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In this paper, four kinds of nitrogenous bases, adenine (A), guanine (G), cytosine (C), and uracil (U), were used as biobased gas sources to regulate the efficiency of an intumescent flame retardant (IFR) in polypropylene (PP). The flame retardant properties of PP composites were evaluated by using the limiting oxygen index (LOI), the vertical burning (UL-94) test, an infrared thermal imager, etc. The thermal degradation behaviors and char morphology were studied by using thermogravimetric analysis (TGA) and scanning electron microscopy. It is found that U and C play great roles in improving the flame retardancy of PP/IFR composites. The PP sample containing 17 wt % IFR and 1 wt % U (or C) achieves the UL-94 V0 rating without melt-dripping and has a LOI value of >27.9%, while the samples with equal amounts of A or G are not classified in the UL-94 test. TGA results showed that U (or C) can react with an IFR, but the interaction between A (or G) and an IFR is weak. U (or C) accelerates the formation of char and regulates its space structure at the right content. They induce the formation of a cellular and intumescent char layer that decreases the surface temperature quickly after ignition and protects the underlying resin from flame, thus improving the efficiency of PP/IFR composites.

Biomass resources are growing in concern in electromagnetic interference (EMI) shielding due to the advantages of low-cost, sustainability, and unique structural feature. From the perspective of “waste to wealth” and sustainable development, novel straw-derived hollow porous carbon-tube arrays (SCAs) have been fabricated through direct carbonization of wheat straw followed by orderly assembly for the first time. The resultant SCAs with increased SC diameter of ∼1.7–3.3 mm showed not only low apparent density of ∼72–33 mg/cm3 due to the presence of arrayed hollow macrostructure, but also high EMI SE of ∼57.7–44.0 dB coming from both the strong EM reflection and conductive dissipation, as well as hierarchical internal multiple reflections. After the further construction of ultralight graphene aerogel (GA) in their hollow interior, the GA/SCAs with slightly increased density of only ∼78–39 mg/cm3 exhibited obvious SE enhancement of ∼66.1–70.6 dB compared to those of neat SCAs. In addition, the performance comparison between our SCAs and other previously reported carbon foams also revealed the more advanced configuration of hollow porous carbon-tube array for lightweight and high-performance EMI shielding application.

Natural cotton was selected as a cheap and renewable carbon source to fabricate novel carbon networks with porous three-dimensional conductive frameworks composed of numerous unique hollow carbon fibers by pyrolysis, and outstanding electromagnetic interference (EMI) shielding effectiveness (SE) of ∼26.9–46.9 dB was observed for the samples (∼0.3 mm in thickness) with density of ∼0.14–0.06 g/cm3. Moreover, the combination of cotton-derived carbon networks with graphene through the construction of a sandwich configuration, where graphene sheets were dispersed inhomogeneously on both sides of carbon networks, was further developed and the resultant carbon composite networks with ultrathin skin layers of graphene film in thickness of only ∼2 μm possessed higher EMI SE of ∼48.5–87.0 dB than that (∼33.7–55.6 dB) of pure carbon networks in thickness of ∼0.3–0.7 mm, possibly due to the enhanced EM reflection and absorption of EM waves penetrating the material. The SE increment of ∼26–41% was also observed in the sandwiched samples in comparison with the counterparts with homogeneous graphene dispersion, demonstrating a very promising configuration for the significant SE enhancement.

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