Flame Retardant Mechanism Research Articles

Improved flame retardancy and mechanical properties of bacterial cellulose fabrics via solvent exchange and entrapment of zein and gluten

This study aimed to improve the flame retardancy and mechanical properties of bacterial cellulose (BC) by introducing cereal proteins, namely zein and gluten. The production conditions were determined by observing residual masses of samples at 1000 ℃ using thermogravimetric analysis (TGA). According to the TGA results, the optimized production conditions for the BCs with zein and gluten were combined solvent exchange and entrapment of 20 weight% (wt.%) of zein, and entrapment of 40 wt.% of gluten, respectively. Surface characterization of BC prepared with zein and gluten under the optimal conditions confirmed that the cereal proteins were incorporated into the BC nanostructures via solvent exchange and/or entrapment and the original chemical and crystal structures of BC were not significantly changed. Limiting oxygen index (LOI) analysis confirmed that cereal proteins improved the flame retardancy of BC. In particular, the LOI of BC entrapped with gluten was 50%, which was better than that of cowhide leather. Char morphology analysis confirmed that the as-produced BCs with cereal proteins exhibited condensed-phase flame-retardant mechanism by forming intumescent chars. Analysis of the mechanical properties confirmed that compared with cowhide leather, as-produced BCs with cereal proteins possessed high tensile strength and dimensional stability, making them suitable leather substitutes.

MXene assisted simple recycle of waste cellulose fiber with alginate fiber into fireproof and electromagnetic interference shielding composite

Textile wastes rapidly grow into a challenge when a significant portion of them are processed by landfilling or incineration, leading to hazardous solid and volatile pollutants. This work investigated the utilization of wasted cellulose fiber by recycling it with calcium alginate fiber into a fireproof composite filler as a circular economy strategy, followed by the modification with MXene dispersion to further enhance its fire resistance and offer it the electromagnetic interference shielding ability. A comprehensive investigation elucidated the flame retardant mechanism of the composite felt via studying its combustion behavior, the microstructural morphology of residue char, and the gasous compounds produced. The results indicated that this composite felt generated a large number of nonflammable gas species and fibrous residue char, serving as a natural barrier to impede the fuel supply and suppress heat diffusion, thereby endowing the composite felt with an outstanding fire retardant performance and reduced carbon footprint. Compared to other textile waste recycling processes, the opening-carding-needling punch technique employed in this study was more energy-efficient and environmentally friendly. The recycling of waste cellulose fiber into functional fireproof composites not only extended the practical applications of waste resources but also mitigated the negative environmental impact of textile disposal.

Fire alarm nano-coating with the controlled release of phosphorus-containing free radical for considerable flame retardant performance

The colloidal properties and surface charge characteristics of graphene oxide (GO) often lead to flocculation during the layer-by-layer (LBL) assembly. Innovatively, the charged flame retardant molecule, amino-tris(methylene phosphonic acid) (ATMP), is encapsulated within the inner cavity of halloysite nanotubes (HNTs). This integration exploits the unique structural features of HNT's inner cavity and outer wall. A composite nano-coating is constructed on the three-dimensional skeletal structure of melamine foam (MF) by assemblying GO with HNT-ATMP. This composite nano-coating exhibits both condensed-phase and gas-phase flame retardant functions. During the thermal decomposition process, phosphorus-containing radicals released from the HNTs' inner cavities enhance the flame retardancy. Moreover, the composite nano-coating demonstrates sensitive fire warning performance. A composite MF coated with 10 layers of this nano-coating emits a warning signal within 8 s fire exposure and maintains this signal without circuit failure. This study elucidates the mechanisms of flame retardancy and fire warning based on the thermal decomposition process and char layer analysis. By addressing the issue of GO flocculation during the assembly process, this research not only clarifies the underlying flame retardant and fire warning mechanisms of composite nano-coating but also proposes solutions for prolonging the duration of fire warning signals in advanced materials.

