Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol–gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

Ultrathin thickness (<1 mm) and ultralow density (<10 mg cm⁻³) are urgent challenges for microwave absorption materials. In this manuscript, we tackle these problems by developing a novel CoNi/reduced graphene oxide (rGO) aerogel absorbent via a facile in situ solvothermal and carbonization process. The resultant CoNi/rGO aerogel with an ultralow density of 7 mg cm⁻³ exhibited a hierarchical porous structure and a high surface area, in which CoNi nanospheres with a diameter of about 50–80 nm were evenly decorated onto the surface of the rGO aerogel matrix. Benefitting from these attributes, the CoNi/rGO aerogel exhibited an excellent microwave absorption performance. The minimum RL value of −53.3 dB was achieved with an ultrathin thickness of 0.8 mm at a low filler loading of 7 wt% in the paraffin template, and the effective absorption bandwidth was >3.5 GHz. The investigation of the absorption mechanism revealed that moderate dielectric loss, magnetic loss, good impedance matching and the porous structure contributed to the high microwave absorption. This work opens up a potential strategy to prepare excellent microwave absorbents with ultrathin thickness and ultralow density.

Ammonium polyphosphate (APP) is not an efficient flame retardant for polypropylene (PP) when it is used alone. In order to improve its flame-retardant efficiency, ethanolamine (ETA) was used to chemically modify APP via ion exchange reaction. The resulting ethanolamine-modified ammonium polyphosphate (ETA-APP) was alone applied to flame retard PP, the limiting oxygen index (LOI) value could reach 35.0% and the vertical burning test (UL-94) could pass the V-0 rating at a loading of 35 wt% ETA-APP. Moreover, cone calorimeter (CC) test results showed that the heat release rate (HRR), the total heat release (THR), the mass loss rate (MLR), the smoke production rate (SPR) and the total smoke production (TSP) of PP/35 wt% ETA-APP composite largely decreased, for example, by 77.2%, 88.5% and 77.9% for THR, TSP and the fire growth rate (FGR), respectively, compared with PP containing an equal amount of APP. In addition, the residual char of PP/35 wt% ETA-APP increased by 195.6% compared with that of PP/35 wt% APP. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the flame retardant mechanism of ETA-APP. It was confirmed that the formation of P–O–C and P–N–C structures, resulting from the incorporation of ETA could greatly improve the stability of intumescent char layer and consequently lead to the much better flame retardancy of ETA-APP than that of unmodified APP. Experimental results demonstrated that the prepared ETA-APP acted not only as the acid source and blowing source as efficient as unmodified APP, but also as an excellent charring agent beyond the unmodified APP.