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This research studies natural rubber (NR) composite blends prepared with recycled polyethylene (PE), polyurethane waste (PU), silica (SiO2), and aluminum trihydroxide (ATH) under the proper mixing conditions using an internal mixer and a two-roll mill. The mechanical, impact, dynamic mechanical, and thermal properties, together with flammability, were investigated. NR/PU composites filled with a specific SiO2/ATH concentration resulted in excellent flame-retardant properties without using PE. Adding PE causes poor flammability, while using PU and SiO2 prevents flame extensibility of the composites. In addition, SiO2 and ATH synergistically improved both mechanical and dynamical mechanical properties. This is attributed to the reinforcement of SiO2 particles inside the matrix, whereas the ATH releases water as a flame retardant. The V-0 composites tested with UL-94 showed acceptable heat resistance, strength, and durability, making them suitable for interior and exterior applications in buildings without the lightweight requirement. [ABSTRACT FROM AUTHOR]

This study focuses on examining the influence of bast fibers on the flammability and thermal properties of the polylactide matrix (PLA). For this purpose, Urtica dioica and Vitis vinifera fibers were subjected to two types of modifications: mercerization in NaOH solution (M1 route) and encapsulation in an organic PLA solution (M2 route). In a further step, PLA composites containing 5, 10, and 15 wt% of unmodified and chemically treated fibers were obtained. The results of the tests show that only biocomposites containing mercerized fibers had a nearly 20% reduced flammability compared to that of PLA. Moreover, the biofiller obtained in this way belongs to the group of flame retardants that generate char residue during combustion, which was also confirmed by TGA tests. The M2 modification route allowed to achieve higher mass viscosity than the addition of unmodified and M1-modified fibers. The reason is that fibers additionally encapsulated in a polymer layer impede the mobility of the chain segments. The inferior homogenization of the M2-modified fibers in the PLA matrix translated into a longer combustion time and only a 15% reduction in flammability. [ABSTRACT FROM AUTHOR]

Biomass aerogels have attracted wide attention due to their excellent thermal insulation properties, but their low mechanical strength and high susceptibility to combustion limit their application. To address these limitations, a novel composite aerogel was prepared by combining chitosan aerogel (CS) and hydroxyapatite nanowires (HAP) via phytic acid (PA) cross‐linking and freeze‐drying. It was found that the maximum compressive strength and modulus of CS/HAP aerogel were 1.13 and 0.67 MPa, respectively. The minimum thermal conductivity of CS/HAP(0.5) composite aerogel was 0.03921 W m−1 K−1, indicating its good thermal insulating property. Moreover, the CS/HAP composite aerogel also showed excellent flame‐retardant properties. The heat release rate (HRR) and total heat release from combustion (THR) were significantly lower than those of the CS aerogel, with values of 35.2 kW m−2 and 3.7 MJ m−2, respectively, compared to 169.6 kW m−2 and 5.4 MJ m−2. The total smoke release (TSR) was also at a low level, reaches 0.4 m2 m−2. Highlights: Propose a novel chitosan aerogel composited with inorganic nano‐reinforced HAP.High mechanical strength of CS/HAP composite aerogel are illustrated.Exhibit excellent thermal insulation performance of CS/HAP aerogel.HAP and PA largely improves the flame retardancy of the chitosan aerogel. [ABSTRACT FROM AUTHOR]

This study focuses on examining the influence of bast fibers on the flammability and thermal properties of the polylactide matrix (PLA). For this purpose, Urtica dioica and Vitis vinifera fibers were subjected to two types of modifications: mercerization in NaOH solution (M1 route) and encapsulation in an organic PLA solution (M2 route). In a further step, PLA composites containing 5, 10, and 15 wt% of unmodified and chemically treated fibers were obtained. The results of the tests show that only biocomposites containing mercerized fibers had a nearly 20% reduced flammability compared to that of PLA. Moreover, the biofiller obtained in this way belongs to the group of flame retardants that generate char residue during combustion, which was also confirmed by TGA tests. The M2 modification route allowed to achieve higher mass viscosity than the addition of unmodified and M1-modified fibers. The reason is that fibers additionally encapsulated in a polymer layer impede the mobility of the chain segments. The inferior homogenization of the M2-modified fibers in the PLA matrix translated into a longer combustion time and only a 15% reduction in flammability.

Abstract In this study, walnut shell particles obtained through the grinding of walnut shells were used as a reinforcing material and pumice powder as a filler for developing epoxy-based composites characterized by reduced flammability. Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), and Underwriters Laboratories (UL)-94 vertical tests were carried out for evaluating the effectiveness of these pumice powder treatments. Under the UL-94 vertical test, composites (S1, S2, S3, S4, S5 and S6) with 20% pumice powder (i.e., by mass content of walnut particles were not self-extinguished, and could not be classified. S7 and S8 composites (40wt% and 50%) assigned a V-2 rating, which was the least flammable composite However, the mechanical tensile tests showed that the pumice powder treated composites increased their tensile strength. The morphological analysis showed an enhancement of the interfacial adhesion of the composites achieved by pumice powder.