Synthesis of phosphorus fluorine containing polymers for flame-retardant, low surface energy and good dielectric performance epoxy resin electronic packaging materials

In order to satisfy the application of epoxy resin (EP) in high-end electronic packaging, phosphorus fluorine containing polymers were synthesized to simultaneously enhance the flame retardant, dielectric, and hydrophobic properties of EP. Through the reaction of 2-hydroxyethyl methacrylate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a monomer named HEMA-P was synthesized. By copolymerizing (2,2,2-trifluoroethyl methacrylate and 1H, 1H, 7H-dodecafluoroheptyl methacrylate) with HEMA-P through the typical reversible addition-fragmentation chain transfer (RAFT) polymerization, two phosphorus fluorine containing polymer modifiers named 3FOP and 12FOP with different lengths of fluorine side chain were obtained. The flame-retardant level of FOP/EP composites reached V-1 level. The limited oxygen index (LOI) values of 3FOP/EP and 12FOP/EP composites (10 wt% additive amount) increased to 33.6 ± 0.5 % and 32.8 ± 0.3 %, respectively, with corresponding peak heat release rates (pHRR) decreased by 37.8 % and 33.2 % compared with neat EP, suggesting the FOP modified EP composites have good flame retardant and smoke suppression effects. The mechanical properties of the FOP/EP composites can also be improved. Notably, with the 10 wt% addition of 12FOPs, the water contact angle of 12FOP/EP composite reached 116.5°, which was 40.7 % higher than that of EP. Moreover, the dielectric constant decreased with the increasing fluorine content. The thermal stability and possible thermal degradation pathways of 3FOP and 12FOP were characterized by TG-IR, Py-GC/MS, and Raman spectroscopy. Based on experimental results, we innovatively revealed a phosphorus fluorine synergistic flame retardancy mechanism.

Functional thermoelectric composite endows cellulose paper with superior fire safety

Due to intrinsic defect of fire hazard security, improving the flame retardant capacity of paper is still insufficient in case of precombustion. Herein, we integrate the flame retardant with flame detection performance on the surface of paper, the restricts of graphene oxide (GO) are overcome between high thermoelectric performance and flexibility. A flexible lamellar thermoelectric composite (GO-LA-HP) is constructed through the co-assembly of GO, ascorbic acid (LA), and phenoxycycloposphazene (HP), lamellar GO-LA-HP avoid GO's toughness decline after modification, but also enhance fire sensitivity and flame resistance. The composite could significantly decrease the temperature rise stage (<150 °C), and trigger the fire-warning within 2 s. The hybrid coating composed of phytic acid/phosphoric acid (PyA/PA) and modified thermoelectric GO-LA-HP becomes excellent compatibility on the surface of the modified paper (GPP). GPP is able to extinguish itself immediately after leaving the fire in the vertical combustion, and display the excellent flame resistance. Furthermore, GPP's alarm signal could be timely generated as little as 3 s of contacting the flame, and the response time can exceed 600 s. According to the structure observation and analysis, the related synergistic fire detection reinforcing and flame-retardant mechanisms are also proposed and clarified.

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Fabrication of green montmorillonite modified bio-based rigid polyurethane foam with improved flame retardancy and enhanced mechanical properties

A low-carbon and sustainable green rigid polyurethane foam was prepared by compounding montmorillonite (MMT) with homemade barium phytate (BAPA). The flame retardancy, thermal stability and mechanical properties of the modified RPUFs investigated using the limiting oxygen index (LOI) method, cone calorimetry (CONE) and thermogravimetry. The results showed that the BAPA/MMT2 composite containing 2 wt% MMT had the highest LOI (25.1 %), and its peak heat release rate (PHRR) and total heat release (THR) were reduced by 14.33 % and 34.68 %, respectively, compared with that of the BAPA/MMT0 material without added MMT. In addition, the smoke production rate (SPR) and total smoke release (TSR) were reduced by 20.54 % and 30.77 %, respectively. BAPA/MMT2 had good flame retardancy and smoke suppression effect. The mechanical properties of BAPA/MMT2 with 2 wt% MMT were improved. The flame retardant mechanism confirmed that BAPA and MMT synergistically improved the quality of the carbon layer. At the same time, phosphorus-containing compounds (PO·), CO2 and water vapor were produced, which diluted the combustible gas in the gas phase and inhibit the flames spread. The current results provided a new strategy for the preparation of high-performance RPUFs.

