Properties of 3D Printed Continuous Fiber-Reinforced CNTs and Graphene Filled Nylon 6 Nanocomposite

Nanomaterials have attracted much attention due to the excellent properties they possess and their promising applications. The combination of 3D printing and composite materials has redefined the mechanical properties of 3D printed products.;In this research, nylon (PA) 6 nanocomposites filled with either carbon nanotubes(CNTs), graphene or graphene-NH2 were 3D printed together with Kevlar fibers into specimens for mechanical tests and other characterizations. Different weight percentages of CNTs and graphene were used to produce the nanocomposites, in order to figure the properties of each nanoparticle reinforced PA 6. The melt mixed CNTs or graphene nanocomposites were extruded into filaments and used in the 3D printer. A Markforged printer allowed the production of continuous Kevlar fiber reinforced nanocomposites.;The tensile and flexural tests revealed that the best weight percentage of CNTs is 0.5wt%, where the entanglements and agglomerates of CNTs were not so obvious. Surprisingly, the CNTs filled PA 6 nanocomposites did not show as significant improvements in mechanical properties as graphene filled PA 6, due to the weak interfacial interactions between the CNTs and the PA 6 matrix. The addition of Kevlar fibers increased the tensile strength and flexural modulus of PA 6 by 526% and 1388%. Also, the tensile fatigue results showed that 1%CNT/PA 6+Kevlar specimens have the longest fatigue life among the materials tested.;Graphene filled PA 6 presented much better improvements in mechanical properties. With only 0.1wt% of graphene, the tensile modulus improved by 101% and with 1wt% of graphene the modulus improved by 153%. Additionally, although Kevlar fibers dominate the main mechanical properties of these composite materials, the existence of graphene also contributes to the enhancement of strengths and moduli, unlike CNTs.;Strong interfacial bonding allows efficient load transfer between matrix and reinforcement. Therefore, graphene-NH2/PA 6 showed significant improvements in both tensile and bending strengths. The tensile modulus of 0.1% graphene-NH2/PA 6 and 1% graphene-NH2/PA 6 are increased by 212% and 253%.;Flexural tests showed obvious difference between different nanoparticle fillers. However, the anisotropic specimens did not show much difference between different weight percentages of the same kind of nanocomposite.;It is found that the well-dispersion of nanoparticles in the matrix and strong interfacial bonding between the filler and the matrix are the main reasons for the enhancement of mechanical properties of nanocomposites. The addition of Kevlar fibers improved the stiffness and strength of the composites significantly.