Microscale Combustion Calorimeter Research Articles

A reactive melamine-DOPO based flame retardant for superior thermal stability and flame retardancy in rigid polyurethane foam

The flame-retardant effect of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives in reducing the flammability of polymeric materials are well known. In this study, flame-retardant rigid polyurethane foams (FR-RPUF) were synthesized using a melamine-DOPO-based flame-retardant (MDFR). Additionally, MDFR was also used for preparation of a flame-retardant elastomeric polyurethane (FR-PUE). The chemical structure and thermal properties of the FR-RPUF and FR-PUE samples were studied with Fourier transform infrared (FTIR), field emission-scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). TGA results revealed that the incorporation of MDFR into the PU matrix significantly increased the char residue. The char residue of FR-RPUF with 0.5 wt% MDFR increased from 4.75% to 44.36%, as compared to the pure RPUF. Results from the microscale combustion calorimeter (MCC) test illustrated that the peak of heat release rate (pHRR), total heat release (THR), and heat release capacity (HRC) of the FR-RPUF and FR-PUE samples were reduced, as compared to the pure PU samples. The pHRR value of FR-RPUF with 3 wt% of MDFR decreased 12%, as compared to the pure RPUF, while the pHRR was obtained 34% lower than of the pure PUE. Furthermore, FR-RPUFs successfully passed the UL94 testing, achieving a V-0 grade.

Inclusion of modified nano-magnesium hydroxide as an adjuvant flame retardant in the development of PLA/hydroxyapatite nanocomposites

For the preparation of thermal stable and flame-retardant polylactic acid (PLA) nanocomposites two new modified nano-structures including imide-carboxylated chitosan modified Mg(OH)2 (ICMH) and imide-silane functionalized hydroxyapatite nanoparticles (ISHA) were prepared. The structure, morphology, and properties of ICMH and ISHA were investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). The PLA nanocomposites were prepared via solution casting method. The results of Transmission electron microscopy (TEM) and SEM indicated a homogeneous structure for the PLA nanocomposites. The TGA results revealed that the presence of hydroxyapatite nanoparticles (HA) led to increase the thermal resistance of the PLA nanocomposites containing Mg(OH)2 (MDH). Compared to pure PLA, the Tmax value of the PLA sample containing 3 wt% of each filler (the PMH6 sample) enhanced from 364°C to 372°C. The results from the microscale combustion calorimeter (MCC) test illustrated that the key parameter values of the PLA nanocomposites were reduced, as compared to the pure PLA. The peak heat release rate (pHRR) and heat release capacity (HRC) values of PMH6 decreased 27% and 35%, respectively, as compared to the pure PLA. Also, flammability of PMH6 was reduced, as compared to the pure PLA, with UL-94 V-1 rating and LOI value 26.8%. Furthermore, the tensile strength of the mentioned sample increased from 36.04 MPa to 38.58 MPa.

Synthesis and Polymerization of the Bio‐Benzoxazine Derived from Resveratrol and Thiophenemethylamine and Properties of its Polymer

AbstractResveratrol and 2‐thiophenemethylamine have been employed in the synthesis of a novel tri‐functional benzoxazine (RES‐th) to develop the bio‐benzoxazine monomer. The chemical structure of the synthesized monomer is confirmed by various characterization technics. The polymerization behavior is monitored by in situ Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The in situ FTIR results reveal distinct reaction mechanisms for the three oxazine rings presented in RES‐th, with both ether and phenolic Mannich bridge structures observed in the products. The activation energy values of RES‐th are calculated to be 119.05, 120.97, and 119.44 kJ mol−1 by Kissinger, Ozawa, and Starink methods, respectively, which are all based on the heat flow curves at various heating temperatures. The thermal stability and flame retardancy of the resulting polybenzoxazine (poly(RES‐th)) are investigated by thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC). The values of Td5 and Td10 of polybenzoxazine are found to be 356 °C and 399 °C, respectively, with a char yield of 66.3% at 800 °C. The prepared polybenzoxazine also demonstrates nonflammability characteristics with the values of heat release capacity (HRC) and total heat release rate (THR) of 18.65 J (g K)−1 and 2.69 kJ g−1, respectively. These findings suggest that the thermoset, poly(RES‐th), is a promising candidate for fire‐resistant applications.

