Flame Retardant Thermoplastic Polyurethane Research Articles

Facile-controllable synthesis of 3D cross-shaped ZIF-67 to achieve highly efficient flame retardancy and smoke suppression for TPU composites

Zeolite imidazolium frameworks (ZIFs), as a subcategory of metal-organic frameworks (MOFs), are widely used in many fields. And, the physical morphology, particle size, and shape of ZIFs have an important influence on their application performance, such as flame retardancy for polymer. Here, three types of ZIF-67 were prepared with different physical morphology structures including dodecahedron (ZIF-67), cube (ZIF-67 NC), and cross-shaped (ZIF-67 H), by adjusting the proportion between 2-methylimidazole and cobalt (Ⅱ) nitrate hexahydrate together with the suitable amount of surfactant (CTAB), and they were used to enhance the flame retardancy and smoke suppressing properties of thermoplastic polyurethane (TPU). It has been found the novel ZIF-67 H with 3D cross-shaped superior catalytic and flame-retardant capabilities than the other two during the burning process of TPU composites. Compared with those of pure TPU, the peak heat release rate (pHRR), total smoke production (TSP), and smoke factor (SF) of TPU/2wt%ZIF-67 H were decreased by 45.4%, 50.2%, and 72.9%, respectively. At the same time, both TPU/1wt%ZIF-67 H and TPU/2wt%ZIF-67 H samples showed stronger tensile properties than pure TPU at the same elongation. This work further enriches the study of multi-structured ZIFs for flame retardant TPU.

Enhanced smoke/toxicity suppression of intumescent flame retardant thermoplastic polyurethane composites with the addition of graphene

Enhanced smoke/toxicity suppression of intumescent flame retardant thermoplastic polyurethane composites with the addition of graphene

Constructing lignin based nanoparticles towards flame retardant thermoplastic polyurethane composites with improved mechanical and oxidation resistant properties

A multifunctional lignin derivative nanoparticle (C-P-Lignin) was synthesized by grafting phenyl dichloro sphosphineoxid and 1, 4-dimethoxyacetylene stepwise on the lignin, then it was applied to prepare the thermoplastic polyurethane (TPU) composite with improved mechanical properties, oxidation resistance, and flame retardancy. The tensile strength, the elongation at break, and the toughness of the TPU/2C-P-Lignin sample reached 28.3 MPa, 941 %, and 139.0 MJ/m2 respectively, which were increased by 39.0 %, 3.4 %, and 33.9 % respectively compared with that of the control TPU sample. The anti-fatigue property was also improved. More importantly, the mechanism of the improved mechanical properties was also calculated and simulated by FTIR and Materials Studio software. The TPU/2C-P-Lignin sample exhibited superior oxidation resistance during the process of photoaging and thermal oxidative aging. Furthermore, the peak heat release rate and the smoke production rate for theTPU/2C-P-Lignin sample was reduced by 50.0 % and 53.8 % compared with that of the control TPU. The reason was that the C-P-Lignin is conducive to the formation of uniformly distributed carbon layers. It is expected that this work can provide a new method for expanding the utilization of waste wood as a multifunctional lignin-based filler to improve fire safety and extend the service life of TPU polymers.

Synergistic effects of silicon based material with intumescent flame retardant in thermoplastic polyurethane: Pre‐polymerization and dynamic vulcanization based facile approach

AbstractA flame retardant thermoplastic polyurethane (TPU) was prepared using the silicon based (Si)‐intumescent (IFR) synergistic flame‐retardant system, which combined the advantages of additive and reactive types. Silicone rubber was introduced into the matrix of hydroxybutanyl terminated polydimethylsiloxane (PDMS) block TPU via dynamic vulcanization, which enabled the combination of silicon based material and TPU. Then, the IFR system was used to supplement the defects of single Si based flame retardancy, which realized the synergistic flame retardancy of Si‐IFR. Under the Si‐IFR system, when IFR uses 15%, the TPU reached the V‐0 flame retardant level and the limiting oxygen index was 29.6. Moreover, the toughness of the Si‐IFR flame‐retardant TPU was better than PDMS block TPU. The silicon based material improved the matrix and cooperated with IFR to form a composite carbon layer, which protected the inner material, enhanced the strength of the carbon layer and eliminated dropping.

