Kinds Of Low-density Polyethylene Research Articles

Combined effects of 1-MCP and MAP on the fruit quality of pear (Pyrus bretschneideri Reld cv. Laiyang) during cold storage

To identify the most effective modified-atmosphere packaging (MAP) and/or 1-methylcyclopropene (1-MCP) treatment to maintain the fruit quality of ‘Laiyang’ pear (Pyrus bretschneideri Reld cv. Laiyang) during 210 days of cold storage (0–2°C), two kinds of low-density polyethylene (LDPE) packaging films with different O2 and CO2 permeabilities were evaluated with and without 1-MCP (0.5μL/L or 1.0μL/L). The results showed that 0.5μL/L 1-MCP plus micro-perforated film packaging maintained the color, firmness, titratable acidity, and vitamin C content of the fruit flesh and was the most appropriate treatment for ‘Laiyang’ pear fruit during cold storage. Treatment with 0.5μL/L 1-MCP plus micro-perforated film packaging inhibited respiration and ethylene production; maintained the activity levels of super oxidase dismutase, peroxidase, and catalase; decreased the cell-membrane permeability and malondialdehyde content; and inhibited the lipoxygenase and polyphenol oxidase activity of the fruit during cold storage.

Superiority of dielectric properties of LDPE/MgO nanocomposites over microcomposites

Dielectric properties were compared between two kinds of low-density polyethylene (LDPE) composites prepared by adding near spherical MgO fillers with different diameters of around several ten nm and several ¿m. In the whole range of temperature from 0°C to 90°C, the conductivity is decreased and the permittivity is increased by the addition of fillers, irrespective of their sizes. However, the decrement in the conductivity is more significant and permittivity increment is suppressed more in the case of the nm fillers. In addition, a drastic increase in dielectric loss factor, observed at low frequencies, is suppressed more significantly by the addition of the nm fillers. While the formation of packet-like charge, observed in LDPE, is suppressed by both fillers, the effect is far more significant in the nanocomposites. This means that the nano-fillers suppress the conductivity enhancement by the voltage application more effectively.

Effect of Blending on Electrical Conduction and Breakdown of Low-Density Polyethylene Films with Different Densities

In this study, the effect of blending on physical and electrical properties of low-density polyethylene (LDPE) was investigated. Two kinds of LDPEs whose densities are evaluated to be 0.9179 g/cm3 and 0.9192 g/cm3, respectively, were used and blended according to different blend ratios. The LDPE with a blend ratio of 50 wt% had the lowest impulse breakdown strength, FBImp, at 30°C. However, the LDPE with a blend ratio of 50 wt% also had the highest FBImp at 90°C among all specimens. The DC breakdown strength, FBDC, decreased with the increase of the blend ratio at 30°C but increased at 60°C and 90°C. However, the FBDC did not depend on the blend. The current densities for all specimens were almost the same at 30°C, but decreased with a blend ratio up to 75 wt% at 90°C. By analyzing X-ray diffraction (XRD) patterns, we found that the crystal size in the (020) plane increased with a blend ratio up to 50 wt%, and the LDPE with a blend ratio of 50 wt% had the largest crystal size in the (020) plane among all specimens. It was found that the FBImp was strongly related to the crystal size in the (020) plane.

Effects of molecular structure on electrical conduction in low-density polyethylene above its melting point

The electrical conduction of various kinds of low-density polyethylene (LDPE) has been studied above the melting point. LDPEs are characterized by the amount and types of branches, double bonds, and oxygen-containing groups. Two components of conduction currents were found: one obeyed Ohm's law in the low field range and the other was proportional to the square of the field at lower temperatures in the high field range, and was also inversely proportional to sample thickness for a constant field. The conduction mechanism of the latter component is ascribed to space charge limited current (SCLC). Among the features of the LDPE molecular structure, only the oxygen-containing groups were well correlated with the SCLC. In fact, the oxygen-containing groups reduced the SCLC, suggesting that they act as traps even in the molten state. Branches and double bonds are also known to act as traps in the solid state, but they bore no consistent relation to the electrical conduction in the molten state.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>