Investigation of Thermal Behaviors of γ-Form Nylon 6 Prepared by Ammonia Vapor from Phosphoric Acid Solutions
GE Jia-wen1, 2, LIU Shao-xuan2, ZHANG Cheng-feng2, 3, LI Qin1, XIA Jin-ming4, XU Yi-zhuang2*, WU Jin-guang2
1. College of Pharmacy, Henan University, Kaifeng 471003, China 2. College of Chemsitry and Molecular Engineering, Peking University, Beijing 100871, China 3. Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China 4. Shenyang Dootel Biological Pharmacy Research Center, Shenyang 110031, China
Abstract：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 γ 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 γ form rather than in meta-stable b form. DSC characterization indicates that the nylon 6 sample exhibits two melting peaks (213 and 220 ℃) when the sample is heated at a heating rate of 10 ℃·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 (Ts) and kept at that temperature for an hour. Subsequently, the sample was cooled down to 100 ℃ at a cooling rate of 1 ℃·min-1, and then cooled down to room temperature at a cooling rate of 10 ℃·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 Ts ranges from 130 to 160 ℃, no significant changes were observed. When Ts is 170 ℃, 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 Ts from 170 to 198 ℃. When Ts amounts to 200 ℃, the pre-melting peak and the melting peaks 213 ℃ merge into one melting peak and two melting peaks are observed at 212 and 220 ℃ 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 γ phase. As Ts increases from 200 to 209 ℃, the melting peak at lower temperature moves to higher temperature with increasing its peak area. On the other hand, the melting peak at 220 ℃ decreases in intensity but does not show any peak shift. As Ts reaches 209 ℃, 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 γ phase nylon 6 sample began to transform to α phase at the heat-treatment temperature of 170 ℃, which is far below the melting point of the original sample (221 ℃). This is different from the results reported in the literature, which state that γ phase nylon 6 will not transform to α-phase until nylon is melt.
[1] Wunderlich B. Macromolecular Physics, Vol. 1, Crystal Structure, Morphology, Defects; New York: Academic Press, 1973. [2] Holmes D R, Bunn C W, Smith D J. J. Polym. Sci., 1955, 17: 159. [3] Arimoto H, Ishibashi M, Hirai M, et al. J. Polym. Sci., Polym. Chem., 1965, 3: 317. [4] Tsuruta M, Arimoto H, Ishibashi M. Kobunshi Kagaku, 1958, 15: 619. [5] Ueda S, Kimura T. Kobunshi Kagaku, 1958, 15: 243. [6] Kinoshita Y. Makromolekulare Chemie., 1959, 33(1): 1. [7] Stepaniak R F, Garton A, Carlsson D J, et al. J. Polym. Sci., Polym. Phys., 1979, 17: 987. [8] Parker J P, Lindenmeyer P H. J. Appl. Polym. Sci., 1977, 21: 821. [9] Penel-Pierron L, Depecker C, Seguela R, et al. J. Polym. Sci. Polym. Phys., 2001, 39(5): 484. [10] Persyn O, Miri V, Lefebvre J M, et al. Polym. Eng. Sc., 2004, 44(2): 261. [11] Zhang C F, Liu Y H, Liu S X, et al. Science in China Series B-Chemistry, 2009, 52(11): 1835. [12] Murthy N S, Aharoni S M, Szollosi A B. J. Polym. Sci., Polym. Phys., 1985, 23: 2549. [13] Murthy N S. Polym. Commum., 1991, 32: 301. [14] Murthy N S, Curran S A, Aharoni S M, et al. Macromol., 1991, 24: 3215. [15] Murthy N S, Minor H, Latif R A. J. Macromol. Sci. Phys., 1987, B26: 427. [16] Murthy N S, Bray R G, Correale S T, et al. Polym., 1995, 36: 3863. [17] Rotter G, Ishida H. J. Polym. Sci., Polym. Phys., 1992, 30: 489. [18] Starkweather H W Jr., Moore G E, Hansen J E, et al. J. Polym. Sci., 1956, 21: 189. [19] Ramesh C, Gowd E B. Macromol., 2001, 34: 3308. [20] Li H Z, et al. Macromol., 2009, 42: 1175. [21] Müller A J, Arnal M L. Prog. Polym. Sci., 2005, 30(5): 559. [22] Hoffman J D, Miller R L. Polym. 1997, 38(13): 3151.
