MELTING AND CRYSTALLIZATION BEHAVIORS OF ISOTACTIC POLY-1-BUTENE UNDER CO 2 ATMOSPHERE

Transcription

1 MELTING AND CRYSTALLIZATION BEHAVIORS OF ISOTACTIC POLY-1-BUTENE UNDER ATMOSPHERE Lei Li, Tao Liu, Feng He, Ling Zhao State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai , People s Republic of China Abstract The melting behaviors of three isotactic poly-1-butenes with different crystal structure, Form I, Form II and Form III, were studied by high pressure differential calorimetry (DSC) and high pressure in-situ fourier transform infrared spectroscopy (FTIR) under atmosphere from 0.1 MPa to 10 MPa. The results showed the melting temperatures of three crystal forms decreased linearly with increasing the pressure. The slopes dtm/dp of Form I, Form II and Form III are -1.38,-4.19 and -1.54, respectively. Under the higher Pressure (more than 5 MPa), the Form II would transform totally to Form I during the heating process., but the Form III to Form II transformation during the Form III melting process was inhibited. It was found that the can accelerate the transformation rate of Form II to Form I during the melting and crystallization process of ipb-1. Moreover, the decreased the crystallization temperature of ipb-1 when it was cooled from melt to Form II. Introduction Isotactic poly-1-butene (ipb-1) is one of the most used commercial polyolefins[1]. ipb-1 has five different crystalline structure: I, II, III, I' and II'[2-4]. The unstable Form II crystallizes from the melt[5]. Form II can transform to Form I at room temperature and atmosphere pressure[6-8]. The Form III is usually formed by crystallization from dilute solution of suitable solvent[9-11]. Form I' can be obtained by crystallization under high pressure or by crystallization from certain solvent[12, 13]. Form II' can be generated from melt crystallization under pressure. Form I and Form I' are rhombohedral or twined hexagonal modification with 3/1 helix conformation[14, 15]. They have the same X-ray diffraction pattern. The only difference is the Form I have a higher melting temperature ( )[16] than Form I' (-100 o C)[17]. Form II has a tragonal crystal structure with 11/3 helix conformation and a melting temperature of 110 o C-120 o C[18-20]. The orthorhombic crystalline Form III with 4/1 helix conformation has a melting temperature of -100 o C [21, 22]. The melting and crystallization behaviors of ipb-1 under pressure are more complicated than those under atmosphere. Nakafuku and Miyaki[23] studied the effect of pressure on the melting and crystallization behavior of ipb-1 under high hydrostatic pressure up to 5 kbar. They reported above 900 bar Form II transform to Form I totally during the heating process. Form I' and Form II' are crystallized from the melt. Kishore and Vasanthakumari[24] published an investigation of melting process of Form I in high pressure N 2 and Ar from atmosphere pressure to 0.07 Kbar by DSC. The can assist the melting of semicrystalline polymers[25]. The melting and Corresponding author. zhaoling@ecust.edu.cn 1

2 crystallization processes of the ipb-1 under are still unknown. The aim of this work is to investigate the effects of atmosphere on the melting and crystallization behaviors of three different kinds of modification and the crystallization process from melt. Experimental Samples and sample preparation The sample (PB 0110M) used in this study was pellets obtained from Basell Polyolefins. The sample was purified by acetone at least 24 hours, and was dried in vacuum for 2 days. The films of Form II for DSC and FTIR were prepared by melting the pellets at 160 o C and pressing at 10 MPa for 30 min, followed by a quench at liquid nitrogen. Form I film was obtained from annealed the form II film at room temperature for 6 months. Form III film was prepared by evaporation of 1% (by weight) ipb-1 solutions from carbon tetrachloride and drying at room temperature. High Pressure DSC measurements A NETZSCH 204 HP was used for the high pressure DSC measurements. The 4-5 mg samples were heated in atmosphere from to 170 o C; the temperature axis was calibrated by In, Bi, Sn, Pb and Zn. The heating rate of the DSC experiments was 10 o C /min. High pressure FTIR measurements For in-situ FTIR measurements a BRUKER EQUINOX-55 with a high pressure cell (TFC-M13) was used. The FTIR spectral were collected by signal averaging 32 scans at a resolution of 4 cm -1 in the wave number range of cm -1. The heating rate at the heating process is 1 /min form to 170 o C, and the cooling rate form 170 o C to 100 o C and 100 o C to are 10 o C /min and 1 o C /min respectively. Results and discussion Melting behavior of ipb-1with different crystal structures under Pressure Figure 1 shows the high pressure DSC curves of ipb-1 Form I melting process at different pressures. As shown in Figure 1, the melting point of Form I decrease with the pressure increasing form 0.1 MPa to 10 MPa. The melting points, T m, the endothermic peak temperatures, as a function of pressure P CO2 are shown in Figure 2. It shows that the melting point decrease linearly with increasing the pressure. The slope of the line (dt m /dp) is Endo 10 MPa 132 T m = *P CO2 (MPa) 8 MPa 128 DSC 6 MPa 5 MPa 4 MPa 2 MPa 0.5 MPa 0.1 MPa R = Fig 1. DSC scan measurements of ipb-1 Form I at different pressures Pressure, MPa Fig 2. The ipb-1 Form I melt temperature as a function of pressure. The high pressure DSC curves of ipb-1 Form II melting process at different pressures are shown in Figure 3. There is only one endothermic peak existed on DSC curves when the pressures are lower than 0.5 MPa. When the pressures are 2 MPa and 4 2

