Although peroxisome proliferators are considered non-genotoxic agents, most of them, nevertheless, were found to promote and/or induce, hepatocellular carcinoma (HCC) in rodents. The aim of the present study is, first, to investigate whether the peroxisome proliferator perfluorooctanoic acid (PFOA) possesses inherent liver cancer promoting activity, and second, to study the possible mechanisms involved. To acheive these aims two protocols have been applied, a biphasic protocol (initiation by diethyl-nitrozamine (DEN) 200 mg/kg i.p. followed by treatment with 0.005% or 0.02% perflourooctanoic acid (PFOA) for 14 and 25 weeks) and a triphasic initiation, selection-promotion (IS) protocol (initiation by giving 200 mg/kg DEN i.p. followed by a selection procedure for 2 weeks consisting of giving 0.03% 2-acetylaminofluorene (2-AAF) in diet). In the middle of this treatment a single oral dose of carbon tetrachloride (2.0 ml/kg) was given, followed by giving diet containg 0.015% of PFOA for 25 weeks. After applying both protocols, our results showed slight increase in the catalase activity while acyl CoA oxidase activity was markedly increased. Both experiments indicated that PFOA has a liver cancer promoting activity. Other groups of rats were given either basal diet or diet containing 0.02% PFOA. Five or nine weeks later they were sacrificed and the levels of 8-hydroxydeoxyguanosine in the isolated DNA were estimated. The data showed a slight nonetheless insignificant increase in 8-hydroxydeoxyguanosine. From the present data, it is concluded that PFOA is a true liver cancer promoter that may not require extensive initial DNA damage for its promoting activity.

Thermal insulation layer in solid rocket motors is a vital component during the rocket flight. Many factors can affect the performance of this insulation layer. Bonding property between rocket propellant and the thermal insulation layer are examined in this study. Hydroxyl terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) as a curative was chosen as the most common type of rocket propellant. The effect of two types of polymeric insulation layer such as nitrile butadiene rubber (NBR) and ethylene-propylene-diene monomer (EPDM), on the bonding performance at the interface between (HTPB/IPDI) propellant and the respective insulation layer has been investigated. Results revealed that both types of insulation layer considerably decreased the interfacial bonding performance of the (HTPB/IPDI) propellant. NBR was proven to be more severe on weakening the adhesion strength than that of the EPDM. We further investigated the effects of the thickness and water content of NBR on the bonding performance, and proved that bonding strength was inversely proportional to the thickness and the water content.

polybutadiene is the most common polymeric binder for composite solid propellants. This polymer suffers from oxidative degradation reactions on storing with deterioration in mechanical properties. Certain anti-oxidant materials can retard such reaction offering enhanced aging characteristics. In this study, two different primary antioxidants including phenol-based (AO2246) and amine-based (Flexzone 6H) were employed to stabilize polybutadiene polymer. Oxidation induction time (OIT) was evaluated using isothermal DSC. High OIT value means high resistance to oxidative degradation. The impact of anti-oxidant on mechanical properties was evaluated using shore A. Flexzone 6H significantly improved binder oxidative stability with an increase in OIT value by 20 folds with significant decrease in oxidation enthalpy. Flexzone 6H can offer enhanced resistance toward oxidative reactions; as it can act as efficient H atom donor to break down chain degradation reaction. Additionally, the three stabilized aromatic rings can capture free radicals. AO2246 enhanced the binder mechanical characteristics during aging at 80 0C using Shore A test. In the meantime, AO2246 could enhance the mechanical properties due to its integration into the polymeric matrix due to –OH functional groups. The two anti-oxidants demonstrated controversy effects. Whereas Flexzone 6H offered enhanced resistance to oxidative degradation; AO2246 offered enhanced mechanical properties.

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