Showing papers on "Charring published in 2021"

MXene based core-shell flame retardant towards reducing fire hazards of thermoplastic polyurethane

Abstract: Amounts of heat and toxic fumes are released during the combustion of polymeric materials, which severely threats to the human health and causes the environmental pollution. Therefore, it is vital to find an effective way to address these problems. Herein, titanium carbide (Ti3C2Tx) and chitosan (CS) were firstly adopted to functionalize ammonium polyphosphate (APP) via the microencapsulation and layer-by-layer assembly. Afterwards, the as-synthesized core-shell-structured hybrid (APP@CS@Ti3C2Tx) was used to enhance the interface compatibility, thermal stability and fire safety of thermoplastic polyurethane (TPU) composites. The results demonstrated that the APP@CS@Ti3C2Tx hybrid presented a strong interface interaction with the TPU matrix. Besides, TPU/APP@CS@Ti3C2Tx composites exhibited the improved thermal stability. The TPU composite containing 9.5APP@CS@0.5Ti 3C2Tx achieved V-0 rating in the UL-94 testing. The cone calorimetry results illustrated that introduction of 9.5APP@CS@0.5Ti 3C2Tx into TPU caused remarkable reduction in the total heat release (73.0%) and total smoke release (77.3%). Furthermore, the total carbon monoxide yield and total carbon dioxide yield of TPU/9.5APP@CS@0.5Ti3C2Tx were significantly decreased by 75.3% and 75.3%, respectively, compared to those of pure TPU. The synergistic charring effect between APP@CS and Ti3C2Tx, the thermal oxidization action and “tortuous path” effect of Ti3C2Tx nanosheets combined with the trapping effect of APP@CS resulted in the dramatically improved fire resistance of the polymeric material. This work offers an innovative strategy to fabricate the high-performance polymer composites with superior fire safety.

Convenient synthesis of one-dimensional a-SEP@LDH via self-assembly towards simultaneously improved fire retardance, mechanical strength and thermal resistance for epoxy resin

Abstract: It is essential to develop a class of EP composite with improved fire retardance, mechanical strength and thermal resistance performances for some practical applications, such as in aeronautic and automobile fields. Due to the highly tunable structure of layered double hydroxides (LDHs), transition metals Ni2+ and Fe3+ were selected as the cation components considering their excellent catalytic charring ability. To overcome the easy agglomeration of LDH during polymer process, sepiolite nanofiber (SEP) was used as a carrier for LDH and thus a novel low-cost one-dimensional flame retardant a-SEP@LDH was successfully synthesized via facile self-assembly. With the addition of 2.3 wt% a-SEP@LDH alone, EP composite owns a V-1 rating in UL-94 test, an LOI value of 31.1%, 21% reduction of peak heat release rate and decreased 16.0% total smoke production. Additionally, the total carbon monoxide production has been decreased by 25.3%. Combining the analyses of the char residue and thermogravimetric infrared spectrometry (TG-FTIR) of EP/a-SEP@LDH systems, the flame-retardant mechanism has been drawn as follows: a) physical solidified char residue by sepiolite nanofibers; b) reinforced char residue thanks to the catalytic charring effect of both Ni/Fe alloy catalyst (originated from partially reduced oxide metals) and Bronsted acid sites in sepiolite. Moreover, the tensile strength and glass transition temperature of EP composite have been enhanced simultaneously. In a nutshell, it is an economically effective channel targeting to improve the comprehensive properties of EP through loading Ni–Fe LDH assisted by sepiolite nanofibers.

