Improving flame retardancy of IFR/PP composites through the synergistic effect of organic montmorillonite intercalation cobalt hydroxides modified by acidified chitosan

With the increasing emphasis on environmental protection, the development of flame retardants for epoxy resin (EP) has tended to be non-toxic, efficient, multifunctional and systematic. Currently reported flame retardants have been capable of providing flame retardancy, heat resistance and thermal stability to EP. However, many aspects still need to be further improved. This paper reviews the development of EPs in halogen-free flame retardants, focusing on phosphorus flame retardants, carbon-based materials, silicon flame retardants, inorganic nanofillers, and metal-containing compounds. These flame retardants can be used on their own or in combination to achieve the desired results. The effects of these flame retardants on the thermal stability and flame retardancy of EPs were discussed. Despite the great progress on flame retardants for EP in recent years, further improvement of EP is needed to obtain numerous eco-friendly high-performance materials.

Recent Developments in the Flame-Retardant System of Epoxy Resin.

Polypropylene (PP), one of five general-purpose plastics, is widely used in many fields. However, the intrinsic alkane structure of PP makes it relatively easy to burn, leading to limiting its scope of application. Here, this article reviews the most commonly flame retarding strategies used in PP matrices, including the flame-retardant compounds, application methods as well as flame-inhibition mechanism and also focuses on recent advances and foresees the future outlook of such applications. It is seen that traditional flame retardants and some new compounds are considered in modifying the fire behaviors of PP. At present, with the enhancement of environmental awareness, the application frequency of novel materials in this field is increasing. Thus, the harmonious combination of traditional flame retardants with the newly derived flame retardants has broadened the choice of researchers to come up with novel strategies for improving the fire performance of PP matrices.

Flame retardant treatments for polypropylene: Strategies and recent advances

Metal-organic flame retardants (MOFRs) have been constantly applied to enhance fire safety of polymers. Metallic compounds positively improve the MOFRs’ performance in suppressing smoke and toxic gases emissions during combustion of polymers. While organics endow MOFRs with the possibility of high efficiency and excellent compatibility. Based on the combination types between organics and metallic compounds, MOFRs are systematically divided into three categories in this review, that is, organic modified inorganic flame retardants (OMIFRs), metal-organic salts (MOSs) and metal-organic frameworks (MOFs). Metallic components in OMIFRs are bonded with organics in three approaches: encapsulation, intercalation and chemical grafting. Metal ions in MOSs can be replaced via ion-exchange method and thus produce different organometallic salts. Based on sodium alginate, phytic acid and phosphate, various high-efficiency flame-retardant alginates, phytates and metal-organic phosphates are synthesized and applied. As burgeoning flame-retardant substance, MOFs are divided into different types based on types of ligands, that is 2-MIM, aromatic polyacids, and other synthesized materials. Under guidelines of molecular design and metal-organic synergistic flame-retardant mechanisms, MOFRs will be continuously updated and developed. This review summarizes combustion behaviors of polymer/MOFRs composites and presents short comments about upcoming research opportunities and challenges in this field.

A review on metal-organic hybrids as flame retardants for enhancing fire safety of polymer composites