Biobased polysulfides prepared via inverse vulcanization with properties of intrinsic self-extinguishment and thermal remodeling

Developing high-performance polymers with intrinsic self-extinguishment and thermal remodeling from biobased resources has attracted increasing attention due to both safety and environmental concerns. In this work, two biobased crosslinkers, trieugenylcyanuric (TEC) and trieugenylphosphate (TEP), were designed and synthesized, and then five novel biobased polysulfides were synthesized via inverse vulcanization with different combinations of elemental sulfur, eugenol (Eug) and crosslinkers. The chemical structure of crosslinkers and polysulfides were confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopies (FT-IR), respectively. In addition, molecular weight of the linear polysulfide was measured by gel permeation chromatography (GPC). Various techniques, such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), microscale combustion calorimeter (MCC) and scanning electron microscopy (SEM) were used to characterize the properties of the polysulfides. Notably, the crosslinked polysulfide (P(S-TEP)) shows self-extinguishment with heat release apacity (HRC) value of 165 J/g⋅K and total heat release (THR) value of 7.9 kJ/g, and it can melt completely at 180℃ (thermal remodeling) without any extra treatment. Overall, the current work provides a high-efficiency and sustainable synthetic route access to a series biobased polysulfides with self-extinguishment and thermal remodeling.

Study of using cork powder as an adjuvant bio-flame retardant in acrylonitrile-butadiene-styrene flame retardant formulations

By having a challenging prospect of developing more environmentally friendly flame-retardant (FR) acrylonitrile-butadiene-styrene (ABS) formulations, an initial study related to the effect of combining ammonium polyphosphate (APP) with cork powder (C), a bio-waste of the cork industry on ABS-FR thermal stability and fire performance is proposed and discussed in the present work. ABS composites with a global filler weight content of 30 wt.% were prepared by using a melt-compounding process. Two different types of thermal decomposition behavior, assessed by means of thermogravimetric analysis (TGA), were observed for ABS/C/APP composites. For formulations with C/APP weight ratio < 1, the thermal decomposition of APP polyphosphate network was shifted to lower temperature. On the other hand, when C/APP ratio was ≥ 1, a new thermal decomposition (TD) step related to an earlier thermal decomposition of cork components was registered between 320 °C and 370 °C. Moreover, by means of Fourier-transform infrared spectroscopy (FTIR) analysis of the pyrolysis gasses, a broader temperature range of ammonia and water release was noticed when APP and C were simultaneously incorporated in ABS. In addition, a micro-scale combustion calorimeter (MCC) analysis revealed that replacing APP by cork led to a decrease of the heat release capacity (HRC) and an increase of the residue formation compared to when only APP was present in ABS composite. Furthermore, forced flaming fire characterization of ABS formulations, studied by means of cone calorimetry (CC), revealed that replacing 20 wt.% of APP by cork (ABS/20C/10APP) led to a similar fire performance to the ABS formulation with 30 wt.% of APP (ABS/30APP). A similar trend under horizontal UL-94 was observed, nevertheless, for the composite with cork in its composition no dripping was noticed. Additionally, by only replacing a 3 wt.% of APP (ABS/3C/27APP) by cork an optimum improvement in fire retardancy was achieved, with the highest efficiency in reducing the peak heat release rate (pHRR) of 21 % regarding ABS/30APP. These results have been related to the chemical interaction between APP and cork components in the condensed phase confirmed by the observance of a more intense P-O-C absorbance peak of the CC residue of ABS/3C/27APP, analyzed by means of FTIR. This composite also showed a more cohesive and expanded char layer, observed by scanning electron microscopy (SEM), which acted as a more efficient protective barrier, reducing heat and mass transfer phenomena during combustion which also led to the highest reduction in linear burning rate (LBR) under horizontal UL-94.

Effortless impregnation method for melamine formaldehyde foams exhibiting elevated thermal stability and exceptional flame retardant characteristics

AbstractMelamine‐formaldehyde (MF) foam, while intrinsically flame retardant, necessitates further refinement to meet stringent fire safety standards, particularly in terms of heat release rate and thermal stability. In this study, an innovative approach was adopted wherein an inorganic substance, potassium water glass (WG), was employed to create an encapsulation layer on the surface of the MF foam structure via a straightforward dip‐coating technique. The composite foam underwent a comprehensive analysis of its structure and flame retardant characteristics, using test evaluations such as micro‐scale combustion calorimeter (MCC) testing, cone calorimeter testing (CCT), and thermogravimetric‐Fourier infrared spectrometer (TG‐IR) assessments. It was found that the even coating of WG on the MF foam surface profoundly enhanced the foam's structural integrity. Utilizing the shielding properties of this inorganic layer, the hybrid foam's thermal stability experiences a remarkable augmentation. The peak of heat release rate (pHRR) and the total heat release rate (THR) of the MF foam experienced an impressive reduction of 85.2% and 78.8%, correspondingly. Notably, this advancement is concomitant with a substantial decrease of 39.2% in the total smoke release (TSR) and a notable amelioration in mechanical characteristics. Such developments undeniably broaden their application horizons across diverse domains.

