Role of annealing and isostatic compaction on mechanical properties of 3D printed short glass fiber nylon composites

Among many thermoplastics that are used in engineering, polyamide 6 (nylon 6) is an extremely versatile engineering thermoplastic. 3D printed nylon glass fiber composites, based on fused filament modeling, typically suffer from poor bead-to-bead interfacial bonding and relatively high void content, limiting their mechanical properties. This work explores the effect of isostatic compaction pressure and annealing on improving the mechanical properties of 3D printed short fiber polymer composites. Tensile testing was performed in-printing and transverse directions with samples that were compacted at 0.55 MPa (80 psi) and annealed at different temperatures and compared to as-printed untreated samples. The results indicate that by selecting appropriate isostatic compaction temperature, both strength and modulus in principal directions of 3D printed composites can be significantly improved. Strength was improved by over 50% and 100% in printing and transverse directions, respectively, and a twofold increase of the modulus in printing direction was found for samples compacted at 0.55 MPa (80 psi) and 200 degrees C.The observed mechanical behavior was explained in terms of various parameters such as degree of compaction, crystalline structure, orientation state and void content.