UL-94 Vertical Burning Test Research Articles

A recyclable, toughening, extreme-condition resistant flame retardant for unsaturated polyester: Bridging performance and sustainability

Recycling thermosets presents significant economic benefits and social implications, and to date, a series of controllable recycling strategies have been proposed. However, prior research has primarily focused on neat polymers, neglecting the impact of the recycling process on composites whose additives may lose performance post-recycling. The paradigm shift towards sustainability necessitates the development of additives that not only exhibit high performance but also endure recycling conditions. Herein, taking flame-retardant unsaturated polyester (FRUP) as an example, we designed a new flame retardant (DPPONSi) with multiple flame-retardant elements and a low phosphorous oxidation state. FRUP with 16.7 wt% of DPPONSi achieves a V-0 rating in the UL-94 vertical burning test, and its limiting oxygen index (LOI) reaches 27.1%. Moreover, its peak heat release rate and total heat release are distinctively reduced by 65% and 42%, respectively. The high flame-retardant efficiency structure also protected DPPONSi from by-reactions. Without complex separation processes, FRUP degradation products were integrated with polyvinyl alcohol (PVA) to create flame-retardant aerogels with high flame retardancy. Additionally, we systematically studied the influence of flame retardants with varying oxidation states on FRUP, the corresponding flame-retardant mechanisms, and the degradation process of FRUP. This work realizes the organic combination of strategies to enhance the high efficiency of flame retardants with design methods for flame retardants that are resistant to existing unsaturated polyester degradation systems.

Enhanced thermal and mechanical properties of flame-retardant expandable graphite modified silk fibroin-based rigid polyurethane foam

At present, in order to reduce the environmental pollution caused by the use of petrochemical products, the preparation of flame-retardant polyurethane foam (PUF) using green raw materials is increasingly attracting widespread attention. A biomass protein-based green flame-retardant rigid PUF (RPUF) with expandable graphite (EG) and silk fibroin (SF) was prepared in a one-step process. Thermal stability, combustion characteristics and compression properties of modified RPUFs were investigated by thermogravimetric analysis, cone test, limiting oxygen index (LOI) test, UL-94 vertical burning test and mechanical compression test. The RPUF with 10 wt% EG (RPUF-SF/EG10) exhibited superior heat resistance, with the highest initial decomposition temperature (Ti), integral programmed decomposition temperatures (IPDT) and activation energy (E). And RPUF-SF/EG10 had the lowest peak heat release rate (PHRR) and total heat release (THR), and it also showed the highest LOI and had a flammability rating of V-0. In Addition, the apparent density and compressive strength of RPUF-SF/EG10 were the largest among the four EG-added materials. The results indicated that RPUF-SF/EG10 had excellent thermal stability, flame retardancy and compression resistance, which was attributed to the synergistic effect of SF and EG in the system. This provided a valuable reference for the development of new, environmentally friendly and high-performance RPUFs.

Excellent flame-retardant polycarbonate composites with improved notched impact toughness via introducing imine-functionalized polysiloxane

Polycarbonate (PC) is known to suffer from damage over time, particularly in low-temperature settings besides its inherent flammability, where it can develop notches and lose its impact toughness. To address these issues, we synthesized schiff-based polysiloxane containing the benzene substituted with methoxy (referred to as PSOMe-X, X being the number of methoxy substitution on the benzene ring). Interestingly, by merely increasing the number of methoxy substitutions in PSOMe-X, the PC/PSOMe-X composites demonstrated significantly improved comprehensive performance. The PC/PSOMe-3 composite successfully passed the UL-94 (vertical burning test for Flammability of Plastic Materials for Parts in Devices and Appliances developed by Underwriters Laboratories) V-0 rating, and the limiting oxygen index (LOI) was increased to 29.9 %. This improvement was accompanied by a notable reduction in the peak heat release rate (PHRR) by 64 % and total smoke generation (TSP) by 18 %. Meanwhile the notched impact strength of the PC/PSOMe-3 composite was improved by 190 % at room temperature and 72 % at −25 °C. The mechanism for improved flame retardancy and impact tougheness for PC/PSOMe-X composites were unveiled.

Novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties

As one of the most commonly used thermosetting resins, the flammability of epoxy resins (EPs) has become a key factor limiting the expansion of their application range. Herein, a novel phosphorous-containing epoxy monomer (EDPPO) was synthesized using diallyl amine and diphenyl phosphoryl chloride as the starting materials. Subsequently, EDPPO was thermally cured with two diamine hardeners, 4, 4′-diaminodiphenyl sulfone (DDS) and 4,4′-dithiodianiline (DTDA). Additionally, commercial diglycidyl ether of bisphenol A (DGEBA)-type epoxy pre-polymers were cured with DDS and DTDA as comparative samples. The cured EDPPO-based thermosets showed excellent flame-retardant properties coupled with smoke suppression. Specifically, the limiting oxygen index (LOI) for the EDPPO/DDS (P content 6.4 wt.%) reached 32.0 %, and the UL-94 vertical burning test reached a V-0 rating. In addition, the PHRR, THR, and TSP values of EDPPO/DDS were 61.6 %, 49.1 %, and 58.5 % lower than those of DGEBA/DDS, respectively. The flame retardant mechanism analysis indicated that the excellent flame retardancy for cured EDPPO-based thermosets was attributed to the combined modes of action in condensed (promoting the charring capacity) and gaseous phases (quenching the active radicals). More importantly, EDPPO/DDS and EDPPO/DTDA exhibited lower dielectric constant and dielectric loss than DGEBA/DDS and DGEBA/DTDA. This work provided novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties.

Effect of cage and ladder configuration of polyphenyl silsesquioxane on mechanical performance and flame retardancy of ethylene–vinyl acetate composites

Improving the flame retardancy of ethylene–vinyl acetate copolymer (EVA) while maintaining its mechanical properties is critical for EVA applications. Polyhedral oligomeric silsesquioxane (POSS) can be a molecular structure designed to improve the flame retardancy of polymers while minimizing damage to the mechanical properties of polymers. In this study, two types of POSS with the same chemical structure but different spatial structures, which are named cage octaphenyl POSS (OPS) and ladder polyphenyl silsesquioxane (PPSQ) are prepared. The miscibility and dispersibility of these two types of POSS in the EVA matrix and their effects on mechanical properties, dielectric properties, and fire behaviors are also investigated. Compared to OPS-based EVA composite, the PPSQ with ladder structure has good miscibility and dispersion state in EVA matrix, obtaining better toughness, dielectric properties, and flame retardancy under cone calorimeter test. However, OPS-based EVA composite obtains superior flame retardancy than that of PPSQ-based EVA composite under small fire test (limiting oxygen index and UL-94 vertical burning tests). The mechanism of these two separate flame-retardant performances under various scenarios is explored. A novel flame-retardant model is proposed, as well as a new understanding of the role of POSS in EVA combustion. This study provides powerful guidance for obtaining EVA composites with excellent flame retardant and mechanical properties.

Non-combustible polymer composites with extremely high filler loading via polytetrafluoroethylene fibrillation

The incorporation of halogen-free flame retardants (FRs) into polymer matrices is a cost-effective and eco-friendly method for suppressing flames and smoke and enhancing fire safety. In energy applications, a high FR loading (e.g., >80 wt%) is often necessary owing to the excessive heat and toxic gases generated by the devices and components. However, achieving this in conventional polymer composites is significantly impeded by poor processability stemming from increased melt viscosity. This study proposes a new approach to fabricate highly loaded flame-retardant composites with an extremely high FR content of 95 wt% via fibrillation of thermally stable polytetrafluoroethylene (PTFE), which holds two different types of FRs, magnesium hydroxide (MH) and expandable graphite (EG). The hybrid composites exhibit excellent flame retardancy owing to the synergistic effects of the distinct mechanisms of the two fillers, securing a top V-0 rating in the UL-94 vertical burning test and a limiting oxygen index (LOI) exceeding 95 %. Importantly, their total heat release (THR) from the cone calorimeter test is less than 1 MJ/m2, an anomalously low value that meets the criteria for non-combustible materials (THR <8 MJ/m2). Alongside their non-combustible attributes, the composites also have high thermal conductivity, reaching up to 1.60 W/m·K, due to the presence of thermally conductive EGs. We believe that these composites and their fabrication methodology can offer new insights into the design of flame-retardant composites, which are likely to be applicable in practical applications involving severe fire hazards, such as batteries, electronics, and electric vehicles.