Synthesis and Flame Retardant Behavior of Phosphorous- and Nitrogen-Containing Copolymer and Its Application in Polypropylene.

In this study, a 4-(hydroxymethyl)-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxide (PEPA)-functionalized acrylate monomer, PEPAA, is designed and utilized for the synthesis of macromolecular flame retardants poly(PEPAA-co-AM) with varying PEPAA/AM ratio through copolymerization with acrylamide (AM). The poly(PEPAA-co-AM) is then incorporated into polypropylene (PP) to prepare PP/poly(PEPAA-co-AM) composites. The flame retardant effect of poly(PEPAA-co-AM) on PP is investigated using cone calorimetric test (CCT), and compared with that of PEPAA homopolymer (P-PEPAA), AM homopolymer (PAM), and blends of P-PEPAA/PAM. The results demonstrate that, in comparison with P-PEPAA, PAM, and blends of P-PEPAA/PAM, the incorporation of poly(PEPAA-co-AM) significantly enhances the flame retardancy of PP. Notably, the best flame retardancy is achieved when the ratio of PEPAA/AM copolymerization in poly(PEPAA-co-AM) is 2/8. The morphology and composition of residual chars from combustion are analyzed using SEM-EDS while the residual graphitization degree is examined through Raman spectroscopy. Additionally, TG-FTIR-MS is utilized to investigate the pyrolysis products in gas phase during thermal decomposition of poly(PEPAA-co-AM). Based on these experimental results, a flame retardant mechanism for poly(PEPAA-co-AM) is proposed. The PP/poly(PEPAA-co-AM) composites not only retain the excellent processing properties of pure PP but also exhibit enhanced mechanical properties.

Flame-retardant performance of a novel lignin-based rigid polyurethane foam prepared from pulping black liquor

To improve the flame retardancy of rigid polyurethane foam (RPUF), black liquor lignin-based rigid polyurethane foam (LRPUF) was prepared in this work through a one-step foaming method using lignin and inorganic salt in black liquor lignin as the structural modifier and the additive flame retardant, respectively. Effect of the addition of carbon dioxide treated black liquor lignin (CBL) on the structure and flame retardancy of LRPUF, as well as the flame flame-retardant mechanism of LRPUF, were investigated. The limiting oxygen index (LOI) test and cone calorimetric tests showed that compared to the RPUF, the LOI of LRPUF with 40 wt% CBL increased from 18.9 % to 21.3 %, and the peak heat release rate, total heat release, and total smoke production decreased by 19.5 %, 25.3 %, and 20.5 %, respectively, indicating that the addition of CBL improved the flame retardancy of LRPUF. The flame-retardant mechanism was investigated by analyzing the structure and components of the char residue. We found that a dense protective layer, consisted of char residue and a considerable amount of sodium sesquicarbonate on the surface of the char residue, was formed after combustion. This study provided a novel strategy for the resource utilization of black liquor lignin.

Preparation of phosphorus-containing organic-hybrid layered double hydroxide as a flame retardant for thermoplastic polyurethane

Developing polymers with both flame-retardant and smoke-suppressing properties is a great challenge in the field of fire-safety thermoplastic polyurethane (TPU). This study involved synthesizing a synergistic organic-hybrid layered double hydroxide (O-LDH) and phosphorus/nitrogen-containing substance (PD) inspired by the observed synergistic effect between them. The incorporation of PD significantly enhanced the flame-retardant properties of TPU in conjunction with cobalt/aluminum- layered double hydroxide. The composite containing 10 wt% O-LDH achieved a limiting oxygen index of 26.5% and met the vertical burning V-0 rating. Moreover, the heat and smoke release were decreased compared to pure TPU in cone calorimeter tests. The systematic characterization of the synergistic flame-retardant mechanism emphasized the crucial contribution of cobalt and phosphorus species in catalyzing charring effects, resulting in the compact and highly carbonized char layer in the condensed phase. The incorporation of the hybrid flame retardant significantly enhanced the advancement of the flame-retardant TPU materials.

