Sol–gel treatments for enhancing flame retardancy and thermal stability of cotton fabrics: optimisation of the process and evaluation of the durability

Cotton fabrics have been treated by sol–gel processes in order to create a silica compact coating on the fibres to enhance their thermal stability and flame retardancy. The effect of process parameters such as silica precursor:water molar ratio and drying conditions (temperature and time) has been thoroughly investigated, aiming at optimization of target properties. Thermogravimetry and cone calorimetry have been respectively used to assess thermal stability and combustion behaviour of treated fabrics. Coating durability to different washing programmes has been evaluated as well.     

Influence of surface activation by plasma and nanoparticle adsorption on the morphology, thermal stability and combustion behavior of PET fabrics

Plasma surface activation at different process parameters (namely, power and etching time) has been combined with nanoparticle adsorption (i.e., a natural montmorillonite) in order to improve the thermal stability and flame retardancy of PET fabrics. Scanning electron microscopy coupled to elemental analysis has put in evidence a direct relationship between the distribution of nanoparticles on fibers and process parameters. The presence of the above nanoparticles affects the thermal stability of fabrics in air, as assessed by thermogravimetric analysis: a delay of the mass loss process has been observed for the treated samples.Combustion behavior has been investigated by cone calorimetry: plasma activated fabrics have shown a remarkable improvement in terms of time to ignition (up to 104%) and a slight reduction of the heat release rate (ca. 10%) as compared to neat PET.     

表面化学接枝改性阻燃棉织物的制备与性能

采用高碘酸钠对棉织物表面进行选择性氧化生成醛基,选取乙二胺与醛基反应,通过膦氢化加成反应将阻燃剂亚磷酸二甲酯接枝到棉织物表面,最后通过三羟甲基三聚氰胺对棉织物表面进行接枝改性,制备了含三羟甲基三聚氰胺/乙二胺/亚磷酸二甲酯阻燃棉织物.通过傅里叶红外光谱（FTIR）对改性后棉织物的结构进行了表征,通过极限氧指数（LOI）测试研究了其阻燃性能,通过锥形量热测试研究了其燃烧行为,通过在40℃皂水中洗涤10次考察了其耐水性能,通过扫描电子显微镜测试了其表面及燃烧后炭层的形貌.研究结果表明,经表面改性后,棉织物的LOI值由（19.5±1.0）%提高到了（43.1±1.0）%,经耐水洗测试后,LOI值仅下降至（42.6±1.0）%,保持了非常好的阻燃性能,表明通过表面接枝方法制备的三羟甲基三聚氰胺/乙二胺/亚磷酸二甲酯阻燃棉织物具有非常好的耐水洗性能.表面阻燃改性提高了棉织物在燃烧过程中的成炭性能,形成的连续膨胀的炭层较好地保护了内部织物,抑制了织物的降解和燃烧,从而提高了棉织物的阻燃性能.     

Tailoring of multifunctional cellulose fibres with “lotus effect” and flame retardant properties

This research aimed to create multifunctional cellulose fibres with water- and oil-repellent, self-cleaning, and flame retardant properties. A sol mixture of fluoroalkyl-functional siloxane, organophosphonate and methylol melamine resin was applied to cotton fabric by the pad-dry-cure method. Successful coating was verified by atomic force microscopy and Fourier transform infrared spectroscopy. The functional properties of the coated fibres were investigated using the static contact angles of water and n-hexadecane, the water sliding angles, the vertical test of flammability, the limiting oxygen index, and simultaneous thermal analysis. The results reveal that a homogeneous composite inorganic–organic polymer film formed on the cotton fabric surface exhibited the following properties: static contact angle of water of 150° and of n-hexadecane of 128°, water sliding angle of 10°, limiting oxygen index of 34 %, and high thermal stability. These results demonstrate the synergistic activity of the compounds in the coating, which resulted in the creation of a “lotus effect” on the fabric surface as well as excellent flame retardancy and thermal stability.     