Synthesis of DOPO Derivatives for the Fabrication of Flame Retardant Epoxy Composites

Four flame retardant DOPO derivatives were succesfully synthesized by Pudovik reaction, including 6,6'-(([1,1'-biphenyl]-4,4'-diylbis(azanediyl))bis (thiophen-2-ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5a, 6,6'-(((sulfonylbis(4,1-phenylene))bis(azanediyl)) bis(thiophen-2-ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5b, 6,6'-((1,4-phenylenebis(azanediyl))bis(furan-2ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5c and 6,6'-((oxybis(4,1-phenylene))bis(1-(thiophen-2-yl)ethane-2,1-diyl))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5d. Among them, flame retardants 5a and 5d were synthesized for the first time. DOPO derivatives were combined with functionalized ammonium polyphosphate using polyethyleneimine (PEI-APP) as flame retardant systems for epoxy composites. The combination of compound 5a and PEI-APP gave the materials with the best flame retardancy. 6wt% of PEI-APP/6% of 5a promoted the composite material to V-0 rating in UL-94 vertical burning test and the limiting oxygen index reached 28.9%. The impact of flame retardants towards the mechanical and physical properties of epoxy resin was also evaluated. The combination of 5a with PEI-APP showed the least decrease in mechanical strength of epoxy composite.

Elaboration of Thermally Performing Polyurethane Foams, Based on Biopolyols, with Thermal Insulating Applications.

In this work, biobased rigid polyurethane foams (PUFs) were developed with the aim of achieving thermal and fireproofing properties that can compete with those of the commercially available products. First, the synthesis of a biopolyol from a wood residue by means of a scaled-up process with suitable yield and reaction conditions was carried out. This biopolyol was able to substitute completely the synthetic polyols that are typically employed within a polyurethane formulation. Different formulations were developed to assess the effect of two flame retardants, namely, polyhedral oligomeric silsesquioxane (POSS) and amino polyphosphate (APP), in terms of their thermal properties and degradation and their fireproofing mechanism. The structure and the thermal degradation of the different formulations was evaluated via Fourier Transformed Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Likewise, the performance of the different PUF formulations was studied and compared to that of an industrial PUF. From these results, it can be highlighted that the addition of the flame retardants into the formulation showed an improvement in the results of the UL-94 vertical burning test and the LOI. Moreover, the fireproofing performance of the biobased formulations was comparable to that of the industrial one. In addition to that, it can be remarked that the biobased formulations displayed an excellent performance as thermal insulators (0.02371-0.02149 W·m-1·K-1), which was even slightly higher than that of the industrial one.

Rapidly recyclable, monomer recovery and flame-retardant bio-based polyimine networks

With the development of a circular economy and sustainable environment, efficient and sustainable recycling of useful chemicals from thermosets is of great significance. However, most commercial thermosetting materials are difficult to reprocess, degrade, and recycle due to their permanent cross-linked network, and the preparation process consumes much fossil energy and causes serious environmental pollution problems. Furthermore, the high flammability makes them unsafe during service life and limits their applications. Herein, we used renewable lignin derivative vanillin as bio-based materials to synthesize a trialdehyde monomer (TMP) with phosphorus element and developed the bio-based polyimine dynamic networks with excellent comprehensive properties including outstanding reprocess ability, degradation recyclability, and fire resistance performance based on polyetherimide and 4-aminophenyl disulfide. The prepared bio-based polyimine materials with the dual dynamic networks (BPDNs) exhibited outstanding mechanical property with tensile strength of 61.6 MPa, super-rapid degradation rate and high monomer recovery rates of 70.5 %. The prepared BPDNs samples showed great flame retardancy with V0 rating and V1 rating in UL-94 vertical burning test and high LOI value of 29 %. Moreover, BPDNs could be reprocessed within 10 min at elevated temperatures (150 °C). This work provides a very effective method to prepare bio-based advanced thermosetting materials with multiple functions.

