Polyethylene (PE) is one the most used plastics worldwide for a wide range of applications due to its good mechanical and chemical resistance, low density, cost efficiency, ease of processability, non-reactivity, low toxicity, good electric insulation, and good functionality. However, its high flammability and rapid flame spread pose dangers for certain applications. Therefore, different flame-retardant (FR) additives are incorporated into PE to increase its flame retardancy. In this review article, research papers from the past 10 years on the flame retardancy of PE systems are comprehensively reviewed and classified based on the additive sources. The FR additives are classified in well-known FR families, including phosphorous, melamine, nitrogen, inorganic hydroxides, boron, and silicon. The mechanism of fire retardance in each family is pinpointed. In addition to the efficiency of each FR in increasing the flame retardancy, its impact on the mechanical properties of the PE system is also discussed. Most of the FRs can decrease the heat release rate (HRR) of the PE products and simultaneously maintains the mechanical properties in appropriate ratios. Based on the literature, inorganic hydroxide seems to be used more in PE systems compared to other families. Finally, the role of nanotechnology for more efficient FR-PE systems is discussed and recommendations are given on implementing strategies that could help incorporate flame retardancy in the circular economy model.

Packed columns are an important part of the broad selection of mass and heat transfer equipment. Nowadays, the use of packed columns is increasing, which is because of its lower pressure drop, higher capacity and higher mass transfer in comparison to tray columns. The experiential tests and the hypothetical analysis display that the chemical dehumidification of air by hygroscopic salt solutions confirms the stable reduction in humidity ratio, which is appropriate for uses to air conditioning or drying processes The mass transfer factors in the pulse were found to correspond nearly to the factors that would be achieved in the distributed bubble flow regime In the present study, parameters that affect column performance, such as, fluid retention and gas-phase mass transfer coefficient in a humidification column using random packing in towers with 0.1 m and 0.2 m diameters and 1m height, were measured Air velocity was 1.32 to 3.92 m 3 per hour and liquid velocity was 10 to 70 m 3 per hour. In this research, the Nakajima model was used to calculate the effective area. Thereafter, experimental values for gas-phase mass transfer coefficients were compared to Zech, Shi, Grouff, Shulman, Billet and Ondamodels The mean relative errors of these models with the present study's experimental findings were 7%, 15%, 29%, 21%, 45% and 195%. Findings showed that by decreasing the column diameter, the gas-phase mass transfer coefficient (K g .ae) also increases Further, the obtained retention values showed that retention in the column with a 0.1 m diameter was higher than the column with a 0.2 m column.