3 MPa, there are two endothermic peaks, the second peak at the higher temperature corresponds to the melting of Form I that is formed by the -assisted Form II to Form I transformation. The area of the second endothermic peak is increasing as the pressure increasing. At a higher pressure (5 MPa) there is only one endothermic peak. It reveals that during the heating process the Form II can transform to Form I totally during the heating process when the pressure above 5 MPa. These results demonstrate that a high pressure can promote the Form II to Form I transformation. Endo 5 MPa 115 T m = *P CO2 (MPa) DSC 4 MPa 2 MPa 0.5 MPa Temperature / o C R = MPa Fig 3. DSC scan measurements of ipb-1 Form II at different pressures Pressure / MPa Fig 4. The ipb-1 Form II melt temperature as a function of pressure. The melting temperature of Form II decreases with increasing the pressure before the Form II transform to Form I totally. The Form II melting temperature as a function of pressure is shown in Figure 4. The Form II melting point decrease linearly with increasing of the pressure. The slope of the line (dt m /dp) is Figure 5 shows the effect of pressure on the DSC curves of melting process of Form III. At the low pressure, there are two endothermic peaks on the DSC curves. The first endothermic peak is the melting of Form III and the second peak at the higher temperature corresponds to the Form II that is recrystallized during the Form III melting[26]. With increasing the pressure the Form II melt peak area is reducing. At 4 MPa and above, there is only one endothermic peak in the DSC curves. It shows that the high pressures can inhibit the recrystallization of Form II during the Form III melting process under the. At the same time the Form III melt peak move to the lower temperature as the pressure increasing. The Form III melting temperature as a function of pressure is shown in Figure 6. The Form II melting point decrease linearly with increasing of the pressure. The slope of the line (dt m /dp ) is Endo DSC 10 MPa 8 MPa 6 MPa 5 MPa 4 MPa 2 MPa 0.5 MPa 0.1 MPa T m = *P CO2 (MPa) R = Pressure, MPa Fig 5. DSC scan measurements of ipb-1 Fig 6. The ipb-1form III melt temperature Form III at different pressures. as a function of pressure. The pressure has different effect on the melting process. The crystal structure and molecular chain have significant influences on the melting temperature decreasing trend. The Form I is the most stable state of three modifications. It has a more compact molecular chain 3