Effect of layered double hydroxide on the flame retardancy of intumescent flame retardant thermoplastic polyurethane composites prepared by selective laser sintering

AbstractPresently, layered double hydroxides (LDHs) are pervasively adopted as part of flame retardant polymer composite materials due to its favorable synergism effect with certain flame retardants. In addition, it is environmentally friendly. Meanwhile, selective laser sintering (SLS) is a powder‐based three‐dimensional (3D) printing technology, providing a novel path to manufacturing polymer composite materials with complex shapes. In this research, flame retardancy of thermoplastic polyurethane (TPU) was enhanced based on LDHs and intumescent flame retardant (IFR). Being prepared by SLS technology. First, TPU composite powders based on LDHs and IFR were obtained using a two‐stage mixing method. Morphology analysis revealed that IFR and LDHs were dispersed uniformly in TPU powder. Subsequently, flame retardant TPU composites were prepared with TPU composite powders using the SLS process under appropriate 3D printing parameters, thereby enabling flame retardant TPU parts to be obtained. With 23 wt% IFR and 2 wt% LDHs filler, the limiting oxygen index of TPU composite was reached to 31.7%, while passing the UL‐94 V‐0 level during the vertical burning test. The cone calorimeter test showed that the heat release rate, smoke production rate, as well as production of carbonic oxides, all decreased significantly following the addition of LDHs. Thermogravimetric analysis indicated that LDHs and IFR were characterized by a favorable synergism effect, with the TPU/23IFR/2LDHs possessing good thermal stability. Char residue analysis, including SEM, energy dispersive X‐ray, Fourier transform infrared, and Raman spectra, further testified that a synergism effect existed between LDHs and IFR in the TPU composite. Overall, in this study the TPU composites fabricated by SLS technology exhibited excellent flame retardant ability.

Flame retardant thermoplastic polyurethane based on a combination of chitosan and phosphotungstic acid

Flame retardant thermoplastic polyurethane based on a combination of chitosan and phosphotungstic acid

Ammonium polyphosphate/montmorillonite nanocomposite with a completely exfoliated structure and charring–foaming agent flame retardant thermoplastic polyurethane

A completely exfoliated structure of ammonium polyphosphate/montmorillonite (APP–MMT) nanocomposite was prepared and applied to thermoplastic polyurethane (TPU) to prepare TPU composites containing APP–MMT and a charring–foaming agent (CFA), after which the properties were compared with those of TPU/APP/CFA composites. The thermal decompositions of TPU composites were investigated by thermal gravimetric analysis. The synergistic effect between APP–MMT and CFA was superior to that of APP and CFA, and the char residue was greatly improved. The flame retardancy of TPU composites was studied by limited oxygen index (LOI) measurements, UL-94 testing, and cone calorimeter test. The APP–MMT nanocomposite promoted the compactness and strength of the char layer formed by the combustion of the TPU composites. The CFA improved the thermal stability of TPU. Compared with TPU/APP/CFA composites, the peak release rate (pHRR) of TPU/APP–MMT/CFA composites were lower and the LOI were higher. When the APP–MMT/CFA compound proportion was 3:1 in weight, the LOI was 25.4%, the pHRR and total heat release of the TPU composites decreased by 78.2% and 36.6%, respectively, and the smoke production and CO emission were restrained. The mechanical properties and morphology of TPU composites were analyzed by tensile strength, elongation at break, and scanning electron microscopy. The APP–MMT composite improved the dispersion of CFA in the TPU, and the mechanical properties of TPU/APP–MMT/CFA composites were higher than that of TPU with only CFA. The structure of residual carbon was studied by X-ray photoelectron spectroscopy, and it was confirmed that the APP–MMT composite promoted the formation of a good protective carbon layer during the combustion of the TPU composites and improved its flame retardancy.

Cooperative Effect of ZIF-67-Derived Hollow NiCo-LDH and MoS2 on Enhancing the Flame Retardancy of Thermoplastic Polyurethane.

