Facile construction of polypyrrole microencapsulated γ-Fe2O3 for simultaneously enhancing the flame retardancy and smoke toxicity suppression of intumescent flame-retardant epoxy resins

For effectively strengthening the comprehensive properties of intumescent flame-retardant epoxy resins (EPs), a microencapsulating γ-Fe₂O₃ by polypyrrole (PPy) named PPy-Fe₂O₃ was synthesized and used as a synergist to simultaneously enhance the flame retardancy, smoke toxicity suppression and mechanical strength of EP composites containing diaminodiphenylmethane modified ammonium polyphosphate (DDP). The results demonstrate that the mixture of PPy-Fe₂O₃ and DDP exhibits a surprising synergistic effect on strengthening the comprehensive properties of EP composites. Specifically, EP composite containing 0.2 wt% PPy-Fe₂O₃ and 9.8 wt% DDP achieves the UL94 V-0 rating with a limiting oxygen index (LOI) value of 35.5%, while 10 wt% DDP only imparts a UL94 V-1 rating and a LOI value of 34.0% to EP. Furthermore, 0.2 wt% PPy-Fe₂O₃ shows a 11.0% reduction in peak smoke production rate and a 12.3% reduction in peak heat release rate of the EP/DDP system. The enhanced fire security of EP/DDP/PPy-Fe₂O₃ is attributed to the formation of more phosphorus-rich structures retained in the char, thus reducing the release of harmful gases including NH₃, CO, and CO₂, and generating more incombustible gases including H₂O to weaken burning intensity. Meanwhile, the satisfactory compatibility of PPy-Fe₂O₃ with epoxy matrix imparts a superior mechanical strength to EP composites.     

Preparation of the organic–inorganic double-shell microencapsulated aluminum hypophosphite and its improved flame retardancy and mechanical properties of epoxy resin composites

To develop the functional particles with better flame-retardant and compatibility with epoxy resin (EP) matrix, organic–inorganic double-shell microencapsulated aluminum hypophosphite (MSiAHP) was prepared by situ polymerization. The water contact angles of MSiAHP (62.4°) is significantly larger than that of aluminum hypophosphite (34.4°), which shows that the organic shell material of MSiAHP endows excellent hydrophobicity and water resistance. With the incorporation of MSiAHP, EP/30%MSiAHP composite exhibits limiting oxygen index value of 27.3% and V-0 rating. Furthermore, the cone calorimetry test reveals that MSiAHP reduces the peak heat release rate, total heat release and total smoke release of EP matrix by 33.3%, 24.4% and 56.6%, respectively. Besides, due to the unique organic–inorganic double-shell structure of MSiAHP particles, EP/30%MSiAHP composite achieves greater thermal stability and higher char yields than pure EP. The investigation of the products in the gas and condensed phase demonstrates that MSiAHP is beneficial to the generation of a high-density and compact carbon layer structure with a high graphitization degree, and delay the generation time of pyrolysis products in the gas phase, which can improve the fire safety of EP composites effectively. Furthermore, preeminent dispersion and compatibility of MSiAHP lead to EP/MSiAHP composites with excellent mechanical properties.     

Effect of phosphorus–nitrogen compound on flame retardancy and mechanical properties of polylactic acid

A phosphorus-nitrogen flame retardant (PN) was synthesized by using cytosine and diphenylphosphinic chloride. The flame retardancy and thermal stability of polylactic acid (PLA)/PN composites were investigated by the UL-94 vertical burning test, limited oxygen index (LOI), cone calorimeter test, and thermogravimetric analysis. The PN performs efficiently on improving the flame retardancy of PLA. The PLA composite achieves the UL-94 V-0 rating and its LOI increases to 30.4 vol% by adding 0.5 wt% PN. The flame retardant mechanism analysis showed that PN catalyzes the degradation of PLA to improve the flame retardancy by melting-away mode. Meanwhile PN reduces the release of flammable gasses during thermal degradation of PLA by promoting the transesterification of PLA, which is helpful for extinguishing flame. Moreover, triglycidyl isocyanurate (TGIC) was used as a micro-crosslinking agent to reduce the loss of mechanical properties of PLA/PN composites caused by degradation. Adding 0.1 wt% TGIC and 1.0 wt% PN into PLA, the tensile strength and elongation at break of PLA/PN are increased to the same level as that of PLA. Therefore, PLA with excellent comprehensive performance can be obtained.     