P/N-containing SiO2 flame retardant particles formed by in-situ hydrolysis for significantly improve the flame retardancy and toughness of epoxy resins

To obtain flame retardants with more efficient and multidimensional flame retardant modes, this work formed P/N-containing silica flame retardants (PBPSi) by hydrolysis and used them in epoxy resins (EP) to give them good flame retardant properties. The hydrolyzed SiO2 flame retardant builds an integrated flame-retardant structure and a concentrated stress-bearing point, the EP has good fire resistant properties and toughness. Allowing the addition of 7-PBPSi/EPPBPSi to enable EP to achieve a UL-94 rating of V-0, and the impact strength of 5-PBPSi/EP reached 52.9 kJ/m2. In addition, PBPSi has good performance in inhibiting heat release and toxic gas release, and the PHRR and THR of 7-PBPSi/EP were reduced by 54.6 % and 24.6 %, respectively, compared with pure EP, the content of CO and CO2 also decreased. The analysis of the flame retardant mechanism indicated that PBPSi played a flame retardant role in the biphasic phase through the catalytic carbon formation in the condensed phase and the synergistic dilution of flammable gases and trapping of free radicals by P/N synergistic.

Preparation and properties of toughened/flame‐retardant PA6/glass‐fiber composites reinforced by linear polyphosphazene elastomers

AbstractIn this study, the challenges of brittleness and flammability in Polyamide 6/glass fiber (PA6/GF) composites, which are crucial for heat‐resistant and stress‐bearing structural parts, are addressed. Polyphosphazene (PZ) elastomers, known for their exceptional flame‐retardant properties, are introduced to enhance the robustness and safety of these composites. Specifically, poly(diaryloxy)phosphazene (PDAP) and poly(difluoroalkoxy)phosphazene (PDFP) are utilized, both contributing to the improved toughness and flame resistance of the PA6/GF composites. Experimental results show that PDAP mainly played the role of solid‐phase flame retardant, while PDFP mainly acted the role of gas‐phase flame retardant. For PA/PZs composites without adding GF, PDFP plays a more efficient flame retardant effect than PDAP. By introducing 15 Vol% of PDFP, the limiting oxygen index (LOI) of the composite reached 26.1%, while the notched impact strength increased by 297%. For PA/PZs/GF composites, PDAP plays a better flame retardant role than PDFP. Under the action of 30 vol% GF and 15 vol% PDAP, the LOI of PA6/PDAP/GF composite reached 26.8%, and the notch impact strength improved to 18.7 kJ/m2, which is 165% higher than that of PA6/GF, and the UL‐94 test reaches V‐0 level. The findings of the study highlight the potential of PDAP and PDFP to act as dual‐function modifiers. These modifiers can considerably ameliorate both the impact resistance and flame retardancy of PA6 and PA6/GF composites. Such dual enhancement surpasses the typical trade‐offs seen in conventional composites, indicating a constructive direction for future material innovation.Highlights Polyphosphazenes simultaneously enhance PA6's toughness &amp; flame resistance. Distinct flame retardant mechanisms found in PDAP and PDFP. GF presence alters PDAP and PDFP's flame retardant efficacy. PDAP shows superior flame resistance in GF‐reinforced PA6 composites. Without GF, PDFP outperforms PDAP in enhancing flame retardancy.

Construction of Fire Safe Thermoplastic Polyurethane/Reduced Graphene Oxide Hierarchical Composites with Electromagnetic Interference Shielding.

