Experimental Investigations into 4-D Printing of Barium Titanate and Graphene Reinforced PVDF Matrix Composites

Abstract

3D printing of smart materials is one of the disruptive innovations in the field of advanced manufacturing. From the past one decade significant advancements have been reported in this sector with respect to printers, materials, and processes. Fused deposition modelling (FDM) (one of the low cost 3D printing technologies) has entered into the field of smart manufacturing, in which active materials are being used particularly for dynamic 4D applications. FDM has been widely explored for different range of thermoplastics and thermosetting composites. Researchers have worked on the in-house development of thermoplastic composite based feedstock filaments by using various polymers such as polyvinyl chloride (PVC), poly lactic acid (PLA), polypropylene (PP), acrylonitrile butadiene styrene (ABS) etc. for numerous applications. But, hitherto little has been reported on the preparation of smart polymer based feedstock filament for 3D printing of functional prototypes having 4D properties. In this research work an electro-active polymer, polyvinylidene fluoride (PVDF) was reinforced with graphene (Gr), and barium titanate (BTO) for the preparation of composite. Two different methods of blending have been explored for the development of smart polymer based composite (i) mechanical blending (MB) of materials and (ii) chemical assisted mechanical blending (CAMB). In the first stage, based upon the melt flow index (MFI), different proportions/compositions of PVDF-Gr-BTO were selected for extrusion with twin screw extruder (TSE). Further to optimize the process parameters of TSE three input parameters (a) extruder temperature, (b) rotational speed (rpm) and (c) composition were selected. The prepared feed stock filaments of MB based composites were subjected to mechanical, thermal dimensional and morphological analysis. The analysis of variance (ANOVA), suggested the optimised settings of TSE for fabrication of MB based composite feedstock filament as: extruder temperature 200°C, rotation speed 40 rpm with composition PVDF (78%) + Gr (2%) + BTO (20%) (by weight %). The prepared feedstock filament was used to run on low cost open source FDM setup for 3D printing of standard prototypes by selecting the infill speed (IS), infill angle (IA) and infill density (ID) as input parameters. Prepared samples were subjected to tensile, flexural, pull-out and morphological testing. The fabricated specimens were also subjected to dimensional variation, shore-D testing and dynamic mechanical analysis (DMA). Further 3D printing of scaffolds was performed at optimised settings for process capability analysis to ascertain the industrial usability for batch production. vii In the second stage, process parameters of TSE were optimised for the preparation of CAMB composite based feedstock filament. Further the prepared filament at optimised settings of TSE was used for 3D printing of standard scaffolds. The process parameters of FDM were also optimised for 3D printing of parts using prepared composite by CAMB. The 3D printed standard tensile and flexural samples were tested for process capability analysis. In final stage optimised settings of FDM obtained for 3D printing of parts using MB and CAMB composites were used for fabrication of thin cylindrical discs (diameter 10 mm and thickness 0.4 mm), followed by electric poling (for possible piezoelectric characterization). The results of X-ray diffraction (XRD) and Fourier transmission infrared spectroscopy (FTIR), analysis shows more β-phase formation in the electrically poled sample as compared to non-poled specimen. Finally, a comparative study of mechanical, thermal, morphological, and 4D properties of PVDF-BTO-Gr nano-composites prepared by MB and CAMB was performed. The differential scanning calorimetry (DSC) analysis suggested that composite prepared by MB is thermally more stable as it absorbs more heat -31.09J/g during heating cycle. Further, the results of the study suggested that 3D printed functional prototypes prepared by CAMB are having better mechanical, morphological, and dielectric properties. The piezoelectric coefficient (d33) 20 pC/N and 30.2 pC/N was observed on 3D printed specimen (prepared from filament processed with MB and CAMB respectively), suitable for pressure sensors, touch sensitive buttons or other user interface control, actuators for biomimetic based 4D applications.