Dental radiography has been linked in numerous studies to an elevated risk of brain cancer, meningioma cranial tumors, and parotid gland tumors. Unfortunately, not much attention has been given to ...this problem. This research aims to determine and quantify the radiation shielding properties of High-Density Polyethylene/Bismuth Oxide composite (HDPE-Bi2O3) including the linear attenuation coefficient (μ), mass attenuation coefficient (μ/ρ), half-value layer (HVL) and tenth-value layer (TVL) for photons at 59.5 keV. First, the MCNP code—which showed a reasonable degree of consistency with the XCOM data—was used to simulate the variables μ, μ/ρ, HVL, and TVL that were connected to different concentrations of the composite. Then, the nanocomposite containing of 60 wt% Bi2O3 was chosen and fabricated via the casting method. There were XRD, and FESEM tests performed. Two techniques using the CsI(Tl) scintillation detector and the Geiger counter were applied to measure the shielding quantities at 59.5 keV gamma-rays of the 241Am radioactive source. Finally, results of the measurements revealed a comparatively good agreement with the values from the MCNP and XCOM simulations, with a maximum 3% discrepancy. The artifact test at the presence of the composites shield using a dental radiographic system at 60 kV have not been influenced adversely. This composite at the optimal weight fraction and thickness has potential application to be used as a radiation shield for jaw in dental radiography.
•Radiation shielding characteristics of HDPE/Bi2O3 composite were investigated.•μ, μ/ρ, HVL and TVL quantities were obtained using the simulation and experiment.•CsI(Tl) detector and the Geiger counter were applied using the 241Am source.•Simulation results (MCNP and XCOM) exhibited a good agreement with the experiment.•The artifact test on an animal jaw sample at 60 kV did not show any adverse effect.
Display omitted
•First study on pretreatment of Ga promoted zeolite on HDPE and PP aromatization.•H2-O2 treatment maximized aromatic to 65% yield, with 90% BTEX selectivity.•BTEX yield of HDPE ...decreased with increasing pore size.•Ga promoted Hβ displayed 82% selectivity of ethylene and propene in gas.
The effects of pretreatment and structure of zeolite on aromatization of high-density polyethylene (HDPE) and polypropylene (PP) over different Ga-promoted zeolites (HZSM-5, hierarchical HZSM-5, HY, Hβ, and USY) were investigated. Hydrogen reduction of Ga-promoted HZSM-5 resulted in a higher yield of alkenes during HDPE pyrolysis but did not lead to increased production of total aromatic hydrocarbons. The reduction and subsequent oxidation of Ga/Z5 led to the formation of GaO+ species with high dehydrogenation activity. This resulted in a remarkable 65% yield of aromatics, with a BTEX (benzene, toluene ethylbenzene and xylene) overall yield of 60% and a selectivity of 90% of the liquid product. Increasing the Ga loading decreased the BTEX yield due to pore blockage and a decrease in the amount of Brønsted acid sites. The BTEX yield over Ga-promoted zeolites was found to be strongly related to the pore size of the zeolite, whereas its yield over the parent zeolite was not strongly dependent on the pore size. Diffusion of the cracking intermediates was found to have a more significant impact on the aromatization of PP than HDPE. The highest BTEX yield for HDPE was achieved with Ga-promoted HZSM-5, while Ga-promoted hierarchical HZSM-5 exhibited the highest BTEX yield for PP. Furthermore, Ga(1)/Hβ-Redox demonstrated remarkable selectivity (90%) towards ethylene and propylene in the gas phase, surpassing other zeolites (37%-68%).
Display omitted
•The structure of HDPE during crazing in liquid medium was visualized.•The lamellae serve as walls of the craze.•The separation of lamellae makes the main contribution to the ...deformation.•The crazing model of HDPE is constructed based on the AFM images.
Atomic force microscopy (AFM) was employed to study structural transformations occurring in high-density polyethylene (HDPE) during deformation in a liquid medium by crazing mechanism. Processing of the obtained images yielded the parameters of HDPE structure at different tensile strains. It was shown that crazing causes the development of a fibrillar–porous structure in the interlamellar space, the fragmentation of lamellae, and the displacement of lamella fragments relative to each other. Moreover, the deformation is accompanied by the separation of lamellae and the long period increases in the proportion to the tensile strain. The scheme of HDPE deformation upon crazing in liquid medium was constructed based on the AFM images.
