Investigation of the oxygen depletion properties of low density polyethylene resins filled with thermally stable oxygen scavengers

摘要

The thermal stability, oxygen depletion and tensile properties of low density polyethylene (LDPE) resins filled with ascorbic acid (Vc), sodium ascorbate (SA), iron (Fe) and modified iron (Mfe) oxygen scavengers were systematically investigated. Thermogravimetric analysis (TGA) results clearly suggest that the thermal stability of SA powder and L_(95)(SA)_5 specimen is significantly better than that of Vc powder and L_(95)(Vc)_5 specimen, respectively. The oxygen depletion efficiency of L_(95)(SA)_5 is significantly better than that of L_(95)(Vc)_5, L_(95)(Fe)_5 and L_(95)(Mfe)_5 specimens, although the virgin SA powders exhibit worse oxygen depletion efficiency than Vc, Fe or Mfe powders before melt blending. Moreover, at a fixed weight ratio of Vc (or SA) to Mfe of the oxygen scavenger compounds, the oxygen depletion efficiency of L95[Sax(Mfe)y]5 series specimens is always significantly better than that of L95[Vcx(Mfe)y]5 series specimens. In fact, at weight ratios of Vc/Mfe and SA/Mfe higher than 3/7 and 5/5, respectively, the residual oxygen concentration values present in the airtight flask of L95[Vcx(Mfe)y]5 and L95[Sax(Mfe)y]5 series samples at any time are even lower than those of the L_(95)(Vc)_5 and L_(95)(SA)_5 specimens, respectively. Further tensile experiments show that the tensile properties of the L95[Sax(Mfe)y]5 series samples are always higher than those of the corresponding L95[Vcx(Mfe)y]5 series samples with the same loadings of oxygen scavenger compounds, respectively. In order to understand these interesting thermal stability, oxygen depletion and tensile properties of these LDPE oxygen-scavenging plastics, scanning electron microscope and energy dispersive X-rays analysis of the compositions on the surfaces of L95[Sax(Mfe)y]5 and L95[Vcx(Mfe)y]5 series samples were performed. Possible reasons accounting for these interesting properties of these LDPE oxygen-scavenging plastics are proposed.