RECENT DEVELOPMENTS IN PHOTOINITIATED CROSSLINKING OF POLYETHYLENE AND ITS INDUSTRIAL APPLICATIONS

The recent developments in the photoinitiated cross-linking of polyethylene and the significant breakthrough of its industrial application are reviewed. The enhanced photo-initiation system, the dynamics of photoinitiated crosslinking, the optimum conditions, the crystal morphological structures and related properties, and the photo- and thermo-oxidation stability of photocrosslinked polyethylene (XLPE) materials have been elucidated systematically. A new technique for producing photocrosslinked XLPE-insulated wire and cable is described in detail. It can be expected that the future applications of photocrosslinking technique of polyolefins will be very promising.

Synthesis and Characterization of PE-g-MA/MgAl-LDH Exfoliation Nanocomposite via Solution Intercalation

An organo modified MgAl layered double hydroxide (OMgAl LDH) was successfully exfoliated in the xylene solution of polyethylene grafted maleic anhydride (PE g MA) under refluxing condition. A PE g MA/MgAl LDH exfoliation nano composite was formed after the precipitation of PE g MA from the dispersion system. The structure and thermal property of the PE g MA/MgAl LDH exfoliation nanocomposite were characterized by X ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry analysis (TGA). The disappearance of d 001 XRD peak of OMgAl LDH at 2 θ =3 2° suggests that the MgAl hydroxide sheets are exfoliated in the nanocomposite. The TEM image shows that the MgAl hydroxide sheets of less than 70 nm in length or width are exfoliated and dispersed disorderly in PE g MA matrix. TGA profiles indicate that the PE g MA/MgAl LDH nanocomposite with 5 wt% OMgAl LDH loading shows a faster charring process in temperature range from 210 to 390 ℃ and a greater thermal stability beyond 390 ℃ than PE g MA does. The decomposition temperature of the nanocomposite is 25 ℃ higher than that of PE g MA as measured at 50% weight loss. The PE g MA/MgAl LDH nanocomposite is promising for application of flame retardant polymeric materials.

Preparation of LLDPE/MgAI-LDH Exfoliation Nanocomposites with Enhanced Thermal Properties by Melt Intercalation

The interlayer surface of MgAl layered double hydroxide （MgAl-LDH） was modified by exchanging about half of the interlayer nitrate anions by dodecyl sulfate anions （DS） to get MgAl（H-DS） LDH, and then the MgAl（H-DS） was melt intercalated by LLDPE to get the LLDPE/MgAl-LDH exfoliation nanocomposites. The samples were characterized by Fourier transform infrared （PTIR） spectroscopy, X-ray diffraction （XRD）, ion chromatography, transmission electron microscopy （TEM）, and thermogravimetry analysis （TGA）. The nanoscale dispersion of MgAl-LDH layers in the LLDPE matrix was verified by the disappearance of （001） XRD reflection of the modified MgAl-LDH and by the TEM observation. The TGA profiles of LLDPE/MgAl-LDH nanocomposites show a faster charring process between 210 and 370 ℃ and a higher thermal stability above 370 ℃than LLDPE. The decomposition temperature of the nanocomposites with 10 wt% MgAl（H-DS） can be 42 ℃ higher than that of LLDPE at 40% weight loss.