Nonflammable Gases Research Articles

Real-time Monitoring of Carbon Dioxide with IoT ThingSpeak using TiO2 Thick Film Gas Sensor

Carbon dioxide is a colorless, odorless, and non-flammable gas and is claimed to be the fourth most abundant in the earth's atmosphere. Carbon dioxide emission is mainly generated by human and animal exhalation, decomposition of organic matter, and forest fires. Moreover, human activities in the industrial sector emit high levels of carbon dioxide gas, such as through fossil fuel burning, transportation, and deforestation. It is also an asphyxiant and high exposure to it may lead to health effects in humans such as headaches, breathing difficulty, tiredness, coma, and elevated blood pressure. Therefore, in this paper, a carbon dioxide gas sensor with IoT using TiO2 is proposed to observe varying concentrations of carbon dioxide gas at room temperature. Three similar gas sensors were fabricated via screen-printing technology to compare their performance towards carbon dioxide. The hardware development consisted of an Arduino Uno R3 with ESP 8266 Wi-Fi module, wires, LCD display, red and green LEDs, and a 5V power supply. The ThingSpeak application was integrated with the gas sensor and hardware parts to monitor the carbon dioxide concentration in a real-time system. Gas sensor G1 produced the highest response and highest sensitivity with values of 2.120 and 0.245, respectively.

Direct ink writing 3D printed graphene oxide nanocomposite aerogel for intelligent fire-warning and exceptional fire-shielding

Fabricating intelligent fire-warning sensors with controllable 3D structures and shapes by advanced manufacturing technology is a formidable challenge but remains the critical factor in broadening fire prevention and protection. Herein, the novel fire-warning aerogel with a high-fidelity 3D porous structure and diversiform geometrical features based on graphene oxide (GO), cellulose nanofiber (CNF) and ammonium polyphosphate (APP) was fabricated via direct ink writing (DIW) 3D printing combined with freeze-drying technology. Benefiting from the hydrogen bonding multi-interactions between the molecules as well as the ideal rheological properties, the ink containing 20 wt% of CNF (GA-CNF-20) had a dynamic yield stress of 620 Pa. As a result, the corresponding aerogel had a significantly improved elasticity modulus of 153 kPa and a compressive stress of 400 kPa at a deformation of 39.7 %. Meanwhile, GA-CNF-20 displayed an ultrafast fire-warning trigger time (1.32 s) and a long-term response time (170 s) because of the thermal reduction property of GO together with the in-situ phosphorus doping reaction of APP under fire. Besides, the GA-CNF-20 also exhibited a strong heat-insulating capability, high char-forming property, self-extinguishing performance as well as structure integrity in the burning test. The relevant improvement mechanisms were attributed to the non-flammable gas diluting effect, intumescent char layer barrier effect and fire blowing-out effect in both gas and condensed phases. Such self-supporting printed aerogel can potentially be used as a fire-warning sensor for designated systems with specific precision structure in multi-domains of electrical and traffic engineering.

Effects of novel halogen-free flame-retardant binary additives on thermal stability, degradation kinetics and flame retardancy of cotton cellulose biomacromolecule

The principal component of cotton fibers is the cellulose biological macromolecule. However, its highly flammable nature has significantly constrained its utilization in fields where flame retardancy is essential. Herein, in this work, a highly effective binary composite flame retardant coating (APP/MEL-SWCNHs) with ammonium polyphosphate and modified single-walled carbon nanohorns (MEL-SWCNHs) was chemically attached to cotton fabric. With the add-on of 11.3 %, the treated cotton fabric (APP/MEL-SWCNHs)4 exhibited remarkable flame-retardant and self-extinguishing properties. Its LOI value increased to 23.7 ± 0.1 %, and the damage length was significantly reduced from 30.0 ± 0.1 % cm to 7.9 ± 0.1 % cm compared to the pristine cotton fabric. Despite partial carbonization, (APP/MEL-SWCNHs)4 preserved its original structure. Importantly, in the cone calorimeter test, both the pHRR and THR of (APP/MEL-SWCNHs)4 were drastically decreased by 71.8 % and 35.8 %, respectively. The APP/MEL-SWCNHs coating functioned as a flame retardant by inhibiting the emission of flammable volatiles, releasing non-flammable gases, and encouraging the formation of char layer during combustion. Significantly, thermal degradation kinetic analysis revealed that the third-order kinetic equation (O3) was found to have the strongest correlation with (APP/MEL-SWCNHs)4 in both air and N2 atmospheres. The higher activation energy (E) for (APP/MEL-SWCNHs)4 confirmed that incorporating MEL-SWCNHs improved the thermal stability of the char layer.