Flame-retardant smoke-suppressing and antibacterial poplar wood enabled by a bio-based flame retardant containing transition metal

Utilizing bio-based flame retardants like chitosan (CS) and tannic acid (TA) is an effective way to enhance the flame retardancy of wooden products. In this work, the poplar wood was impregnated with composite flame retardants containing CS, TA, Cu (CH3COO)2·H2O and silane coupling agent (KH550). When KH550 bound these substances together to form a stable compound, a highly efficient flame-retardant wood (wood/CTA-Cu-Si) was prepared under vacuum pressure impregnation. The results of the functional group test show that bio-based flame retardants have been successfully synthesized. The limiting oxygen index (LOI) of the treated sample was reached 31.5%, the sample also passed the V-0 grade in the UL-94 vertical burning test, and in the Cone colorimeter test, the total smoke release was reduced by 50.2% compared to that of the Control. The energy dispersive spectroscopy proved that Cu and Si elements were evenly distributed in the wood before and after combustion. Raman spectra of the residues after the burning of treated wood were compared and it was found that the degree of graphitization of wood/CTA-Cu-Si was significantly increased, which ID/IG reached 1.85. After impregnation, the flame-retardant treated wood sample exhibited no negative effect on mechanical properties. The flame-retardant mechanism was probed and summarized as the Cu and Si synergistic promotion on charring and suppression on heat and smoke release. Simultaneously, the existences of Si-C, Si-O and Si-N strengthened the char layer and enhanced flame retardancy of poplar wood. Such resulted poplar wood with flame retardancy will be an excellent application prospect as engineering biomaterial.

Novel preparation method and fire performance study of EPS composites based on calcium sulphate hemihydrate

A novel approach was used to prepare a new expanded polystyrene (EPS) composite based on calcium sulphate hemihydrate that significantly improves its fire performance. Negative pressure was applied to open cavities between the EPS beads and promoted the absorption of flame retardant slurry. Three fire retardant EPS (FR-EPS) composites with different densities were obtained. Although, a large number of inorganic additives were added, causing the increase in thermal conductivity to 0.043–0.045 W/(m∙K) and water absorption to 4.7–5.8%, the properties remained within an acceptable range. The results of limiting oxygen index (LOI), UL-94 vertical burning and Cone Calorimeter tests revealed that the FR-EPS1 increased LOI from 18.1% to 35.8%, achieved UL94 V-0 grade, decreased PHRR from 384.12 to 81.39 kW/m2, and reduced PSPR from 0.159 to 0.014 m2/s. With the continued increase of sample density, the measured LOI was further improved, while heat release and smoke production were better suppressed. TG results, and carbon residue after burning indicate that the endothermic dehydration reaction of calcium sulphate dihydrate and the physical barrier effect of the carbonaceous layer contribute to the extraordinary flame retardancy and smoke suppression of the FR-EPS composites.

