Enhancement of the intumescent flame retardant efficiency in polypropylene by synergistic charring effect of a hypophosphite/cyclotetrasiloxane bi-group compound

Phosphorus-Based Flame-Retardant Acrylonitrile Butadiene Styrene Copolymer with Enhanced Mechanical Properties by Combining Ultrahigh Molecular Weight Silicone Rubber and Ethylene Methyl Acrylate Copolymer

The present work proposes to investigate the effect of an ultrahigh molecular weight silicone rubber (UHMW-SR) and two ethylene methyl acrylate copolymers (EMA) with different methyl acrylate (MA) content on the mechanical and fire performance of a fireproof acrylonitrile butadiene styrene copolymer (ABS) composite, with an optimum amount of ammonium polyphosphate (APP) and aluminum diethyl phosphinate (AlPi). ABS formulations with a global flame retardant weight content of 20 wt.% (ABS P) were melt-compounded, with and without EMA and UHMW-SR, in a Brabender mixer. During this batch process, ABS P formulations with UHMW-SR and/or EMA registered lower torque values than those of ABS P. By means of scanning electron microscopy (SEM), it was possible to observe that all ABS composites exhibited a homogenous structure without phase separation or particle agglomeration. Slightly improved interfacial interaction between the well-dispersed flame-retardant particles in the presence of EMA and/or UHMW-SR was also noticed. Furthermore, synergies in mechanical properties by adding both EMA and UHMW-SR into ABS P were ascertained. An enhancement of molecular mobility that contributed to the softening of ABS P was observed under dynamic mechanical thermal analysis (DMTA). An improvement of its flexibility, ductility and toughness were also registered under three-point-bending trials, and even more remarkable synergies were noticed in Charpy notched impact strength. Particularly, a 212% increase was achieved when 5 wt.% of EMA with 29 wt.% of MA and 2 wt.% of UHMW-SR in ABS P (ABS E29 S P) were added. Thermogravimetric analysis (TGA) showed that the presence of EMA copolymers in ABS P formulations did not interfere with its thermal decomposition, whereas UHMW-SR presence decreased its thermal stability at the beginning of the decomposition. Although the addition of EMA or UHMW-SR, as well as the combination of both in ABS P increased the pHRR in cone calorimetry, UL 94 V-0 classification was maintained for all flame-retarded ABS composites. In addition, through SEM analysis of cone calorimetry sample residue, a more cohesive surface char layer, with Si-O-C network formation confirmed by Fourier transform infrared (FTIR), was shown in ABS P formulations with UHMW-SR.

Toward flame-retardant and toughened poly(lactic acid)/cross-linked polyurethane blends via the interfacial reaction with the modified bio-based flame retardants

Incorporating bio-based flame retardants into polylactic acid (PLLA) to improve flame retardancy has always been the focus of research, but the improvement of flame retardancy is usually at the expense of mechanical properties. How to successfully balanced the material's mechanical and combustion properties has puzzled many scholars. Herein, ammonium polyphosphate (APP) and chitosan (CS) were used as acid source and carbon source respectively. Biological flame retardant APP@CS was designed and synthesized by electrostatic self-assembly method. In addition, toughened PLLA composites were prepared by reactive blending with the in-situ formed polyurethane (PU) as toughening phase. The results show that the CS shell not only reduces the hydrophilicity of the flame retardant, but also has good flame retardant property because of its excellent char forming property. The addition of 10 phr APP@CS can endow PLLA/crosslinked PU (CPU) with UL-94 V-2 rating and a LOI value of 24.9 %. Interestingly, CS shell participates in the in-situ reaction, which improves the mechanical properties of the composite with elongation at break of 74 %, which is higher than that of sample doped with the same amount of APP. This work provides guidance for the high performance modification of PLLA and is expected to expand the practical application range.