In this work, a novel three-dimensional (3D) hollow nickel-cobalt layered double hydroxide (NiCo-LDH) was synthesized using zeolitic imidazole framework-67 (ZIF-67) as a template, and then utilized to functionalize molybdenum disulfide (NiCo-LDH/MoS2) via electrostatic force. Flame retardant thermoplastic polyurethane (TPU) composites were prepared by the melt blending method. Compared to pure TPU, NiCo-LDH/MoS2 filled TPU composite was endowed with a decrease of 30.9% and 55.7% of the peak heat release rate (PHRR) and the peak smoke production rate (PSPR), respectively. Furthermore, the addition of NiCo-LDH/MoS2 can significantly improve the thermal stability and char yield of the TPU composite. The catalytic carbonization effect and dilution effect of NiCo-LDH, and the barrier effect of MoS2 nanosheets enable TPU composites with excellent flame retardancy and toxic gas suppression ability.

Zn-doped carbon microspheres as synergist in intumescent flame-retardant thermoplastic polyurethane composites: Mechanism of char residues layer regulation

Despite thermoplastic polyurethane (TPU)/ammonium polyphosphate (APP) being an excellent intumescent flame-retardant TPU composite (IFR-TPU), it is still not a "fire-safety" TPU composite. In this work, the Zn-doped carbon microspheres (CMSs-Zn) were prepared and added into the TPU/APP composite as a synergist to fabricate an IFR-TPU composite with excellent fire safety performance (TPU/CMSs-Zn). Cone calorimeter tests exhibited the peak heat release rate (pHRR), total heat release (THR), peak smoke production rate (pSPR), total smoke release (TSR) of TPU/CMSs-Zn composites were decreased by 65.4 %, 50.7 %, 65.3 %, and 63.4 % respectively. Moreover, the smoke density tests showed that the luminous flux (LF) of TPU/CMSs-Zn increased from 1.4 % to 40.1 %. In addition, the investigation of the flame-retardant mechanism for TPU/CMSs-Zn revealed that CMSs-Zn amplifies the role of APP in condensed phase by participating in char formation and catalysis effect, thus forming a dense protective char residues layer. The char residues layer regulation mechanism can provide a novel strategy for facilitating fire-safety TPU composite.

Synthesis of 3D Hollow Layered Double Hydroxide-Molybdenum Disulfide Hybrid Materials and Their Application in Flame Retardant Thermoplastic Polyurethane.

The development of high-performance thermoplastic polyurethane (TPU) with high flame retardancy and low toxicity has always been the focus of its research. In this paper, the novel 3D hollow layered double hydroxide/molybdenum disulfide (LDH/MoS2) hybrid materials were synthesized by hydrothermal method using the MIL-88A as in situ sacrificial template and MoS2 as synergistic flame retardant. Among all TPU composites, the peak heat release rate, total heat release rate, and total smoke release rate of TPU/NiFeTb-LDH/MoS2 were reduced by 50.9%, 18.2%, and 35.8% compared with pure TPU, respectively. The results of the thermogravimetric infrared analysis demonstrated that the contents of combustible volatiles (hydrocarbons) and toxic volatiles (CO and HCN) emitted from TPU/LDH/MoS2 were significantly reduced, indicating that LDH/MoS2 hybrid materials can dramatically enhance the fire safety of TPU composites. Combined with the analysis of carbon residues and thermal stability of TPU composites, the enhanced flame retardancy and smoke suppression performances are primarily attributed to the catalytic carbonization of LDH and the physical barrier effect of MoS2.

The synergism effect of montmorillonite on the intumescent flame retardant thermoplastic polyurethane composites prepared by selective laser sintering

AbstractSelective Laser Sintering (SLS) is a powder‐based 3D printing technology. It offers a new means of fabricating complex modules with special properties, such as mechanical, flame retardant, electrical and thermal properties. In this paper, the effect of an intumescent flame retardant (IFR) and montmorillonite (MMT) on the fire resistance of thermoplastic polyurethane (TPU) was investigated. TPU composites powders were prepared by mixing with a two‐step method and can be effectively applied to SLS. Morphology characters exhibited that the fillers disperse well in the TPU powder. The structure analysis and hydrophilia analysis of sodium montmorillonite (Na‐MMT) and organically modified montmorillonite (OMMT) demonstrates the different compatibility in TPU, which reflects diverse flame retardant behavior. With 22% IFR and 3% OMMT fillers, the LOI of TPU composites increased from 17.2% to 28% and subsequently a UL‐94 V‐0 ranking was obtained. In the CCT results, the formula of 22% IFR and 3% OMMT showed the lowest heat release and smoke production. The study also explored the effects of flame retardant fillers on the thermal stability of TPU composites and melting and crystallization behaviors in SLS processing. In addition, the char residues after heating were analyzed via scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy and laser Raman spectroscopy. The results demonstrate that the composites have favorable flame retardant properties, thermal stability, char forming performance, and SLS process properties. The TPU composites prepared via SLS in this study demonstrated extensive potential in fire protection materials.

