RESUMO
This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO2 foaming. PIF processing widened the foaming window of PLA to 40-120 °C, while supercritical CO2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (Ts). Both micron and nano cells showed decreasing cells size and increasing cell density as Ts elevated. The orientation factor as well as internal stress of PLA foams decreased with increased Ts. Compared with P-PLA samples, PLA foam prepared at Ts of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm-1). Furthermore, PLA foam prepared at Ts of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.
Assuntos
Poliésteres , Fenômenos Químicos , Poliésteres/química , TemperaturaRESUMO
Through regulating the reaction solvent and temperature, two Tb-based metal-organic frameworks, ((CH3)2NH2)2[Tb9(µ3-OH)8(µ2-OH)3(PTB)6]·(DMF)14·(H2O)19 (1) and ((CH3)2NH2)3{[Tb9(µ3-O)2(µ3-OH)12(H2O)6][Tb3(µ3-O)(HCO2)3 (PTB)6]}·(DMF)12·(H2O)7 (2) (H3PTB = pyridine-2,4,6-tribenzoic acid), have been synthesized. Structural analysis showed that the cluster node of 1 is a Tb9 cluster, while 2 contains two different nodes of a Tb3 cluster and a Tb9 cluster, which leads to their different pore structures and may potentially separate C2H2/CO2. Gas adsorption demonstrates that both MOFs can separate C2H2 and CO2, but 2 has a more optimized pore environment than 1 and can exhibit better selective separation of C2H2/CO2.
RESUMO
Poly(butylene succinate) (PBS)/polytetrafluoroethylene (PTFE) composites, including three types of PTFE powders, were prepared by melt blending using a HAAKE torque rheometer. Microcellular foams were successfully fabricated by batch foaming with supercritical fluids (scCO2). The effects of PTFE powder type on crystallization, rheological properties and foaming behavior were studied. PTFE L-5 and PTFE JH-220 powders showed good dispersion in the PBS matrix, and PTFE FA-500 powder underwent fibrillation during the melt blending process. All three PTFE powders gradually increased the crystallization temperature of PBS from 78.2 to 91.8 â and the crystallinity from 45.6 to 61.7% without apparent changes in the crystal structure. Rheological results revealed that PBS/PTFE composites had a higher storage modulus, loss modulus, and complex viscosity than those of pure PBS. In particular, the complex viscosity of the PBS/P500 composite increased by an order of magnitude in the low-frequency region. The foamed structure of PBS was obviously improved by adding PTFE powder, and the effect of fibrillated PTFE FA-500 was the most remarkable, with a pore mean diameter of 5.46 µm and a pore density of 1.86 × 109 cells/cm3 (neat PBS foam: 32.49 µm and 1.95 × 107 cells/cm3). Moreover, PBS/P500 foam always guarantees hydrophobicity.
RESUMO
Poly(lactic acid) (PLA) foams, with the combination of shish-kebab and spherulite nanoporous structure in skin and core layer respectively, was prepared using a novel technique comprising loop oscillating push-pull molding (LOPPM) and supercritical carbon dioxide low-temperature foaming process (SC-CO2LTFP). The foams present superior impact toughness which is 6-fold higher than that of neat PLA, and no significant decrease was observed for the storage modulus. Moreover, SC-CO2LTFP at soaking temperature ranging from 110 to 150 °C were performed to determine the evolution of pore morphology. The ultratough and supermoduli are unprecedented for PLA, and are in great need for broader applications.