Synergistic Effect of Nano-Silica and Intumescent Flame Retardant on the Fire Reaction Properties of Polypropylene Composites

Silica nanoparticles (nano-silica) were used as synergistic agents with ammonium polyphosphate (APP) and pentaerythritol (PER) to enhance flame retardancy of polypropylene (PP) in this research. The composites were prepared using a melt-mixing method. The influences of nano-silica on the fire performance of composites were thoroughly discussed, which promotes understanding of nano-silica on the flame-retardant performance of polypropylene composite. Scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) results indicated that the nano-silica with a diameter of about 95 ± 3.9 nm were dispersed favorably in the composite matrix, which might elevate its synergistic effect with intumescent flame retardant and improve the flame retardancy of polypropylene composite. The synergistic effects between nano-silica and intumescent flame retardant on PP composites were studied using the limiting oxygen index (LOI), UL-94 test, and cone calorimeter test (CCT). The total amount of flame retardant was maintained at 30%. When the dosage of nano-silica was 1 wt.%, the LOI value of PP/IFR/Si1.0 composite reached 27.3% and its UL-94 classification reached V-1. Based on the parameters of the CCT, the introduction of nano-silica induced composites with depressed heat release rate (HRR) and peak heat release rate (PHRR). The PHRR of PP/IFR/Si0.5 was only 295.8 kW/m², which was 17% lower than that of PP/IFR. Moreover, the time to PHRR of PP/IFR/Si0.5 was delayed to 396 s, which was about 36 s later than that without nano-silica. EDS was used to quantitatively analyze the distribution of silica in charred residue. The EDS results indicated that the silica tended to accumulate on the surface during the fire. The surface accumulation characteristic of silica endows it with the enhanced flame-retardant properties of polypropylene composite at a very small dosage (as low as 1 wt.%).

Optimisation of Additives to Maximise Performance of Expandable Graphite-Based Intumescent-Flame-Retardant Polyurethane Composites

The effect of varying the weight percentage composition (wt.%) of low-cost expandable graphite (EG), ammonium polyphosphate (APP), fibreglass (FG), and vermiculite (VMT) in polyurethane (PU) polymer was studied using a traditional intumescent flame retardant (IFR) system. The synergistic effect between EG, APP, FG, and VMT on the flame retardant properties of the PU composites was investigated using SEM, TGA, tensile strength tests, and cone calorimetry. The IFR that contained PU composites with 40 wt.% EG displayed superior flame retardant performance compared with the composites containing only 20 w.t.% or 10 w.t.% EG. The peak heat release rate, total smoke release, and carbon dioxide production from the 40 wt.% EG sample along with APP, FG, and VMT in the PU composite were 88%, 93%, and 92% less than the PU control sample, respectively. As a result, the synergistic effect was greatly influenced by the compactness of the united protective layer. The PU composite suppressed smoke emission and inhibited air penetrating the composite, thus reducing reactions with the gas volatiles of the material. SEM images and TGA results provided positive evidence for the combustion tests. Further, the mechanical properties of PU composites were also investigated. As expected, compared with control PU, the addition of flame-retardant additives decreased the tensile strength, but this was ameliorated with the addition of FG. These new PU composite materials provide a promising strategy for producing polymer composites with flame retardation and smoke suppression for construction materials.

How Do Phosphorus Compounds with Different Valence States Affect the Flame Retardancy of PET?

This work investigated the effect of different valence states of phosphorus-containing compounds on thermal decomposition and flame retardancy of polyethylene terephthalate (PET). Three polyphosphates-PBPP with +3-valence P, PBDP with +5-valence P and PBPDP with both +3/+5-valence P-were synthesized. The combustion behaviors of flame-retardant PET were studied and the structure-property relationships between the phosphorus-based structures with different valence states and flame-retardant properties were further explored. It was found that phosphorus valence states significantly affected the flame-retardant modes of action of polyphosphate in PET. For the phosphorus structures with +3-valence, more phosphorus-containing fragments were released in the gas phase, inhibiting polymer chain decomposition reactions; by contrast, those with +5-valence phosphorus retained more P in the condensed phase, promoting the formation of more P-rich char layers. It is worth noting that the polyphosphate containing both +3/+5-valence phosphorous tended to combine the advantage of phosphorus structures with two valence states and balance the flame-retardant effect in the gas phase and condensed phase. These results contribute to guiding the design of specified phosphorus-based structures of flame-retardant compounds in polymer materials.

