Ahmed Ali Basfar

Comparison of thermal stability of sulfur, peroxide and radiation cured NBR and SBR vulcanizates

A comparison of thermal stabilities of NBR and SBR vulcanizates cured by different curing agents namely sulfur, peroxide and gamma radiation was performed by thermogravimetric analysis (TGA), assessed on the basis of comparison of DTG peak maxima and temperature for loss of 50% mass. Compared to sulfur and peroxide-cured vulcanizates, radiation-cured formulations demonstrated much improved thermal stability. The influence of the variation of the amount of coagent and other additives on the thermal stabilities of formulations of radiation-cured NBR and SBR vulcanizates was investigated. A comparison of thermal stability of various radiation-cured NBR vulcanizates with SBR counterparts was also conducted.

Radiolytic degradation of atrazine aqueous solution containing humic substances

Degradation of atrazine herbicide in humic substances (HS) aqueous solutions and distilled water solutions was investigated on a laboratory scale upon gamma-irradiation from a (60)Co source. In addition, the effect of ionizing radiation on the atrazine residues removal efficiency was investigated in relation to degradation of by-products. gamma-Irradiation experiments were carried out for three targeted concentrations (i.e. 0.464, 2.318 and 4.636 microM) with doses over the range 0.1-60 kGy. The initial concentration of herbicide, scavengers and irradiation doses play a significant role in the degradation efficiency as shown by decay constants of atrazine residues. gamma-Radiolysis showed that atrazine exhibited high degradation percentages at low absorbed doses in HS aqueous solutions compared to distilled water solutions. Absorbed doses from 0.6 to 21 kGy and from 6 to 72 kGy at a dose rate of 14.52 kGyh(-1) achieved 90% degradation for atrazine with initial concentrations over the range 0.464-4.636 microM in humic and distilled water solutions, respectively. The radiolytic degradation by-products and their mass balances were qualitatively determined with good confidence using gas chromatography/quadruple mass spectrometry (GC/MS) with electron impact ionization (EI(+)) mode.

Influence of different curing systems on the physico-mechanical properties and stability of SBR and NR rubbers

The physical properties of radiation, sulfur and peroxide-cured styrene–butadiene rubber (SBR) and natural rubber (NR) were compared. The dependence of the mechanical properties of the radiation-vulcanized SBR and NR on the coagent concentration and radiation dose was studied. The effect of thermal aging on the mechanical properties of the different rubber formulations was discussed. The radiation-cured formulations of SBR have superior mechanical properties and thermal stability compared with those of the chemically vulcanized compounds. Whereas, the radiation-cured formulations of NR have similar mechanical properties but superior thermal stability (based on the % change in E after thermal aging), when compared with those of the sulfur-vulcanized compounds and slightly better than those of the peroxide-vulcanized compounds.

UV stability and radiation-crosslinking of linear low density polyethylene and low density polyethylene for greenhouse applications

Abstract Ultraviolet (UV) radiation stability and γ-radiation crosslinking of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) for greenhouse film applications was investigated. Various combinations of primary antioxidant (i.e. Irganox 1010), secondary antioxidant (i.e. Irgafos 168), UV absorber (i.e. Chimassorb 81) and hindered amine light stabilizer (HALS) were used to prepare thin PE films (60 μm thick). The films were cross-linked by γ-rays with doses of 20–200 kGy. Accelerated weathering test up to 1146 h and natural (outdoor) weathering up to 165 days were performed for the prepared films. In addition, gel content and mechanical properties of these films were determined. Improved UV stability was achieved with films of LLDPE and LDPE containing HALS along with other additives.

Gamma-ray induced degradation of diazinon and atrazine in natural groundwaters.

Degradation of diazinon and atrazine pesticides present in natural groundwaters was investigated on a laboratory scale upon gamma-irradiation from a (60)Co source. The effects of pesticide type, initial concentration, characteristics of natural groundwater, potential radical scavengers and absorbed dose on efficiency of pesticide degradation were investigated using GC-MS. gamma-Irradiation experiments were carried out for three concentrations (i.e. 0.329, 1.643 and 3.286 microM/diazinon and 0.464, 2.318 and 4.636 microM/atrazine) with irradiation doses over the range 0.5-5.6 kGy for diazinon and 0.2-21 kGy for atrazine. gamma-Radiolysis showed that diazinon was much easier to degrade by ionizing radiation compared to atrazine in all natural groundwater samples. This was observed at the three initial concentrations over the range irradiation doses. The irradiation doses required for degradation of 50 and 90% diazinon (distilled water) and atrazine (humic aqueous solution) at the three concentrations were not sufficient to degrade the same concentrations in different natural groundwater samples. Moreover, the presence of naturally occurring inorganic scavengers in solutions of diazinon and atrazine decreased significantly the efficiency of radiolytic degradation of pesticides, especially at higher concentrations.