Fabrication of CoFe‐layered double hydroxide for flame retardant and smoke suppression of silicone rubber foam

AbstractIn order to improve the flame retardancy and smoke suppression of silicone rubber foam (SRF), the CoFe‐LDH was fabricated by coprecipitation method and used as flame‐retardant ingredient in SRF. The influence of CoFe‐LDH on the flame retardancy, combustion behavior, and thermal stability of SRF was investigated. The results demonstrate that SRF containing only 1.0 phr CoFe‐LDH can pass V‐0 rating in the vertical combustion test, with a limiting oxygen index of 28.6%. The total heat release and total smoke production are 22.2% and 61.1% lower than that of SRF, respectively. Moreover, CoFe‐LDH can improve the thermal stability of SRF in the high temperature range, and the char residue at 900°C of SRF/LDH composite is obviously higher than that of pure SRF. In addition, to further understand the flame‐retardant mechanism of CoFe‐LDH, the micromorphology of the char residue and the gaseous products during heating for SRF and SRF/LDH composite were analyzed. The results indicate that CoFe‐LDH exhibits excellent flame‐retardant effects in both condensed and gaseous phases for its functions of catalysis, carbonization, and nonflammable gas release. This study provides a more efficient and convenient strategy for the flame retardant and smoke suppression research of SRF.

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.

Effect of Surfactants on the Synthesis and Dissociation of Gas Hydrates

The synthesis and dissociation of methane hydrate and carbon dioxide hydrate were studied. Nonflammable gas hydrates can be used to extinguish flames in confined spaces. To increase the extinguishing efficiency, it is necessary to increase the dissociation rate (gas release rate) by using surfactant. The work investigates gas hydrates synthesized using sodium dodecyl sulfate (SDS). Experimental studies were carried out in wide ranges of surfactant concentration, the number of the stirrer revolutions and the initial water volume. To achieve the maximum rate of synthesis and dissociation, optimization of the specified parameters was performed. The influence of the key parameters on the dissociation rate was investigated experimentally and theoretically. The novelty of the work lies in solving a complex of interrelated tasks on the synthesis and dissociation of gas hydrate. It is shown that in order to achieve the maximum dissociation rate of carbon dioxide hydrate, it is necessary to optimize the following parameters: the diameter of the particles and their porosity, the porosity of the layer and the external heat flux.

Preparation of a Highly Flame-Retardant Urea-Formaldehyde Resin and Flame Retardance Mechanism.

Urea-formaldehyde (UF) resin is the most widely used adhesive resin. However, it is necessary to improve its flame-retardant performance to expand its applications. In this study, exploiting electrostatic interactions, anionic phytic acid and cationic chitosan were combined to form a bio-based intumescent flame-retardant, denoted phytic acid-chitosan polyelectrolyte (PCS). The molecular structure of the urea-formaldehyde resin was optimized by crosslinking with melamine and plasticizing with polyvinyl alcohol-124. Thus, by combining PCS with the urea-formaldehyde resin and with ammonium polyphosphate and ammonium chloride as composite curing agents, flame-retardant urea-formaldehyde resins (FRUFs) were prepared. Compared to traditional UF resin, FRUF showed excellent flame retardancy and not only reached the UL-94 V-0 level, but the limit of oxygen index was also as high as 36%. Compared to those of UF, the total heat release and peak heat release rate of FRUF decreased by 86.44% and 81.13%, respectively. The high flame retardancy of FRUF originates from the combination of oxygen and heat isolation by the dense carbon layer, quenching of phosphorus free radicals, and dilution of oxygen by a non-flammable gas. In addition, the mechanical properties of the FRUF remained good, even after modification. The findings of this study provide a reference for the flame-retardant application of FRUF for applications in multiple fields.