A novel sustainable phosphorus-containing heteroatom-based coating for polyamide 6.6 textiles: Enhanced flame retardancy and hydrophilicity

The demand for "green" materials increases due to concerns about the effects of flame-retardant textiles. Using natural plant-base compounds such as phytic acid (PA) and the most abundant green amino polysaccharide chitosan (CS) as effective and durable flame retardants for textiles is essential for creating sustainable and ecological textile products. This study aims to develop a novel, eco-friendly, phosphorus- and nitrogen-containing flame retardant known as ammonium phytate (AP), intending to improve the flame retardant properties of polyamide 6.6 (PA6.6) textiles. UV-induced grafting with 2-acrylamide-2-methylpropane sulfonic acid (AMPS) increases the surface functional groups of PA6.6 fabrics. Later, the surface-modified fabrics were coated with phosphorus-containing heteroatom-based components, namely, sulfur, nitrogen, silicon, and boron, onto a single flame retardant system via layer-by-layer (LBL) deposition of positively charged chitosan/boron drop (3-aminopropyl) triethoxysilane/silicon dioxide (CS/BAPTES/SiO2) sole solution and negatively charged AP solution to enhance superior hydrophilic and durable flame retardant performance. According to the data, a weight pick-up of 56.5% is attributable to only 4 BLs. However, all the flame-retardant-coated fabrics can completely stop the melting-dripping tendency and achieve B-3 to B-2 ratings after the UL-94 vertical burning test. In addition, the LOI values of treated fabrics increase from 18.5% to 23.5% compared to a pure sample. The AMPS grafted with a 4BL-deposited fabric sample exhibits a maximum decrease in peak heat release rate (PHRR) of more than 54%. Moreover, the thermogravimetric analysis (TGA) test reveals a significant increase in thermal stability and char yield. Additionally, the as-prepared phosphorus-containing heteroatom-based coatings impart a water contact angle value of approximately 0⁰ within 2 s, demonstrating that the treated fabrics exhibit superior hydrophilic performance. Moreover, using AMPS-grafted and only 2-BL-deposited treatments improves coating stability in washing and imparts durable flame retardancy that can resist up to 20 washing cycles. It is proposed that the sustainable phosphorus-containing heteroatom-based coating may be a potentially effective replacement for existing durable flame retardants routinely used in textile finishing operations.

A versatile, highly effective intumescent flame-retardant synergist for polypropylene and polyamide 6 composites

A novel phosphorus-based macromolecular flame-retardant synergist named DPS was designed and synthesized via three steps from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), dihydroxybenzophenone (DHBP) and pentaerythritol (PER). The prepared synergist was used in combination with a base flame-retardant (melamine-coated ammonium polyphosphate (APP-M), or aluminum diethylphosphinate (ADP)) to create novel binary intumescent flame retardant (IFR) systems for polypropylene (PP) and polyamide 6 (PA6) matrices. The structure of DPS was characterized by fourier transform infrared (FTIR), phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and gel permeation chromatography (GPC) analysis. The thermal stability and combustion behaviors of the flame-retardant polymer composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 vertical burning tests. It was found that with a low fraction of DPS (20–25 wt%), the developed binary IFR systems significantly enhanced the flame-retardant performance of both PP and PA6. The results indicate that owing to the rich phosphorus content and abundant aromatic structures, DPS has synergistic actions with the base flame retardants to scavenge free radicals and promote char formation in the gaseous and condensed phases, respectively. Additionally, the mechanical properties of the PP composites were also evaluated, revealing the mechanical reinforcement effect of the binary IFR, i.e., simultaneous improvement of tensile modulus, ultimate tensile strength and impact toughness. This further demonstrates the effectiveness of the developed IFR formulations in terms of well-balanced flame-retardant performance and mechanical properties.

Combining hyperbranched polyol containing three flame retardant elements, P, N and Si, with expanded graphite to improve the flame retardancy of bio-based rigid polyurethane foam

The preparation of rigid polyurethane foam (RPUF) from vegetable oil and the improvement of its flame retardant properties are of great importance to broaden the application field of RPUF, which can satisfy the green environment and reduce the fire accidents caused by its flammability. In this paper, a reactive hyperbranched flame retardant polyol (DOPO-MASi) containing three flame retardant elements of P, N and Si was prepared by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a phosphorus-containing compound, with maleic anhydride, diethanolamine and Triethoxy(3-glycidyloxypropyl)silane (KH-561), respectively, and mixed with expandable graphite (EG) to obtain a vegetable oil-based flame retardant RPUF with the multi-flame retardant system. This foam has excellent flame retardant properties and smoke-suppressing effect, with a limiting oxygen index (LOI) of 30% and a “V-0″ level in the UL-94 vertical burning test, as well as its pHRR, THR, and TSP were reduced by 47.5%, 57.9% and 62.8%, respectively. More importantly, 5% EG/20% FR-RPUF also has good mechanical properties. The above properties provide a reference for the practical application of RPUF in environmental protection and flame retardant.

