聚乳酸多孔微球的制备及其表征

以聚乳酸（PLLA）/四氢呋喃（THF）为淬火溶液，无其他添加剂条件下，通过低温淬火、萃取、洗涤和干燥得到直径为30.92μm±1.55μm的PLLA多孔微球，多孔微球由直径为0.34μm±0.06μm向外辐射的纤维组成。偏光显微镜表明多孔微球为球晶结构。XRD结果表明，多孔微球属于α晶型，晶粒尺寸大小为17.25nm。DSC结果表明，PLLA多孔微球的结晶度为36.05%。与熔融挤出造粒得到PLLA原料（结晶度小于10%）相比，低温淬火得到的多孔微球的结晶度大大提高。N₂吸附-脱附结果分析表明，多孔微球的平均孔径和孔体积分别为42.92nm和0.1135cm³/g，大部分为大孔和介孔结构，比表面积和孔隙率分别为14.18cm²/g和93.15%。采用等温DSC模拟低温淬火过程研究了PLLA在THF溶液中结晶动力学，利用Avrami方程得到Avrami指数n平均值为2.29，说明PLLA在THF溶液中为异相成核和三维生长。

Fabrication and characterization of poly(L-lactic acid) porous microspheres

Poly (L-lactic acid) porous microspheres with diameter of 30.92μm±1.55μm were prepared from its tetrahydrofuran solution through four steps of low-temperature quenching,extraction,washing and drying while without the assistance of other additives. The microspheres were composed of radicalized nanofibers with diameter of 0.34μm±0.06μm. The polarized optical microscope observations show that the PLLA porous microspheres are spherulites,while the XRD patterns show that they belong to α form with grain size of 17.25nm. DSC results show that the crystallinity of the microspheres obtained from low-temperature quenching are 36.05%,higher than the raw PLLA prepared by the melt-extrusion. N₂ adsorption-desorption results indicate that the average pore size and volume of the microspheres are 42.92nm and 0.1135cm³/g,respectively,and most pores are macropore and mesopore. The specific surface area and porosity are 14.18m²/g and 93.15%,respectively. DSC was used to study the isothermal crystallization kinetics of PLLA in THF solutions to mimic the low-temperature quenching process. The Avrami equation was used to analyze the data. Avrami exponent n was 2.29,indicating that the nucleation and crystal growth mechanism were heterogenous nucleation and three-dimensional,respectively.