Characterization of pyrolysis behavior for rigid polyurethane foam wastes with different densities through TGA-FTIR-DSC-MCC and Hill Climbing Optimization methods

Pyrolysis technology is one of the most effective thermal treatment methods recycling rigid polyurethane foam (RPUF) waste. To optimize pyrolysis recovery efficiency, quantifying the pyrolysis reaction kinetics and the heat required for the thermal treatment process is critical. This work focuses on establishing a systematic methodology to quantify pyrolysis reaction kinetics and thermodynamics for RPUF waste. RPUF waste with two different densities (RPUFρ100 and RPUFρ45) were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) under anaerobic atmosphere to measure mass and heat flow information. The obtained data were inversely analyzed using a numerical framework known as ThermaKin2Ds. Pyrolysis reaction mechanisms with four and three consecutive first-order reactions were developed to reproduce the TGA data for RPUFρ100 and RPUFρ45, respectively. The Hill Climbing Optimization Algorithm was employed to adjust the reaction kinetics for an improved agreement between the ThermaKin2Ds-reproduced and experimental data. Based on the heat flow data from DSC tests, the specific heat capacity of each condensed-phase component was determined by using the inverse modeling method. Additionally, the micro-scale combustion calorimeter was used to generate the heat release data that served as the target data for inversely determining the heats of complete combustion, hc, of each pyrolyzate. The established pyrolysis reaction models was further validated by predicting the TGA results collected under different external heating conditions. Subsequently, the generated combustion-inhibiting gases (CO2) and combustion-promoting gases (olefins, alkanes, carboxylic acids, etc.) were characterized through TGA coupled with Fourier-transform infrared spectroscopy (TG-FTIR). This allowed us to elucidate the gas-phase combustion phenomena observed in MCC experiments. This work provides a core set of parameters for optimizing the thermal treatment conditions of RPUF waste.

Synthesis, polymerization kinetics, and thermal properties of novel bismaleimides containing twisted structure

AbstractIn this study, two types of ortho‐oxazine functionalized bismaleimides with exceptional thermal properties and solubility were synthesized. The excellent solubility in many solvents is attributed to the stable twisted structure of the monomer. The monomer containing the cyano group showed enhanced solubility. It was found that the curing mode of ortho‐oxazine functionalized bismaleimide was autocatalytically cured. In situ FT‐IR spectroscopic studies indicated that the structure of bismaleimide resin undergoes a structural transformation at higher temperatures to form benzoxazole resin with enhanced thermal stability. The carbon residue rates of bismaleimide and benzoxazole resins at 800°C were 69% and 77%, respectively. The new bismaleimide and benzoxazole resins were analyzed using Microscale Combustion Calorimeter (MCC), and it was found that they also possess excellent flame‐retardant properties, specifically benzoxazole resin.

Influence of hollow glass microsphere on flame retardancy of ethylene-vinyl acetate/9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide composites

To improve combustion resistance properties of EVA resin, a series of flame-retardant EVA composites were prepared by melt blending 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with hollow glass microspheres (HGM), abbreviated as EVA/HGM/DOPO. Attributable to the capture of free radicals by DOPO, the promotion of carbonation by HGM and the synergistic effects between HGM and DOPO, EVA/HGM/DOPO composites (4.0 wt% DOPO) exhibit better flame retardant performance, thermal stability, and smoke suppression performance. The limited oxygen index (LOI) results show that 4.0 wt% DOPO is replaced by HGM (EVA-5), the LOI value can be increased to the maximum value of 24.2%, and the vertical combustion reaches the V-2 level. Moreover, the peak of heat release rate (PHRR) value of sample EVA-5 was reduced by 26.5% and 42.8% in the microscale combustion calorimeter (MCC) and cone calorimeter test (CCT) compared to the pure EVA, respectively. The digital photographs and mass loss curves also give positive evidence of the synergistic condensed phase flame-retardant effects between HGM and DOPO. Particularly, the maximum smoke density (Ds, max) of EVA-5 composite is the lowest. The thermogravimetry analysis (TGA) results revealed that HGM/DOPO/EVA samples show higher thermal stability at high temperatures than EVA samples. Furthermore, the addition of HGM improved Young’s modulus compared to EVA. These results suggested the synergetic effect of DOPO and HGM additions, the high efficiency of the proposed strategy and the wide application prospect of the produced EVA flame retardant composite materials.