Despite a recent sustained preoccupation for developing biobased epoxies with enhanced applicability, such products have not been widely accepted for industry because of their inferior characteristics compared to classic petroleum-based epoxy thermosets. Therefore, significant effort is being made to improve the flame retardance of the most commonly used epoxies, such as diglycidyl ether-based bisphenol A (DGEBA), bisphenol F (DGEBF), novalac epoxy, and others, while continuously avoiding the use of hazardous halogen-containing flame retardants. Herein, a phosphorus-containing bisphenol, bis(4-(((4-hydroxyphenyl)amino)(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphinin-6-yl)methyl)phenyl) phenylphosphonate (BPH), was synthesized by reacting bis(4-formylphenyl)phenylphosphonate with 4-hydroxybenzaldehyde followed by the addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to the resulting azomethine groups. Environmentally friendly epoxy-based polymer thermosets were prepared by using epoxy resin as polymer matrix and a mixture of BPH and 4,4′-diaminodiphenylsulfone (DDS) as hardeners. A hyperbranched phthalocyanine polymer (HPc) and BaTiO3 nanoparticles were incorporated into epoxy resin to improve the characteristics of the final products. The structure and morphology of epoxy thermosets were evaluated by infrared spectroscopy and scanning electron microscopy (SEM), while the flammability characteristics were evaluated by microscale combustion calorimetry. Thermal properties were determined by thermogravimetric analysis and differential scanning calorimetry. The surface morphology of the char residues obtained by pyrolysis was studied by SEM analysis. [ABSTRACT FROM AUTHOR]

Polybenzoxazine (PBa) composites based on phosphorous-containing bio-based furfurylamine type benzoxazines (D-fu) and bisphenol-A type benzoxazines (Ba) were developed for flame retardation. The structure of D-fu was analyzed by Fourier transform infrared (FTIR) spectroscopy and 1H-NMR spectroscopy. The curing temperature of Ba/D-fu mixtures was systematically studied by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) demonstrated the excellent char formation ability of the PBa composites with the addition of phosphorous-containing D-fu. The flame retardancy of the PBa composite materials was tested by the limited oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CONE). The LOI and UL-94 level of PBa/PD-fu-5% reached 34 and V0 rate, respectively. Notably, the incorporation of 5% D-fu into PBa led to a decrease of 21.9% at the peak of the heat-release rate and a mass-loss reduction of 8.0%. Moreover, the fire performance index increased, which demonstrated that the introduction of D-fu can diminish fire occurrence. The role of D-fu in the condensed and gas phases for the fire-resistant mechanism of the PBa matrix was supported by SEM-EDS and TGA/infrared spectrometry (TG-FTIR), respectively. Dynamic mechanical analysis (DMA) revealed that the Tg of PBa flame-retardant composites was around 230 °C. Therefore, PBa composites are promising fire-retardant polymers that can be applied as high-performance functional materials. [ABSTRACT FROM AUTHOR]

Wood fiber filled high density polyethylene composites (WPCs) were prepared using twin screw extruder and maleated polyethylene as a coupling agent. Bamboo fibers were initially treated with alkali (NaOH), boric acid - borax (Ba-Bx) and borax (Bx). The treated and untreated fibers were used in combination with ammonium polyphosphate (APP) to investigate their synergistic effects on thermal stability, flame retardancy and mechanical properties. Alkali pretreatment (5 % NaOH) of fibers showed significant improvement in performance of APP by increasing thermal stability in WPCs. The derivative thermogravimetric (DTG) results indicate significance of Ba-Bx in promoting char induction at lower temperatures (340 ºC) and thereby, improved the thermal stability in WPCs. Flammability decreased with addition of flame retardant additives. As compared to pure WPCs, composites containing APP 10 % / Ba-Bx 5 % exhibited maximum reduction in average heat release rate (HRR) by 69 %, peak heat release rate (PHRR) by 59 %, total heat released rate (THR) by 48 % and also increased time to ignition (TTI) by 62 %. However, no significant difference was found among the combinations i.e., APP with or without compounds towards reducing the flammability of WPCs. The strength properties also reduced significantly when boron compounds were added along with APP. In general, APP alone (15 %) is enough for imparting thermal stability and flame retardancy in WPCs.

Abstract Aiming to overcome poly(lactic acid) (PLA) limitations regarding flammability and high costs, a highly refractory clay (RC) was employed to produce PLA/RC composites. The composites with clay contents of 0, 2.5, 10 and 15 wt% were produced by extrusion, conformed by injection molding, and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical analysis, scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), statistical analysis of variance (ANOVA) and flammability tests. The overall thermal stability of the materials was not affected by the incorporation of clay to the polymer matrix; improvements around 25% for Young’s modulus and slight increase in flexural and impact strength, when compared to neat PLA, were obtained; ANOVA showed the possibility of incorporating higher loads of clay, 10-15 wt%, in order to make the final material more cost effective. PLA/RC composites demonstrated self-extinguish behavior for the flame even at a lower clay content.