Silicone filled halloysite nanotubes for polypropylene composites: Flame retardancy, smoke suppression and mechanical property

Abstract: The halloysite nanotubes (HNTs-Si) was filled with poly-siloxane and introduced into polypropylene (PP) composite containing intumescent flame retardants (IFR) in order to simultaneously improve the fire performance and mechanical properties. The fire behavior investigation indicated that the peak heat release rate and the peak smoke release rate of PP/IFR sample containing HNTs-Si were reduced by 31% and 26% respectively compared with that of the PP/IFR sample containing HNTs. The elongation at break was greatly increased by the presence of HNTs-Si. The charring mechanism analysis suggested that HNTs-Si was capable of keeping the original tube structure and twisting with degraded PP chains to form “fiber-like” compact char layers in the high temperature range. Consequently, the combination of HNTs-Si and IFR exhibited excellent heat and smoke suppression during the combustion of PP composite. This work has proved that HNTs-Si is an effective synergist in producing flame retardant PP composites with comprehensive properties.

Thermal Response of Timber Slabs Exposed to Travelling Fires and Traditional Design Fires

Abstract: Engineered timber is an innovative and sustainable construction material, but its uptake has been hindered by concerns about its performance in fire Current building regulations measure the fire performance of timber using fire resistance tests In these tests, the charring rate is measured under a series of heat exposures (design fires) and from this the structural performance is deduced Charring rates are currently only properly understood for the heat exposure of a standard fire, not for other exposures, which restricts the use of performance-based design This paper studies the charring rates under a range of design fires We used a multiscale charring model at the microscale (mg-samples), mesoscale (g-samples), and macroscale (kg-samples) for several wood species exposed to different heating regimes and boundary conditions At the macroscale, the model blindly predicts in-depth temperatures and char depths during standard and parametric fires with an error between 5% and 22% Comparing simulations of charring under travelling fires, parametric fires, and the standard fire revealed two findings Firstly, their charring rates significantly differ, with maximum char depths of 42 mm (travelling), 46 mm (parametric), and 59 mm (standard fire), and one (standard fire) to four (travelling fire) charring stages (no charring, slow growth, fast growth, steady-state) Secondly, we observed zero-strength layers (depth between the 200 °C and 300 °C isotherm) of 7 to 12 mm from the exposed surface in travelling fires compared to 5 to 11 mm in parametric fires, and 7 mm in the standard fire Both traditional design fires and travelling fires, therefore, need to be considered in structural calculations These results help engineers to move towards performance-based design by allowing the calculation of charring rates for a wide range of design fires In turn, this will help engineers to build more sustainable and safe structures with timber

Geometric Effects on Charring Ablator: Modeling the Full-Scale Stardust Heat Shield

Abstract: The multidimensional geometric effects within the heat shield of the Stardust sample return capsule are studied over its reentry trajectory, using a material response solver. The solver models mate...

Sustainable and efficient flame retardant materials for achieving high fire safety for polystyrene composites

Abstract: Novel porous carbon sheets were developed as green, renewable, cost-effective, and efficient flame retardant material for thermoplastic polymers. Renewable porous graphite sheets were directly obtained from one pot recycling process of agriculture bio-waste sugar beet leaves at low temperature and used as scalable and efficient flame retardant for polystyrene. Thus providing dual benefits to environment for recycling of harmful bio-waste and developing new scalable and efficient flame retardant. The developed renewable flame retardant has specific surface area of 214 m2 g−1 and average pore size of 2.1 nm in addition to natural doping of precious metal residues. The sustainable porous graphite sheets were dispersed well in polymer matrix and their mass loading was altered and optimized giving rise to different polymer composites. Furthermore, different mass loadings of magnesium hydroxide were incorporated with porous graphite sheets in polymer composite. The thermal stability and flammability measurements of developed polymer composites elucidated the significant improvement in fire safety and flame retardancy of developed polystyrene composites. Thus, the reduction in peak heat release rate (PHRR) and total heat release rate (THR) of polymer composites were found to be 62 and 48%, respectively. This is in addition to a significant reduction in rate of burning and improvement in limiting oxygen index (LOI) value achieving reduction and improvement by 84 and 33%, respectively. Additionally, excellent suppression of emission of CO2 and CO gases was recorded (~ 40%). The outstanding flame retardancy and toxic gases suppression effect of developed porous graphite sheets was attributed to its charring capability and porous structure effect in conjunction to natural doping of desirable elemental composition. This study presents a new tool for production of scalable, green, renewable, and cost-effective flame retardant and smoke suppressant materials for thermoplastic polymers.