Synthesis of Daidzein and Thiophene Containing Benzoxazine Resin and Its Thermoset and Carbon Material.

In this work, a novel bio-based high-performance bisbenzoxazine resin was synthesized from daidzein, 2-thiophenemethylamine and paraformaldehyde. The chemical structure was confirmed using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transform infrared spectroscopy (FT-IR). The polymerization process was systematically studied using differential scanning calorimetry (DSC) and in situ FT-IR spectra. It can be polymerized through multiple polymerization behaviors under the synergistic reaction of thiophene rings with benzopyrone rather than a single polymerization mechanism of traditional benzoxazines, as reported. In addition, thermogravimetric analysis (TGA) and a microscale combustion calorimeter (MCC) were used to study the thermal stability and flame retardancy of the resulting polybenzoxazine. The thermosetting material showed a high carbon residue rate of 62.8% and a low heat release capacity (HRC) value of 33 J/gK without adding any flame retardants. Based on its outstanding capability of carbon formation, this newly obtained benzoxazine resin was carbonized and activated to obtain a porous carbon material doped with both sulfur and nitrogen. The CO2 absorption of the carbon material at 0 °C and 25 °C at 1 bar was 3.64 mmol/g and 3.26 mmol/g, respectively. The above excellent comprehensive properties prove its potential applications in many advanced fields.

Phosphorus-free curcumin-derived epoxy resin with exceptional flame retardancy, glass transition temperature and mechanical properties

The fabrication of bio-based epoxy resins having better intrinsic flame retardancy and mechanical performances than petroleum-based epoxy thermosets is important for alleviation of energy and health concerns. In this study, bio-based monomer of diglycidyl ether of curcumin (DGEC) was successfully synthesized from a natural and renewable curcumin through a facile one-step process. The biocompatible epoxy resin obtained was then cured with 4,4′-diaminodiphenyl sulfone (DDS) and compared with petroleum-based diglycidyl ether of bisphenol A (DGEBA). The DGEC/DDS exhibited a higher glass-transition temperature (300 °C) than DGEBA/DDS (215 °C), indicating the outstanding heat resistance. The tensile strength of DGEC/DDS was 65.9 MPa, higher than that of DGEBA/DDS (56.1 MPa). Furthermore, DGEC/DDS showed excellent charring ability with char yield of 50.15% at 800 °C in N2, which was approximatively 3.5 times as much as that of the cured DGEBA/DDS (14.68%). Microscale combustion calorimeter (MCC) test demonstrated that the DGEC/DDS possessed lower heat release capacity (HRC, 130 J/gk), peak heat release rate (PHRR, 115.0 W/g) and total heat release (THR, 9.9 kJ/g), which were reduced by 80.2%, 74.8% and 59.4%, respectively, compared to those of DGEBA/DDS (658 J/gk, 457.3 W/g, 24.4 kJ/g). The DGEC/DDS passed the UL-94 test and attained the V-0 rating, revealing the good flame retardancy. This work provided an opportunity to prepare bio-based epoxy resins with better properties than DGEBA, which exhibited promising applications in high heat and flame retardancy fields.

Flame-retardant finishing of cotton fabrics using DOPO functionalized alkoxy- and amido alkoxysilane