Durable flame-retardant, smoke-suppressant, and thermal-insulating biomass polyurethane foam enabled by a green bio-based system

Bio-based polyurethane foam has attracted increasing attentions due to eco-friendliness and fossil feedstock issues. However, the inherent flammability limits its application in different fields. Herein, we demonstrate a green bio-based flame-retardant system to fabricate polyurethane foam composite with durable flame retardancy, smoke suppression, and thermal insulation property. In this system, the green bio-based polyol (VED) with good reactivity and compatibility plays a role of flame retardant and EG acts as a synergistic filler. As a result, the LOI value of foam composite increased to 30.5 vol.% and it achieved a V-0 rating in the UL-94 vertical burning test. Additionally, the peak heat release rate (pHRR) and the total smoke production (TSP) decreased by 66.1% and 63.4%, respectively. Furthermore, the foam composite maintained durable flame retardancy after accelerated thermal aging test, whose thermal-insulating property was maintained even after being treated in high-humidity environment with 85% R.H. for a week. This work provides a facile strategy for durable flame retardancy and long-term thermal insulation performance, and creates opportunities for the practical applications of bio-based foam composites.

A Novel P/N/Si-Containing Vanillin-Based Compound for a Flame-Retardant, Tough Yet Strong Epoxy Thermoset.

It is still extremely challenging to endow epoxy resins (EPs) with excellent flame retardancy and high toughness. In this work, we propose a facile strategy of combining rigid-flexible groups, promoting groups and polar phosphorus groups with the vanillin compound, which implements a dual functional modification for EPs. With only 0.22% phosphorus loading, the modified EPs obtain a limiting oxygen index (LOI) value of 31.5% and reach V-0 grade in UL-94 vertical burning tests. Particularly, the introduction of P/N/Si-containing vanillin-based flame retardant (DPBSi) improves the mechanical properties of EPs, including toughness and strength. Compared with EPs, the storage modulus and impact strength of EP composites can increase by 61.1% and 240%, respectively. Therefore, this work introduces a novel molecular design strategy for constructing an epoxy system with high-efficiency fire safety and excellent mechanical properties, giving it immense potential for broadening the application fields of EPs.

Facile synthesis of soybean protein-based phosphorus-nitrogen flame retardant for poly(lactic acid)

An eco-friendly P-N-containing flame retardant, soybean protein-based methylphosphonate (SPDP), was synthesized based on soybean protein for PLA by Mannich reaction. The grafting of dimethyl phosphite onto soybean protein molecule by the short reaction process, improved the flame retardant efficiency of protein-based flame retardants significantly, and the high-efficiency flame-retardant PLA/SPDP composites were successfully prepared. The addition of 7wt.% SPDP increased the limited oxygen index (LOI) value of PLA from 19.4% to 26.3%, and achieved V0 rating in the UL-94 vertical burning tests. And the heat release rate (HRR) and total heat release (THR) of PLA/SPDP composites decreased observably. The results of TGA, TG-IR, FTIR, XPS and SEM indicated that SPDP increased the condensed components by producing P-containing composites in condensed phase and decreased the flammable gaseous compounds releasing the un-flammable NH3, resulting the positive effect on char formation of PLA.