Incorporating outstanding flame retardancy and electromagnetic interference shielding effectiveness (EMI SE) into polymers is a pressing requirement for practical utilization. In this study, we first employed the principles of microencapsulation and electrostatic interaction-driven self-assembly to encapsulate polyethyleneimine (PEI) molecules and Ti3C2Tx nanosheets on the surface of ammonium polyphosphate (APP), forming a double-layer-encapsulated structure of ammonium polyphosphate (APP@PEI@Ti3C2Tx). Subsequently, flame-retardant thermoplastic polyurethane (TPU) composites were fabricated by melting the flame-retardant agent with TPU. Afterwards, by using air-assisted thermocompression technology, we combined a reduced graphene oxide (rGO) film with flame-retardant TPU composites to fabricate hierarchical TPU/APP@PEI@Ti3C2Tx/rGO composites. We systematically studied the combustion behavior, flame retardancy, and smoke-suppression performance of these composite materials, as well as the flame-retardant mechanism of the expansion system. The results indicated a significant improvement in the interface interaction between APP@PEI@Ti3C2Tx and the TPU matrix. Compared to pure TPU, the TPU/10APP@PEI@1TC composite exhibited reductions of 84.1%, 43.2%, 62.4%, and 85.2% in peak heat release rate, total heat release, total smoke release, and total carbon dioxide yield, respectively. The averaged EMI SE of hierarchical TPU/5APP@PEI@1TC/rGO also reached 15.53 dB in the X-band.

Research Progress on the Oxidation Behavior of Ignition-Proof Magnesium Alloy and Its Effect on Flame Retardancy with Multi-Element Rare Earth Additions: A Review.

The phenomenon of high-temperature oxidation in magnesium alloys constitutes a significant obstacle to their application in the aerospace field. However, the incorporation of active elements such as alloys and rare earth elements into magnesium alloys alters the organization and properties of the oxide film, resulting in an enhancement of their antioxidation capabilities. This paper comprehensively reviews the impact of alloying elements, solubility, intermetallic compounds (second phase), and multiple rare earth elements on the antioxidation and flame-retardant effects of magnesium alloys. The research progress of flame-retardant magnesium alloys containing multiple rare earth elements is summarized from two aspects: the oxide film and the matrix structure. Additionally, the existing flame-retardancy models for magnesium alloys and the flame-retardant mechanisms of various flame-retardant elements are discussed. The results indicate that the oxidation of rare earth magnesium alloys is a complex process determined by internal properties such as the structure and properties of the oxide film, the type and amount of rare earth elements added, the proportion of multiple rare earth elements, synergistic element effects, as well as external properties like heat treatment, oxygen concentration, and partial pressure. Finally, some issues in the development of multi-rare earth magnesium alloys are raised and the potential directions for the future development of rare earth flame-retardant magnesium alloys are discussed. This paper aims to promote an understanding of the oxidation behavior of flame-retardant magnesium alloys and provide references for the development of rare earth flame-retardant magnesium alloys with excellent comprehensive performance.

Microcapsule Modification Strategy Empowering Separator Multifunctionality to Enhance Safety of Lithium-Metal Batteries.

The uncontrollable growth of lithium dendrites and the flammability of electrolytes are the direct impediments to the commercial application of high-energy-density lithium metal batteries (LMBs). Herein, this study presents a novel approach that combines microencapsulation and electrospinning technologies to develop a multifunctional composite separator (P@AS) for improving the electrochemical performance and safety performance of LMBs. The P@AS separator forms a dense charcoal layer through the condensed-phase flame retardant mechanism causing the internal separator to suffocate from lack of oxygen. Furthermore, it incorporates a triple strategy promoting the uniform flow of lithium ions, facilitating the formation of a highly ion-conducting solid electrolyte interface (SEI), and encouraging flattened lithium deposition with active SiO2 seed points, considerably suppressing lithium dendrites growth. The high Coulombic efficiency of 95.27% is achieved in Li-Cu cells with additive-free carbonate electrolyte. Additionally, stable cycling performance is also maintained with a capacity retention rate of 93.56% after 300 cycles in LFP//Li cells. Importantly, utilizing P@AS separator delays the ignition of pouch batteries under continuous external heating by 138s, causing a remarkable reduction in peak heat release rate and total heat release by 23.85% and 27.61%, respectively, substantially improving the fire safety of LMBs.