In the present study, DOPO-based alkoxysilane (DOPO-ETES) and amido alkoxysilane (DOPO-AmdPTES) were synthesized by one-step and without by-products as halogen-free flame retardants. The flame retardants were applied on cotton fabric utilizing sol–gel method and pad-dry-cure finishing process. The flame retardancy, the thermal stability and the combustion ehaviour of treated cotton were evaluated by surface and bottom edge ignition flame test (according to EN ISO 15025), thermogravimetric analysis (TGA) and micro-scale combustion calorimeter (MCC). Unlike CO/DOPO-ETES sample, cotton treated with DOPO-AmdPTES nanosols exhibits self-extinguishing ehaviour with high char residue, an improvement of the LOI value and a significant reduction of the PHRR, HRC and THR compared to pristine cotton. Cotton finished with DOPO-AmdPTES reveals a semi-durability after ten laundering cycles keeping the flame-retardant properties unchanged. According to the results obtained from TGA-FTIR, Py-GC/MS and XPS, the major activity of flame retardant occurs in the condensed phase via catalytic induced char formation as physical barrier along with the activity in the gas phase derived mainly from the dilution effect. The early degradation of CO/DOPO-AmdPTES compared to CO/DOPO-ETES, triggered by the cleavage of the weak bond between P and C=O, as the DFT study indicated, provides the beneficial effect of this flame retardant on the fire resistance of cellulose.Graphical abstract

Facile Fabrication of Superhydrophobic and Flame-Retardant Coatings on Cotton Fabrics.

The hydrophilicity and inherent flammability of cotton textiles severely limit their usage. To solve these drawbacks, a superhydrophobic and flame-retardant (SFR) coating made of chitosan (CH), ammonium polyphosphate (APP), and TiO2-SiO2-HMDS composite was applied to cotton fabric using simple layer-by-layer assembly and dip-coating procedures. First, the fabric was alternately immersed in CH and APP water dispersions, and then immersed in TiO2-SiO2-HMDS composite to form a CH/APP@TiO2-SiO2-HMDS coating on the cotton fabric surface. SEM, EDS, and FTIR were used to analyze the surface morphology, element composition, and functional groups of the cotton fabric, respectively. Vertical burning tests, microscale combustion calorimeter tests, and thermogravimetric analyses were used to evaluate the flammability, combustion behavior, thermal degradation characteristics, and flame-retardant mechanism of this system. When compared to the pristine cotton sample, the deposition of CH and APP enhanced the flame retardancy, residual char, heat release rate, and total heat release of the cotton textiles. The superhydrophobic test results showed that the maximal contact angle of SFR cotton fabric was 153.7°, and possessed excellent superhydrophobicity. Meanwhile, the superhydrophobicity is not lost after 10 laundering cycles or 50 friction cycles. In addition, the UPF value of CH/APP@TiO2-SiO2-HMDS cotton was 825.81, demonstrating excellent UV-shielding properties. Such a durable SFR fabric with a facile fabrication process exhibits potential applications for both oil/water separation and flame retardancy.

Transparent and flame-retardant hybrid protective coating with high surface hardness, yet foldability

With the rapid development of flexible OLED display technology, Poly(ethylene terephthalate) (PET) has also received extensive attention as a protective film. However, it is still a challenge to endow PET with abrasion resistance and flame retardancy while maintaining transparency and flexibility. Here, we developed an epoxy-amine curing hybrid coating based on phosphorus-containing organic amine (DPNP) and ladderlike epoxy-oligosiloxane (AEOS). The ratio of DPNP and AEOS was changed to study the effect of phosphorus and silicon content on the performance of hybrid coatings. All the coatings were transparent. The PET/AE-DP3 sample achieved the limiting oxygen index of 28 % and exhibited self-extinguishing in vertical burning test. In microscale combustion calorimeter (MCC) test, the minimum peak heat release rate was 236.4 W/g with a reduction of 29.5 %, compared with pure PET. In addition, the AE-DP3 coating could withstand the abrasion of copper mesh and cheese cotton with a pencil hardness of 8H, and showed good foldability with a bending diameter of 5 mm. At the same time, the coating exhibited satisfactory adhesion without plasma treatment and good UV resistance. These results indicated the hybrid coating overcome the inherited weakness of PET film such as poor scratch-resistance and flammability, promoting the wider application of PET.

