Improved Flame-Retardant and Ceramifiable Properties of EVA Composites by Combination of Ammonium Polyphosphate and Aluminum Hydroxide

Effect of Compounded Aluminum Hydroxide Flame Retardants on the Flammability and Smoke Suppression Performance of Asphalt Binders

Compounded aluminum hydroxide (ATH) flame retardants have been widely used for their low cost and environmentally friendly characteristics. However, previous research lacks a systematic and comprehensive comparison. In addition, the combustion characteristics and phase characterization of asphalt binders are not taken into account either. In this work, flame retardants, for instance, APP, Sb2O3, ZB, and LDHs, were compounded with ATH. The flame retardant behavior, together with the smoke suppression behavior, of asphalt binders with compounded flame retardants was determined by LOI and CCT. Furthermore, mechanisms on flame retardants were investigated. It was found that ATH compounded with ZB significantly reduced the heat smoke release and suppressed the formation of toxic volatiles during asphalt combustion. This was because ATH/ZB facilitated the formation of polyaromatic structures and improved the resistance of the char layer. ATH compounded with APP showed an antagonistic effect in the limiting oxygen test because the reaction between ATH and APP inhibited and delayed the decomposition of ATH during asphalt combustion with more aluminum phosphate presenting relatively poor barrier properties produced.

Thermoplastic elastomers based on recycled high-density polyethylene/ground tire rubber/ethylene vinyl acetate: Effect of ground tire rubber regeneration on morphological and mechanical properties

This work investigates the properties of different types of regenerated recycled rubbers (RR1 and RR2) to produce thermoplastic elastomers (TPE) based on recycled high-density polyethylene (RHD) as the matrix. The higher regeneration degree of RR2 (24%) compared to RR1 (15%) was able to better restore the plasticity and processability of the ground tire rubber (GTR). So better entanglement between RR2 free chains and the thermoplastic macromolecules was obtained inducing stronger interfacial interaction leading to higher elongation at break (159%) and impact strength (342 J/m) of the blends filled with 80 wt.% RR2. To further improve the adhesion and achieve rubber-like properties, ethylene vinyl acetate (EVA) was used as a compatibilizer. The microstructure analysis showed that uniform dispersion of the particles and ground tire rubber encapsulation by EVA increased the resistance to crack propagation and failure of the compatibilized blends. The swelling, mechanical and physical properties of the ternary blends (RHD/GTR/EVA) showed that EVA improved the interfacial interactions between GTR and RHD which was confirmed by enhanced elongation at break (203%) and impact strength (379 J/m) by the addition of 10 wt.% EVA.

Understanding the Flame Retardant Mechanism of Intumescent Flame Retardant on Improving the Fire Safety of Rigid Polyurethane Foam

Combinations of multiple inorganic fillers have emerged as viable synergistic agents for boosting the flame retardancy of intumescent flame retardant (IFR) polymer materials. However, few studies on the effect of multiple inorganic fillers on the flame retardant behavior of rigid polyurethane (RPU) foam have been carried out. In this paper, a flame retardant combination of aluminum hydroxide (ATH) and traditional flame retardants ammonium polyphosphate (APP), pentaerythritol (PER), melamine cyanurate (MC), calcium carbonate (CC), and expandable graphite (EG) was incorporated into RPU foam to investigate the synergistic effects of the combination of multiple IFR materials on the thermal stability and fire resistance of RPU foam. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) revealed that 8 parts per hundred polyols by weight (php) filler concentrations were compatible with RPU foam and yielded an increased amount of char residue compared to the rest of the RPU samples. The flame retardancy of multiple fillers on intumescent flame retardant RPU foam was also investigated using cone calorimeter (CCTs) and limiting oxygen index (LOI) tests, which showed that RPU/IFR1 (APP/PER/MC/EG/CC/ATH) had the best flame retardant performance, with a low peak heat release rate (PHRR) of 82.12 kW/m², total heat release rate (THR) of 15.15 MJ/m², and high LOI value of 36%. Furthermore, char residue analysis revealed that the use of multiple fillers contributed to the generation of more intact and homogeneous char after combustion, which led to reduced decomposition of the RPU foam and hindered heat transfer between the gas and condensed phases.

