Optimization of Filler Compositions of Electrically Conductive Polypropylene Composites for the Manufacturing of Bipolar Plates.

In this research, polypropylene (PP)-graphite composites were prepared using the melt mixing technique in a twin-screw extruder. Graphite, multi-walled carbon nanotubes (MWCNT), carbon black (CB), and expanded graphite (EG) were added to the PP in binary, ternary, and quaternary formations. The graphite was used as a primary filler, and MWCNT, CB, and EG were added to the PP-graphite composites as secondary fillers at different compositions. The secondary filler compositions were considered the control input factors of the optimization study. A full factorial design of the L-27 Orthogonal Array (OA) was used as a Design of Experiment (DOE). The through-plane electrical conductivity and flexural strength were considered the output responses. The experimental data were interpreted via Analysis of Variance (ANOVA) to evaluate the significance of each secondary filler. Furthermore, statistical modeling was performed using response surface methodology (RSM) to predict the properties of the composites as a function of filler composition. The empirical model for the filler formulation demonstrated an average accuracy of 83.9% and 93.4% for predicting the values of electrical conductivity and flexural strength, respectively. This comprehensive experimental study offers potential guidelines for producing electrically conductive thermoplastic composites for the manufacturing of bipolar fuel cell plates.

Development, processing and characterization of Polycaprolactone/Nano-Hydroxyapatite/Chitin-Nano-Whisker nanocomposite filaments for additive manufacturing of bone tissue scaffolds.

This paper focuses on utilizing the Fused Deposition Modeling (FDM) to manufacture Polycaprolactone/Nano-Hydroxyapatite/Chitin-Nano-Whisker nanocomposite scaffolds and their subsequent characterization for biomedical applications. FDM nanocomposite filaments were manufactured in multiple nanocomposite formulations of Polycaprolactone/Nano-Hydroxyapatite (nHA), Polycaprolactone/Chitin-Nano-Whisker (CNW), and Polycaprolactone/nHA/CNW using a green method. The FDM processing conditions were optimized using Taguchi orthogonal array method. The mechanical, biodegradation, and biocompatibility properties of the bone tissue scaffolds were assessed. A preosteoblast mouse bone cell line was used for cell proliferation and attachment assays. The results indicated that CNW content in the filaments slightly increases the mechanical properties of the 3D printed parts, and the nanocomposite with 3% CNW content exhibited significant improvement in the cell proliferation and attachment properties of the scaffolds. The nHA content considerably improved the mechanical properties of the scaffolds. The nHA and CNW nanofillers increased the biodegradation rate of PCL. In general, considering all types of responses, a green manufactured nanocomposite of PCL/nHA/CNW can significantly increase the biological and mechanical properties of the 3D printed products for bone tissue scaffolds.

Effects of design, porosity and biodegradation on mechanical and morphological properties of additive-manufactured triply periodic minimal surface scaffolds.

The main aim of this paper is to assess the impacts of design, porosity, and biodegradation on the mechanical and morphological properties of triply periodic minimal surface (TPMS) scaffolds. The TPMS scaffolds were designed and manufactured with different porosities by using fused deposing modeling (FDM) technique. The biodegradation test on the scaffolds was performed for four and six months. The mechanical properties were assessed employing ASTM standard compression test and an in-situ mechanical testing stage. Microcomputed tomography (Micro-CT) technique was used to investigate detailed morphological properties of the scaffolds in 3D. Results indicate that the Schwarz-D scaffolds exhibit the highest compressive strength in lower porosity scaffolds but lose mechanical properties when the porosity was increased. On the contrary, Gyroid scaffolds maintain their strength as the porosity was increased. In addition, Gyroid scaffolds preserve a higher percentage of their compressive strength after six months of biodegradation. It was also observed that biodegradation phenomenon transformed the mechanical failure mode of the scaffolds from ductile to brittle. Morphological analysis of the scaffolds revealed detailed information, which support and clarify the observed variations in the mechanical properties.