The Influence of Epitaxial Crystallization on the Mechanical Properties of Polyamide 66/Reduced Graphene Oxide Nanocomposite Injection Bar

In Situ SAXS and WAXD Investigations of Polyamide 66/Reduced Graphene Oxide Nanocomposites During Uniaxial Deformation

Epitaxial crystallization between Polyamide 66 (PA66) and reduced graphene oxide (RGO) can enhance the interfacial interaction and the mechanical properties of PA66/RGO nanocomposites. In situ two-dimensional synchrotron radiation wide angle X-ray diffraction and small angle X-ray scattering were used to track the structural evolution of the PA66/RGO nanocomposites with an epitaxial crystal during uniaxial deformation. In the PA66/RGO nanocomposites, the structural evolution of non-epitaxial and epitaxial crystals could be clearly analyzed. The non-epitaxial crystal, whose crystal plane can slip, shows the rearrangement and the Brill transition during uniaxial deformation. While the PA66 chains of an epitaxial crystal are held by RGO, the crystal plane could therefore not slip. The epitaxial crystal also constrains the deformation of the amorphous phase and the crystal form transition of non-epitaxial crystals around them. With the content increase of epitaxial crystals, the constraint effect becomes more obvious. Therefore, the rigid epitaxial crystals in the PA66/RGO nanocomposites promote mechanical properties. The present findings can deepen the understanding of structural evolution during the tensile deformation of PA66/RGO nanocomposites and the influence of the epitaxial crystals on the mechanical property in semicrystalline polymers with a H-bond.

Rediscovery of nylon upgraded by interactive biorenewable nano-fillers

Inorganic nanomaterials can only stiffen nylon with a significant loss of its toughness and ductility. Furthermore, they are not eco-friendly. In this study, the facile tuning of nylon's mechanical properties from stiff to tough was achieved, using cellulose nanocrystals (CNC) and chitosan nanowhiskers (CSW) as biorenewable fillers. The interaction between the matrix and filler was controlled by varying the types of fillers and the employed processing methods, including in situ interfacial polymerization and post-solution blending. Particularly with CSW, the in situ-incorporated filler with a 0.4 wt% loading strengthened nylon and led to a 1.9-fold increase in its Young's modulus (2.6 GPa) and a 1.7-fold increase in its ultimate tensile strength (106 MPa), whereas the solution-blended filler with a 0.3 wt% loading toughened the polymer with a 2.1-fold increase (104 MJ m^-3). Compared with inorganic nanocomposites, these interactive biofiller-nanocomposites are unrivaled in their reinforcing performance when normalized by filler content. This stiff-to-tough tuning trend is more pronounced in the CSW system than in the CNC system. Covalent polymer grafts on the amine surface of CSW enhanced interfacial interactions in the in situ method, whereas its cationic surface charges plasticized the polymer matrix in the blending method. This proteinaceous composite-mimicking all-organic nylon nanocomposite opens new possibilities in the field of reinforced engineering plastics.

A Review of Current Development of Graphene Mechanics

Graphene, a two-dimensional carbon in honeycomb crystal with single-atom thickness, possesses extraordinary properties and fascinating applications. Graphene mechanics is very important, as it relates to the integrity and various nanomechanical behaviors including flexing, moving, rotating, vibrating, and even twisting of graphene. The relationship between the strain and stress plays an essential role in graphene mechanics. Strain can dramatically influence the electronic and optical properties, and could be utilized to engineering those properties. Furthermore, graphene with specific kinds of defects exhibit mechanical enhancements and thus the electronic enhancements. In this short review, we focus on the current development of graphene mechanics, including tension and compression, fracture, shearing, bending, friction, and dynamics properties of graphene from both experiments and numerical simulations. We also touch graphene derivatives, including graphane, graphone, graphyne, fluorographene, and graphene oxide, which carve some fancy mechanical properties out from graphene. Our review summarizes the current achievements of graphene mechanics, and then shows the future prospects.