Surface Modification of Ammonium Polyphosphate for Enhancing Flame-Retardant Properties of Thermoplastic Polyurethane.

Currently, the development of efficient and environmentally friendly flame-retardant thermoplastic polyurethane (TPU) composite materials has caused extensive research. Ammonium polyphosphate (APP) is used as a general intumescent flame retardant to improve the flame retardancy of TPU. In this paper, we developed a functionalized APP flame retardant (APP-Cu@PDA). Adding only 5 wt% of APP-Cu@PDA into TPU can significantly improve the flame-retardant’s performance of the composite material, reflected by a high LOI value of 28% with a UL-94 test of V-0 rating. Compared with pure TPU, the peak heat release rate, total heat release, peak smoke release rate, and total smoke release were reduced by 82%, 25%, 50%, and 29%, respectively. The improvements on the flame-retardant properties of the TPU/5%APP-Cu@PDA composites were due to the following explanations: Cu2+-chelated PDA has a certain catalytic effect on the carbonization process, which can promote the formation of complete carbon layers and hinder the transfer of heat and oxygen. In addition, after adding 5% APP-Cu@PDA, the tensile strength and elongation at the break of TPU composites did not decrease significantly. In summary, we developed a new flame-retardant APP-Cu@PDA, which has better flame-retardant properties than many reported TPU composites, and its preparation process is simple and environmentally friendly. This process can be applied to the industrial production of flame retardants in the future.

Grafting alkynyl groups on the surface of nano‐aramid fibers towards flame retardant thermoplastic polyurethane

AbstractIn this work, para‐aramid fibers were dispersed into para‐aramid nanofibers (ANF) by deprotonation process, and then modified by 3‐chloropropyne (PC) via covalent bonding interaction. The resultant nanofiber (ANF‐PC) as a flame retardant was blended with thermoplastic polyurethane (TPU) to obtain fire‐retardant TPU nanocomposites. The addition of 0.250 wt% ANF‐PC reduced the peak heat release rate, total heat release, total smoke release, and peak CO release rate of TPU by 47.7%, 31.5%, 16.4%, and 45.1%, respectively. The char yield of TPU/ANF‐PC0.250 was increased from 7.7% (TPU/ANF0.250) to 13.7%. The flame‐retardant effect of ANF‐PC in TPU composites can be attributed to its carbonization effect in the condensed phase, which increased the char yields and graphitization degree of char residue. In addition, the presence of ANF‐PC increased the tensile strength and breaking strain of TPU by 645% and 578% compared to untreated ANF, due to the improved dispersion state of ANF‐PC.

Fabrication of Enhanced Mechanical Properties and Intrinsic Flame-Retardant Polyurethane Elastomer Containing 4-(Phenylethynyl) Di(Ethylene Glycol) Phthalate.

In this study, the aromatic acetylene compound 4-(phenylethynyl) di(ethylene glycol) phthalate (PEPE) was used as a chain extender, partially replacing 1,4-butanediol. To synthesize an intrinsic flame-retardant thermoplastic polyurethane elastomer (TPU) with an aromatic acetylene structure, PEPE was synthesized by a two-step polymerization. The flame retardancy, thermal stability, and mechanical properties of TPU were studied. The microstructure of TPU char was investigated by scanning electron microscopy to analyze the flame-retardant mechanism. The tensile strength of TPU containing 1.35 wt% PEPE was 39.2 MPa, which was almost twice as much as neat TPU, showed a dramatic decrease in the peak heat release rate and total heat release, and declined by 46.2% and 24.5%, respectively. After the flame-retardant TPU burned, a cross-linked network foaming char structure was formed. The results showed that PEPE improved the mechanical properties of TPU and conferred good stability that promoted the formation of charcoal and reduced heat release during the combustion of TPU.

