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In the current study, polystyrene/carbon nanotubes/glass fiber (PS/CNT/GF) hybrid foam with a bimodal cellular-structure has been fabricated via microwave heating as a novel energy source. Microwave-assisted (MA) samples not only demonstrated the lowest density as compared to traditional methods but also represented superior compressive mechanical properties. Since the bimodal morphology has not been seen so far, the role of selective microwave heating has been thoroughly investigated from the microstructural point of view. Accordingly, the amount of receiving microwave radiations to heat up the system is controllable via the CNTs (as nucleating agents and absorbers) as well as radiation time. Moreover, 1-15 wt% fibers were incorporated to enhance mechanical performance, which led to turning uniform cellular structure to the bimodal pattern, and its cell morphological was studied thereafter. Electrical conductivity and dielectric permittivity properties have not been deprived of bimodality benefits which have been rigorously proven.

This article aims to investigate the effect of dispersion and uniformity of fiber length distribution on the rheological and mechanical behavior of polypropylene reinforced with short glass fiber. The composites were prepared through melt compounding with three various glass fiber concentrations using a twin-screw extruder. Multiple extrusion processing was used to alter and manipulate the fibers’ length inside the composites. The fiber length distribution was analyzed via the photomicrograph technique. Rheological measurements indicated that the molten samples were visco-plastic fluids and the Herschel–Bulkley model is the best model for fitting on the rheological behavior diagram. Variables of the fitted model are noticeably altered by the fiber length distribution. Moreover, rheological assessments revealed that the non-Newtonian behavior of the molten composites significantly diminished after the second extrusion processing, while it did not have much effect on the fiber length reduction. In the second phase, tensile and flexural properties were determined to detect the mechanical properties. The results indicated that the tensile strength of the composite has a direct relation with the fiber length distribution factor while the flexural strength is independent of fiber length. Furthermore, the highest tensile and flexural strength attained from the composite containing the highest fiber volume fraction.

In this work, polystyrene was filled with carbon black (CB) at 1, 3, and 5 wt% and were foamed via microwave-assisted (MA) foaming. The composite morphology was tracked by scanning electron microscopy, transmission electron microscopy, and rheology. CB played the dominant role as the selective microwave absorbers to provide the required heat for the cell nucleation and growth. MA foaming is a controllable technique to reach proper foam density and cell size by controlling microwave energy. MA foams microstructurally were compared with the foams created via the conventional foaming procedures, including oil bath heating and fast pressure drop. One advantage of the MA method is increasing the temperature of the bulk and surface of the thick specimen simultaneously. As a result, cell nucleation and growth are uniform throughout the thick composite. Samples with a thickness of 1 cm were foamed via the MA method.