Crystal transition and thermal behavior of Nylon 12

The polyamide 12 (PA12) with different crystal forms is prepared with three crystallization paths. The crystal structures and corresponding thermal properties are systematically investigated. The results reveal that an alpha-form and a mixed (alpha + gamma)-form of PA12 can be obtained by casting at 30 degrees C and (40-80 degrees C), respectively. Meanwhile, the gamma-form of PA12 can be obtained by both casting at 90 degrees C and slow melt cooling. However, the gamma'-form is obtained only by melt quenching. Both the gamma and gamma' forms of PA12 exhibit a single melting peak, whereas the alpha-form exhibits two melting peaks. The higher peak is attributed to the melting of gamma-PA12, which originates from the melting-recrystallization of the alpha-PA12. It is found that the tensile properties of PA12 depend on the crystal forms. Both the gamma and gamma'-PA12 are strong and tough polymer materials, while alpha-PA12 is a strong but brittle polymer material