A hydrophobic associating polymer named DiPHAM (acrylamide/sodium acrylamide-2-methylpropanesulfonic/sodium acrylate/N,N-di-n-dodecylacrylamide) with good salt tolerance was synthesized via photo-initiation polymerization. The critical association concentration (CAC) of DiPHAM was determined by viscosity changes to be 490 mg/L with different DiPHAM concentrations and particle sizes varied under such dynamic conditions. The influences of aqueous metal ions with different charges on its aqueous solution were investigated by measuring apparent viscosity, viscoelasticity, thixotropy, rheology, and particle size, and by SEM observation. The apparent viscosity of the DiPHAM solution was affected by metal ions to some extent, but the viscosity of the polymer can be still maintained at 55 mPa·s under 20 × 104 mg/L NaCl. Divalent metal ions show greater impact on DiPHAM aqueous solutions, but the polymer solutions showed resistance to the changes caused in viscosity, structure, and viscoelasticity by Ca2+ and Mg2+ ions. The salt tolerance of DiPHAM is due to the combination of hydrophobic association, the electrostatic shield, and double layer compression of the hydration shell. Increasing the ion concentration enhances the dehydration and further compresses the hydration shell, making the non-structural viscosity decrease, even “salting out”. Measurements of rheological properties showed that DiPHAM solutions could maintain a relatively high viscosity (0.6%-71 mPa·s/0.3%-50 mPa·s) after 120 min of continuous shearing (170 s−1) at 140 °C. Under high-salinity (5000 mg/L Ca2+/3000 mg/L Mg2+) conditions, the solution with 0.6 wt% DiPHAM still maintained a high viscosity (50 mPa·s/70 mPa·s) after continuously shearing for 120 min at 120 °C and 170 s−1. The good salt tolerance of DiPHAM can lead to a variety of applications, including in fracturing fluids for enhanced oil recovery (EOR) and in sewage treatment.

Novel Hydrophobic Associating Polymer with Good Salt Tolerance.

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

Effect of nickel phytate on flame retardancy of intumescent flame retardant polylactic acid

Study on the antioxidant activities of benzofuranones in melt processing of polypropylene

A novel phosphorus-silicon flame retardant (P5PSQ) was prepared by bonding phosphate to silicon-based polysilsesquioxane (PSQ) and used as flame retardant of poly (lactic acid) (PLA). The results show that PLA with 10 wt % P5PSQ has a limiting oxygen index (LOI) 24.1%, the peak heat release rate (PHRR) and total heat release (THR) of PLA decrease 21.8% and 25.2% compared to neat PLA in cone calorimetric test, indicating that P5PSQ shows better flame retardancy in comparison to PSQ. Furthermore, the study for the morphology and composition of carbon residue after the combustion of PLA and the gas release of PLA during combustion illustrate that P5PSQ has flame retardancy in condensed phase and gas phase simultaneously. In condensed phase, phosphorus from phosphate promotes the formation of more stable and better carbon layer containing Si and P, which inhibits the transfer of heat and oxygen in the combustion. In gas phase, the phosphate in P5PSQ emits phosphorus-containing compound that can restrain the release of C-O containing products, which may have effective flame retardancy for PLA in gas phase to a certain extent. In one word, P5PSQ is denoted as a good phosphorus-silicon synergistic flame-retardant.

https://www.mdpi.com/2073-4360/11/8/1304/pdf

Flame Retardancy and Mechanism of Novel Phosphorus-Silicon Flame Retardant Based on Polysilsesquioxane.

To improve the stability and ductility of polylactic acid (PLA), chain extender or crosslinking agent of phosphite functional polysilsesquioxane (PPSQ) was synthesized by the reaction of phosphite group with the amino group of poly(amino-epoxy)silsesquioxane (PSQ). First, the reaction of PPSQ with PLA was characterized by molecular weight (Mw) and melt mass flow rate (MFR) of PLA after melting reaction. The results showed a 6.6% increase in the Mw of PLA and a 24.5% decrease in MFR value at the PPSQ loading content of 2 wt% in PLA, indicating that PPSQ takes chain extension or crosslinking in PLA. Then, this result was further supported by the thermal stability improvement of PLA, which was testified by the increase of oxidative activation energy and the oxygen onset temperature (OOT) value. PPSQ improved the water resistance and mechanical properties of PLA. The hydrolysis rate decreased by 46.8%, and the tensile strength and impact strength increased by 17.2% and 89.4%. Taken together, these results indicate that the addition of PPSQ can produce the PLA with excellent thermal stability, hydrolytic stability and mechanical properties.

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Weiguang Gong

Papers

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

Effect of nickel phytate on flame retardancy of intumescent flame retardant polylactic acid

Study on the antioxidant activities of benzofuranones in melt processing of polypropylene

Flame Retardancy and Mechanism of Novel Phosphorus-Silicon Flame Retardant Based on Polysilsesquioxane.

Improving the stability and ductility of polylactic acid via phosphite functional polysilsesquioxane