Summary: The cold crystallization process of initially amorphous poly(L ‐lactic acid), PLLA, with two different molecular weights, during a heating at 2 °C/min, was investigated by DSC and time‐resolved simultaneous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D‐SAXS patterns showed that the average Bragg long period (LB) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re‐crystallization process that took place before the nominal melting peak seen by DSC. LB values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non‐isothermal cold crystallization of the two PLLA samples corresponded mainly to a three‐dimensional growth, although an imperfect crystallization process was involved at early times. The crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.
SAXS profiles of PLLA2 as a function of temperature. The inset shows the 2D‐SAXS pattern obtained at 180 °C. 相似文献
To develop a novel degradable poly (L-lactic acid)/β-tricalcium phosphate (PLLA/β-TCP) bioactive materials for bone tissue engineering, β-TCP powder was produced by a new wet process. Porous scaffolds were prepared by three steps, I.e. Solvent casting, compression molding and leaching stage. Factors influencing the compressive strength and the degradation behavior of the porous scaffold, e.g. Weight fraction of pore forming agent-sodium chloride (NaCl), weight ratio of PLLA: β-TCP, the particle size ofβ-TCP and the porosity, were discussed in details. Rat marrow stromal cells (RMSC) were incorporated into the composite by tissue engineering approach. Biological and osteogenesis potential of the composite scaffold were determined with MTT assay, alkaline phosphatase (ALP) activity and bone osteocalcin (OCN) content evaluation. Results show that PLLA/β-TCP bioactive porous scaffold has good mechanical and pore structure with adjustable compressive strength needed for surgery. RMSCs seeding on porous PLLA/β-TCP composite behaves good seeding efficacy, biocompatibility and osteoinductive potential. Osteoprogenitor cells could well penetrate into the material matrix and begin cell proliferation and osteogenic differentiation. Osseous matrix could be formed on the surface of the composite after culturing in vitro. It is expected that the PLLA/β-TCP porous composites are promising scaffolds for bone tissue engineering in prosthesis surgery. 相似文献
Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed. 相似文献
Polymer microparticles are useful for numerous applications such as stationary phases in chromatography, adsorbents and catalyst supports, as well as for drug delivery systems. In recent decades the application of supercritical fluids for microparticle precipitation has been developed to a point where it is an ideal alternative to conventional processes. In this work poly(l-lactic acid) (PLLA), a biodegradable and biocompatible thermoplastic aliphatic polyester, has been processed using supercritical fluids, particularly by rapid expansion of supercritical solutions (RESS) and supercritical antisolvent (SAS) processes over a wide miscibility range. Particle morphology was greatly improved from irregular blocks to spherical microparticles on applying the SAS process. The effects of changes in polymer concentration, liquid flow rate, nozzle diameter, solvent, pressure and temperature have also been evaluated on the particle size of PLLA in the SAS precipitation. A higher concentration of the initial solution led to a decrease in particle size. Dichloromethane was the best of the chlorinated solvents investigated. The nozzle diameter had a negligible effect on particle size and the highest liquid flow rate gave the largest particle size. A larger particle size was also obtained on increasing the operating temperature. In contrast, the particle size decreased on increasing the operating pressure. 相似文献
Water-repellent surfaces were fabricated on blend sheets of poly(l-lactic acid)/poly(butylene succinate) with various blending ratios by the successive processing; (1) plasma etching, followed by (2) the hydrophobic plasma polymer coating. Rough morphology was formed effectively on the mosaic structured surface of blend sheets via the oxidative etching, and advanced water repellency was achieved after the thin membrane coating was synthesized with a hydrophobic plasma polymer coating by use of hexamethyldisiloxane or hexamethyldisilazane. High water repellency is expressed through the columnar hair-like structured model, where the air-water surface interaction in the voids is taken into account. 相似文献