Preparation of a novel phosphorus–nitrogen flame retardant and its effects on the flame retardancy and physical properties of polyketone

In this study, a novel phosphorus–nitrogen flame retardant (PNFR) was synthesized, and its flame retardancy for polyketone (PK) was systematically investigated. The chemical structure of PNFR was characterized using NMR spectroscopy. The PNFR was considered to generate phosphoric acid, which catalyzed the char formation reaction of PK via condensed-phase decomposition. When 7 wt% PNFR was incorporated into PK, the limiting oxygen index value was increased from 20.2 to 25.9%. In addition, this PK-PNFR sample achieved the rating of VTM-0 because it exhibited self-extinguishable properties and did not drip when fire was removed from it. As the PNFR content increased, while the initial decomposition temperature decreased, the amount of residual char considerably increased. Thus, the PNFR was thought to impart flame-retarding ability to PK via superior condensed-phase mechanism. Additionally, the decrease in melting temperature and enthalpy of fusion was observed after the addition of PNFR, which implied that the PNFR could act as plasticizer for PK.     

Preparation of organic–inorganic intumescent flame retardant with phosphorus,nitrogen and silicon and its flame retardant effect for epoxy resin

According to the requirement of fire life cycle assessment (LCA), chitosan ethoxyl urea phosphate (CEUP), an organic–inorganic intumescent flame retardant (IFR) containing phosphorus, nitrogen, and silicon, was synthesized by the reaction of chitosan, phosphorus pentoxide, and urea. FTIR, ¹H NMR, SEM, and XRD were employed to characterize the compounds. As a result, CEUP was successfully prepared with higher thermal stability, favorable to enhance fire resistance. Combined with OMMT, the organic/inorganic IFR was applied as EP flame-retardant agents. The combustion behavior of EP composite was investigated by LOI, UL-94, CCT, SEM, TGA, and TG-IR. It was observed that using 15% CEUP and 3% OMMT (EP3), LOI value reached 34.8% and passed the UL-94 V-0 rating, while THR and TSP of EP composite reduced 65 and 72% compared with pure EP. The char residue of EP composite was up to 22.4%. The thermal decomposition mechanism was traced from 100 to 600°C by TG-IR. It was suggestive that CEUP decomposition commenced at 100°C to create phosphoric acid and sublimation of urea occurred at 300°C. EP3 exhibited a strong thermal stability, namely even at 600°C, the volatile substances were detectable. Dense and expanded carbon layer was confirmed in SEM images.     

Effect of N–Ni coordination bond on the electrical and thermal conductivity of epoxy resin/nickel-coated graphite

The agglomeration of nickel-coated graphite (NCG) in epoxy resin (EP) composites leads to low electrical conductivity of EP composites, which limits their development in electronic devices and multilayer circuits. In order to improve the electrical and thermal conductivity of NCG/EP composites, ethylenediamine (EDA) was used to modify NCG and compared with pure NCG-filled EP composites. It was found that the conductive effect of modified composites with 20 wt% filler is better than that of unmodified composites with 40 wt% filler. The results of Fourier transform infrared spectroscopy and thermogravimetric analysis of EDA-modified NCG (ENCG) showed that a coordination adsorption reaction occurred between EDA and NCG, forming N–Ni coordination bonds. When the filling amount of ENCG was 40 wt%, the conductivity and thermal conductivity of the composite are improved most significantly. The volume resistivity was reduced from 2.636 to 0.109 Ω cm, a decrease of 95.85%, and the thermal conductivity was improved from 0.517 to 0.968 W/(m K), an increase of 87.23%, respectively. Meanwhile, ENCG has better dispersion in the EP matrix than NCG.     

