The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer–clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references)

Polymer/graphene (oxide) nanocomposites exhibit enhanced mechanical properties at low volume fractions of graphene-based nanofillers. An understanding of the reinforcement behaviour was developed through the investigation of interfacial interactions between graphene oxide (GO) nanoplatelets and polymer matrix (PLLA, PCL, PS or HDPE) by combination of microstructure characterization and micromechanical modeling methods. The interfacial interaction determines the degree of dispersion of GO in polymers, interfacial adhesion strength as well as reinforcement efficiency, which can be tailored by the surface chemistry of GO and functionality of polymers. Homogeneous dispersion of GO nanoplatelets with high aspect ratios was found in PLLA and PCL matrices, as well as in lower polar polymer PS due to the preferable interactions between the aromatic rings and the graphene layers, while stacked GO layers with a lower aspect ratio were observed in HDPE matrix even with the presence of an organic compatibilizer. The theoretical elastic moduli of the four kinds of polymer/GO nanocomposites calculated by using the Halpin–Tsai model or a combination of Laminate theory and Mori–Tanaka model underestimated the experimental results. Considering the interfacial interactions, an effective volume fraction was introduced to the above composite models which interpreted the experimental data well. The interphase zone was thus quantified by using micromechanical modeling based on the measured mechanical properties of polymer/GO nanocomposites.

Biomedical applications of graphene have recently attracted intensive attention, with graphene-based nanomaterials being reported as promising candidates in, for example, drug delivery, biosensing and bioimaging. In this paper, mechanical properties and bioactivity of nanofibrous and porous membranes electrospun from graphene oxide (GO) nanoplatelets reinforced poly(ε-caprolactone) (PCL) were investigated. The results showed that the presence of 0.3 wt% GO increased the tensile strength, modulus and energy at break of the PCL membrane by 95%, 66% and 416%, respectively, while improving its bioactivity during biomineralization and maintaining the high porosity of over 94%. The mechanical enhancements were ascribed to the change in the fiber morphology and the reinforcing effect of GO on PCL nanofibers, whereas the improvements on the bioactivity stemmed from the anionic functional groups present on the GO surface that nucleated the formation of biominerals. Systematic studies on the PCL/GO nanocomposite films with varying GO concentrations revealed that the reinforcing effect of GO on PCL was due to the strong interfacial interactions between the two phases characterized by Fourier transform infrared spectroscopy, the good dispersion of GO in the matrix and the intrinsic properties of GO nanoplatelets. The strong and bioactive PCL/GO nanofibrous membranes with a high porosity have great potential for biomedical applications.

Bioactive gelatin–graphene oxide (GO) nanocomposites with varying GO contents were fabricated by a solution-casting method. With the addition of 1 wt% GO, the tensile strength, Young's modulus and energy at break of gelatin were found to increase by 84%, 65% and 158%, respectively. Such reinforcement effects were investigated in detail in terms of the size and morphology of GO sheets, the dispersion degree of GO sheets in gelatin matrix and the interactions between the two phases. The Young's moduli of the nanocomposites were well predicted by the Mori–Tanaka model with application of the effective volume fraction of reinforcement that takes into account the nanofiller and a fraction of the macromolecules adsorbed onto its surface. The GO nanosheets also improved the bioactivity of gelatin by inducing more calcium phosphate nanocrystals on the composites. GO acts as both an effective reinforcement filler and a biological activator in hydrophilic biopolymers such as gelatin, offering the biopolymer–GO nanocomposites great potential to be further developed in biomedical fields.