Studies on the properties of polypropylene with a new silicon‐containing intumescent flame retardant

A new intumescent flame retardant (PSiNII), which contains silicon, phosphorus, and nitrogen elements, has been synthesized and incorporated into polypropylene (PP). Its effect on the properties of PP is investigated based on flame retardancy, thermal properties, mechanical properties, and morphologies. The flame retardancy is evaluated by the limiting oxygen index value. The thermal properties (oxidative behaviors and thermal stability) are investigated by thermogravimetric analysis under nitrogen and air atmosphere. The mechanical properties are researched based on the maximum tensile stress and relative strain at break. The morphologies of PP/PSiNII are studied by the scanning electron micrograph. Their flame retardancy and thermal stability are improved by introducing PSiNII. PP/PSiNII blends can achieve high fire performance and keep high mechanical property at the same time. During a fire, the melt‐dripping behaviors of PP‐containing PSiNII are improved. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2548–2556, 2005     

Synergistic effect of DOPO immobilized silica nanoparticles in the intumescent flame retarded polypropylene composites

The synergistic effect of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) immobilized silica (SiO₂‐DOPO) nanoparticles with an intumescent flame retardant (IFR) on the flame retardancy of polypropylene (PP) was investigated by UL 94 vertical tests and limiting oxygen index (LOI) measurements. It was found that the PP/IFR composites (25 wt%) achieved the UL94 V0 grade and LOI increased to 32.1 with an incorporation of 1.0 wt% SiO₂‐DOPO nanoparticles. Based on thermogravimetric analysis, scanning electronic microscopy and rheological analysis, it is speculated that three factors are mainly contributed to the improvement of the flame retardancy. First, the thermal stability of PP/IFR composites was improved by incorporating SiO₂‐DOPO nanoparticles. Second, the presence of SiO₂‐DOPO nanoparticles could induce the formation of a continuous char skin layer during combustion. The compact char layer could effectively impede the transport of bubbles and heat. Third, rheological analysis indicated that SiO₂‐DOPO nanoparticles could increase viscosity of the PP/IFR composites, which was also benefited to increase flame retardancy. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of kaolin on the thermal stability and flame retardancy of polypropylene composite

Kaolin clay was introduced into an intumescent flame retardant (IFR) system containing ammonium polyphosphate as an acid source and pentaerythritol as a carbonization agent in order to improve the thermal stability and flame retardancy of polypropylene (PP) composite. The flame retardancy and smoke suppression was evaluated by the limiting oxygen index, vertical burning UL‐94, and cone calorimeter (CONE) tests. The limiting oxygen index value was increased from 30 to 33 at the presence of 2 phr kaolin. The peak heat release rate value decreased from 1002 kW/m² of neat PP to 318 kW/m² of PP/40 phr IFR and then to 222 kW/m² of PP/38 phr IFR/2 phr kaolin. The time of the peak heat release rate was significantly prolonged after the introduction of kaolin. The morphology of char after combustion was characterized by a scanning electron microscope, and it revealed more compact char structure that was obtained at the presence of kaolin. The mechanism of kaolin on improving the retardancy and smoke suppression of PP/IFR composite was proposed on the basis of X‐ray photoelectron spectroscopy analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Synergistic effect of graphene oxide and boron-nitrogen structure on flame retardancy of natural rubber/IFR composites

In this paper, GO-BN(graphene oxide grafted boron nitride) was synthesized from graphene oxide and boron nitride by silane coupling agent KH550. Furthermore, GO-BN and intumescent flame retardant (IFR) were added into natural rubber (NR) simultaneously to improve its flame retardancy. The structure of GO-BN was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The analysis showed that GO-BN was successfully synthesized. The enhanced flame retardancy performance of flame retardant natural rubber (FRNR) was evaluated by limiting oxygen index (LOI) and UL-94 tests. Moreover, the combustion action of FRNR in fire was evaluated by cone calorimetry. Notably, the results showed that the sample with a GO-BN content of 12 phr showed the best flame retardancy performance. The heat release rate (HRR) and total heat release rate (THR) were remarkably decreased by 42.8% and 19.4%, respectively. Carbon residues were analyzed by infrared spectroscopy and scanning electron microscopy, which showed that GO-BN and IFR had a synergistic catalytic effect. The formation of compact thermal stable carbon layer after combustion was the key to protect engineering materials from combustion.     

