Fused deposition modeling 3D printing of polyamide-based composites and its applications

Highlights

• A brief review of notable advances in fused deposition modeling (FDM) 3D printing of polyamide-based composites and the properties of the printed parts as well as their practical or potential applications is presented.

• The formation and the performance of polyamide/polymer blends, inorganic particle reinforced polyamide composites, and fiber reinforced polyamide composites have been particularly emphasized.

• The significant limitations, opportunities, and challenges are identified to motivate the future research on FDM 3D printing of polyamide-based composites and its applications.

Abstract

Fused deposition modeling (FDM) is one of the most commonly utilized low-cost 3D printing technology, which employs the hot-melt and adhesive properties of thermoplastic materials. As one of the most important classes of engineering thermoplastic polymer materials, polyamide (PA) possesses excellent comprehensive performance. However, the FDM fabricated products based on pure PA are seriously warped, distorted, and lack of shape stability due to the accumulation of shrinkage stress generated from the crystallization of polymer, which severely restrict the application of PA in FDM 3D printing. In this article, notable advances in FDM 3D printing of polyamide-based composites and the properties of the printed parts as well as their practical or potential applications are highlighted. The particular emphasis is placed on the formation and the performance of polyamide/polymer blends, inorganic particle reinforced polyamide composites, and fiber reinforced polyamide composites. Finally, the significant limitations, opportunities, and challenges are identified to motivate the future research on the FDM 3D printing of polyamide-based composites and its applications.

Introduction

3D printing (3DP), also known as additive manufacturing (AM), rapid prototyping (RP), and solid-freeform (SFF), is an exponentially evolved manufacturing technology covering a process of joining materials to make objects from 3D model data, usually layer-by-layer, which has received significant attentions in recent years by offering numerous advantages over traditional subtractive methods since it was first described in 1986 by Charles Hull [1]. The 3DP technology provides the ability to directly create objects with intricate geometrical features in a cost-effective way, which requires no mold tool and offers near-net-shape manufacturing in a relatively short period of time [2]. In addition, the 3DP is most beneficial in fabrication of customized parts and products with complex and tailored designs while being capable of harnessing digital information for the realization of a robust and decentralized 3D manufacturing system [3]. Among the various 3DP techniques, fused deposition modeling (FDM) is one of the most commonly utilized low-cost processes due to its simplicity and availability of machines at affordable prices, which employs the hot-melt and adhesive properties of thermoplastic materials [[4], [5], [6], [7]]. During the FDM process, the un-melted filament acts as a piston for pushing the melted polymer out of the nozzle after that the molten filament is deposited onto a platform in a raster pattern in order to form each layer of the model, while the final 3D product is fabricated through building up successive layers (see Fig. 1) [8,9]. Therefore, the materials based on which the filament is fabricated must have adequate stiffness and melt flow-ability [9]. Usually, the thermoplastic polymer-based filaments are used as feedstock materials in FDM, including acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polycarbonate (PC), etc. [10].

Despite the wide variety of polymers are available, whereas, the commercial polymeric materials for FDM are still limited, costly, and lack of high properties, which severely hinders the use of FDM technology for manufacturing. Therefore, new filament with low cost and excellent properties for FDM need to be developed urgently. As one of the most important classes of engineering thermoplastic polymers, polyamide (PA or nylon) possesses excellent comprehensive performance. Unfortunately, a large number of attempts indicated that the FDM fabricated products based on pure PA are seriously warped, distorted, and lack of shape stability. Such drawbacks severely restrict the application of PA in FDM 3D printing. The reason why for severe warpage of 3D printed PA is ascribed to the accumulation of shrinkage stress generated from the crystallization of polymers. The successive stacking of crystalline polymers leads to asynchronous volumetric shrinkage, and the regular arrangement of molecular chains critically aggravates the shrinkage and warpage. Therefore, the critical factor to prevent the warpage in FDM is to hinder the regular arrangement of molecular chains and weaken its ability to crystallize [8,11]. In the FDM process, the filament melt into a liquid or semi-liquid state at nozzle and then was extruded layer-by-layer onto the former deposited layer or build platform, where the layers are fused together and then solidify into final parts. To some extent, the quality of FDM 3D printed parts can be tailored by altering printing parameters, such as layer thickness, printing orientation, raster width, raster angle, and air gap, which have been discussed by Sood et al. [12]. By contrast with processing parameters, the development of new FDM 3D-printable material or filament is of much more crucial of importance in determining the properties of the final fabricated products.

With the high demands for practical applications, the polymer matrix composites have become state-of-the-art in material design and development for 3D printing, which could improve the properties of polymers by combining the matrix and reinforcements to achieve a composite system with more useful structural or functional properties non attainable by any of the constituent alone [10,[13], [14], [15]]. In recent several years, the sophisticated development of polymer composite materials that are compatible with the available 3D printers has certainly created more opportunities for PA in FDM applications, especially in the development of advanced and multifunctional PA-based composites. Also, there has been considerable achievements in developing new FDM 3D printable polyamide-based composites with improved performance. Hence, in this review, we present, analyze, and summarize the advanced progress in FDM 3D printing of polyamide-based composites and its applications. Based on the type of reinforcement, the main part of this review article is organized into three sections including polyamide/polymer blends, inorganic particle reinforced polyamide composites, and fiber reinforced polyamide composites. In the final section, we make an attempt to point some future directions for the further development of FDM 3D printing of polyamide-based composites and its applications.