Innovative multifunctional fire retardance of poly(butylene adipate-co-butylene terephthalate)-based bio-composite formulation

Poly(butylene adipate-co-butylene terephthalate) (PBAT), a biodegradable aromatic-aliphatic copolyester, has been widely applied in various fields, but it shows the flammability, resulting in serious fire risk. The flame retardancy of some PBAT/polymer blend systems have been studied, but that of neat PBAT was seldom reported. In particular, the research and development of the bio-based green flame retardant agent is highly desired. In this work, fully bio-derived modified chitosan particles (C-CS), were synthesized and used to prepare a novel PBAT-based multifunctional flame-retardant composite. The PBAT/3%C-CS composite (PC3) exhibited an excellent anti-dripping and self-extinguishing performance and achieved the highest fire safety rating (V-0). Peak of heat release rate and total heat release reduced by 39.8 % and 14.9 %, respectively. The char residue yield of the PC3 increased by 211.6 % in the PC3, compared with that of neat PBAT. Both condensed- and gas-phase played dual roles on increasing the flame-retardant performance of the PC3. The PC3 showed a relatively compact and continuous char layer which acted as a physical barrier to suppress the heat exchange and O2 entry (into the matrix) in the combustion process. Meanwhile, the concentration of O2 and H·/HO· free radicals were diluted by a small portion of non-flammable gas products in the pyrolysis process. Also, the PC3 presented elevated crystallizability and anti-bacterial effect, and reduced UV-transmittance characteristic.

Eco-friendly multifunctional coating for polyester-cotton blended fabrics with superior flame retardancy and antibacterial properties

Since the fire hazards of polyester-cotton blended (PTCO) fabrics and the hidden dangers of bacterial infection concerns caused by the contained cotton fiber, the design of flame retardant and antibacterial PTCO fabrics has received considerable attention. In this work, flame-retardant PTCO fabrics with satisfactory antibacterial properties were fabricated via a convenient and eco-friendly impregnation treatment involving guanidine phosphate (GP) and polyethylenimine (PEI). The prepared PTCO fabrics demonstrated excellent flame retardancy with a high limiting oxygen index value of 30.5 % and self-extinguishing capability, the damaged length was only 34 mm in the vertical flammability test. Furthermore, the peak heat release rate and the total heat release of coated PTCO fabrics were reduced significantly by 49 % and 38 %, respectively, indicating a substantial enhancement in fire safety. According to the analysis of the char residues and volatiles, GP presented great catalytic carbonization property, and PEI assisted the formation of the dense and stable carbon layer. The stable carbon layer effectively restricted mass and oxygen transfer between the PTCO fabrics and the environment. In addition, the introduction of PEI also produced more nonflammable gases to enhance the flame retardancy of the PTCO fabrics. Importantly, the GP/PEI coating barely deteriorate the physical and mechanical properties of the PTCO fabrics. The antibacterial rate of the GP/PEI-coated PTCO fabrics against Escherichia coli and Staphylococcus aureus was 99.99 %, similar to that of GP-coated fabrics, indicating the efficacy antibacterial properties of GP, and the addition of PEI did not compromise the antibacterial properties of GP. This work offers an efficient and simple approach to producing multifunctional PTCO fabrics with excellent flame retardancy and antibacterial properties, which are hopeful to expand the promising application of PTCO fabrics.

