It is known that for the production of halogen-free cable insulation materials based on polyethylene, very high amounts of traditional metal hydroxide flame retardants such as 65 wt% aluminum hydroxide are required to fulfill international directives. In this respect, the aim of this study was to reveal possible enhancement effects of three boron compounds on the flame retardancy of two cable insulation materials: low-density polyethylene and its blend with ethylene vinyl acetate both loaded with aluminum hydroxide. For this purpose, a certain fraction of aluminum hydroxide was replaced with various amounts of zinc borate, boron oxide, and boric acid. The materials were compounded by the melt mixing method with a twin-screw extruder, while specimens were shaped by compression and injection molding. Limiting oxygen index, UL-94 vertical burning and mass loss cone calorimeter analyses indicated that replacement of certain amount of aluminum hydroxide with boron compounds could lead to certain levels of enhancement in many flame retardancy parameters. Residue analyses revealed that these improvements were basically due to further contribution of boron compounds to the physical barrier mechanism of aluminum hydroxide in both gas and condensed phases.

The main aim of this study was to investigate contribution of nanoclays to the flame retardancy of two cable insulation materials: low-density polyethylene and its blend with ethylene vinyl acetate. For this purpose, nanoclays were first incorporated alone, then together with traditional flameretardant aluminum hydroxide, and then together with aluminum hydroxide-zinc borate system. Compounds and nanocomposites were prepared by melt mixing method with a twin-screw extruder, while specimens were shaped by compression and injection molding. X-ray diffraction analysis and transmission electron microscopy revealed that nanoclay silicate layers were mainly intercalated with certain level of exfoliation in both matrices. Limiting oxygen index, UL-94 vertical burning, and mass loss cone calorimeter analyses indicated that for both matrix materials even use of nanoclays alone could improve many flammability parameters including peak heat release rate, time to ignition, and fire growth index. Contributions of nanoclays were much more significant when they were incorporated together with traditional aluminum hydroxide or together with aluminum hydroxide-zinc borate system. Residue analysis revealed that contribution of nanoclays to the flame retardancy mechanisms of aluminum hydroxide and zinc borate was mainly by formation of strong and tough char structure via well-dispersed and intercalated/exfoliated silicate layers shielding the underlying polymer matrices from heat and mass transfer.

Immobilization of invertase in conducting copolymer matrix of 2,5-di(thiophen-2-yl)-1-p-tolyl-1H-pyrrole with pyrrole (poly(DDTPco-Py)) was achieved via electrochemical polymerization. Kinetic parameters, Michaelis-Menten constant, K m and the maximum reaction rate, V max were investigated. Operational stability and temperature optimization of the enzyme electrodes were also examined.Immobilized invertase reveals maximum activity at 50 • C and; pH 8 and pH 4 for two copolymer matrices. Although the same two monomers are utilized for the copolymer synthesis, the way the copolymer is produced results in quite different responses in terms of enzyme activity, optimum pH and kinetic parameters. Excellent operational stability of the enzyme electrodes enables their repetitive use in the determination of invert sugar.