Ceramifiable Silicone Rubber Composites with Enhanced Self-Supporting and Ceramifiable Properties

Ceramifiable silicone rubber (SR) composites with excellent self-supporting properties and ceramifiable properties were prepared by incorporating silicate glass frits (SGFs) and sodium tripolyphosphate (STPP) into the SR. Ceramic residues were obtained by firing ceramifiable SR composites at 700, 850, and 1000 °C for 30 min. The bending angles of the composites were tested for evaluating the self-supporting property. To evaluate the ceramifiable properties of the ceramifiable SR composite, flexural strength, water absorption, and bulk density of its residues were tested. It was found that the addition of STPP improved the shape stability and the self-supporting property of the composites at high temperatures. The flexural strength of the ceramic residue of the composite with STPP firing above 850 °C is more than 5 MPa. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis showed that the relative content of the crystalline phase was enhanced by about 25% due to the addition of STPP. Furthermore, a possible mechanism for the formation of the crystalline phase was proposed. Scanning elector microscope (SEM) and energy dispersive spectrometry (EDS) analysis demonstrated that with the temperature increase, the inter-infiltration between these melts became easier, which implies that the bulk density of the ceramic residue was improved.

Preparation of Magnesium Hydroxide Flame Retardant from Hydromagnesite and Enhance the Flame Retardant Performance of EVA

In this study, hydromagnesite, a rare natural hydrated alkaline magnesium carbonate, was used to synthesize magnesium hydroxide (MH) as a flame retardant for ethylene-vinyl acetate (EVA) to enhance its fire resistance and smoke suppression. Various concentrations of sodium hydroxide (NaOH) were used to alter the morphology and the flame-retardant efficiency of synthesized MH. EVA/MH composites were prepared through melt blending, and the influence of NaOH on the flame retardancy and mechanical properties was investigated by means of the limiting oxygen index (LOI), cone calorimeter test (CCT) and tensile test. The flame retardancy results demonstrated that composites exhibited remarkably improved flame retardant properties after introducing MH, reflected by an increase in the LOI value from 20% for neat EVA to roughly 38%. Additionally, the peak of heat release rate (pHRR), the total heat release (THR) and the peak of the smoke production rate for EVA3 were decreased by 37.6%, 20.7% and 44.4% compared with neat EVA, respectively. In the meantime, increasing char residues were also observed. The incorporation of different MH concentrations had a limited effect on the mechanical properties of the EVA/MH composites.

Preparation of Well-Exfoliated Poly(ethylene-co-vinyl acetate)/α-Zirconium Phosphate Nanocomposites

Poly(ethylene-co-vinyl acetate) (PEVAc) nanocomposites containing exfoliated α-zirconium phosphate (ZrP) have been prepared using a simple solution mixing method to improve their barrier and mechanical properties. ZrP was pre-exfoliated with a surfactant, followed by additional targeted surface functionalization and surfactant exchange to allow for hydrogen bonding of ZrP with the acetate functionality on PEVAc and to improve ZrP surface hydrophobicity. The solvent is found to play an important role in stabilizing ZrP exfoliation in the presence of PEVAc to retain full exfoliation and homogeneous dispersion upon the removal of the solvent. The PEVAc/ZrP nanocomposite exhibits greatly improved oxygen barrier, melt strength, and mechanical properties. The usefulness of the present study for the preparation of olefinic polymer nanocomposites is discussed.

Investigation of Different Types of Biochar on the Thermal Stability and Fire Retardance of Ethylene-Vinyl Acetate Copolymers

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.

Basalt Fiber Modified Ethylene Vinyl Acetate/Magnesium Hydroxide Composites with Balanced Flame Retardancy and Improved Mechanical Properties

In this study, we selected basalt fiber (BF) as a functional filler to improve the mechanical properties of ethylene vinyl acetate (EVA)-based flame retardant materials. Firstly, BF was modified by grafting γ-aminopropyl triethoxysilane (KH550). Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to comprehensively prove the successful modification of the BF surface. Subsequently, the modified BF was introduced into the EVA/magnesium hydroxide (MH) composites by melt blending. The limiting oxygen index (LOI), UL-94, cone calorimeter test, tensile test, and non-notched impact test were utilized to characterize both the flame retardant properties and mechanical properties of the EVA/MH composites. It was found that the mechanical properties were significantly enhanced without reducing the flame retardant properties of the EVA/MH composites. Notably, the surface treatment with silane is a simple and low-cost method for BF surface modification and the pathway designed in this study can be both practical and effective for polymer performance enhancement.