4 packing structure. The influence on the molecular chain motion is weaker than other two phases. Then the plasticization effect on the Form I is weakest. Form III is a stable modification than Form II. From the slopes of three lines we conclude that the plasticization effect on the ipb-1 increases in the order: Form I< Form III< Form II. The melting process of Form III is also studied by using a in-situ FTIR. The infrared spectrums of melting behavior of Form III at 2 MPa are shown in Figures 7 and 8. The intense band at 900 cm -1 is the characteristic band of Form III and Form II and the band at 925 cm -1 is characteristic of Form I[27-31]. Below the temperature, the 905 cm -1 has no substantial change with temperature. From 90 to the absorbance intensity of 905 cm -1 decreases with the temperature, which indicates the melting process of Form III. At it is in the molten state. However, with increasing the temperature from 108 o C to 114 o C the absorbance intensity of 905 cm -1 increases. That indicates more and more Form II was formed. From 114 o C to 118 o C the intensity of 905 cm -1 decreases with increasing the temperature, and at 120 o C the polymer melts completely. The melting behaviors of Form III at 0.1 MPa and 0.5 MPa are same with the melting behaviors under 2 MPa. 120 o CO C 2 pressure = 2MPa 118 o C 114 o C 110 o C 108 o C 100 o C 114 o C 120 o C Fig. 7. IR spectra of ipb-1 Form III melting process (heating rate = 1 K/min) at 2 MPa Fig. 8. Scale-expanded infrared spectra of Form III in the range of taken at different temperature Figure 9 and Figure 10 show the infrared spectra of form III melting process at 4 MPa. It is evident that from to 120 o C the intensity of the characteristic band of Form III decreases with increasing the temperature. The melting behavior of Form III above 4 MPa is same as that under 4 MPa. The intensity of 905 cm -1 band doesn t change with increasing the temperature indicating that beyond 4 MPa the Form III melt directly to the molten state with increasing the temperature. Moreover, there is no recrystallization of Form III to Form II. pressure = 4 MPa 120 o C 110 o C pressure = 4 MPa Absrobance 104 o C 100 o C 94 o C 94 o C 100 o C 104 o C Fig. 7. IR spectra of ipb-1 Form III melting Fig. 8. Scale-expanded infrared spectra of Form III process (heating rate = 1 K/min) at 4 MPa in the range of taken at different temperature Those results demonstrate that at the heating rate of 1 o C/min the can inhibited the recrystallization of Form II during the Form III melting. Both the high pressure DSC and the 4

5 infrared spectral results above the 4 MPa show that the recrystallization of molten state from Form III to Form II is inhibited. The crystallization of molten state under high pressure The crystallization from ipb-1 melt to the solid state was studied by using a high pressure in-situ FTIR. Figure 9 and Figure 10 show the molten state ipb-1 cooling to the solid state at 8MPa. The infrared spectra has no significant changes during the cooling process form 170 o C to 65 o C indicating that no phase transformation occurs in ipb-1 film and the film is kept in molten state. The band at 905 cm -1 starts to emerge obviously at 60 o C during the further cooling. The molten state ipb-1 transforms to Form II at this temperature. Under the high pressure, the formed Form II transit to Form I at 56 o C. At the end of the cooling process the ipb-1 totally transforms to Form I. Pressure = 8 MPa Pressure = 8 MPa 56 o C 58 o C 60 o C 65 o C 70 o C 56 o C 70 o C 60 o C 170 o C Fig. 9. IR spectra of ipb-1 crystallization Fig. 10. Scale-expanded infrared spectra of crystallization process (heating rate = 1 K/min) at 4 MPa in the range of taken at different temperature The infrared spectra of the molten state ipb-1 crystallization under the of 6, 4, 2 and 0.1 MPa are shown in Figure 11. Pressure = 6 MPa 50 o C 40 o C 70 o C Pressure = 4 MPa 40 o C 75 o C 80 o C 73 o C Pressure =2 MPa Pressure=0.1MPa 35 o 80 o C C 85 o C 95 o C Temperature / o C T = P CO2 ( MPa) R = Fig. 11. Scale-expanded infrared spectra of crystallization process in the range of taken at different temperature Pressure / MPa Fig. 12. The melt to Form II transformation temperature with pressure These observations indicate that the ipb-1 crystallization from the molten state is firstly transform to the Form II. At a high pressure the Form II can transform to the stable Form I during the cooling process. The difference between the Figure 10 and Figure 11 is the temperature at which Form II is transformed from the molten state. The pressure-depended ipb-1 molten state to Form II transition temperature is shown in Figure 12. The transformation temperatures decrease linearly with the increasing the pressure. Conclusions The can assist the melt of ipb-1 three different modifications. The melting 5