[Display omitted] • A novel phosphorus-containing tertiary amine hardener (DCM) is synthesized. • DCM endows epoxy resin with desired heat resistance and char-forming capacity. • DCM improves the mechanical stiffness, robustness and toughness of epoxy resin. • DCM imparts superior flame retardancy and smoke suppression to epoxy resin. Although current phosphorus (P)-based hardeners endowed epoxy resins (EPs) with intrinsic flame retardancy, their addition usually reduced thermal and mechanical properties. In this work, a novel phosphorus-containing tertiary amine hardener (DCM) was synthesized using diphenylphosphinic chloride and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and applied to fabricate high-performance EP/DCM. Introducing P-containing group reduced the reactivity of tertiary amine of DCM, but EP/DCM gelled at 100 °C within 11.3 min, showing modest-temperature curing character. EP/DCM exhibited higher glass-transition temperature (T g) and char yield than virgin EP/DMP-30. Moreover, EP/DCM featured superior mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 61.2%, 72.0% and 198.5%, respectively, relative to those of EP/DMP-30. DCM endowed EP thermosets with remarkable flame retardancy and smoke suppression. The limiting oxygen index (LOI) and UL-94 rating of EP/DCM reached 35.7% and V-0, respectively, with 36.2% and 22.6% reductions in peak heat release rate (PHRR) and peak smoke production rate (PSPR) compared with those of EP/DMP-30. This work pioneers an innovative strategy for creating high-performance EPs with satisfactory heat resistance, fire safety, and mechanical properties by curing with P-containing tertiary amine hardeners. [ABSTRACT FROM AUTHOR]

In transport sectors such as aviation, automotive and railway, materials combining a high lightweight potential with high flame retardant properties are in demand. Polymeric foams are suitable materials as they are lightweight, but often have high flammability. This study focuses on the influence of different flame retardants on the burning behavior of Novolac based epoxy foams using Isophorone Diamine carbamate (B-IPDA) as dual functional curing and blowing agent. The flame retardant properties and possible modifications of these foams are systematically investigated. Multiple flame retardants, representing different flame retardant mechanisms, are used and the effects on the burning behavior as well as mechanical and thermal properties are evaluated. Ammonium polyphosphate (APP), used with a filler degree of 20 wt.% or higher, functions as the best performing flame retardant in this study. [ABSTRACT FROM AUTHOR]

This work is devoted to the influence of phosphazene modifiers with different substituents on the curing process, thermal properties and flammability of benzoxazine resin. Novel catalysts with m-toluidine substituents were introduced. The catalytic activity of studied phosphazene compounds decreased in the row: hexachlorocyclotriphosphazene (HCP) > tetra m-toluidine substituted phosphazene PN-mt (4) > hexa m-toluidine substituted phosphazene PN-mt (6) > hexaphenoxycyclotriphosphazene (HPP), where HPP is totally inactive. Two types of catalysis: basic and acid were proposed. A brief study of resulting properties of polybenzoxazines was presented. The addition of any studied modifier caused the decrease of glass transition temperature and thermal stability of polymers. The morphology of cured compositions was characterized by matrix-dispersion phase structure. All phosphazene containing polybenzoxazines demonstrated the improved flame resistance. [ABSTRACT FROM AUTHOR]

Biocomposites comprising a combination of natural fibres and bio-based polymers are good alternatives to those produced from synthetic components in terms of sustainability and environmental issues. However, it is well known that water or aqueous chemical solutions affect natural polymers/fibres more than the respective synthetic components. In this study the effects of water, salt water, acidic and alkali solutions ageing on water uptake, mechanical properties and flammability of natural fibre-reinforced polypropylene (PP) and poly(lactic acid) (PLA) composites were compared. Jute, sisal and wool fibre- reinforced PP and PLA composites were prepared using a novel, patented nonwoven technology followed by the hot press method. The prepared composites were aged in water and chemical solutions for up to 3 week periods. Water absorption, flexural properties and the thermal and flammability performances of the composites were investigated before and after ageing each process. The effect of post-ageing drying on the retention of mechanical and flammability properties has also been studied. A linear relationship between irreversible flexural modulus reduction and water adsorption/desorption was observed. The aqueous chemical solutions caused further but minor effects in terms of moisture sorption and flexural modulus changes. PLA composites were affected more than the respective PP composites, because of their hydrolytic sensitivity. From thermal analytical results, these changes in PP composites could be attributed to ageing effects on fibres, whereas in PLA composite changes related to both those of fibres present and of the polymer. Ageing however, had no adverse effect on the flammability of the composites. [ABSTRACT FROM AUTHOR]