Processing Effects on the Through-Plane Electrical Conductivities and Tensile Strengths of Microcellular-Injection-Molded Polypropylene Composites with Carbon Fibers

Abstract

Polymers reinforced with conducting fibers to achieve electrical conductivity have attracted remarkable attention in several engineering applications, and injection molding provides a cost-effective way for mass production. However, the electrical performance usually varies with the molding conditions. Moreover, high added content of conducting fibers usually results in molding difficulties. In this study, we propose using microcellular (MuCell) injection molding for polypropylene (PP)/carbon fiber (CF, 20, and 30 wt%) composites and hope that the MuCell injection molding process can improve both electrical and mechanical performance as compared with conventional injection molded (CIM) parts under the same CF content. Both molding techniques were also employed with and without gas counter pressure (GCP), and the overall fiber orientation, through-plane electrical conductivity (TPEC), and tensile strength (TS) of the composites were characterized. Based on the various processing technologies, the results can be described in four aspects: (1) Compared with CIM, microcellular foaming significantly influenced the fiber orientation, and the TPECs of the samples with 20 and 30 wt% CF were 18–78 and 5–8 times higher than those of the corresponding samples molded by CIM, respectively; (2) when GCP was employed in the CIM process, the TPEC of the samples with 20 and 30 wt% CF increased by 3 and 2 times, respectively. Similar results were obtained in the case of microcellular injection molding—the TPEC of the 20 and 30 wt% composites increased by 7–74 and 18–32 times, respectively; (3) although microcellular injection molding alone (i.e., without GCP) showed the greatest influence on the randomness of the fiber orientation and the TPEC, the TS of the samples was the lowest due to the uncontrollable foaming cell size and cell size uniformity; (4) in contrast, when GCP was employed in the microcellular foaming process, high TS was obtained, and the TPEC was significantly enhanced. The high foaming quality owing to the GCP implementation improved the randomness of fiber orientation, as well as the electrical and mechanical properties of the composites. Generally speaking, microcellular injection combined with gas counter pressure does provide a promising way to achieve high electrical and mechanical performance for carbon-fiber-added polypropylene composites.

An Experimental Study on Non-Destructive Evaluation of the Mechanical Characteristics of a Sustainable Concrete Incorporating Industrial Waste

“…Thus, these two samples also showed the highest compressive strength. This might have been due to their pozzolanic behavior, which ultimately fills the voids and cracks [ 23 ]. Thus, CBA and WGS are both good replacements for cement binders.…”

“…In addition to silica, iron and alumina, CBA contains sulfate, magnesium, calcium and other minerals [ 18 , 19 ]. Researchers have used different nano-sized materials as fillers and binders to study their influence and applicability in concrete [ 20 , 21 , 22 , 23 ].…”

Lightweight and High Impact Toughness PP/PET/POE Composite Foams Fabricated by In Situ Nanofibrillation and Microcellular Injection Molding

“…First, the PP molecular chain is prone to be disentangled due to its linear molecular chain structure, leading to its low melt strength and viscoelasticity [ 11 ]. Thus, cell collapse and coalescence usually happen at relative high foaming temperature in the MIM process, resulting in poor mechanical performance [ 12 ]. Second, unlike the batch foam in a static condition, MIM contains a complex behavior of fountain flow.…”

“…Third, the mechanical properties of foamed products, especially stiffness or hardness, are generally inferior to that of solid samples [ 14 , 15 ]. It is due to the fact that the internal cells, which normally act as stress concentration points, may decrease the mechanical properties corresponding to the weight reduction [ 12 ].…”

Modelling and Simulation of MuCell®: The Effect of Key Processing Parameters on Cell Size and Weight Reduction

“…The second approach is to stop bubbles from getting trapped between the mould cavity and melt in the filling stage. Techniques, such as gas counter pressure (GCP) system [ 13 , 14 , 15 , 16 , 17 , 18 ], gas-assisted microcellular injection moulding (GAMIM) [ 19 ] and pressure-temperature (P-T) control system [ 20 , 21 ], were developed based on this principle by increasing the mould cavity pressure to a certain level at the beginning of the filling stage. It was also reported that both GCP technology [ 22 ] and GAMIM [ 19 ] can improve mechanical properties by increasing solid skin thickness.…”