Fabrication of Poly(Vinylidene Fluoride)/Graphene Nano-Composite Micro-Parts with Increased β-Phase and Enhanced Toughness via Micro-Injection Molding.

Wu Guo,Li Li,Zhaogang Liu,Yan Zhu

doi:10.3390/polym13193292

Abstract

Based on poly(vinylidene fluoride)/graphene (PVDF/GP) nano-composite powder, with high β-phase content (>90%), prepared on our self-designed pan-mill mechanochemical reactor, the micro-injection molding of PVDF/GP composite was successfully realized and micro-parts with good replication and dimensional stability were achieved. The filling behaviors and the structure evolution of the composite during the extremely narrow channel of the micro-injection molding were systematically studied. In contrast to conventional injection molding, the extremely high injection speed and small cavity of micro-injection molding produced a high shear force and cooling rate, leading to the obvious “skin-core” structure of the micro-parts and the orientation of both PVDF and GP in the shear layer, thus, endowing the micro-parts with a higher melting point and crystallinity and also inducing the transformation of more α-phase PVDF to β-phase. At the injection speed of 500 mm/s, the β-phase PVDF in the micro-part was 78%, almost two times of that in the macro-part, which was beneficial to improve the dielectric properties. The micro-part had the higher tensile strength (57.6 MPa) and elongation at break (53.6%) than those of the macro-part, due to its increased crystallinity and β-phase content.

Highlights

With the mushrooming growth of the electronic industry, the miniaturization and light weight of electronic products have become research hotspots [1], producing cutting-edge technology in the 21st century, i.e., micro-electromechanical systems (MEMS) technology, as well as the rapid development of devices toward miniaturization and functionalization [2]
For the different cavity size of micro-injection molding from conventional injection molding, the established flowing and filling theories based on the conventional injection are no longer suitable
The studies on the filling behaviors of Poly(vinylidene fluoride) (PVDF)/GP composites at different process parameters in the extremely narrow channel of the micro-injection molding become necessary

Summary

Introduction

With the mushrooming growth of the electronic industry, the miniaturization and light weight of electronic products have become research hotspots [1], producing cutting-edge technology in the 21st century, i.e., micro-electromechanical systems (MEMS) technology, as well as the rapid development of devices toward miniaturization and functionalization [2]. By adopting the special equipment self-designed in our research group, i.e., pan-mill mechanochemical reactor, which could exert strong multiple stresses, including squeezing, shear and hoop stress on materials in-between, PVDF active powder and PVDF/functional filler composite powder, e.g., PVDF/graphene, with high content of β-phase crystals (more than 90%) were obtained in our laboratory, and the conventionally injected samples with good comprehensive properties, especially dielectric properties, were prepared [22,23]. This provides a good base for the micro-injection of PVDF and its nano-composites. Graphene (GP, SE1231) was provided by Sixth Element (Changzhou) Materials Technology Co., Ltd., Changzhou, China

Sample Preparation

Characterization

Results and Discussion

Conclusions