3D printing of polymer matrix composites: A review and prospective

Abstract

The use of 3D printing for rapid tooling and manufacturing has promised to produce components with complex geometries according to computer designs. Due to the intrinsically limited mechanical properties and functionalities of printed pure polymer parts, there is a critical need to develop printable polymer composites with high performance. 3D printing offers many advantages in the fabrication of composites, including high precision, cost effective and customized geometry. This article gives an overview on 3D printing techniques of polymer composite materials and the properties and performance of 3D printed composite parts as well as their potential applications in the fields of biomedical, electronics and aerospace engineering. Common 3D printing techniques such as fused deposition modeling, selective laser sintering, inkjet 3D printing, stereolithography, and 3D plotting are introduced. The formation methodology and the performance of particle-, fiber- and nanomaterial-reinforced polymer composites are emphasized. Finally, important limitations are identified to motivate the future research of 3D printing.

Introduction

3D printing, also referred to as additive manufacturing(AM), rapid prototyping(RP), or solid-freeform(SFF), is a ‘process of joining materials to make objects from 3D model data, usually layer by layer’ [1], which was first described in 1986 by Charles Hull [2]. This technology creates objects by adding materials to reduce waste while reaching satisfactory geometric accuracy [3]. It begins with a meshed 3D computer model that can be created by acquired image data or structures built in computer-aided design (CAD) software. A STL (Surface Tessellation Language) file is commonly created. The mesh data will be further sliced into a build file of 2D layers and sent to the 3D printing machine.

Thermoplastic polymer materials such as acrylonitrile butadiene styrene(ABS) [4], [5], [6], polylactic acid(PLA) [4], [6], [7], polyamide(PA) [8] and polycarbonate(PC) [9] as well as thermosetting polymer materials like epoxy resins could be processed by 3D printing technology. Epoxy resins are reactive materials that require thermal or UV-assisted curing to complete the polymerization process, and they initially exhibit a low viscosity, which rises as the curing proceeds [10], [11], [12]. Therefore, epoxy resins are suitable for heat or UV assisted printing process. Based on the various selections of materials, 3D printing of polymers has found their possible applications in aerospace industries for creating complex lightweight structures [13], architectural industries for structural models [14], art fields for artifact replication or education [15], and medical fields for printing tissues and organs [16]. However, most of 3D printed polymer products are still now used as conceptual prototypes rather than functional components, since pure polymer products built by 3D printing are lack of strength and functionality as fully functional and load-bearing parts. Such drawbacks restrict the wide industrial application of 3D printed polymers.

3D printing of polymer composites solves these problems by combining the matrix and reinforcements to achieve a system with more useful structural or functional properties non attainable by any of the constituent alone [17]. Incorporation of particle, fiber or nanomaterial reinforcements into polymers permits the fabrication of polymer matrix composites, which are characterized by high mechanical performance and excellent functionality. Conventional fabrication techniques of composites such as molding, casting and machining create products with complex geometry through material removal processes [18]. While the manufacturing process and performance of composites in these methods are well-controlled and understood, the ability to control the complex internal structure is limited. 3D printing is able to fabricate complex composite structures without the typical waste. The size and geometry of composites can be precisely controlled with the help of computer aided design. Thus, 3D printing of composites attains an excellent combination of process flexibility and high performance products.

Although 3D printing has attracted a lot of attentions over the past three decades, most of published review articles focused on introductions of processing techniques and printing of pure polymer materials. However, in the recent several years, there has been considerable achievements in developing printable polymer composites with improved performance. Hence, we present, analyze and summarize information pertinent to 3D printing of polymer composites in this review. We first provide a brief introduction of 3D printing technique used for polymer composites and their characteristics. Next, we investigate the detailed printing technique implementations and properties improvements of polymer composites. Biomedical, electronics and aerospace applications of polymer composites are explored then. In particular, work done in last five years are emphasized to show the progress in this area. Finally, we discuss the limitations of current technologies and future perspective.