Preparation of polylactic acid (PLA) foams with supercritical carbon dioxide and their applications for reflectors of white light-emitting diode (LED) lamps

Abstract

By batch as well as extrusion supercritical carbon dioxide (CO2) foaming processes, polylactic acid (PLA) foams exhibiting high physical properties (i.e. tiny cell sizes (average diameters ≦10μm), excellent reflectivities (99%), high resistance to discoloration (no color stain happens under UV illumination at 340nm for 200h), low densities (≦0.05g/cm3), and high environmental stabilities (no deformation under 100 times of thermal shock examination at −30°C to 60°C)) have been prepared with the appropriate prescription. Experimental results reveal that physical performances of PLA foams with extrusion supercritical CO2 foaming processes are superior to those with batch ones. Among lab-made PLA foams (i.e. PLA foam a–g), PLA foam g, whose density, average cell size, thickness, and reflectance are respectively 0.04g/cm3, 5μm, 2mm, and 99%, possess the best physical properties.Furthermore, we have also applied PLA foam f and g for reflectors of white light-emitting diode (LED) lamps. Experimental results manifest that LED lamps with PLA foam f and g have better optical properties (i.e. higher luminance, larger viewing angles, and higher reflectivities) than those without PLA foams. The luminance, viewing angles, and reflectance of LED lamps with PLA foam g are respectively 15,200cd/m2, 123°, and 99% while those without PLA foams are respectively 13,100cd/m2, 112°, and 91%.