Synergistic flame retardant effects of ammonium polyphosphate in ethylene-vinyl acetate/layered double hydroxides composites

Synthesis and application of waste-based layered double hydroxide: A review

The synthesis of layered double hydroxide (LDH) from industrial wastes is a sustainable approach to aid circular economy and hazardous material disposal. In this review, the researches on the synthesis and application of waste-based LDH from 2010 to 2023 are summarized and discussed. At present, there are mainly four types of waste-based LDH produced from red mud, slag, fly ash and wastewater, with co-precipitation being the most typical synthesis method. Red mud is used as the trivalent metal source supplemented by chemical reagents or other types of waste as divalent metal source to produce red mud-based LDH. Slag can act as the sole metal source providing both divalent and trivalent metal sources for slag-based LDH. Fly ash was used either as the trivalent metal source or both divalent and trivalent metal sources to produce fly ash-based LDH. Wastewater-based LDH was typically synthesized by in-situ co-precipitation method to achieve the self-purification of wastewater. The impurities in waste-based LDH can act as a two-edged weapon. It may either hinder or promote the performance of waste-based LDH. The challenge in the synthesis of waste-based LDH lies in the efficient extraction of available metals. The future research prospects for waste-based LDH are suggested.

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part II: Thermal Degradation, Gas Phase, and Elemental Analyses

Bamboo charcoal (BC) and aluminum hypophosphite (AHP) singly and in combination were investigated as flame-retardant fillers for polylactic acid (PLA). A set of BC/PLA/AHP composites were prepared by melt-blending and tested for thermal and flame-retardancy properties in Part I. Here, in Part II, the results for differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), X-ray diffraction (XRD), and X-ray photoelectron analysis (XPS) are presented. The fillers either singly or together promoted earlier initial thermal degradation of the surface of BC/PLA/AHP composites, with a carbon residue rate up to 40.3%, providing a protective layer of char. Additionally, BC promotes heterogeneous nucleation of PLA, while AHP improves the mechanical properties and machinability. Gaseous combustion products CO, aromatic compounds, and carbonyl groups were significantly suppressed in only the BC-PLA composite, but not pure PLA or the BC/PLA/AHP system. The flame-retardant effects of AHP and BC-AHP co-addition combine effective gas-phase and condensed-phase surface phenomena that provide a heat and oxygen barrier, protecting the inner matrix. While it generated much CO₂ and smoke during combustion, it is not yet clear whether BC addition on its own contributes any significant gas phase protection for PLA.

The synergistic effect of layered double hydroxides with other flame retardant additives for polymer nanocomposites: a critical review

Layered double hydroxides (LDHs) are a new type of inorganic flame retardant additive for polymer nanocomposites. Although their unique structural properties and tunable chemical compositions make them highly promising, it has been noticed that on their own, LDHs can hardly fulfill all the requirements for commercial applications. In recent years, the application of LDHs together with other synergistic additives has been proposed as a new route for obtaining highly efficient flame retardant polymer nanocomposites. It is believed that the synergistic additives can overcome the shortcomings of LDHs. As great progress has been made in this field so far, we believe that a timely review is warranted. Thus, in this contribution, the synergistic effect of LDHs with other flame retardant additives including (1) phosphorus-containing compounds, (2) graphene and carbon compounds, (3) intumescent flame retardants, (4) magnesium hydroxide, (5) borate-containing compounds, and (6) some other flame retardant compounds will be critically reviewed. For each type of additive, the synergistic mechanism with LDHs, and their performance on both flame retardancy and thermal stability will be discussed. We believe that this work will inspire and guide researchers from a wide range of backgrounds and help to pave the way for major breakthroughs in both fundamental studies and industrial applications in this field.

Ammonium Polyphosphate Intercalated Layered Double Hydroxide and Zinc Borate as Highly Efficient Flame Retardant Nanofillers for Polypropylene

We found in our previous study that layered double hydroxides (LDHs) which undergo aqueous miscible organic solvent treatment (AMOST) can tune the hydrophobicity surface of LDHs to be hydrophobic, and then the solvent mixing method can be used to prepare polymer/LDH nanocomposites. However, flame retardant property is not very high if LDHs are only used. In this present work, ammonium polyphosphate (APP) intercalated LDHs and zinc borate (ZB) was incorporated into a polypropylene (PP) matrix using the solvent mixing method. The structures, morphologies, and performance of the composites were characterized carefully. The peak heat release rate (PHRR) reduction of PP containing 10 and 20 wt % APP-LDH reached 27% and 55%, respectively, which increased up to 63% compared with PP/CO₃-LDH. After incorporating 2 wt % ZB in the PP/APP-LDH system, the flame retardant property was further improved. Polypropylene composites with 20 wt % APP-LDH and 2 wt % ZB showed a 58% PHRR reduction. In addition, thermogravimetric analyzer (TGA) results indicated that the addition of APP-LDH and ZB improved the temperature at 50% weight loss (T_50%) and the char formation of the materials significantly.