Mass attenuation coefficients, effective atomic numbers and effective electron densities for some polymers.

In this study, the total mass attenuation coefficients (µ(m)) for some homo- and hetero-chain polymers, namely polyamide-6 (PA-6), poly-methyl methacrylate (PMMA), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were measured at 59.5, 511, 661.6, 1173.2, 1274.5 and 1332.5 keV photon energies. The samples were separately irradiated with (241)Am, (22)Na, (137)Cs and (60)Co (638 kBq) radioactive gamma sources. The measurements were made by performing transmission experiments with a 2″×2″ NaI(Tl) scintillation detector having an energy resolution of 7 % at 662 keV gamma ray from the decay of (137)Cs. The effective atomic numbers (Z(eff)) and the effective electron densities (N(eff)) were determined experimentally and theoretically using the obtained µ(m) values for the investigated samples. Furthermore, Z(eff) and N(eff) of each polymer were computed for total photon interaction cross-sections using theoretical data over a wide energy region from 1 keV to 10 MeV. The experimental values of the selected polymers were found to be in good agreement with the theoretical values.

Use of nanoclay as an environmentally friendly flame retardant synergist in polyamide-6.

Due to their very high levels of flame retardancy, chlorinated and brominated flame retardants had been the most widely used flame retardant additives in plastics industry. However, these flame retardants lead to formation of very toxic volatiles and by-products during fire. Therefore, the recent trend is to replace all of them with non-halogenated flame retardants. In this respect, the use of nanoclays as a synergist flame retardant is becoming more and more important. Thus, the main aim of this work was to investigate the synergistic flame retardant effect of nanoclays with phosphorous compounds in polyamide-6 composites. For this purpose, exfoliated clay nanocomposites of flame retarded/glass fiber reinforced polyamide-6 were prepared by melt compounding. A flame retardant based on phosphorus compounds was used at various levels in glass fiber reinforced polyamide-6 and nanocomposites. Flammability and fire behaviors were evaluated by limiting oxygen index, UL94 and cone calorimeter tests. Substitution of a certain fraction of the flame retardant with nanoclays was found to significantly reduce the peak heat release rate and delay the ignition in cone calorimeter. Moreover, remarkable improvements were obtained in limiting oxygen index along with maintained UL94 ratings.