Waterborne hybrid polyurethane coatings containing Casein as sustainable green flame retardant through different synthesis approaches

Waterborne polyurethane (WPU) dispersions were prepared for flame retardant coatings. Specifically, alkoxysilane-capped polycaprolactone-based WPUs were synthesized employing the acetone process, and Casein, as a green and sustainable flame retardant additive, was added by two different methods (in situ and ex situ). These two strategies made possible to evaluate the effect of the Polyurethane/Casein interaction in the final properties of the dispersions and films. FTIR and solid-state 29Si NMR, confirmed the formation of the siloxane network during film generation process. The addition of Casein during the synthesis (in situ) resulted in a covalent bonding between the polyurethane and Casein, which significantly increased the particle size. However, the incorporation after phase inversion of the WPU (ex situ), did not change the particle size. Tensile tests revealed that the covalent bond promoted an increase in the brittleness of the material compared to ex situ approach due to a better dispersion of the Casein in the system. TGA results showed that Casein increased the thermal stability of all the coatings, especially of those obtained by the ex situ route. Moreover, and according to the microscale combustion calorimeter (MCC) and vertical burning test (UL-94) measurements Casein delayed the combustion of the material. Consequently, due to their characteristics, these Casein-WPU dispersions could potentially be used as combustion retardant coatings, where good physicochemical properties are essential for effective performance.

Wood-burning processes in variable oxygen atmospheres: Thermolysis, fire, and smoke release behavior

Revealing the effect of variable oxygen concentrations during wood-burning processes, have great importance for understanding the wood-burning behavior and drawing attention to the properties of burning lignocellulosic biomass. Herein, we focus on the thermal decomposition and burning behavior of wood in a variable oxygen atmosphere. The thermal-decomposition products and the kinetic analysis are verified combining the thermogravimetric analysis (TGA), TGA-FTIR, and TGA-MS. Although the main thermolysis products are similar at different oxygen atmospheres, the thermal-decomposition follow different reaction mechanisms, obtained by the calculated kinetic parameters. The combustibility is explored by the micro-scale combustion calorimeter that analyzes the heat release capacity, peak heat release rate, and total heat release. The oxygen concentrations affect the thermal-decomposition of woods and then influence the release of combustible fuels. Further, we construct a controlled atmosphere smoke chamber (CASC) to analyze the heat and smoke release during the burning of variable oxygen concentrations. The oxygen concentrations exhibit competition between inhibiting and promoting combustion, thus leading to the max smoke release at 19 vol% oxygen concentration. Overall, the combustion parameters at different oxygen concentrations obtained in our study reveal the role of oxygen concentration in the wood-burning processes and have positive implications for understanding the wood-burning behavior.

Preparation and enhanced flame retardancy of co‐polybenzoxazines containing diacetal structure

AbstractA comparative study on the flame retardancy of two polybenzoxazines with and without a diacetal structure, p(A) and p(B), is firstly carried out by microscale combustion calorimeter (MCC). It is proved that the presence of the diacetal structure can endow p(A) with good flame retardancy with a low heat release capacity (HRC). Then, the monomer of this diacetal containing p(A), A‐boz, is used to modify a typical diamine type benzoxazine (M‐boz) to improve its flame retardancy. The effects of A‐boz with different ratios on curing behavior, heat resistance and thermal stability of the co‐polybenzoxazines of M‐boz and A‐boz, p(M/A)s, are analyzed by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Furthermore, the flame retardancy of p(M/A)s is investigated by UL‐94 test, limiting oxygen index (LOI) and MCC, and the degradation and flame retardant mechanisms are investigated by scanning electronic microscopy (SEM), Raman spectra and TGA‐FTIR. When the addition amount of A is 20 wt%, the LOI value of p(M/A) is as high as 39.5% and its flame retardant rating reaches UL‐94 V‐0. In addition, the mechanical properties of p(M/A)s are tested. The results suggest that the Tg and char yield at 800°C in N2 of p(M/A)s increase from 210 to 243°C and 45% to 51%, respectively. This work suggests that the incorporation of the diacetal structure is an effective strategy to improve the flame retardancy of resins.

A comparative study on the physicochemical properties of tobacco ash from lit bright cigarettes with different cut tobacco fillers

