Following a waste-to-wealth approach, humic acid (HA) was exploited as a flame retardant additive. The effect of its addition alone and in combination with urea (UR) and ammonium polyphosphate (APP) on the thermal, fire, and mechanical performances of a bisphenol A diglycidyl ether (DGEBA)-based epoxy resin modified with (3-aminopropyl)-triethoxysilane (AP) and cured with aliphatic isophoronediamine (IDA) has been investigated. Unlike in previous studies, a UL 94-V-0 classification was achieved for epoxy resin containing HA at 6 wt % and APP at only 1 wt % phosphorus (P) loading. The presence of silicon-modified epoxy chains ameliorated the distribution of the biowaste within the resin, and the addition of HA alone avoided melt dripping. Besides, APP and UR promoted a remarkable reduction (up to 52%) of the peak heat release rate (pHRR) values and a significant delay (up to 21%) of the time to ignition in cone calorimetry tests, and hence an increase (up to 1.8 min) of the time to flashover, without any detrimental effect on the overall mechanical behavior. The evolved gas, thermal, and fire analysis was used to propose the combined mode of action of HA, UR, APP, and silicon in the fire performance improvement of the hybrid epoxy system.

Polypropylene (PP) nanocomposites containing graphene nanoplatelets (GNPs) with different loadings were fabricated via masterbatch compounding-melt blending processing technique. Morphological studies showed that the method employed provided uniform GNPs dispersion in the matrix, orienting the nanoplatelets along the same direction the flow of matter. Enhancements of storage and Young's modulus occurred, increasing GNP content, and the improvement was more obvious when a compatibilizer, the PP-grafted-maleic anhydride, was introduced to achieve a better GNP dispersion and distribution within the matrix. For all the nanocomposites, even for those compatibilized, it was not possible to fully exploit the GNP toughening effect since a stiffening and embrittling effect prevailed. Thermogravimetric analysis showed that GNP incorporation has improved the thermal stability of the nanocomposites. In addition, cone calorimetry results showed that GNPs can act as intumescent flame retardant and significantly reduced the heat release rate, thus improving the flame retardancy of the PP matrix. POLYM. ENG. FIG. 2. SEM images representing the ability of the nanocomposite production method to disperse and orientate the GNPs: The magnifications show how the nanoplatelets perfectly follow the direction of the flow of matter established during the manufacture of the specimens. [Color figure can be viewed at wileyonlinelibrary.com]

In this work, three biochars, deriving from soft wood, oil seed rape, and rice husk and differing as far as the ash content is considered (2.3, 23.4, and 47.8 wt.%, respectively), were compounded in an ethylene vinyl acetate copolymer (vinyl acetate content: 19 wt.%), using a co-rotating twin-screw extruder; three loadings for each biochar were selected, namely 15, 20, and 40 wt.%. The thermal and mechanical properties were thoroughly investigated, as well as the flame retardance of the resulting compounds. In particular, biochar, irrespective of the type, slowed down the crystallization of the copolymer: this effect increased with increasing the filler loading. Besides, despite a very limited effect in flammability tests, the incorporation of biochar at increasing loadings turned out to enhance the forced-combustion behavior of the compounds, as revealed by the remarkable decrease of peak of heat release rate and of total heat release, notwithstanding a significant increase of the residues at the end of the tests. Finally, increasing the biochar loadings promoted an increase of the stiffness of the resulting compounds, as well as a decrease of their ductility with respect to unfilled ethylene vinyl acetate (EVA), without impacting too much on the overall mechanical behavior of the copolymer. The obtained results seem to indicate that biochar may represent a possible low environmental impact alternative to the already used flame retardants for EVA, providing a good compromise between enhanced fire resistance and acceptable mechanical properties.

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