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ABSTRACTIn this study, two kinds of polyethylene (PE) with different molecular weight were processed into the pipes via rotation extrusion and the failure behaviours under hydrostatic pressure as well as molecular relaxation were investigated. The experimental results showed that the high molecular weight PE exhibited slower relaxation behaviour with higher relaxation activation energy to facilitate the formation of shish-kebab under flow field, while for the low molecular weight one, the stretching molecules easily relaxed back coil state and spherulites were prone to form. Therefore, the low molecular weight PE pipes via convention and rotation extrusions had similar isotropic spherulite morphology and short failure times. In the case of high molecular weight PE, during the convention extrusion, polymer melts flowed along the axial direction to induce the alignment of shish-kebab accordingly, which went against to the hoop stress in hydrostatic pressure. With the rotation of mandrel and die, the direction deviated from the axis so that PE pipe exhibited better resistance to the hoop stress. The failure time was 182 h, 264% longer than the convention-extruded one. Accordingly, a new strategy to prepare high hydrostatic pressure PE pipe under cooperative effects of rotation extrusion and long molecular relaxation time was proposed.

In this study, two kinds of polyethylene (PE) with different molecular weight were processed into the pipes via rotation extrusion and the failure behaviours under hydrostatic pressure as well as molecular relaxation were investigated. The experimental results showed that the high molecular weight PE exhibited slower relaxation behaviour with higher relaxation activation energy to facilitate the formation of shish-kebab under flow field, while for the low molecular weight one, the stretching molecules easily relaxed back coil state and spherulites were prone to form. Therefore, the low molecular weight PE pipes via convention and rotation extrusions had similar isotropic spherulite morphology and short failure times. In the case of high molecular weight PE, during the convention extrusion, polymer melts flowed along the axial direction to induce the alignment of shish-kebab accordingly, which went against to the hoop stress in hydrostatic pressure. With the rotation of mandrel and die, the direction deviated from the axis so that PE pipe exhibited better resistance to the hoop stress. The failure time was 182 h, 264% longer than the convention-extruded one. Accordingly, a new strategy to prepare high hydrostatic pressure PE pipe under cooperative effects of rotation extrusion and long molecular relaxation time was proposed.

The current paper proposes a new methodology to improve the power quality of a 1200 W PEM fuel cell connected to the grid. For this purpose, after using a buck converter for reducing the voltage, an inverter has been utilized. To optimal firing of the controllers, a new technique, which is the Amended Penguin Optimization algorithm (APOA) is used. The results of the controller based on the suggested APOA are put in comparison with several other latest techniques. Simulations show that the highest efficiency in the PEM fuel cell is 53% and at 7 A and the highest power is 1200 W at 26 A and 46 V. The results of simulation validated by comparing with some other methodologies and the results show that the proposed APOA with 0.01445 Steady-state error provides the minimum error which indicates that using the optimized controllers based on the proposed APOA provides higher efficiency toward the others t under sagging and swelling conditions in all terms of maximum overshoot, minimum error, and the steady-state error among the reference voltages and the point of common coupling.