Polyester-supported Chitosan-Poly(vinylidene fluoride)-Inorganic-Oxide-Nanoparticles Composites with Improved Flame Retardancy and Thermal Stability

Polyester(PET) was pre-activated by atmospheric air plasma and coated by various inorganic oxide nanoparticles(MOx) such as titanium dioxide(TiO2), zinc oxide(ZnO), and silicon oxide(SiO2), using poly(vinylidene fluoride)(PVDF) and chitosan(CT) as binders. The resulting PET-PVDF-MOx-CT composites were thermally compressed and then characterized by scanning electron microscopy, Fourier infrared spectroscopy, thermal gravimetric analysis, and flame retardancy(FR) ability tests. PET modifications resulted in more thermally stable and less harmful composites with weaker hazardous gas release. This was explained in terms of structure compaction that blocks pyrolysis gas emissions.CT incorporation was found to reduce the material susceptibility to oxidation. This judicious procedure also allowed improving flame retardancy ability, by lengthening the combustion delay and slowing the flame propagation. Chitosan also turned out to contribute to a possible synergy with the other polymers present in the synthesized materials. These results provide valuable data that allow understanding the FR phenomena and envisaging low-cost high FR materials from biodegradable raw materials.     

Study of flammability and thermal properties of high-impact polystyrene nanocomposites

To increase thermal stability and flammability of high-impact polystyrene (HIPS) nanocomposites with silica nanoparticles and two types of polyphosphate flame retardants were prepared by extrusion. Nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, limiting oxygen index (LOI) analysis and the evaluation of mechanical properties. It was found that organic polyphosphate in combination with silica increased thermal stability and fire retardancy by 50% in LOI test. Morphology characterization revealed existence of crystalline order which affected mechanical properties; tensile strength was approximately the same as virgin HIPS while elasticity was sharply decreased. Ammonium polyphosphate did not affect mechanical properties as much as the organic material but was not equally efficient in flame retardancy which was just marginally increased.     

Functionalization of cotton fabrics with corona/air RF plasma and colloidal TiO2 nanoparticles

This study discusses the possibility of using a corona discharge at atmospheric pressure and air RF plasma at low pressure for the cotton fibre activation prior to deposition of colloidal TiO₂ nanoparticles in order to enhance antibacterial, UV protective and self-cleaning properties. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of TiO₂ nanoparticles on the surface of cotton fibres. XPS elemental mapping indicated that TiO₂ nanoparticles were more evenly distributed across the surface of untreated and corona pre-treated cotton fabrics in comparison with RF plasma pre-treated fabric. Atomic absorption spectroscopy measurements revealed that the equivalent total content of TiO₂ in the cotton fabrics pre-treated by corona and RF plasma was 31% higher than in the fabric that did not undergo any treatment prior to loading of TiO₂ nanoparticles. In order to achieve maximum bacteria (Gram-negative bacteria Escherichia coli) reduction, untreated cotton fabric had to be loaded with colloidal TiO₂ nanoparticles twice, but only once following corona or RF plasma pre-treatment. Deposition of TiO₂ nanoparticles onto cotton fabrics provided maximum UV protective rating of 50+. Extraordinary photocatalytic activity of TiO₂ nanoparticles deposited onto cotton fabrics was proved by self-cleaning of blueberry juice stains and photodegradation of methylene blue in aqueous solution under UV illumination.     

Synergistic Effect Between Sb2O3 Nanoparticles–Trichloromelamine and Carbon Nanotube on the Flame Retardancy and Thermal Stability of the Cellulose Acetate

Sb₂O₃ nanoparticles were synthesized via a simple surfactant-free sonochemical reaction. Multi-walled carbon nanotubes (MWCNT) have been successfully functionalized with amino groups. Cellulose acetate (CA) as a polymeric matrix was choosing in this work. In order to improve the thermal stability and flame retardancy of the CA, nanoparticles, aminated-MWCNT and trichloromelamine (TCM) were added to the polymeric matrix. The nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and UL-94 analysis. Flame retardancy of the nanocomposite was improved as a result of synergistic effect between Sb₂O₃ and TCM. Result show that thermal decomposition of the nanocomposites was shifted towards higher temperatures.     

Synthesis and thermal behaviour of polyamide 6/bentonite/ammonium polyphosphate composites

In order to achieve acceptable levels of flame retardancy of polymers, phosphorus-based flame retardant (FR) additives at about 20-30% w/w are required which is too high for conventional synthetic fibres. To know whether more finely sized particles of conventional FRs with or without nanoclay are more effective at the same concentration, composites of PA6 with bentonite and ammonium polyphosphate (APP) have been prepared by melt processing in a twin-screw extruder. XRD peaks and TEM images of PA6/Org-bentonite composite show partially ordered intercalation and ordered exfoliation. Thermal analysis in He shows that thermal stability of PA6 nanocomposite has increased by 18 °C compared with pure PA6 during degradation after 425 °C but it has decreased by 100 °C on inclusion of APP in PA6/nanoclay composites. The char yield is increased by 20% in PA6/bentonite/APP composites. No effect on thermal stability or char yield is observed by reducing the particle size of APP.     