Improved Self-Supporting and Ceramifiable Properties of Ceramifiable EPDM Composites by Adding Aramid Fiber

Ceramifiable ethylene propylene diene monomer (EPDM) composites with fiber network structures were prepared by using aramid fiber (AF), ammonium polyphosphate (APP), and silicate glass frits (SGF). The effect of AF on the curing characteristic of the ceramifiable EPDM composites was studied. The morphology of AF in the composites system was observed by optical microscopy (OM) and scanning electron microscope (SEM). The effects of the observed AF network structures on the solvent resistance, mechanical properties, ablative resistance, self-supporting property, and ceramifiable properties of the composites were investigated. Results suggested that the existence of the AF network structure improved the vulcanization properties, solvent resistance, thermal stability, and ablative resistance of the EPDM composites. An excellent self-supporting property of the EPDM composites was obtained by combining the formation of the AF network and the formation of crystalline phases at higher temperature (above 600 °C). The thermal shrinkage performance of AF and the increased thermal stability of the EPDM composites improved the ceramifiable properties of the EPDM composites.

Ammonium Polyphosphate with High Specific Surface Area by Assembling Zeolite Imidazole Framework in EVA Resin: Significant Mechanical Properties, Migration Resistance, and Flame Retardancy

A zeolite imidazole framework (ZIF-67) was assembled onto the surface of ammonium polyphosphate (APP) for preparing a series multifunctional flame-retardant APP-ZIFs. The assembly mechanism, chemical structure, chemical compositions, morphology, and specific surface area of APP-ZIFs were characterized. The typical APPZ1 and APPZ4 were selected as intumescent flame retardants with dipentaerythritol (DPER) because of their superior unit catalytic efficiency of cobalt by thermogravimetric analysis. APPZ1 and APPZ4 possessed 6.8 and 92.1 times the specific surface area of untreated APP, which could significantly enhance the interfacial interaction, mechanical properties, and migration resistance when using in ethylene-vinyl acetate (EVA). With 25% loading, 25% APPZ4/DPER achieved a limiting oxygen index value of 29.4% and a UL 94 V-0 rating, whereas 25% APP/DPER achieved a limiting oxygen index value of only 26.2% and a V-2 rating, respectively. The peak of the heat release rate, smoke production rate, and CO production rate respectively decreased by 34.7%, 39.0%, and 40.1%, while the char residue increased by 91.7%. These significant improvements were attributed to the catalytic graphitization by nano cobalt phosphate and the formation of a more protective char barrier comprised of graphite-like carbon.

Facile synthesis of a novel transparent hyperbranched phosphorous/nitrogen-containing flame retardant and its application in reducing the fire hazard of epoxy resin

In this study, a novel hyperbranched phosphorus/nitrogen-containing flame retardant (HPNFR) was facilely synthesized via the transesterification reaction of dimethyl methylphosphonate and tris (2-hydroxyethyl) isocyanurate and characterized successfully by ¹H NMR and FTIR. The sample with 4 wt% HPNFR can achieve V-0 rating in UL-94 test and possess a LOI value as high as 34.5%. Conspicuous blowing-out effect was observed during the vertical burning test. TG results indicated that the presence of HPNFR significantly improved the thermal stability of EP thermosets. From cone test, THR, p-HRR, p-SPR and TSP values of HPNFR/EP composites were decreased in comparison to those of pure EP, revealing the reduced fire hazard of EP composites with HPNFR. SEM images of EP thermoset with 4 wt% of HPNFR after cone test exhibited compact and continuous char layers, while those of pure EP are fragmentary and broken. From TG-IR test, the yield of toxic CO and other pyrolysis products was significantly reduced, indicating a decrease in toxicity. Phosphorus-containing compounds were detected in gas phase, which verified the gaseous phase flame retardant effect of HPNFR. Besides, HPNFR would not significantly damage the transparence of EP thermosets, consequently reserved it's application value in some special fields.