Influence of Magnesium Hydroxide and Huntite Hydromagnesite on Mechanical Properties of Ethylene Vinyl Acetate Compounds Cross-linked by DiCumyl Peroxide and Ionizing Radiation:

Flame retardants including magnesium hydroxide (MH) and huntite hydromagnesite (HH) were used to develop halogen free flame retardant (HFFR) compounds based on ethylene vinyl acetate (EVA) for wire and cable applications. Cone calorimeter and limiting oxygen index (LOI) results show that cross-linking affects not only mechanical properties, but also flame retardancy. Consequently, flame retardancy is mainly influenced by type of flame retardants and mixing ratio of base polymers and to a lesser extent by cross-linking. Tensile strength increased with increase of MH, while elongation at break decreased with increase of MH in cross-linked formulations. On the other hand, elongation at break increased with increase of HH while tensile strength decreased with increase of HH in cross-linked formulations. HFFR compounds with tensile strength of 12 MPa, elongation at break of 200%, LOI of 40% was developed to meet the stringent specifications of wire and cable industry.

Flame retardancy of radiation cross-linked poly(vinyl chloride) (PVC) used as an insulating material for wire and cable

Various formulations of radiation cross-linked poly(vinyl chloride) (PVC) were prepared to improve the flame retardancy for wire and cable insulation applications. Limiting oxygen index (LOI) was used to characterize the flammability of the developed formulations. The effect of different plasticizers, dioctyl phthalate (DOP), di-isodecyl phthalate (DIDP) and tri- 2 -ethylhexyl trimellitate (TOTM) and different flame-retardant fillers, Sb 2 O 3 , zinc borate, Al(OH) 3 and Mg(OH) 2 on the mechanical properties and flammability was investigated. The influence of radiation dose on the mechanical properties was minimal both at room temperature and after thermal aging for 168 h at 136 °C. The highest LOI was 39% for PVC formulations containing DOP as a plasticizer and TMPTA at absorbed doses of 90 and 120 kGy. Both DTG peak maxima and temperature for loss of 50% mass decreased with increasing irradiation dose. No influence of plasticizer type or flame-retardant filler on the thermal properties was observed.

Disinfection of wastewater from a Riyadh Wastewater Treatment Plant with ionizing radiation

Abstract The goal of this research was to establish the applicability of the electron beam treatment process for treating wastewater intended for reuse. The objective of this study was to determine the effectiveness of gamma irradiation in the disinfection of wastewater, and the improvement of the water quality by determining the changes in organic matter as indicated by the measurement of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC). Samples of effluent, before and after chlorination, and sludge were obtained from a Riyadh Wastewater Treatment Plant. The studies were conducted using a laboratory scale 60Co gamma source. The improvement in quality of the irradiated samples was demonstrated by the reduction in bacteria, and the reduction in the BOD, COD and TOC. Radiation of the wastewater provided adequate disinfection while at the same time increasing the water quality. This treatment could lead to additional opportunities for the reuse of this valuable resource. Limited studies, conducted on the anaerobically digested secondary biosolids, showed an improvement in bacterial content and no change in COD.

Radiation resistant polypropylene blended with mobilizer,: antioxidants and nucleating agent

Abstract Post-irradiation storage of medical disposables prepared from isotactic polypropylene renders them brittle due to degradation. To avoid this, isotactic polypropylene [(is)PP] was blended with a mobilizer, dioctyl pthallate (DOP), three antioxidants (hindered amines and a secondary antioxidant) and benzoic acid to obtain radiation-resistant, thermally-stable and transparent material. Different formulations prepared were subjected to gamma radiation to doses of 25 and 50 kGy. Tests of breakage on bending after ageing in an oven at 70°C up to 12 months have shown that the addition of DOP and the antioxidants imparts improved radiation and thermal stability as compared to (is)PP alone or its blend with DOP. All the formulations irradiated or otherwise demonstrated excellent colour stability even after accelerated ageing at 70°C for prolonged periods.

Stabilization of γ-radiation vulcanized EPDM rubber against accelerated aging

The influence of different polyfunctional compounds on the radiation vulcanization of ethylene–propylene diene monomer (EPDM) rubber was investigated. The effect of different antioxidants and their mixtures on the thermal aging and accelerated weathering of γ-radiation vulcanized EPDM rubber was also investigated. The compounds used were synergistic blends of phenolic and phosphite antioxidants, i.e. 1:4 Irganox 1076:Irgafos 168, and a blend of arylamine and quinoline type antioxidants, i.e. 1:1 IPPD:TMQ, at different concentrations. The Tinuvin 622 LD hindered amine light stabilizer was also used. The response was evaluated by the tensile strength and elongation at break of irradiated samples after thermal aging at 100°C for 28 days and accelerated weathering (Xenon test) up to 200 h. The correlations between the type of antioxidant, concentration and efficiency were also investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).