(Physical Chemistry Chemical Physics) Difference of the Micro-Dynamics Mechanism between Aromatic Nylon and Aliphatic Nylon during Water Absorption: Spectroscopic Evidence
writer：Liyang Jia, Gehong Su, Qiang Yuan, Xueqian Zhang, and Tao Zhou*
keywords：MXD6, barrier property; water absorption; scaling-MW2D; two-diemsional correlation ATR FITR spectroscopy
source：期刊
Issue time：2018年
The difference of the micro-dynamics mechanism between aromatic nylon and aliphatic nylon during water absorption was studied to explore the reason of phenomenon that the decline of the barrier performance of poly(m-xylene adipamide) (MXD6) film is significantly lower than that of polyamide 6 (PA6) film under the environment with high humidity. Attenuated total reflection (ATR) FTIR combined with the scaling moving-window 2D correlation spectroscopy (scaling-MW2D) and the generalized 2D correlation analysis was used. The scaling-MW2D confirmed that the water absorption of MXD6 had two processes, named process I (2.0?12.0 min) and process II (12.0?27.0 min). According to the sequential order of the functional groups’ movement obtained from the generalized 2D correlation analysis, it showed that the processes I and II have three steps and two steps, respectively. It revealed the process I is the process of water plasticizing MXD6, which primarily consists of hydrophilic groups forming hydrogen bonds with water molecules and the hydration of hydrophobic groups. The process II is the strong crystallization of MXD6 induced by water molecules, which is composed of the generation of the double hydrogen bond and the rearrangement of hydrophilic groups into the crystal lattice. However, for PA6, the results confirmed that the water absorption of PA6 only had a single process with two steps, which was actually the process of PA6 macromolecular chains plasticized by water molecules. Therefore, the reason of the barrier performance decline of the MXD6 film being significantly lower than that of the PA6 film is that water molecules induced a large amount of new crystalline regions in MXD6 matrix at the same time of plasticization.