Foaming Of Poly（Lactic Acid）/NaCl Composites With Supercritical CO₂

Owing to its biocompatibility, biodegradability, and bioabsorbable nature, polylacticacid is one of the most important materials used in tissue engineering scaffolds. Thefoaming materials of polylactic acid were prepared with supercritical carbon dioxidefoaming technology and salt particulate leaching techniques, which had goodinterconnected structures.In this paper, PLA/NaCl composites were prepared with different processingtechnology. And mechanical properties, thermal properties, melt strength and structuremorphology was studied.The best comprehensive properties of PLA/NaCl compositematerials were prepared with three screw extrusion new technology and equipment.Theexperiments showed that, PLA/NaCl composite materials were prepared with the traditionaltwin-screw extruder and new three screw extruder, compared with double screw extrusion,PLA/NaCl composite materials (the mass ratio60/40) were mixed more even with triplescrew extrusion and the tensile strength and tensile modulus can be increased by20%and54%respectively.Moreover, the higher NaCl addition of PLA/NaCl composite materials(themass ratio50/50) can be prepared with three screw extruder, which is good for preparingtissue engineering porous scaffolds with better pore structure.On the basis of the study, the effect of the NaCl particle content, particle size, and foamprocess parameters on the foam properties are studied for the foam system of PLA/NaCl.The effects of saturated time, foaming temperature, saturated temperature, and saturatedpress on supercritical carbon dioxide batch foaming properties and the pore structure of thematerials were studied systematicly, the microcellular plastics were obtained, whose qualityis60/40,and its mean cell diameter was13.72μm, cell density was2.5×108cell/cm3. Turnout that the effect of saturated time and foaming temperature on the foam properties wasobvious, and the effect of saturated temperature and saturated press on the bubble porestructure morphology was obvious.Aiming at that the NaCl particles is porogen, the saltparticulate leaching and the cell structure are studied with homemade circulation sink andultrasonic cleaning device, and the interconnected pore structures of a big cell with lotsmicrocell were obtained. The results of the study showed that, PLA/NaCl system of the mass ratio60/40was leaching and most of the NaCl particles of which can be washed away.Through the big cells formed by NaCl particles, whose mean cell diameter was90μm, andmicrocells formed by batch foaming PLA,whose mean cell diameter was6.28μm, theinterconnected structures were obtained.Supercritical carbon dioxide batch foaming and the salt particulate leachingexperiments of the PLA/NaCl composite materials (the mass ratio50/50) prepared by threescrew extrusion are done, which is initially attempted in this paper，and foaming materialswith better interconnected structures are achieved, which will provides feasibility of deeperresearch on foaming of PLA/NaCl composite materials with high quatity of NaCl.