A Novel Intumescent MCA-Modified Sodium Silicate/Acrylic Flame-Retardant Coating to Improve the Flame Retardancy of Wood.

The incompatibility between inorganic flame retardants and organic acrylic coatings represents a significant challenge that requires resolution. This work selected environmentally friendly organic aqueous acrylic coatings as the substrate, sodium silicate hydrate as the inorganic flame retardant, and melamine cyanurate (MCA) as the flame-retardant modifier and the flame-retardant co-modifier, with the objective of improving the dispersion and flame-retardant properties of sodium silicate hydrate in the aqueous acrylic coatings. Subsequently, the sodium silicate/MCA/waterborne acrylic acid flame-retardant coating was prepared. The flame-retardant treatment was then applied to poplar veneer in order to create a flame-retardant poplar veneer. The dispersion of the flame-retardant coating was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and X-ray diffractometry (XRD). Furthermore, the flame-retardant properties of the flame-retardant poplar veneer were analyzed by thermogravimetry (TG), limiting oxygen index (LOI), and cone calorimeter. The results demonstrated that the MCA-modified sodium silicate flame retardant was well dispersed in aqueous acrylic coatings. The results of the flame-retardant properties of the poplar veneer indicated that the ignition time of the 9% flame retardant-treated poplar veneer was increased by 122.7%, the limiting oxygen index value was increased by 43.0%, and the peak heat release rate (pHRR), the peak total heat release rate (pTHR), and the peak mass loss rate were decreased by 19.9%, 10.8%, and 27.2%, respectively, in comparison to the non-flame retardant-treated poplar veneer. Furthermore, the residual char mass increased by 14.4%, and the residual char exhibited enhanced thickness, density, and regularity. The results demonstrated that MCA was an effective promoter of sodium silicate dispersion in acrylic coatings. Furthermore, the sodium silicate/MCA/waterborne acrylic flame-retardant coating significantly enhance the flame retardancy of wood, and its flame retardant mechanism was consistent with the synergistic silicone-nitrogen expansion flame-retardant mechanism. This work presents a novel approach to enhancing the dispersion of inorganic flame retardants in organic coatings, offering a valuable contribution to the advancement of research and application in the domains of innovative flame retardant coatings and flame retardant wood.

Flame-retardant mechanism for platinum coating of nickel-based superalloy

This study presents a novel approach for enhancing combustion resistance of a nickel-based superalloy by the application of platinum coating. The combustion behaviors of Pt-coated samples were studied using the promoted-ignition combustion standard test at 7–25 MPa (≥ 99.5 % oxygen). In contrast to uncoated samples, the Pt-coated samples exhibit notable improvements in resistance to burning, as demonstrated by reduced combustion length and rate. The underlying mechanism can be ascribed to two factors. One notable effect of the Pt coating is the influence on diffusion and distribution of combustion elements. In particular, it impedes the oxidation and combustion of Al with the highest combustion heat. The second one is the comparatively lower heat released by the Pt-coated samples throughout the combustion process, as well as the substantial capacity to reduce the temperature at which combustion ceases. The aforementioned discoveries offer new perspectives on enhancing the compatibility of metal materials with oxygen.

