Microperforation of Three Common Plastic Films by Laser and Their Enhanced Oxygen Transmission for Fresh Produce Packaging

Three different plastic films of biaxially oriented polypropylene (BOPP), biaxially oriented polyethylene terephthalate (BOPET) and low‐density polyethylene (LDPE) were perforated using Nd‐YAG laser. Effects of laser pulse energy were examined by varying energies from 50 to 250 mJ where the pulse duration and pulse repetition were kept constant at 10 ns and 1 Hz, respectively. It was found that perforation diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. Explanation was contributed to material inherent property and its interaction with laser. Incorporation of an inorganic filler (i.e. silica based anti‐blocking agent used in packaging film) of 0.5 wt% into the LDPE films (0.5Si‐LDPE) could improve perforation performance for LDPE. This was attributed to an increased thermal diffusivity of the 0.5Si‐LDPE film. Commercial BOPET and BOPP films containing 97 microholes/m² (hole diameter of ~100 µm) showed an improvement in oxygen transmission rates (OTR) of 18 and 5 times that of the neat films without perforation. In the case of perforated 0.5Si‐LDPE films having similar perforations of 97 microholes/m² and perforation diameter of 100 µm, a two‐fold increase of OTR was obtained. Gas transmission rates of the microperforated films were measured based on the static method. Measured OTR and CO₂TR values of the three films with varying perforation diameters in a range of ~40–300 µm were compared and discussed. Overall results clearly indicate that perforation by laser is an effective process in developing breathable films with tailored oxygen transmission property for fresh produce packaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of Ta5+ doping on microstructure evolution,dielectric properties and electrical response in CaCu3Ti4O12 ceramics

The effects of Ta⁵⁺ substitution on the microstructure, electrical response of grain boundary, and dielectric properties of CaCu₃Ti₄O₁₂ ceramics were investigated. The mean grain size decreased with increasing Ta⁵⁺ concentration, which was ascribed to the ability of Ta⁵⁺ doping to inhibit grain boundary mobility. This can decrease dielectric constant values. Grain boundary resistance and potential barrier height of CaCu₃Ti₄O₁₂ ceramics were reduced by doping with Ta⁵⁺. This results in enhancement of dc conductivity and the related loss tangent. Influence of charge compensations on microstructure and intrinsic electrical properties of grain boundaries resulting from the effects of replacing Ti⁴⁺ with Ta⁵⁺ are discussed. The experimental data and variation caused by the substitution of Ta⁵⁺ can be described well by the internal barrier layer capacitor model based on space charge polarization at the grain boundaries.     

Improved Dielectric and Nonlinear Electrical Properties of Fine‐Grained CaCu3Ti4O12 Ceramics Prepared by a Glycine‐Nitrate Process

Pure CaCu₃Ti₄O₁₂ was successfully prepared by a glycine‐nitrate process using a relatively low calcination temperature and short reaction time of 760°C for 4 h. Fine‐grained CaCu₃Ti₄O₁₂ ceramics with dense microstructure and small grain size were obtained after sintering for 1 h. The nonlinear coefficient of a fine‐grained CaCu₃Ti₄O₁₂ ceramic calculated in the range 1–10 mA/cm² was found to be very high of ~16.39 with high breakdown electric field strength of 1.46 × 10⁴ V/cm. This fine‐grained CaCu₃Ti₄O₁₂ ceramic also exhibited a very low loss tangent of 0.017 at 20°C with temperature stability over the range ?55°C to 85°C. The grain growth rate of the CaCu₃Ti₄O₁₂ ceramics was found to be very fast after increasing the sintering time from 1.5 to 3 h, leading to formation of a coarse‐grained CaCu₃Ti₄O₁₂ ceramic with grain size of about 100–200 μm. The dielectric permittivity of this coarse‐grained ceramic was found to be as high as 1.03 × 10⁵ with a low loss tangent of 0.054.     

Dielectric properties and electrical response of grain boundary of Na1/2La1/2Cu3Ti4O12 ceramics

The dielectric properties and electrical response of grain boundaries of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics were investigated as a function of temperature. High dielectric permittivity (6.1–8.7 × 10³) and low loss tangent (0.032–0.038 at 10 kHz) were observed in Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics. Through analyses using complex impedance and electric modulus, it was found that the dielectric properties of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics are closely related to the electrical response of grain boundaries. The investigation of non-Ohmic characteristics at various temperatures suggests that the potential barrier at the grain boundaries of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics is due to the Schottky effect. The giant low frequency dielectric response in Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics is attributed to Maxwell–Wagner polarization at the grain boundaries.     

High Dielectric Permittivity and Maxwell–Wagner Polarization in Magnetic Ni0.5Cu0.3Zn0.2Fe2O4 Ceramics

Nanocrystalline Ni_0.5Cu_0.3Zn_0.2Fe₂O₄ (NCZFO) powder was fabricated by a modified sol?Cgel method and then the compacted powder of NCZFO was sintered at 950, 1000, and 1100?^°C for 6 h. The dielectric and electrical properties of sintered samples were investigated as functions of frequency and temperature. All of the NCZFO samples exhibit the high dielectric response behavior and show the Debye-like relaxation, which is attributed to the Maxwell?CWagner polarization and thermally activated mechanisms. The impedance spectroscopy analysis reveals that the NCZFO ceramics are electrically heterogeneous. The sintering temperature has significant influence on the dielectric dispersion behavior of the NCZFO samples, which should be mainly attributed to the large variation of the grain conduction activation energies.     

A Novel Route to Greatly Enhanced Dielectric Permittivity with Reduce Loss Tangent in CaCu3−xZnxTi4O12/CaTiO3 Composites

Dielectric and nonlinear properties of a binary compound derived from Ca₂Cu₂Ti₄O₁₂ were greatly improved by doping with Zn²⁺ to deliberately create CaCu_3–xZn_xTi₄O₁₂/CaTiO₃ composites. Ca₂Cu_1.8Zn_0.2Ti₄O₁₂ composition can exhibit an enhanced ε′, ~6,513, with a strong reduction in tanδ to ~0.015 (at 1 kHz). The nonlinear coefficient and breakdown field strength were significantly enhanced. The dielectric and nonlinear properties were described based on the effect of Zn²⁺ substitution on electrical response of internal interfaces.     

CoFe_2O_4-BaTiO_3颗粒复合材料的频率相关电磁性能

通过湿法球磨制备CoFe2O4-BaTiO3颗粒复合材料,研究材料成分和调制频率与电磁效应的关系。结果表明：电磁效应系数随着调制频率由400Hz增加到1000Hz而增加。由于CoFe2O4的电导率在400-1000Hz范围内对频率敏感,电磁效应的曲线特性而发生改变。在烧结过程中形成第三相Ba2Fe2O5,从而导致电磁效应的下降。     

Effects of Li and Fe doping on dielectric relaxation behavior in (Li,Fe)-doped NiO ceramics

High permittivity (Li, Fe)-doped NiO (LFNO) ceramics are prepared by a simple PVA sol–gel route and their dielectric properties are investigated as functions of temperature and frequency. It is found that the concentrations of Li and Fe have strong influences on the microstructure and dielectric properties of the LFNO ceramics. Two thermally activated dielectric relaxations are observed in the Li_0.05Fe_0.10Ni_0.85O ceramic sample with the activation energies of 0.448 and 0.574 eV for the high- and low-frequency relaxations, respectively. By using a complex impedance analysis, it is believed that the high-frequency relaxation is closely related to the transport properties inside the grains, and the low-frequency relaxation might be ascribed to the interfacial polarization at the interface layers of grain boundaries and/or NiFe₂O₄ secondary phase layers.