Effect of different initiators on temperature-sensitive monolithic columns and application in online enrichment of β-sitosterol

Three temperature-sensitive monolithic columns were prepared by atom transfer radical polymerization and oxidation–reduction method using the initiator systems of CCl₄/FeCl₂, BPO/DMA, and APS/TEMED, respectively. The three monoliths were characterized by scanning electron microscopy, nitrogen adsorption, and thermogravimetric analysis. The obtained monolithic columns were used as on-line solid phase extraction sorbent coupled with high-performance liquid chromatography for the enrichment of β-sitosterol. By comparing some influencing factors on the adsorption, the optimum temperature-sensitive monolithic column which was initiated by CCl₄/FeCl₂ was selected for enrichment of β-sitosterol from plant oil. The maximum adsorption capacity of the monolith for β-sitosterol was 10.0031 mg/g. The limit of detection and limit of quantitation were 0.039 and 0.13 mg/mL, respectively. The recovery was in the range of 90.21–98.26%. The results showed that the monolith had better selectivity for β-sitosterol and could be used for enrichment of β-sitosterol in food samples. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47683.     

Compatibilizing effect of β-cyclodextrin in RDP/phosphorus-containing polyacrylate composite emulsion and its synergism on the flame retardancy of the latex film

Resorcinol bis (diphenyl phosphate)/β-cyclodextrin/phosphorus-containing polyacrylate (RDP/β-CD/P-PA) composite emulsion was prepared by using β-CD as a compatibilizer. The flame retardancy of the composite latex film was investigated by microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Mechanical properties of the composite latex films were also studied and a possible compatibilizing mechanism was proposed. The results showed that the mechanical properties and flame retardancy of the RDP/β-CD/P-PA composite latex film were enhanced compared to the RDP/P-PA latex film. When the β-CD content increased from 0 to 10 wt%, the pendulum hardness of the RDP/β-CD/P-PA composite latex film increased from 0.18 to 0.54, and the peak heat release rate decreased from 382.1 to 311.9 W/g. TGA and MCC results demonstrated that both the char residual and the quality of the char formation were improved by the introduction of β-CD.     

Physical and chemical effects of diethyl N,N′-diethanolaminomethylphosphate on flame retardancy of rigid polyurethane foam

Diethyl N,N-diethanolaminomethylphosphate could react with isocyanate because it contained hydroxy group. This was confirmed by FTIR spectrum. It did not produce any effect on the foam structure of rigid polyurethane foam (RPUF). SEM, IR spectrum, and thermal analysis were used for investigation of the physical and chemical changes during the combustion of flame-retardant RPUF. It was shown that the flame retardancy changed the thermal decomposition behavior of RPUF, widened the decomposition temperature region of RPUF, reduced the amounts of decomposition products at high temperatures, and increased the decomposition residuals arisen from charring of flame-retardant RPUF. Those changes improved the flame retardancy of RPUF. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 276–282, 2001     

Influences of 4ZnO·B2O3·H2O whisker based intumescent flame retardant on the mechanical,flame retardant and smoke suppression properties of polypropylene composites

In this work, the influences of 4ZnO·B₂O₃·H₂O zinc borate (ZB) whisker based intumescent flame retardant (IFR) containing ammonium polyphosphate and dipentaerythritol on the mechanical, flame retardant and smoke suppression properties of polypropylene (PP) composites were characterized by the universal testing machine, UL-94, limiting oxygen index (LOI), and cone calorimeter tests, respectively. The results indicate that only 1 phr of ZB could effectively improve the LOI value and slow down the burning rate of PP composite. The peak heat release rate, average of HRR, total heat release, peak smoke production rate, and total smoke production values are all decreased from 413.8 kW/m², 166.3 kW/m², 82.3 MJ/m², 0.0995 m²/s, and 17.9 m² for PPc/20IFR composite to 267.8 kW/m², 128.3 kW/m², 66.8 MJ/m², 0.0478 m²/s, and 12.6 m² for PPc/20IFR/1ZB composite, respectively. The scanning electron microscopy images, energy dispersive spectrometry, and Raman spectra of char residue reveal that ZB is helpful to form a compact and graphitized intumescent char residue so that the heat diffusion and oxygen transmission are greatly hindered. The thermogravimetry analysis-fourier transform infrared spectroscopy (TGA-FTIR) results show that less combustible volatiles and more H₂O vapor are generated with the appearance of ZB. Hence, the combustion mechanism in gas phase is suppressed.     

