B-P-118-聚乳酸在高压下的结晶结构和熔融行为-安立佳

聚乳酸在高压下的结晶结构和熔融行为 黄绍永 蒋世春* 安立佳* 中国科学院长春应用化学研究所高分子物理与化学国家重点实验室 长春 130022 关键词: 聚乳酸 高压 结晶结构 聚乳酸作为医用材料和环境友好材料有着广阔的应用前景,[1]-[3]宏观性能与微 观结构紧密相关, 而结晶对聚合物的性能很重要,所以对聚乳酸的结晶行为, 结 构,形貌[4]-[6]全面的了解是很必要的. 高压下聚乳酸的结晶行为目前还没有报到过, 我们的实验就是研究高压对聚乳酸的结晶结构和熔融行为的影响. 实验通过 PVT100 来制备不同压力、不同温度下等温结晶的样品, 用广角 X射 线衍射和同步广角 X 射线散射和小角 X 射线散射, 研究其结晶情况, 包括晶型和 微晶尺寸、结晶结构, 并用示差扫描量热仪测定其熔点. Fig. 1 表明较低的结晶温度 Tc<90℃, Pc>100Mpa 时, 在 WAXS 图上观察不到 很多的反射峰, 包括典型的α晶型的反射峰(1 0 10), 甚至聚乳酸更普遍的反射 峰(110)(200), 这说明低温高压下结晶很困难. 这是由于低温下晶体生长在压力 作用下, 处于受限状态, 生长变得更加困难的原因. 10 15 20 25 30 (203) (310) (020) (015) (110) (200) (010) Pc=100Mpa T c =80 T c =90 T c =135 T c =145 T c =155 T c =165 In te ns ity 2Thata(degree) 80 100 120 140 160 8 10 16 18 20 22 Pc=50Mpa l c S pa ci ng (n m ) Tc P c =50Mpa L (a) (b) Fig 1. WAXS pattern of poly(L-lactide) isothermally crystallized at the different temperatures at pressures of 100Mpa.(a) Morphological parameters of PLLA isothermally crystallized at different Tcs (/℃) at certain pressure Pc=50Mpa. (b) 我们还发现在 Tc=165℃时, WAXD 图上显示有β晶体的特征衍射峰(003)β, 这表 明聚乳酸在 165℃等温结晶过程中, 发生了α到β晶型转变, 如 Fig 2. 用 WAXD 强度比率 I(003)β/[I(003)β+I(0010)α]来表示β晶型的生成率, 发现它的值随着 Pc的增加而线性的减小. 表明高压对转变起到抑止作用. Fig 3说明, 较低的结晶压力作用下, 聚乳酸的长周期和晶层厚度随着温度的 增加几乎呈现线性增加, 这是因为较高的结晶温度下, 更容易生成完善的晶体, 晶片的厚度也变厚. 而相同的结晶温度下长周期和晶层厚度随 Pc的增加而减小, 28 30 32 34 (0010)a+(023)B (1010)a (003)B Pc=20Mpa Pc=50Mpa Pc=100Mpa Pc=150Mpa Pc=250Mpa Tc=165 In te ns ity 2Theta/(degree) 0 50 100 150 200 250 0.2 0.3 0.4 0.5 I(0 03 ) ß/ [I( 00 3) ß+ I(0 01 0) a] Pc/(Mpa) (a) (b) Fig 2. (a) WAXD meridional profiles of poly(L-lactide) isothermally crystallized (a) at Tc=165℃ at different pressures showing the effect of the crystallization pressure on the α to β crystal transformation (b) Formation of β-form crystals at Tc=165℃ as a function of crystallization pressure as evaluated from the WAXD intensity ratio of I(003)β/[I(003)β+I(0010)α]. 0 50 100 150 200 250 5 10 15 15 20 25 lc Tc=145 Sp ac in g( nm ) Pc(Mpa) L Tc=145 0 50 100 150 200 250 6 9 12 15 160 165 170 175 180 185 Tc=145 lc (n m ) Pc(Mpa) Tc=145 T m (a) (b) Fig 4.Morphological parameters of PLLA isothermally crystallized at different Tcs (/℃) as a function of the crystallization pressure. (a) Fig 5.The corresponding relationship between the crystal thickness lc(nm) and the melting temperature of PLLA isothermally crystallized at 145℃ as a function of the crystallization pressure. (b) 说明压力增加, 受限程度变大, 不利于晶体的生长, 微晶尺寸变小. 我们初步找到了聚乳酸的熔点随晶层厚度的对应关系. 客观地讲, 影响熔点的 微观结构因素很多, 包括晶层厚度, 过渡层厚度, 晶型, 晶体完善程度等等, 但 是, Fig. 5 的对应关系证明了晶片厚度增加, 样品熔点升高这一结论. 参考文献 [1]Nijenhuis, A. J. ; Grijpma, D. W, ; Pennings, A. J. Macromolecules 1992, 25, 6419 [2]Ikada, Y. ; Shikinami, Y. ; Hara, Y. ; Tagawa, M. ; Fukada, E. J. Biomed. Mater. Res. Part A 1996, 30, 553 [3]Masahiro F. ; Yoshiharu, D. Biomacromolecules 2003, 4, 1301 [4]Hoogsteen, W.; Postema, A. R.; Pennings, A. J.; Brinke, G.; Zugenmaier, P. Macromolecules 1990, 23, 634 [5]Alean, C.; Lotz, B.; Puiggali, J. Macromolecules 2001, 34, 4542 [6]Cartier, L.; Okihara, T.;Ikada, Y.; Tsuji, H.; Puiggali, J.;Lotz, B. Polymer 2000, 41, 8921 Crystal Structure and Melting Behavior of Poly(L-lactide) in High Pressure Shaoyong Huang, Shichun Jiang* and Lijia An* State Key Laboratory of Polymer Physics and Chemistry, Chang Chun Institute of Applied Chemistry, Chinese Academy of Science, Chang Chun, 130022 ABSTRACT. The crystal structure and melting behavior of poly(L-lactide) (PLLA) in high pressure were investigated using differential scanning calorimetry (DSC), wide angel X-ray diffraction (WAXD), small- and wide-angel X-ray scattering (SAXS, WAXS). High pressure influenced the structure parameters including the long period and crystal thickness, and we found the corresponding relationship between the melting point and the crystal thickness. The α to β crystalline form transformation also observed at higher crystallization temperature and higher pressure in WAXD patterns. Key Words: Poly(L-lactide) High pressure Crystal structure 国家自然科学基金项目（20574069）