Flame retardant behavior of bio-based epoxy resin bearing pyridazinone and dynamic ester bond via self-blow-out and vesicular carbon formation

Aromatic nitrogen heterocyclic structure is a key building block of high-performance polymer materials and nitrogen-doped porous carbons, yet systematic studies on its flame-retardant effects and carbonization mechanisms in thermoset materials is still lacking. Here, a pyridazinone embedded bio-based epoxy resin (CSPZ-EP) cured by 4,4ʹ-methylenedianiline (DDM) was prepared. Benefiting from the rigid biphenyl-like pyridazinone structure and the high cross-linking density originated from the self-catalyzed transesterification, the cured CSPZ-EP/DDM can easily pass the UL-94 test with a V-0 rating suggesting excellent intrinsic flame retardancy. The cone calorimeter results further demonstrated that the peak heat release rate, the total heat release and flame growth rate of CSPZ-EP/DDM were significantly reduced by 84.4 %, 28.4 % and 90.5 %, respectively, compared with those of bisphenol A epoxy resin. The higher graphitization degree of the char residues and a large amount of non-flammable pyrolysis gas ejection synergistically prevented the further spread of fire. Strong yet tough nitrogen-rich char layer formed after thermal ablation together with the renewable features and the facile preparation route of CSPZ-EP/DDM make it a potential precursor for heteroatom porous carbons.

Production and Characterization of Flame Retardant Leather Waste Filled Thermoplastic Polyurethane.

Discovering new applications for discarded materials, such as leather waste (LW), has proven to be an effective approach to an ecofriendly and sustainable production. The manufacture of halogen-free flame retardant LW containing thermoplastic polyurethane (TPU)-based samples containing an organic phosphinate (OP)-based flame retardant additive would represent an advance in this area. The effects of LW and OP levels on the thermal, flame retardant, and tensile properties of the samples using thermal gravimetric analysis (TGA), limiting oxygen index (LOI), vertical UL-94 (UL-94 V), mass loss calorimetry, and tensile tests have been assessed. OP is highly effective in LW-filled TPU. The highest UL-94 V rating of V0, LOI value of 31.4%, the lowest peak heat release rate (93 ± 3 kW/m2), and total heat evolved (49 ± 2 MJ/m2) values are obtained with the use of 20 wt % OP. OP is primarily promoted through the creation of a compact intumescent residue structure in the condensed phase. LW exhibits an adjuvant effect by producing nonflammable gases in the gas phase and raising the residual yield in the condensed phase. The most remarkable effect of the LW presence is observed in fire performance index (FPI) and fire growth rate (FIGRA) values. The highest FPI value of 0.49 sm2/kW and the lowest FIGRA value of 0.91 kW/m2s are observed with the use of 20 wt % LW.

A universal eco-friendly flame retardant strategy for polylactic acid fabrics and other polymer substrates

Various polymer substrates have their particular combustion features, therefore, developing an effective universal flame retardant strategy for various polymer substrates is of great practical importance. Meanwhile, as substitutes for petroleum-based products, bio-based flame retardants and biodegradable polylactic acid (PLA) meet the requirements of sustainable development. In this work, a fully bio-based flame retardant coating (PAGS) was prepared using phytic acid (PA) and guanosine (GS). PAGS was used as a universal flame retardant coatings for polylactic acid (PLA) fabrics and other substrates, including cotton fabrics, polyethylene terephthalate (PET) fabrics, polyamide (PA) fabrics, polyurethane (PU) foams, polyethylene terephthalate (PET) films, and woods. The PAGS-treated substrates were able to self-extinguish and eliminate molten droplets. Similarly, the PAGS coating significantly suppressed the heat release of each substrate. The P-containing free radicals in the gas phase were able to interact with highly reactive H, HO and alkyl radicals, blocking the chain reaction during combustion. The flammable gas density was also diluted by nonflammable gases. The formed continuous porous and dense intumescent char layer hindered heat and oxygen. It is suggested that this work provides a simple and efficient flame retardant strategy for improving the fire safety of various polymer substrates.