This study analyzed the behavior of three HDPE smooth geomembrane samples of 1.0, 1.5, and 2.0 mm thicknesses under heat exposure for 8760 h and the combined effect of UV radiation for 8760 h ...followed by heat aging for 4380 h. The results show high antioxidant consumption, an increase in viscosity, and stress cracking susceptibility, demonstrating the occurrence of cross-linking and accelerating oxidative degradation. Samples under the combined effect of UV radiation followed by heat exposure showed advanced oxidative degradation in comparison to those under heat exposure. DMA results corroborate the morphological changes in the polymer, exhibiting different thermal behavior for some types of exposure and different samples’ thicknesses.
Sandwich SiMe2-bridged ansa-complexes of zirconium, containing heterocycle-fused η5-cyclopentadienyls, derivatives of 2,5-dimethyl-7H-cyclopenta1,2-b:4,3-b'dithiophene (2), ...5,10-dihydroindeno1,2-bindole (3) and 5,6-dihydroindeno2,1-bindole (4) – 'heterocenes' – catalyzed ethylene homopolymerization and ethylene/oct-1-ene (E/O) copolymerization in the presence of triisobutylaluminum (TIBA) without MAO and perfluoroaryl borate activators, the benchmark bis(η5-fluorenyl) complex 1 was virtually inactive under these conditions. In the absence of MAO, E/O copolymerization resulted in a formation of copolymers not containing EOOE fragments even at E/O ratio of 2.4. Addition of 10 eq. of MMAO-12 resulted in increase of both catalytic activities of 2–4 and oct-1-ene incorporation. E/O copolymers POE-05 (obtained on TIBA activated precatalyst 2) and POE-17 (obtained on TIBA/MMAO-12 activated precatalyst 4) were not inferior to the best commercial E/O copolymers in physico-mechanical characteristics at −45 °C. Extrusion blends of POE-05 and POE-17 with high density polyethylene (HDPE) demonstrated high impact strength and frost resistance.
Display omitted
•TIBA-activated heterocenes catalyze ethylene/oct-1-ene (E/O) copolymerization.•Copolymers without EOOE fragments are formed up to E/O ratio of 2.4•Random E/O copolymers have promising low-temperature mechanical characteristics.•Blends of E/O copolymers with HDPE have improved frost resistance.
Inorganic nanofillers have sparked important research in the field of polymer nanocomposites because they can improve the properties of polymers. Hydrophobic ZnO nanoparticles modified by oleic acid ...(OA) were designed and prepared to accelerate the dispersion state of ZnO in the high viscosity polyethylene (HDPE), and enhance the performance of HDPE. HDPE/ZnO nanocomposites with different kinds and fractions of ZnO were further prepared via melt mixing method. The result showed the hexagonal and spindle-like ZnO nanoparticles with size distribution of 150–300 nm was acquired in the absence and presence of OA. Compared with surface untreated ZnO (U-ZnO), ZnO nanoparticles modified by OA (O-ZnO) can disperse evenly into HDPE at the fraction of O-ZnO below 5 wt%. TG data showed the presence of nanosized U-ZnO and O-ZnO in HDPE can significantly enhance the thermal stability of HDPE through raising the activation energy of HDPE in thermal decomposition process. The thermal decomposition order (n) for HDPE/ZnO nanocomposites was mostly bigger than that of HDPE, demonstrating the decomposition mechanism for HDPE became more complicated because of the addition of ZnO nanoparticles. DSC data showed U-ZnO nanoparticles cannot accelerate nucleation of HDPE and seemed to postpone the crystallization process, and O-ZnO nanoparticles was heterogeneous nucleating agent for HDPE. Moreover, the tensile and impact strength of HDPE was improved by the addition of O-ZnO, and connected with the dispersion state of ZnO nanoparticles in HDPE. The improvement in thermal stability, crystallization and mechanical properties by adding ZnO into HDPE matrix significantly enhance the potential of HDPE in food packaging, electronic packaging, drug and pharmaceutical bottles.
Display omitted
High-density polyethylene (HDPE) is among the most voluminous commodity plastic, which has received increasing public scrutiny about its impact on environment and climate change. There have been many ...efforts to recycle HDPE chemically, though significant hurdles remain. Toward a closed-loop economy, it is considered appealing to design “HDPE-like” materials, which contain built-in degradable groups and preserve thermal and mechanical properties like HDPE. This review provides a concise overview of three major areas: HDPE recycling methods, preparation of “HDPE-like” materials, and perspective towards more sustainable polymers. Each section includes a few inspiring achievements and challenges of the past decade.
Display omitted
•General recycling methods for plastic waste.•HDPE chemical recycling, including traditional means, catalytic hydroconversion for HDPE upcycling, and tandem strategies.•Methods to synthesize “HDPE-like” materials via polycondensation, ROP, ROMP, and ADMET.•Perspectives for green bioplastic developed from renewable natural resources, especially plant oils.
