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Despite extraordinary mechanical properties and excellent biodegradability, poly­(lactic acid) (PLA) still suffers from a highly inherent flammability, restricting its wide applications in the electric and automobile fields. Although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical strength of PLA. Herein, we have demonstrated the fabrication of a novel core–shell nanofibrous flame-retardant system, PN-FR@CNF, through in situ chemically grafting the phosphorus–nitrogen-based polymer onto the cellulose nanofiber (CNF) surface. The results show that adding 10 wt % PN-FR@CNF enables PLA to achieve a V-0 flame resistance rating during vertical burning tests and to exhibit a dramatically reduced peak heat release rate in cone calorimetry measurements, indicating a significantly reduced flammability. In addition, the tensile strength of PLA also increases by around 24% (about 72 MPa). This work offers an innovative methodology for the design of the unique integration of extraordinary flame retardancy and mechanical reinforcement into one hierarchical nanostructured additive system for creating advanced green polymeric materials.

The steady and dynamic rheological behaviors of two cellulose nanocrystal (CNC) suspensions were investigated over a wide range of concentrations. The viscosity, storage and loss modules increased with increasing CNC concentration, and both CNC suspensions showed three regions in a viscosity-concentration graph. The two critical concentrations depended on the aspect ratio and corresponded to the overlap and gelation concentration. Because of the higher aspect ratio, switchgrass CNC suspension transitioned into a biphasic state and formed a hydrogel at lower concentrations than those of cotton CNC suspensions. Furthermore, the complex viscosities of both CNC suspensions were higher than their steady viscosities; therefore, neither CNC suspension followed the Cox-Merz rule, which may be attributed to the existence of a liquid crystal domain in each suspension. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40525.

Despite abundant studies on gas barrier, viscoelastic, and flammability properties of polymer nanocomposites, comprehensive understandings of these performances and their relationships are still lacking. We herein attempt to gain deep insights into the performances by creating several polymer nanocomposites by incorporating three types of nanoparticles, nanoclay (Clay), carbon nanotubes (CNTs), and reduced graphene nanoplates (RGO), into polypropylene (PP). The oxygen permeability, viscoelasticity, and flammability measurements demonstrate that RGO can lead to much more reduction in the gas permeability (by ∼73%) and flammability (peak heat release rate (PHRR) reduction by ∼78%), as well as a higher storage modulus and melt viscosity of polymer matrix relative to clay and CNTs at the same loading (1.0 wt %) due to its higher aspect ratio. Clay performs better than CNTs in terms of gas barrier property due to its lamellar structure while behaves worse than CNTs in terms of increasing the melt viscosity and reducing flammability of polymers. Most important, there is a nearly line correlation among these properties for all polymer nanocomposites despite some deviations.

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The extraordinary properties of carbon nanotubes (CNTs) and graphene stimulate the development of advanced composites. Recently, several studies have reported significant synergies in the mechanical, electrical and thermal conductivity properties of polymer nanocomposites by incorporating their nanohybrids. In this work, we created polypropylene nanocomposites with homogeneous dispersion of CNTs and reduced graphene oxides via a facile polymer-latex-coating plus melt-mixing strategy, and investigated their synergistic effects in their viscoelastic, gas barrier, and flammability properties. Interestingly, the results show remarkable synergies, enhancing their melt modulus and viscosity, O2 barrier, and flame retardancy properties and respectively exhibiting a synergy percentage of 15.9%, 45.3%, and 20.3%. As previously reported, we also observed remarkable synergistic effects in their tensile strength (14.3%) and Young's modulus (27.1%), electrical conductivity (32.3%) and thermal conductivity (34.6%). These impressive results clearly point towards a new strategy to create advanced materials by adding binary combinations of different types of nanofillers.

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