Effect of aluminum diisobutyl hypophosphate in polyethylene terephthalate and its flame retardant mechanism

AbstractAlkyl hypophosphate flame retardants have aroused intense research interests in flame retardancy of polymers owing to the combined effect of gas phase and condensed phase. In this work, aluminum diisobutyl hypophosphate (APBA) was incorporated into polyethylene glycol terephthalate (PET) to investigate its flame retardant effect and mechanism. PET achieved a V‐2 level in UL‐94, with a low LOI of 21.2%. In contrast, PET/APBA‐15% composites showed a 51% increase of LOI value and a V‐0 level, accompanied with the significant reduction of melt droplets. Gas phase analysis by Py‐GC/MS and TG‐FTIR indicated that the phosphorous free radicals and nonflammable gases were generated during the cracking of APBA, resulting in the radical quenching and dilution of combustible gas. Condensed phase analysis by SEM, Raman, and XPS results revealed that APBA could effectively facilitate the formation of dense char layers consisting of aluminophosphate and graphitic structures due to the interaction with PET matrix. The compact barrier layer could insulate heat and inhibit the volatilization of combustible materials, leading to improved flame retardant properties. Furthermore, the introduction of APBA increased the melt viscosity of PET/APBA composites according to rheological analysis, which further promoted the formation of a char barrier layer to further enhance the flame retardant properties.Highlights Aluminum diisobutyl hypophosphate is used as an efficient flame retardant for PET. The flame retardant can degrade to release the phosphorous free radicals. The flame retardant can interact with the PET matrix and promote the charring.

The Strength and Fire Properties of Paper Sheets Made of Phosphorylated Cellulose Fibers.

Phosphorylated cellulose can be an intrinsic flame retardant and a promising alternative for halogenated fire inhibitors. In this study, the mixture of di-ammonium hydrogen phosphate (DAP) and urea (U), containing phosphate and nitrogen groups, was applied to attain fire inhibitor properties. Functional groups of cellulose were grafted with phosphorous by keeping the constant molar ratio of 1/1.2/4.9 between anhydroglucose units of cellulose/DAP/U in different concentrations of bleached kraft pulp. Phosphorus concentrations were determined using the ICP hrOES method, and paper sheets were made using the Rapid Köthen apparatus. The tensile strength of phosphorylated cellulose increased twice compared with unmodified cellulose when the phosphorous concentration increased to 10,000 g/kg. An increase in the tensile index comes from the higher freeness of pulp and cross-linking of the phosphorous group between cellulose fibers. Remarkable fire retardancy effects were achieved in cellulose concentrations above 5 wt%. The raised phosphorous concentration above 10,000 g/kg due to the phosphorylation process caused the formation of a char layer on a cellulose surface and the nonflammable gas emission. That effect was indirectly confirmed by reducing the combustion temperature and HRR by 50 and 45%, respectively. Due to increasing phosphorus concentration in cellulose sheets, cellulose's fire and strength properties increased significantly.

Fabrication of a cinnamaldehyde-based bi-DOPO flame retardant with excellent glass transition temperature, fire safety and mechanical properties for epoxy resins

Manufacturing fire-resistant, tough, and durable epoxy resin (EP) is a challenging task. Traditional flame retardants derived from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) tend to aggregate and plasticize, causing a decline in glass transition temperature (Tg) and mechanical properties of EP. To overcome this issue, a bulky aromatic DOPO-based derivative called PPCANT was synthesized successfully using biomass-derived cinnamaldehyde (CA). The steric hindrance and intermolecular interactions (π-π stacking) of PPCANT's mitigated Tg deterioration and significantly improved mechanical properties. Incorporating 5 wt% PPCANT into the EP (EP/PPCANT-5) achieved a limiting oxygen index (LOI) of 32.6% and UL-94 V-0 rating, reducing both total heat release and smoke production. Moreover, PPCANT endowed the EP with exceptional char-forming ability. Analysis of the flame retardant mechanism indicated that the PPCANT structure imparted an ideal flame quenching mechanism, characterized by the instantaneous extinction of flames caused by the blowout of PO·/PO2 radicals, and a dilution effect of free radicals from non-flammable gases. In addition, the incorporation of nitro and amino groups in PPCANT facilitates the formation of hydrogen bonds with the hydroxyl groups generated in the ring-opened EP, leading to a significant decrease in the hydrophilicity of EP. These findings highlight PPCANT as a promising flame retardant that simultaneously enhances flame retardancy, mechanical strength, and hydrophobicity in EP materials.

