Effect of Polytetrafluoroethylene on the Foaming Behaviors of Linear Polypropylene in Continuous Extrusion

Linear polypropylene (PP) foams, blown in the continuous extrusion process using supercritical CO2 as the blowing agent, exhibited poor cell morphology and narrow foaming window, because of their low melt strength. In this study, polytetrafluoroethylene (PTFE) was blended with PP resin with the aim of improving the foaming behavior of PP. It was found that the PTFE particles were deformed into fine fibers under shear or extensional flows during the extrusion process, which significantly increased the melt strength of PP from 0.005 N to 0.03 N (PP/PTFE with PTFE content of 4.0 wt %) at 230℃. The experimental results indicated that the presence of PTFE improved the cell morphology of PP foams and broadened the foaming window of PP

Lightweight, Multifunctional Polyetherimide/Graphene@Fe3O4 Composite Foams for Shielding of Electromagnetic Pollution

Novel high-performance polyetherimide (PEI)/graphene@Fe3O4 (G@Fe3O4) composite foams with flexible character and low density of about 0.28？0.4 g/cm3 have been developed by using a phase separation method. The obtained PEI/G@Fe3O4 foam with G@Fe3O4 loading of 10 wt % exhibited excellent specific EMI shielding effectiveness (EMI SE) of～41.5 dB/(g/cm3)at8？12 GHz. Moreover, most the applied microwave was verified to be absorbed rather than being reflected back, resulting from the improved impedance matching, electromagnetic wave attenuation, as well as multiple reflections. Meanwhile, the resulting foams also possessed a superparamagnetic behavior and low thermal conductivity of 0.042？0.071 W/(m K). This technique is fast, highly reproducible, and scalable, which may facilitate the commercialization of such composite foams and generalize the use of them as EMI shielding materials in thefields of spacecraft and aircraft

Enhanced interfacial interaction between polycarbonate and thermally reduced graphene induced by melt blending

Melt blending is the most economically choice to disperse graphene into polymer matrix because of its high efficiency, easy to scale up, and no solvent is involved. Therefore, it is meaningful to generate an enhanced interfacial interaction directly through melt blending of graphene and polymers. In this study, the effect of melt blending on the interfacial interaction between thermally reduced graphene oxide (TRG) and polycarbonate (PC) had been investigated. Ultracentrifugation of the melt-mixed PC/TRG composite solutions led to dark-colored supernatants, indicating the improved dispersion of TRG in some solvents, suggesting the existence of enhanced interfacial interaction between TRG and PC. The shift of C=O stretching vibration of PC (interacted with TRG) in the FT-IR spectra as well as the shift of absorption peak of phenyl groups in the UV–vis spectra suggested the formation of chemical bonding between the carbonate groups in PC chains and the carboxyl groups on TRG through transesterification and the formation of noncovalentp–pstacking interaction between PC and TRG during melt blending. Furthermore, the effect of melt blending on mechanical reinforcement of the PC/TRG composites was also evaluated

Chemical functionalization of graphene oxide toward the tailoring of the interface in polymer composites

In this work, we demonstrated that the composites with strong interfacial interactions between graphene–matrix could achieve excellent mechanical properties even the dispersion of graphene is poor. In terms of the above reason, an epoxy resin was coupled onto graphene oxide (GO) sheets via the ‘‘grafting to’’ method. Since each epoxy chain bears two terminated epoxide groups, it is inevitable that one epoxy chain connects two GO sheets together, causing the crosslinking of GO layers via the epoxy chain. When blending these resultant GO (GO–epoxy) with polycarbonate (PC), the dispersion was less-than-ideal due to these crosslinking. However, the residue active sites in the grafted epoxy chains, such as the unreacted epoxide groups as well as hydroxyl groups, could further react with PC carbonate to form chemical bonds,leading to strong interfacial interactions between the matrix and GO sheets. Owing to these strong interfacial interactions, the enhancement of the mechanical properties of PC/GO–epoxy composites was significantly higher than that of PC/(GO/epoxy) samples, as well as those shown in other similar works on thermally reduced graphene oxide (TRG)/PC composites with better dispersio