Effect of polytetrafiuoroethylene on flame retardancy and mechanical properties of silicone rubber filled with Mg ( OH ) 2/Al ( OH ) 3 complex

研究了聚四氟乙烯(PTFE)对Mg(OH)2/Al(OH)3填充硅橡胶阻燃性能和力学性能的影响.结果表明,PTFE不但能够改善硅橡胶的阻燃性能,而且还能使力学性能尤其是撕裂强度得到显著提高.当PTFE用量为2.5份(质量),撕裂强度达17.1 kN·m-1,比不含PTFE的试样提高了51%,而且其极限氧指数也有一定增加.     

Effect of particle morphology on viscoelastic and flexural properties of epoxy–alumina polymer nanocomposites

Nanocomposites were synthesised by dispersing two different types of alumina nanoparticles in epoxy matrix by ultrasonication. Alumina nanoparticles of two shapes, rod and spherical were selected to investigate the effect of particle morphology on viscoelastic and flexural properties of nanocomposites. Specific surface area of both the selected nanoparticles was kept in the similar range. Good dispersion of nanoparticles was observed through transmission electron microscopy. The addition of nanoparticles in epoxy had significant enhancement in the viscoelastic properties and moderate improvement in flexural properties of composites. Composites having alumina nanorods showed higher improvement both in storage modulus as well as in flexural properties in comparison to composites having spherical alumina nanoparticles. Efficacy of Mori-Tanaka method was explored in modelling storage modulus of nanocomposites. Assorted size of alumina nanorods based on particle size distribution was used to model composites with nanorods to see the effect of size assortment on storage modulus.     

Effect of number of graphene layers on mechanical and dielectric properties of graphene–epoxy nanocomposites

In this study, mechanical and dielectric properties of epoxy nanocomposites with two types of graphene, <?10 layer stacks (GEC10) and <?30 layer stacks (GEC30) were investigated. Results showed that the number of graphene layers remarkably affected the dielectric properties of epoxy nanocomposites. The real and imaginary parts of relative permittivity and loss tangent of GEC10 samples were noticeably enhanced and reached to 1.29, 20 and 15.6 times respectively for 1?wt-% graphene sample compared to GEC30 samples. Meanwhile, tensile tests showed a peak for tensile strength of GEC10 and GEC30 samples with 0.1?wt-% graphene, which improved by 13 and 7.9% with respect to pure epoxy respectively. In addition, flexural properties did not change significantly compared to the pure epoxy.     

Effect of β-Cyclodextrin Complexation on Solubility and Enzymatic Conversion of Naringin

In the present paper, the effect of β-cyclodextrin (β-CD) inclusion complexation on the solubility and enzymatic hydrolysis of naringin was investigated. The inclusion complex of naringin/β-CD at the molar ratio of 1:1 was obtained by the dropping method and was characterized by differential scanning calorimetry. The solubility of naringin complexes in water at 37 ± 0.1 °C was 15 times greater than that of free naringin. Snailase-involved hydrolysis conditions were tested for the bioconversion of naringin into naringenin using the univariate experimental design. Naringin can be transformed into naringenin by snailase-involved hydrolysis. The optimum conditions for enzymatic hydrolysis were determined as follows: pH 5.0, temperature 37 °C, ratio of snailase/substrate 0.8, substrate concentration 20 mg·mL⁻¹, and reaction time 12 h. Under the optimum conditions, the transforming rate of naringenin from naringin for inclusion complexes and free naringin was 98.7% and 56.2% respectively, suggesting that β-CD complexation can improve the aqueous solubility and consequently the enzymatic hydrolysis rate of naringin.     