Dissociation of methane and carbon dioxide hydrates: Synergistic effects

The dissociation and combustion of methane hydrate samples were studied experimentally in a laboratory-scale combustion chamber with variable thermal conditions. The temperature in the combustion chamber was varied from 800 °C to 1000 °C to reproduce high-potential reactors and combustion chambers. Ignition delays, combustion times, and combustion product compositions were determined for gas hydrates in the form of granules and tablets. Synergistic effects were analyzed from the simultaneous dissociation of methane and carbon dioxide hydrate samples. Critical conditions were determined in which carbon dioxide prevented methane ignition. The definable parameters were determined as functions of the arrangement schemes of two gas hydrates and input experimental parameters, and the corresponding predictive mathematical expressions were obtained. Methane hydrate granules were found to ignite significantly faster than methane hydrate tablets. An increase in the temperature in the combustion chamber was proved advisable in the case of methane hydrate tablets. Granulated hydrate samples ignited consistently in a wide range of temperatures, and the ignition delay times changed negligibly with varying temperature. The methane hydrate combustion stability was analyzed, and a model was developed describing the patterns and predicting the carbon dioxide hydrate flow rate required for fire suppression. Finally, conditions were identified in which the synergistic effects of simultaneously dissociating hydrates with flammable and nonflammable gases would make it possible to effectively manage their safe and sustainable application in the energy industry.

MoFs decorated TA-MoS2 nanosheets improving the mechanical and fire properties of epoxy resins: Interface engineering design based on virginia creeper

Developing high-performance polymers with outstanding fire safety and mechanical performance remains a thorny challenge. Hence, inspired by Virginia creepers, an interface engineering design was used to load NH2-MIL-Fe onto the surface of tannic acid (TA)-modified molybdenum disulfide (MoS2), gestating TA-MoS2-NMFe nanohybrids with biomimetic structure. The TA-MoS2-NMFe exhibited well dispersion and interfacial compatibility in the epoxy resin (EP) matrix, which facilitated the improvement of the EP nanocomposites properties. Subsequently, the EP/TA-MoS2-NMFe nanocomposites showed a creeper sucker structure that could withstand high external force, resulting in growths of 49.9% in tensile strength and 67.3% in elongation at break. Moreover, the incorporation of TA-MoS2-NMFe decreased the maximum thermal degradation rate from 1.35%/℃ to 1.0%/℃, leading to EP nanocomposites with excellent thermal stability. Likewise, compared to pure EP, EP/TA-MoS2-NMFe achieved reductions of 42.3%, 41.2%, 50.8% and 71.1% in the peak heat release rate, total heat release, peak smoke production rate and smoke factor, respectively, which was better than reported works. It was due to the catalytic carbon formation of metal ions, the expansion charring characteristics of TA, barrier effect of MoS2 and dilution effect of nonflammable gases. Briefly, this work provides an innovative way to developing high-performance polymers from a bionic perspective.

Eco-friendly flame retardant coating based on ammonium polyphosphate and tyramine for lyocell fabrics

Low-carbon emissions are a sustainable development approach, among which lyocell is a renewable and zero carbon biodegradable cellulose fiber. The flammability of lyocell fabric poses a threat to people's lives and property. In response to this issue, a bio-based flame retardant, tyramine polyphosphate (APP-LA), was synthesized and applied to the treatment of lyocell fabrics. The synthesis of APP-LA adopted an eco-friendly and organic solvent-free method. In the combustion test, the limiting oxygen index of APP-LA treated lyocell fabrics increased to 35.8% compared to control lyocell (18.5%), and the damage length was only 6.7 cm. Meanwhile, the peak heat release rate and total heat release decreased by 92.9% and 58.7% respectively, compared to the control lyocell. Besides, the P-containing compounds generated by APP-LA accelerated the decomposition of the matrix to produce a dense char layer. The fewer flammable volatiles and more non-flammable gases were released. This work provided a low-cost and eco-friendly strategy for the simple preparation of commercial flame-retardant lyocell fabrics.