6 temperature decreases with the pressure increasing. The slopes (dt m /dp) of Form I, Form II and Form III are -1.38,-4.19 and -1.54, respectively. The crystal structure has a substantial influence on the dt m /dp. The plasticization effect on the ipb-1 increases in the order: Form I< Form III< Form II. The Form II to Form I transition can be accelerated by applying high pressure. Above 5 MPa Form II can transform to Form I totally during the heating process. When pressure is higher than 4 MPa, due to the assisted molecular chain mobility and reduced of the specific surface free energy, the Form III melt directly without transforming to the metastable From III. ipb-1crystallization from the melt firstly transforms to Form II. At a high pressure during the cooling process Form II can transform to Form I. The temperatures of the ipb-1 melt crystallize to Form II decrease linearly with the pressure increasing. References (1) Men, Y.; Rieger, J.; Homeyer, J. Macromolecules 2004, 37, (2) Luciani, L.; Seppala, J.; Lofgren, B. Progress in Polymer Science 1988, 13, (3) Causin, V.; Marega, C.; Marigo, A.; Ferrara, G.; Idiyatullina, G.; Fantinel, F. Polymer 2006, 47, (4) Jiang, S.; Duan, Y.; Li, L.; Yan, D.; Chen, E.; Yan, S. Polymer 2004, 45, (5) Fu, Q.; Heck, B.; Strobl, G.; Thomann, Y. Macromolecules 2001, 34, (6) Miyoshi, T.; Hayashi, S.; Imashiro, F.; Kaito, A. Macromolecules 2002, 35, (7) Kopp, S.; Wittmann, J. C.; Lotz, B. Journal of Materials Science 1994, 29, (8) Azzurri, F.; Alfonso, G. C.; Gomez, M. A.; Marti, M. C.; Ellis, G.; Marco, C. Macromolecules 2004, 37, (9) Clampitt, B. H.; Hughes, R. H. Journal of Polymer Science Part C: Polymer Symposia 1964, 6, (10) Kaszonyiova, M.; Rybnikar, F.; Geil, P. H. Journal of Macromolecular Science-Physics 2004, B43, (11) Kaszonyiova, M.; Rybnikar, K.; Geil, P. H. Journal of Macromolecular Science-Physics 2005, B44, (12) Nakamura, K.; Aoike, T.; Usaka, K.; Kanamoto, T. Macromolecules 1999, 32, (13) Mathieu, C.; Stocker, W.; Thierry, A.; Wittmann, J. C.; Lotz, B. Polymer 2001, 42, (14) Azzurri, F.; Flores, A.; Alfonso, G. C.; Calleja, F. J. B. Macromolecules 2002, 35, (15) DeRosa, C.; Auriemma, F.; Corradini, P.; Tarallo, O.; DelloIacono, S.; Ciaccia, E.; Resconi, L. J. Am. Chem. Soc. 2006, 128, (16) Alfonso, G. C.; Azzurri, F.; Castellano, M. Journal of Thermal Analysis and Calorimetry 2001, 66, (17) Leute, U.; Dollhopf, W. Colloid & Polymer Science 1983, 261, (18) Danusso, F.; Gianotti, G. Makromolekulare Chemie 1965, 88, (19) D. Maring, M. W. H. W. S. B. M. G. W. Journal of Polymer Science Part B: Polymer Physics 2000, 38, (20) Lu, K. B.; Yang, D. Polymer Bulletin 2007, 58, (21) Cojazzi, G.; Malta, V.; Celotti, G.; Zannetti, R. Makromolekulare Chemie 1976, 177, (22) Danusso, F.; Gianotti, G.; Polizzotti, G. Makromolekulare Chemie 1964, 80, (23) Kallitsis, J. K.; Kalfoglou, N. K. European Polymer Journal 1987, 23, (24) Kishore, K.; Vasanthakumari, R.; Ramesh, T. G. Journal of Polymer Science Part A: Polymer Chemistry 1986, 24, (25) Zhang, Z.; Handa, Y. P. Macromolecules 1997, 30, (26) Kaszonyiova, M.; Rybnikar, F.; Geil, P. H. Journal of Macromolecular Science Part B-Physics 2007, 46, (27) Luongo, J. P.; Salovey, R. Journal of Polymer Science Part B Polymer Letters 1965, 3, (28) Goldbach, G.; Peitscher, G. Journal of Polymer Science Part B Polymer Letters 1968, 6, (29) Luongo, J. P.; Salovey, R. Journal of Polymer Science Part A-2 Polymer Physics 1966, 4, (30) Chau, K. W.; Yang, Y. C.; Geil, P. H. Journal of Materials Science 1986, 21,

7 (31) Lee, K. H.; Snively, C. M.; Givens, S.; Chase, D. B.; Rabolt, J. F. Macromolecules 2007, 40,