The physicochemical properties of tobacco ash under different combustion pyrolysis simulation conditions and in different areas of lit cigarettes rolling from various cut tobacco fillers were investigated using optical image, cigarette ash integrity (CAI), chromatic aberration (CA), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), fourier transform infrared spectrometer (FTIR) and microscale combustion calorimeter (MCC), respectively. The study of ash appearance showed that lit cigarettes rolling from expanded cut stem (ECS) and reconstituted tobacco (RT) had lighter grey for the outer cigarette paper ash and darker color for the inner cut tobacco ash than those rolling from flue-cured tobacco (FCT) and expanded cut tobacco (ECT), respectively. Further study of CA and combustion rate indicated cigarette with ECS showed a highest burning rate and ΔL, followed in order by RT, ECT and FCT. SEM results displayed that various tobacco’s microstructures were still preserved at 450 °C, but fully broken at 750 °C and in the ash area of lit cigarettes, and then replaced by thin surface set with many particles for FCT, many connected lines coated with tiny particles for ECT, surface embedded with many rods for ECS and particle-containing surface for RT at 900 °C. EDX results illustrated that the above newly formed microstructures at 900 °C are mainly composed of O, C, Ca, Mg, K Cl, S and P, with a small amount of Fe, Al, Si, Mn and Co, of which some elements like K, S, P and Cl showed a migration into the gas phase. It can also obtained from EDX results that ECS left maximum C/O, K and Cl in the burning cone and tobacco ash area, followed in order by RT, FCT and ECT. FTIR study showed that carbonates have been produced substantially in the combustion cone for ECS, but just generated a little for FCT, ECT and RT. MCC analysis demonstrated that RT’s coke had the lowest thermal stability, while ECS’s coke began to release heat at lower temperature and ended at higher temperature in comparison with FCT and ECT. The correlation analysis showed that the ash appearance of burning cigarettes can be enhanced via a rise of K/Cl, K/S and K/(Cl+S) and a reduction of nicotine and ratio of sugar to nicotine.

Ethanol inducing self-assembly of poly-(thioctic acid)/graphene supramolecular ionomers for healable, flame-retardant, shape-memory electronic devices

In recent years, flexible electronic devices have great application potential in the fields of healthcare, VR virtual reality, electronic skin and intelligent robots. However, electronic devices fail during operation due to fatigue, corrosion or damage, making it difficult and expensive to maintain highly integrated portable/wearable electronic devices. In this study, highly healable, flame retardant, shape memorized supramolecular PTAZ/GO was fabricated by restricting the crosslinking of zinc ions, carboxyl graphene and poly-(thioctic acid) via self-polymerization in ethanol inducing self-assembly. The rich carboxyl groups associated with hydroxyl and disulfide groups in the system provide excellent self-healing efficiency and shape memory properties for supramolecular ionomers. The results of a microscale combustion calorimeter (MCC) test in this study showed a 65.3 % reduction in the peak heat release rate (pHRR) for ionomers compared to pure polymer, thus implying that ionic coordination cross-linking and GO nanosheets are beneficial for improving the fire safety of the materials. For the shape-memory device, the supramolecular elastomers can switch LED lights on and off by changing the shape, and the conductivity can be restored after reconnection of two damaged parts. Thus, the proposed materials have wide applications in electronic engineering.

A novel ablative material for thermal protection system: Carbon fiber/polysiloxane composites

Fiber reinforced composite materials are widely used in the aerospace industry due to their high strength to weight ratio. One of their applications is as an ablative material placed at the outermost layer of a thermal protection systems (TPS). A TPS requires the ablative material to have low density, low thermal conductivity, high temperature resistance, formation of a stable and high shear strength char. This paper introduces a carbon fiber (CF) reinforced polysiloxane (UHTR) composite material processed and fabricated in a laboratory environment. The fabrication method of this material is illustrated in detail. Thermal, ablation, flammability, and mechanical properties of the CF/UHTR material are characterized and compared to a commercial model ablative material, MX4926. MX4926 is a carbon fiber phenolic (CF/Ph) composite material manufactured by Solvay-Cytec. In this study, the carbon fiber used to make the CF/UHTR material is a PAN-based 8-harness fabric provided by Hexcel. The polymer matrix, UHTR, is a colorless semi-solid polysiloxane resin manufactured by Techneglas LLC. Raw materials are firstly made into CF/UHTR prepreg sheets through a hot-melt process and then compression molded into molding compound (MC) samples or two-dimensional (2D) laminates by a hot press. All samples for testing are post cured in a programmable oven at 350°C for 2 hours. The density of the fully-cured material is measured by the water displacement method. Thermal stability, flammability, and ablation properties of the material (in the format of MC) are characterized using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and oxyacetylene test bed (OTB) with three different heat fluxes. Mechanical properties of the material (in 2D laminates) are measured by a universal testing machine (UTM) to the ASTM standards. Testing results of the CF/UHTR material are compared with the commercial model ablative material, MX4926. Microstructures of the CF/UHTR material before and after mechanical and ablation tests are investigated and compared by an optical microscope and scanning electron microscopy (SEM) to further study the failure mode of the material.