A biomass phosphonamide enables biodegradable polylactide with favorable flame retardancy and rapid crystallization

PLA is widely known as biodegradable plastics whose further application in fields such as automotive and architectural is still constrained by its flammability and unsatisfactory crystallization properties. To address the aforementioned concerns, a novel biomass phosphonamide PDPA was synthesized with chemical structure confirmed by FTIR, NMR and elemental analysis tests. Immediately thereafter, PLA/PDPA composites were prepared by melting blending, with a focus on flame retardancy, crystallization properties and flame-retardant mechanism. As expected, PDPA efficiently enhanced both the flame retardancy and crystallization properties of PLA. Specifically, the PLA/4.0PDPA obtained UL-94 V-0 grade and the LOI value increased to 28.6 % with only 4 wt% PDPA added, which comes down to the superior free radical capture and dilution effect of PDPA in the vapor phase and the melting droplet effect. More appealingly, the crystallinity of PLA/4.0PDPA was significantly enhanced to 43.4 % from 2.5 % of PLA, and the shortest t1/2 was 4 mins in the isothermal crystallization process due to the excellent heterogeneous nucleation of PDPA. Moreover, PLA/PDPA composites maintain almost the same mechanical performance as pure PLA. In brief, this work provides a green strategy for the preparation of PLA composites with excellent comprehensive performance and shows great potential in engineering materials.

High fire-safety epoxy thermosets with a macromolecular phosphorus-nitrogen containing flame retardant at a low loading

In this article, a macromolecular phosphorus-nitrogen containing flame retardant defined as PDPSB was incorporated into epoxy resins (EP). The fire safety, flame-retardant mechanism and mechanical properties of EP/PDPSB thermosets were systematically investigated. The EP-5 sheets containing 5 wt% PDPSB passed V-0 level in the vertical burning tests (UL-94) with a high limiting oxygen index (LOI) value of 30.9%. The results of cone calorimeter tests (CCT) revealed that both the emission of heat and smoke for EP/PDPSB thermosets was substantially suppressed. Compared to pure EP, the values for peak of heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) of EP-5 were dropped by 19.4%, 31.5% and 33.0%, respectively. Remarkably, the char residue mass of EP-5 was enhanced by 87.7%. The maximum smoke density (Ds, max) was slashed by 18.9%. Furthermore, the tensile, flexural and charpy impact strength of EP-5 were maintained to 97.3%, 95.1% and 86.9%, respectively. The investigation of flame-retardant mechanism demonstrated PDPSB exerted flame retardant effect both in condensed and gaseous phase by the scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectra (XPS), laser Raman spectra (LRS) and thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). As PDPSB was a one-component multifunctional additive renowned for its exceptional efficiency, it was anticipated to facilitate the advancement of high-performance epoxy thermosets via researching on EP/PDPSB thermosets.

Towards fire-safe, smoke-suppression and recyclable epoxy composite from bio-derived flame retardant

Epoxy-based vitrimers appear as a promising alternative to common epoxy materials. Nevertheless, the possibility of epoxy vitrimers in practical applications is limited by their high flammability. In this study, a novel bio-based casein phosphopeptide chelating zinc (CPP-Zn) is purposely developed, specifically designed to serve as a flame retardant and smoke suppressant for epoxy vitrimer, operating through a condensed phase mechanism. To further enhance the fire safety of epoxy resins, DOPO derivative (DDP) is synthesized through grafting with bio-based itaconate and subsequently used as a synergistic flame retardant in combination with CPP-Zn. DDP exhibits gas phase flame retardant mechanism through the release of free radical scavangers generated during combustion. As a result of the combination of condensed and gas phase effect, the composite achieves self-extinguishing within 1 second, attains a V-0 rating in UL-94 testing, and boasts an LOI of 32.3 %. Additional, it shows a remarkable 73.7 % reduction in heat release rate (HRR) and 27.2 % in total smoke production (TSP) compared with neat epoxy vitrimer. The experimental results also evidence that the characteristic features of vitrimers, self-healing and recyclability, have been retained in the prepared flame-retarded composites. The remolded 50D/EST-25Cz is still able to maintain 72.2 % of its tensile strength. This opens promising avenues for the development of highly fire-safe and eco-friendly epoxy resins.