Novel hierarchical carbon microspheres@layered double hydroxides@copper lignosulfonate architecture for polypropylene with enhanced flame retardant and mechanical performances

Due to the inherent defect of flammability of polypropylene (PP), a novel and highly efficient carbon microspheres@layered double hydroxides@copper lignosulfonate (CMSs@LDHs@CLS) flame retardant was designed and prepared, which was attributed to the strong electrostatic interaction between carbon microspheres (CMSs), layered double hydroxides (LDHs) and lignosulfonate as well as the chelation effect of lignosulfonate on copper ions, and then it was incorporated into the PP matrix. Significantly, CMSs@LDHs@CLS not only observably improved its dispersibility in PP matrix, but also simultaneously achieved excellent flame retardant properties for composites. With the addition of 20.0 % CMSs@LDHs@CLS, the limit oxygen index of CMSs@LDHs@CLS and PP composites (PP/CMSs@LDHs@CLS) reached 29.3 % and achieved the UL-94 V-0 rating. Cone calorimeter tests indicated that the peak heat release rate, total heat release and total smoke production of PP/CMSs@LDHs@CLS composites exhibited declines of 28.8 %, 29.2 % and 11.5 %, respectively, compared with those of PP/CMSs@LDHs composites. These advancements were attributed to the better dispersibility of CMSs@LDHs@CLS in PP matrix and illustrated that CMSs@LDHs@CLS observably reduced fire hazards of PP. The flame retardant property of CMSs@LDHs@CLS might relate to condensed phase flame retardant effect of char layer and catalytic charring of copper oxides.

A Phosphorous-Based Bi-Functional Flame Retardant Based on Phosphaphenanthrene and Aluminum Hypophosphite for an Epoxy Thermoset

A phosphorous-based bi-functional compound HPDAl was used as a reactive-type flame retardant (FR) in an epoxy thermoset (EP) aiming to improve the flame retardant efficiency of phosphorus-based compounds. HPDAl, consisting of two different P-groups of aluminum phosphinate (AHP) and phosphophenanthrene (DOPO) with different phosphorous chemical environments and thus exerting different FR actions, exhibited an intramolecular P-P groups synergy and possessed superior flame-retardant efficiency compared with DOPO or AHP alone or the physical combination of DOPO/AHP in EP. Adding 2 wt.% HPDAl made EP composites acquire a LOI value of 32.3%, pass a UL94 V-0 rating with a blowing-out effect, and exhibit a decrease in the heat/smoke release. The flame retardant modes of action of HPDAl were confirmed by the experiments of the scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry–Fourier transform infrared spectroscopy–gas chromatograph/mass spectrometer (TG-FTIR-GC/MS). The results indicate that the phosphorous-based FRs show different influences on the flame retardancy of composites, mainly depending on their chemical structures. HPDAl had a flame inhibition effect in the gas phase and a charring effect in the condensed phase, with a well-balanced distribution of P content in the gas/condensed phase. Furthermore, the addition of HPDAl hardly impaired the mechanical properties of the matrix due to the link by chemical bonds between them.

Flame Retardant Coatings: Additives, Binders, and Fillers

This review provides an intensive overview of flame retardant coating systems. The occurrence of flame due to thermal degradation of the polymer substrate as a result of overheating is one of the major concerns. Hence, coating is the best solution to this problem as it prevents the substrate from igniting the flame. In this review, the descriptions of several classifications of coating and their relation to thermal degradation and flammability were discussed. The details of flame retardants and flame retardant coatings in terms of principles, types, mechanisms, and properties were explained as well. This overview imparted the importance of intumescent flame retardant coatings in preventing the spread of flame via the formation of a multicellular charred layer. Thus, the intended intumescence can reduce the risk of flame from inherently flammable materials used to maintain a high standard of living.

A transparent cyclo-linear polyphenylsiloxane elastomer integrating high refractive index, thermal stability and flexibility

A cyclo-linear structured transparent polyphenylsiloxane elastomer combining high refractive index, high thermal stability and superior flexibility was prepared by a one-pot hydrosilylation reaction.