Synergistic effect of combined dimethyl methylphosphonate with aluminum hydroxide or ammonium polyphosphate retardant systems on the flame retardancy and thermal properties of unsaturated polyester resin

A series of flame-retardant unsaturated polyester resin (UPR) were prepared by the addition of dimethyl methylphosphonate (DMMP) with various amounts of aluminum hydroxide (ATH) or ammonium polyphosphate (APP) as the flame retardants. The combustion resistance effects of ATH/DMMP and APP/DMMP systems were evaluated by limiting oxygen index test and vertical burning test (UL-94). The thermal properties of UPR were investigated by thermogravimetric analysis. The structure of char was observed by scanning electron microscopy. DMMP incorporated with ATH or APP improved the flame retardancy and thermal properties of UPR. However, the fire-retardant mechanism of these two systems were different: The ATH/DMMP system provided synergistic effect in charring property of the UPR, produced great amount of residual char, and thus revealed the excellent flame retardancy. The APP/DMMP system further improved the flame retardancy of the UPR due to the change in the residual char structure rather than the increase in the production of char.     

Effect of hybrid phosphorus-doped silica thin films produced by sol-gel method on the thermal behavior of cotton fabrics

The aim of this work was to prepare hybrid organic-inorganic silica thin films to provide cotton fabrics with flame retardant properties and to investigate the films’ influence on the thermal and burning behavior of the treated samples. The fabrics were modified with three different sols in order to study the effect of pure silica sol-gel precursor, γ-aminopropyltriethoxysilane (APTES), and that of the hybrid sols consisting of the APTES and the phosphorus compound diethylphosphite. Furthermore, in order to improve the cross-linking degree and the phosphorus-nitrogen synergistic effect on flame retardancy of the P-doped silica thin film the melamine-based resin was added in the third sol. To evaluate the chemical structure of the coating material, pure xerogels of the treatment solutions were applied to glass slides and tested by ATR FT-IR spectroscopy. The cotton fabrics were impregnated with the sols by a padding-squeezing process and then dried. Thermal behavior of the treated cotton samples was investigated by thermogravimetric/differential scanning calorimetry analysis (TGA-DTG/DSC) and compared to the untreated one. The flame retardancy was tested according to the ASTM D 1230 standard method. The results showed a substantial enhancement of char-forming properties and flame retardancy for the fabrics modified with the thin films.     

Cotton fabrics treated with hybrid organic–inorganic coatings obtained through dual-cure processes

Cotton fabrics were treated with a hybrid organic–inorganic coating obtained through a dual-cure process, i.e. a photopolymerization reaction followed by a thermal treatment for promoting the formation of silica phases through a sol–gel process. To this aim, different amounts of a silica precursor were added to an acrylic UV-curable formulation in the presence of a suitable coupling agent. The thermo-mechanical properties of the treated fabrics were investigated and correlated to the composition and morphology of the hybrid organic–inorganic system. Furthermore, their flame retardancy and combustion behavior were evaluated by flammability tests and cone calorimetry and compared with the performances of pure cotton.     

Thermal decomposition and burning behavior of cellulose treated with ethyl ester phosphoramidates: Effect of alkyl substituent on nitrogen atom