An intumescent flame-retardant layer with β-cyclodextrin as charring agent and its flame retardancy in jute/polypropylene composites

Abstract: A flame-retardant jute/PP composite with excellent flame retarding and mechanical properties was prepared by the surface powder spraying process. The flame-retardant layer used the green and pollution-free β-cyclodextrin as a char agent. To improve the char forming ability of β-cyclodextrin, ammonium polyphosphate (APP) and melamine (MEL) were also used as acid source and a blowing agent, respectively. The results indicated that the char forming ability of β-CD could be improved by the reaction between β-CD and APP. The composite with 20% flame retardants containing β-CD, APP and MEL (1:2:1) showed the better flame-retardant properties. The LOI value of the composite increased to 27.8%, which reached the second fire resistance according to Japan's JISD 1201-77 standard, and the self-extinguishing time reached to 37 s. Compared with pure jute/PP, the PHRR value and Av-EHC value of the composites were reduced by 50% and 21%, respectively. The carbon residual at 700 °C was increased by 10.9%. The tensile strength and bending strength were increased by 5% and 19%. These results revealed that the flame retardancy, thermal stabilities and mechanical properties of composites containing β-CD/APP/MEL system were significantly improved by the surface powder spraying method.

Surface Characteristics of One-Sided Charred Beech Wood.

Abstract: The aim of this paper was to analyze selected properties of beech wood (Fagus sylvatica L.) treated by one-sided surface charring. Specimens were one-side charred with a hot plate using several time-temperature combinations (from 200 to 400 °C). Characteristics such as colour, discoloration, surface roughness, fire resistance, total carbohydrate content at several wood layers and decay resistance were evaluated. Surface charring was applied to the radial and tangential surfaces. Colour measurements showed that the surface of the wood turned grey due to charring. In addition to colour measurements, other experiments showed significant differences between radial and tangential specimens due to their different structures. The higher the temperature used in treating them, the lower the roughness values for radial specimens, while the trend for tangential specimens was the opposite. A smoother surface is more fire resistant, so radial specimens are generally better in this regard. Tangential specimens are more susceptible during preparation to forming cracks that impair flame resistance because a continuous protective densified layer is not formed. The determination of total carbohydrates revealed significant changes at various wood depths after surface charring. These changes were more predictable in radial specimens due to the annual ring orientation, because each layer consisted of a similar earlywood/latewood ratio. Finally, when decay resistance was assessed, weight loss was found to be lower in all specimens than in the references. The results suggest that charring at a particular combination of temperature and time improved the investigated properties of the surface-modified beech.

The Preparation and Characterization of Polylactic Acid Composites with Chitin-Based Intumescent Flame Retardants.

Abstract: In this work, a novel intumescent flame retardant (IFR) system was fabricated by the introduction of chitin as a green charring agent, ammonium polyphosphate (APP) as the acid source, and melamine (MEL) as the gas source. The obtained chitin-based IFR was then incorporated into a polylactic acid (PLA) matrix using melt compounding. The fire resistance of PLA/chitin composites was investigated via the limiting oxygen index (LOI), UL-94 vertical burning, and cone calorimeter (CONE) tests. The results demonstrated that the combination of 10%APP, 5%chitin and 5%MEL could result in a 26.0% LOI, a V-0 rating after UL and a 51.2% reduction in the peak heat release rate during the CONE test. Based on the mechanism analysis from both the morphology and the chemical structure of the char, it was suggested that chitin was a promising candidate as a charring agent for chitin reacted with APP and MEL with the formation of an intumescent layer on the surface.