的样品进行表征。实验结果表明，处理后的尼龙6样品呈现出不同的结晶行为。当T(s)在130至160℃范围内时，未观察到明显变化。当T(s)为170℃时，一小部分尼龙6晶体被破坏并重新结晶成薄片状的α型。结果，DSC结果中出现了一个预熔峰。随着T(s)从170℃增加到198℃，预熔峰向更高温度移动且其峰面积显著增加。当T(s)达到200℃时，预熔峰与213℃的熔点峰合并为一个熔点峰，并且在DSC结果中观察到在212℃和220℃出现两个熔点峰。FTIR光谱表明出现了大量的α型结晶尼龙6，但样品的大部分结晶相仍为γ相。随着T(s)从200℃增加到209℃，较低温度下的熔点峰向更高温度移动且其峰面积增加。另一方面，220℃的熔点峰强度降低但未出现任何峰位移。当T(s)达到209℃时，两个熔点峰合并为一个峰，并且FTIR结果表明α型尼龙6在样品中成为主导相。在整个热处理过程中，γ相尼龙6样品在170℃的热处理温度下开始转变为α相，这远低于原始样品的熔点（221℃）。这与文献报道的结果不同，文献称γ相尼龙6直到尼龙熔融才会转变为α相。