Effect of clay dispersion methods on the mechano-dynamical and electrical properties of epoxy–organoclay nanocomposites

The effect of different clay dispersion methods on the mechano-dynamical and electrical properties of epoxy/clay nanocomposites was investigated. Three different clay dispersion methods (high-speed mechanical shearing, ultrasonication (US), and an optimal combination of high-speed shearing and US) were used for the dispersion of the clay in the epoxy resin. 3 wt% of an organoclay, cloisite 30B, was used as the nanoclay. Wide-angle X-ray diffraction technique and electron microscopic techniques (SEM and TEM) were used to study the morphology of the nanocomposites. Dynamic mechanical analysis was used to study the dynamo-mechanical properties. Studies on the dielectric breakdown strength (EBD) of the nanocomposites show that the EBD strongly depends on the clay dispersion time and clay dispersion method. Pulsed electro-acoustics method measurement shows that the space charge accumulation was considerably reduced in the nanocomposites. In particular, reduction in space charges after polarization depends on the dispersion of the nanofillers, the better the degree of dispersion, the lower the space charges observed.     

Effect of a formulation named “Giral” on mechanical properties of a composite based on silica and unsaturated polyester resin

To improve the performances of a composite based on silica and unsaturated polyester resin, modification of silica surface and addition of a dispersing agent are required. The surface of raw silica was modified with vinyltrimethoxysilane in acidic conditions, adding methacrylic acid. Moreover, to enhance the compatibility between silica and polyester resin, a block copolymer which reacts as a dispersing agent was added. The mixture of these components is named “Giral.” The mechanism of interaction of the different components of the “Giral” with the raw silica is described. Adding this formulation to a mixture of polyester resin and silica leads to a decrease of the viscosity of the polyester resin/silica system and the mechanical properties of the composite thus formed are improved.     

Research on selective laser sintering of Kaolin–epoxy resin ceramic powders combined with cold isostatic pressing and sintering

In order to fabricate traditional products with complex shapes consisting of Kaolin ceramic, selective laser sintering (SLS) combined with cold isostatic pressing (CIP) process was used to consolidate Kaolin powder with additive of epoxy resin E06. To begin preparing the material, epoxy resin (10 wt%) and Kaolin were combined through mechanical mixing, which provided a good fluidity for SLS. Investigations on the shrinkage and micro topography of Kaolin–epoxy resin SLS samples were conducted to optimize the laser sintering parameters. It was found that SLS samples represented acceptable shrinkage and high density when laser energy density was 0.3300–0.3763 J/mm². Then the SLS samples were processed by CIP to eliminate the pores in green ceramics. Finally, the optimized SLS/CIP Kaolin samples were debinded and sintered to produce crack-free Kaolin ceramics. The “Yellow Duck” Kaolin ceramic product was fabricated by combining SLS/CIP with colored glazing. The study shows a novel and promising approach to fabricate complex traditional ceramic products via SLS combined with CIP and sintering.     

Effect of zeolitic metal–organic framework on thermal,mechanical, and electrical properties of Ca/Zn-stabilized polyvinyl chloride

In order to enhance the heat stability of polyvinyl chloride (PVC), several heat stabilizing parameters such as metal content, antioxidant percentage, primary-to-secondary antioxidant ratios, stearic-to-acetylacetonate ratio, the amounts of pentaerythritol and β-diketone were studied using oven and Congo red tests. Results indicated that the percentage contribution of the calcium-to-zinc molar ratio in the static heat stability was 60.78%. Due to the synergistic effects of the calcium/zinc stabilizer and the zeolitic metal–organic framework (MOF) as an effective co-stabilizer, the heat stability was increased from 109 to 148 min. The EDX analysis was carried out to determine the mechanism of HCl gas absorption by the zeolitic imidazolate framework-8 (ZIF-8) existing in the PVC compound. Furthermore, the Ca/Zn thermal stabilizer showed poor electrical insulating properties, but the ZIF-8 improved electrical resistivity of the PVC compounds. Volume resistivity of ZIF-8 was significantly higher than that of the commonly used Ca/Zn stabilizers. Dynamic mechanical thermal analysis and tensile test of the PVC compound containing the ZIF-8 showed increased T_g and enhanced toughness.