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For the sake of improving the flame retardancy of epoxy resin (EP), a novel phosphorus‐containing phenolic resin (PPR) synthesized in our group instead of conventional phenolic resin (PR) was used to cure EP in the present research. The curing processes and the corresponding crosslinking structure and mechanical performance were investigated by differential scanning calorimeter and dynamic mechanical thermal analysis. Because of the introduction of flame‐retarding elements including P and Si, PPR exhibited higher charring capacity in the condensed phase, which is helpful to construct a char layer of higher quality. Correspondingly, PPR‐cured EP displayed remarkably improved flame retardance as compared to conventional PR‐cured EP through the related evaluations including limiting oxygen index, vertical burning test, and microscale combustion colorimeter. As a multifunction agent, it is believable that PPR possesses potential commercial value to prepare flame‐retardant EP with high performance.

A phosphorus-and nitrogen-containing intumescent flame retardant, pentaerythritol di-N-hydroxyethyl phosphamide (PDNP), was synthesized with phosphorus oxychloride, pentaerythritol, and ethanolamine as raw materials. Using the prepared PDNP as a chain extender, a series of flame-retardant waterborne polyurethanes (WPU) were prepared, and their structures were characterized using NMR and Fourier transform infrared spectroscopy (FTIR). Additionally, the thermal properties and flame retardancy of WPU films were investigated by thermogravimetric analysis, limiting oxygen index (LOI) tests, cone calorimeter tests, and thermogravimetry-FTIR. These results indicated that PDNP materials exhibit good char-forming ability at high temperature and that PDNP-modified waterborne polyurethane obtained an LOI value of 26.0% for a PDNP content of 9 wt %. Finally, the morphology and the element distributions of char residues of WPU were analyzed by scanning electron microscopy and energy dispersive spectrometry after combustion.

A novel hybrid flame retardant combining graphene oxide (GO) with long-chain phosphaphenanthrene was fabricated via surface grafting reaction. Taking advantageous of the double barrier effects, including the physical shield contributed by graphene nanoplates during the initial stage and the chemical char contributed by phosphaphenanthrene during the later stage, greatly decreased the release rate of decomposed volatiles from the resin, as well as minimized the release of oxygen and combustion heat. Hence, such hybrid flame retardant can overcome the shortcomings of early acid catalyzed degradation effects caused by conventional flame retardants containing phosphorus. Satisfactory flame retardance was achieved (UL94 V-0 rating) with only 4% addition of the hybrid flame retardant to the epoxy resin laminate. Due to the long-chain and bulky phosphaphenanthrene groups, the interlayer attractive forces of the modified GO were effectively weakened, thus favoring the exfoliation and dispersion of graphene sheets. As a result, the incorporation of the flame retardant slightly enhanced the mechanical properties of the polymer composites, rather than deteriorating them, as occurs with traditional additive flame retardants. As a potential application for graphene, it is believed that the reported hybrid flame retardant has promising future prospect.

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Leather shavings, the by-products of leather industry, are usually treated by the landfill, which probably makes them hazardous to the human health and the environment due to the oxidation of the containing chromium (Cr) (III) to toxic Cr (VI). Therefore, efficient and environment-friendly reusing of leather shavings is not only of great interest but is also a huge challenge. This article reported a reuse method of leather shavings by combing two novel technologies, that is, the solid state shear milling (S3M) to mechanochemically pulverize and activate leather shavings, and the thermal processing of poly (vinyl alcohol) (PVA) to make them filled with PVA. The related mechanism, the structure, and properties of the obtained composites were investigated. The results showed that S3M method could efficiently pulverize and activate leather shavings through very strong shearing and compressing forces, promoting the formation of more hydrogen bonds and the chelation in the interfaces between PVA and leather shavings, and consequently enhancing their compatibility. In this way, PVA/leather shaving composites with pretty good performances, for example, better mechanical properties, thermal stability, and water resistance as compared with neat PVA, were obtained. This is a convenient, cost-efficient, and environment-friendly technology to recycle hazardous chrome-containing leather shavings.