Biomass-based epoxy resin derived from resveratrol with high temperature resistance and intrinsic flame retardant properties

Preparing biomass-based epoxy resin with high temperature resistance and flame retardancy is still an appealing yet challenging task. Now, a high-temperature resistant and flame-retardant resveratrol-based epoxy (RESEP) has been synthesized through a facile one-step method. The structure of RESEP was established using FTIR and NMR spectroscopy. RESEP and petroleum-based epoxy diglycidyl ether of bisphenol A (DGEBA) were each cured with 4,4-diaminodiphenyl methane (DDM) to prepare RESEP/DDM and DGEBA/DDM. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, thermogravimetric analysis (TGA), thermogravimetric analysis-infrared spectroscopy (TG-IR), scanning electron microscopy (SEM), limiting oxygen index (LOI) and the UL-94 vertical burning test were used to systematically evaluate the properties of RESEP and RESEP/DDM. The glass transition temperature (Tg) of RESEP/DDM is 335 ℃, which is significantly higher than that of DGEBA/DDM (168 ℃). In addition, RESEP/DDM displays good thermogravimetric performance and flame retardancy. Typically, it displays a UL-94 V-0 rating, an LOI value was as high as 31.8%, and a char yield as high as 38.6% (800 ℃). The results reported indicate the possibility of preparing biomass-based epoxy resin with high temperature resistance, flame retardancy and mechanical properties, which is potential to be utilized in the fields of electronics and aerospace.

Improvement of Thermal Behavior of Rattan by Lignosulphonate Impregnation Treatment

Lignin derived from black liquor has a lot of potentials, particularly in its thermal stability, for making value-added chemicals. The purpose of this study was to determine the effect of washing frequency during hydrochloric acid lignin isolation on the properties of eucalyptus kraft lignin. To improve its thermal characteristics and enable its usage as an additive flame retardant, the isolated lignin was synthesized into lignosulphonate. The lignin produced by 3× and 5× washing treatments had a purity of 85.88 and 92.85%, respectively. An FTIR analysis indicated that lignosulphonate was successfully synthesized from isolated lignin after 3× and 5× washing treatments, as the S=O bond was detected at around 627 cm−1. The lignosulphonate exhibited a purity of 71.89 and 67.21%, respectively. Thermal gravimetry and differential scanning calorimetry analysis revealed that the lignin and lignosulphonate after 3× and 5× washing treatments had a char residue of 44, 42, 32, and 48%, respectively. Glass transition temperatures (Tg) of 141, 147, 129, and 174 °C were observed. According to the findings, washing frequency increases lignin purity and Tg, thereby improving the thermal properties of lignosulphonate. Furthermore, the flammability of rattan impregnated with lignosulphonate was V-0 in the UL-94 vertical burning test.

Efficient flame retardancy, good thermal stability, mechanical enhancement, and transparency of DOPO-conjugated structure compound on epoxy resin

A novel multifunctional flame retardant EAD with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and conjugated structure was successfully synthesized via addition reaction of PH bond and alkynyl group. The structure was characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) spectra. Thermogravimetric analysis (TGA) showed that EAD possessed high thermal stability with 290 ℃ Tonset and 20.4% char yield at 700 ℃ due to the presence of rigid structure and crosslinking reaction. When incorporating 2 wt% EAD into epoxy resin, the results from TGA indicated that the modified sample had good thermal stability with a Tonset value of 354 ℃ and char-forming performance with 22.9% char yield at 700 ℃, as well as glass transition temperature without any deterioration was obtained. Compared with pure epoxy, the same EAD content with only 0.186 wt% phosphorus loading improved effectively the flame retardancy, reflected by the increased limiting oxygen index (LOI) value of 31.0% and V-0 rating in UL-94 vertical burning test. Results from cone calorimeter test (CCT) further confirmed the positive effect on the fire retardancy, which was expressed as the heat release reduction and smoke suppression. The high-efficient flame retardancy was investigated by analyzing the pyrolysis behavior and char residue, which demonstrated the multiple actions of EAD in gas and condensed phases. The low addition of EAD also brought out the reinforcing and toughening effect for epoxy resin. Moreover, the modified epoxy samples with no more than 2 wt% EAD presented good transparency and UV-shielding performance.