Halogenated polymers as a problematic component in the pyrolysis of waste plastics

The study deals with the complications associated with the pyrolysis of a polymer releasing highly corrosive compounds and other products that are difficult to be utilized in practice. Poly(vinyl chloride-vinyl acetate) was chosen as a sample material. This copolymer was subjected to slow pyrolysis up to a temperature of 650 °C, which was achieved with a temperature ramp of 10 °C min‒1. Thermal decomposition took place in a batch apparatus in nitrogen atmosphere. The evaluation of the experiments included a mass balance using an online recording of gas and condensate formation, which was followed by an analysis of the obtained products. The tests showed very small yields of condensates (pyrolysis tar) in the range of 3.0 – 5.5% compared to gas production reaching 71.1 – 72.1% of the raw material weight. Within the discussion, the problem with the production of non-flammable gas consisting mainly of HCl in the initial stages of pyrolysis was highlighted. Under the given conditions, the release of acid gases, in which HCl was gradually replaced by also non-flammable CO2, continued up to about 400 °C. Only gases collected from this temperature above and having a calorific value of 33.5 MJ m‒3 (20 °C / 101.32 kPa) can be considered energetically usable. Condensates mainly represented by a mixture of aromatic hydrocarbons, acetic acid and chlorobenzene were also evaluated as problematic for possible use. The possibilities of physical activation of solid pyrolysis residues by steam at temperatures of 850 and 900 °C were also tested. All experiments led to obtaining products with very small specific surface areas in the range of 1 – 6 m2 g–1. The process loss during activation reached 25 – 33% of the pyrolysis residue weight, depending on the applied temperature and contact time with steam. These values show that the reaction of the activation medium with the sample took place more or less only on the outer surface of the particles and did not lead to the development of an internal porous structure. The achieved results were compared with the identically processed samples of waste tires, which were evaluated as promising in tests carried out in the past. The contrast be-tween the two materials clearly spoke against the discussed copolymer. The results of the experiments can be interpreted, among other things, as a certain warning against attempts at industrial pyrolysis processing of this type of plastic.

Facile strategy of preparing excellently thermal-insulating and fire-safe building materials based on an aromatic Schiff base dicarboxylic acid without additional flame retardants

Developing excellently fire-safe and thermal-insulating building materials is a critical subject in the building sector. In this work, a novel aromatic Schiff base dicarboxylic acid (FN) was synthesized through a facile strategy to prepare high-performance rigid polyurethane foam (RPUF) composites with excellent thermal insulation and fire safety performance. The uniform dispersion of FN in polyether polyol improved the cellular structure of RPUF composites, which was conducive to increasing the thermal insulation of RPUF composites. Therefore, incorporating only 10 wt% FN into RPUF composite (RPUF/10FN) possessed the lowest wall temperature (51.9 °C) and room temperature (38.8 °C) with the lowest temperature growth rate under the continuous thermal radiation of the heat source among all samples in the small chamber test. Moreover, FN remarkably reduced the peak heat release rate, peak smoke production rate, and peak CO production rate of RPUF/10FN by 41.9%, 58.0%, and 59.6% without additional flame retardants, respectively, compared with those of pure RPUF. In addition, FN endowed RPUF/FN composites with better fire resistance and structural integrity compared with pure RPUF in the building facade fire test and fire protection test. The increased fire safety of RPUF/FN composites is due to the barrier effect of the formation of a dense and continuous char layer and the dilution effect of nonflammable gas generated by the thermal degradation of FN. Furthermore, FN enhanced the water contact angle of RPUF/FN composites from 112.2° for pure RPUF to 120.8° for RPUF/10FN, indicating that FN also enhanced the hydrophobicity of RPUF/FN composites. Therefore, the as-designed RPUF composites containing FN possessed a broad application prospect in the building field.