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1 Introduction The onslaught of pandemic has made cities begin rethinking the evils of high-density environments [ 1 ]. However, the dynamics of high-density environments can hardly be slowed down with urbanization. It is expected that by 2050, more

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Abstract  

Nitrile butadiene rubber (NBR) was mixed with high density polyethylene (HDPE) thermoplastics with different ratio namely (100/20), (100/40), (100/60) and (100/80). The obtained blends were subjected to gamma irradiation with varying dose from 50 to 250 kGy. The induced crosslinking and hence the improvement in the different properties were followed up as a function of irradiation dose. Mechanical properties as tensile strength, tensile modulus at 50 % elongation, elongation at break percent, permanent set and hardness were carried out as a function of irradiation dose and blend ratio. Moreover, physical properties namely, gel fraction % and swelling number were found to improve with the increase of irradiation dose up to 250 kGy and with the increase of the content of HDPE in blend. Moreover, presence of NBR enhances the shrinking properties of the obtained blend which can be used as a good heat shrinkable material.

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, 13 , 14 ], avoiding the drawbacks (embrittlement, loss of transparency and loss of lightness) usually associated to the addition of traditional microfillers [ 15 , 16 ]. High-density polyethylene (HDPE) is one of the most widely used

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The high-density polyethylene, thermoplastic widely-used in the production of industrial domestic utilities, was collected in two situations: virgin high-density polyethylene (JV 060) and post-consumption high-density polyethylene (with features of low-density polyethylene). After collecting the samples, they were submitted to natural aging with the quantification of the incident solar radiation for 180 days. The samples were characterized by melt flow index, differential scanning calorimetry, tensile strength, rupture load, elongation at break and infrared. The results showed that after 180 days of exposure the virgin high-density polyethylene presented physical properties similar to the post-consumption polyethylene.

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Abstract  

The isothermal luminescence at 77 K of gamma-irradiated high density polyethylene, both with and without introduced admixtures (n-hexane, naphthalene) has been measured. The spectrum of emitted light was recorded and found to be identical with that of added compound. A reaction mechanism responsible for the isothermal luminescence consistent with the experimental results is proposed.

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Abstract  

Reversible and irreversible crystallization and melting of high-density polyethylene at low temperature has been re-evaluated and is discussed in terms of the concept of the specific reversibility of a crystal. The concept of the specific reversibility links reversible and irreversible melting of a specific crystal such that reversible melting occurs only at slightly lower temperature than irreversible melting. In this study evidence for irreversible crystallization at low temperature in high-density polyethylene is provided, non-avoidable by primary crystallization and extended annealing at high temperature. The simultaneously observed reversible crystallization and melting at low temperature can be attributed to lateral-crystal-surface activity in addition to the well-established reversible fold-surface melting, dominant at high temperature, and evidenced by small-angle X-ray data available in the literature.

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Abstract  

The co-pyrolytic behaviour of olive residue/high-desity polyethylene mixture was examined with a thermogravimetric analyser. The experiments were done over the temperature range of room temperature to 1273 K at various heating rates (2, 10, 20 and 50 K min−1) and in a nitrogen atmosphere. The results indicated that mass loss process of mixture consists of three distinct stages and the increase of the heating rate shifts in the maximum rate loss to higher temperature. The difference of mass loss (Δm) between experimental and theoretical, calculated as algebraic sums of the mixture for different heating rates of 2, 10, 20 and 50 K min−1, is about 7–11% at 740–900 K. These experimental results indicate a significant synergistic effect during co-pyrolysis of olive residue with high-density polyethylene. In addition, a kinetic analysis was performed to fit thermogravimetric data, the mixture is considered as multi-stage process. A reasonable fit to the experimental data was obtained for all materials and their mixture by isoconversional Friedman method.

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Density 0.938 g/cc Styrene content 21.5–25.5% Synthetics & Chemicals, Ltd Bareily (U. P), India High density polyethylene Injection grade (Relene) (–CH 2 –CH 2 –CH 2 –) n

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Abstract  

Using the positron annihilation lifetime technique, the annihilation parameters have been measured for epoxy and high density polyethylene (HDPE) as a function of AC electric field strength and the exposure time. The lifetime spectra have been resolved into three components, the longest component (I3 3) is attributed to the pick-off annihilation of o-Ps in the amorphous regions. The intermediate one (I2 2) is due to the annihilation of free positrons, while the shorter component (I1 1) stems from self annihilation of p-Ps. In HDPE, the o-Ps parameters 3 andI 3 are measured as a function of electric field strengths in the range from 10 to 100 kV/cm exposed for 24 hours. A decrease inI 3 of 8% is observed from zero to 50 kV/cm followed by an increase of the same order from 50 to 100 kV/cm. By investigating the effect of the exposure time from 2 to 24 hours at 16 and 50 kV/cm, the effect is confirmed and is attributed to the inhibition of o-Ps formation at lower field strength. In epoxy, the effect or exposure time onI 3 at 166 and 133 kV/cm shows a similar behavior as in HDPE. At 133 kV/cmI 3 decreases by only 2.5%. On the other hand, the changes in 3 occur at short exposure times. Again at large times the saturation is obtained. These effects are attributed to the expansion of free volume (increase of 3) competing at longer exposure times with other phenomena, such as liberation of free radicals, which reduce the o-Ps intensityI 3 through the conversion to p-Ps. The reactions between o-Ps and free radicals might also lead to free positrons, which could explain the increase ofI 2 and the decrease of 3 at longer exposure times.

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The hypothesis that epinephrine (noradrenaline, NA) enhances utilisation of high-density lipoproteins (HDL) by bovine luteal cells and that this process involves phospholipase (PL) C and protein kinase (PK) C intracellular pathway was tested. Luteal cells from days 2-4, 5-10 or 11-17 of the oestrous cycle were pre-incubated for 20h. Subsequently DMEM/Ham's F-12 medium was replaced by fresh medium and the cells were treated for 6 h as follows: In Experiment I with HDL (5-75μg cholesterol per ml), NA, isoprenaline (ISO) or luteinising hormone (LH). In Experiment II cells were incubated for further 24h in deficient medium (without FCS) and next treated as in Experiment I. In Experiment III cells were stimulated with NA, ISO or LH alone and together with HDL. In Experiment IV cells were treated with PLC inhibitor (U-73122) or with PKC inhibitor (staurosporine) or stimulator (phorbol 12-myristrate 13-acetate) and with either NA, insulin or LH. Only luteal cells from days 5-10 of the cycle responded on HDL and β-mimetics (P<0.05). LH stimulated progesterone secretion from the luteal cells during all stages of the cycle (P<0.001). Cells incubated in deficient medium and supplemented with HDL secreted as much progesterone as those stimulated by LH in all stages of the cycle. Beta-mimetics were unable to enhance the stimulatory effect of HDL. Blockade of PLC had no influence on progesterone secretion from cells treated with either NA or LH, but this did impair the stimulatory effect of insulin (P<0.05). Similarly, blockade of PKC by staurosporine impaired (P<0.05) the effect of insulin only but not that observed after LH or NA treatment. We suggest that: (a) noradrenergic stimulation does not enhance utilisation of cholesterol from HDL for progesterone secretion; (b) the fasting of luteal cells seems to activate enzymes responsible for the progesterone synthesis; (c) effect of NA on progesterone secretion from luteal cells does not involve the PLC-PKC pathway.

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