This research explores the structural effect of phosphoramidates as flame retardants (FRs) for cotton cellulose. Flame retardant (FR) and thermal decomposition actions of phosphate such as triethyl phosphate (TEP), primary phosphoramidate such as diethyl phosphoramidate (DEPA) and secondary phosphoramidates such as phosphoramidic acid, N(2-hydroxy ethyl) diethylester (PAHEDE), diethyl ethyl phosphoramidate (DEEP) and diethyl 2-methoxyethylphosphoramidate (DEMEP) on cotton cellulose were investigated. Limiting oxygen index (LOI) of treated cotton cellulose showed that all phosphoramidates exhibited better flame retardant properties as compared to TEP. Secondary phosphoramidate PAHEDE had better flame retardant properties as compared to DEMEP and DEEP which indicate that flame retardancy of secondary phosphoramidates is structure related. Test performed on pyrolysis combustion flow calorimeter (PCFC) for treated cellulose showed higher reduction in heat of combustion for efficient FRs (PAHEDE, DEPA). Evolved gas analysis using thermogravimetric analyzer-Fourier transform infrared spectroscopy (TGA-FTIR) and thermogravimetric analyzer-mass spectrometer (TGA-MS) of treated cellulose showed that phosphoramidates could catalyze the dehydration and char formation of cellulose at a lower temperature. The enhanced flame retardant action of phosphoramidate may be due to the catalytic thermal decomposition of the phosphoramidate structure to produce acidic intermediates which could react with cellulose to alter its thermal decomposition.     

Flame retardancy and thermal degradation of intumescent flame retardant polypropylene material

The flame retardancy and thermal degradation properties of polypropylene (PP) containing intumescent flame retardant additives, i.e. melamine pyrophosphate (MPyP) and charring‐foaming agent (CFA) were characterized by limiting oxygen index (LOI), UL 94, cone calorimeter, microscale combustion calorimetry, and thermogravimetric analysis (TGA). It has been found that the PP material containing only MPyP does not show good flame retardancy even at 30% additive level. Compared with the PP/MPyP binary system, the LOI values of the PP/MPyP/CFA ternary materials at the same additive loading are all increased, and UL 94 rating is raised to V‐0 from no rating (PP/MPyP). The cone calorimeter results show that the heat release rate and mass loss rate of some ternary materials decrease in comparison with the binary material. The microscale combustion calorimetry results indicate that the sample containing 22.5 wt% MPyP and 7.5 wt% CFA has the lowest heat release rate among all samples. The TGA results show that the thermal stability of the materials increases with the addition of MPyP, while decreases with the addition of CFA. Copyright © 2009 John Wiley & Sons, Ltd.     

Poly(vinyl alcohol)/melamine phosphate composites prepared through thermal processing: thermal stability and flame retardancy

Poly(vinyl alcohol)/melamine phosphate composites (PVA/MP) as a novel halogen‐free, flame‐retardant foam matrix were prepared through thermal processing, and then their thermal stability and flame retardancy were investigated by thermo‐gravimetric analysis, micro‐scale combustion calorimeter, cone calorimeter, vertical burning test, and limiting oxygen index (LOI) test. It was found that the thermal stability and combustion properties of the PVA/MP composites could be influenced by the addition of MP. Compared with the control PVA sample (B‐PVA), in the PVA/MP (75/25) composites, the temperature at 5% mass loss (T_5%) decreased about 10°C, the residual chars at 600°C increased by nearly 27%, the temperature at the maximum peak heat release rate (T_P) shifted from 292°C to 452°C, and the total heat released and the heat release capacity (HRC) decreased by 28% and 14%, respectively. Moreover, the PVA/MP composites could reach LOI value up to 35% and UL94 classification V‐0, showing good flame retardancy. At the same time, both Fourier transform infrared and X‐ray photoelectron spectroscopy spectra of the residual chars from the PVA/MP composites demonstrated that the catalytic effect of MP on the dehydration and decarboxylation reactions of PVA, and the chemical reactivity of MP during the chars‐forming reactions could be used to account for the changed thermal stability and flame retardancy of the PVA/MP composites. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of nanosized carbon black on thermal stability and flame retardancy of polypropylene/carbon nanotubes nanocomposites

Nanosized carbon black (CB) was introduced into polypropylene/carbon nanotubes (PP/CNTs) nanocomposites to investigate the effect of multi‐component nanofillers on the thermal stability and flammability properties of PP. The obtained ternary nanocomposites displayed dramatically improved thermal stability compared with neat PP and PP/CNTs nanocomposites. Moreover, the flame retardancy of resultant nanocomposites was greatly improved with a significant reduction in peak heat release rate and increase of limited oxygen index value, and it was strongly dependent on the content of CB. This enhanced effect was attributed mainly to the formation of good carbon protective layers by CB and CNTs during combustion. Rheological properties further confirmed that CB played an important role on promoting the formation of crosslink network on the base of PP/CNTs system, which were also responsible for the improved thermal stability and flame retardancy of PP. Copyright © 2013 John Wiley & Sons, Ltd.