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In situ Investigation of Crystallization Behavior of Nylon 6 under Rapid Pressurization
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DOI：10.11777/j.issn1000-3304.2025.25295.png)
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Abstract
En 中文
The driving force for high-pressure crystallization of polymers is undercooling. According to the pressure-melting point phase diagram of nylon 6(PA6), sufficient pressure (target pressure) can generate adequate undercooling to induce crystallization during pressurization. In this work, a self-designed variable-speed diamond anvil cell (s-dDAC) was employed to subject PA6 to rapid pressurization treatment at a pressurization rate of 1 GPa/s. The effect of target pressure on the crystallization behavior of PA6 was investigated in situ using multiple structural characterization techniques. The results demonstrated that target pressure significantly influenced both the crystal polymorphism and crystallization process of PA6. When the target pressure was <= 2.5 GPa, the melt could not completely solidify during pressurization, exhibiting crystallization lag, and the resulting samples consistof a mixed phase dominated by alpha-phase with minor beta-phase content. When the target pressure was >= 3.0 GPa, the crystallization lag disappears, and the samples comprise a mixed phase dominated by beta-phase with minor alpha-phase content. Regardless of target pressure, the critical pressure at which PA6 melt initiated solidification remains nearly constant at approximately 340 MPa. When the target pressure was >= 3.0 GPa, PA6 melt can continuously solidify within a pressure window ranging from 340 MPa to 2.7 GPa. During depressurization, the volume of beta-phase crystals continuously expanded, accompanied by partial crystal destruction. This work represents the first successful preparation of beta-phase-containing PA6 products via rapid pressurization method, with in situ observation of both the pressurization-induced formation process and depressurization-induced destruction process, demonstrating that modulating pressurization conditions can not only control the crystallization kinetics of PA6 but also enable the fabrication of products with distinctive structures.
Keywords:
In situ investigation
Nylon 6
s-dDAC
Target pressure
Crystallization behavior
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