An urethane-based phosphonate ester for improving flame retardancy and smoke suppression of thermoplastic polyurethane

The flame-retardant thermoplastic polyurethane (TPU) with remarkable smoke suppression, anti-dripping and mechanical properties has been still a big conundrum in the field of fire safety science. In this article, an urethane-based phosphonate ester (UPE) flame retardant additive was successfully synthesized and incorporated into TPU. The fire safety, mechanical performance and flame-retardant mechanisms of TPU/UPE composites were lucubrated. With the incorporation of only 10 wt% UPE, TPU/10 wt% UPE composites passed UL-94 V-0 rating without dripping and the limited oxygen index (LOI) value reached 28.8%. Cone calorimetry tests indicated that the peak value of heat release and smoke production of TPU/10 wt% UPE composites were significantly diminished with the reduction of 70.6 and 54.1% in comparison with that of pure TPU. The analysis of flame-retarded mechanism for TPU/UPE indicated that UPE efficiently exerted free radical capture effect in gaseous phase, and stimulated the decomposition and charring of TPU composites in advance and the formation of high-quality char layer exerted isolation role in condensed phase. Therefore, the fire safety of TPU composites was enhanced by the incorporation of UPE. Meanwhile, the mechanical performance of TPU/UPE composite was well remained due to the good compatibility between UPE and TPU matrix. This work supplied a promising way for fabricating fire-safety TPU composites with preferable comprehensive properties.

Flame‐retardant thermoplastic polyurethane based on reactive phosphonate polyol

SummaryPropylene oxide (PO) was used to block polycarboxyethyl phenyl ethylene phosphinate (PCEPEP) synthesized by 2‐carboxyethylphenylphosphinic acid (CEPPA) and ethylene glycol (EG) to obtain a reactive phosphonate polyol. The results of chemical titration analysis and Fourier transform infrared spectrum (FT‐IR) showed that the end‐capping effect was best when the molar ratio of PO to acidic functional groups in PCEPEP was 6:1. Moreover, the obtained phosphorus‐containing polyol was used as a reactive monomer to be introduced into thermoplastic polyurethane (TPU) to prepare flame retardant TPU. Cone calorimetry results demonstrated that TPU containing 20 wt% phosphorus‐containing polyol showed a reduction of 3.8%, 72.2%, and 39.3% in the peak heat release rate, total heat release and total smoke release, and an increment of 351.9% in mass retention. The addition of phosphonate polyol enhanced the char‐forming performance of TPU, which effectively prevented the transfer of combustible gas and heat, and displayed a good flame retardant effect.

Surface modification of bamboo fibers by diammonium phosphate and their applications in flame retardant thermoplastic polyurethane

AbstractBamboo fibers (BF) were used as charring agent in thermoplastic polyurethane (TPU), together with ammonium polyphosphate (APP) to prepare intumescent flame retardant composites. In order to improve the dispersibility and flame retardant efficiency, BF was grafted with diammonium phosphate (DAP), named as modified bamboo fibers (M‐BF). By the presence of 8 wt% APP and 2 wt% M‐BF, the sample could achieve the maximal limiting oxygen index (LOI) value of 30.5% and V‐0 rating in UL‐94 test. The peak heat release rate for TPU/8APP/2 M‐BF is 190 kW/m2, which is 86.0% lower than that of neat TPU. Besides, TPU/8APP/2 M‐BF sample presented a tensile strength of 23.0 MPa, which was slightly lower than neat TPU sample. The thermogravimetric analysis for TPU composites and the morphology observation of the char demonstrated that APP and M‐BF took effects on condensed phase through promoting the formation of intumescent char structure and free radical trapping. Meanwhile, it could release inert gases in gas phase. Therefore, M‐BF exhibited great potential in applying as renewable charring agent for alleviating the depletion of petroleum resources.

Influence of nickel citrate in flame retardant thermoplastic polyurethane elastomer composites based on ammonium polyphosphate

Influence of nickel citrate in flame retardant thermoplastic polyurethane elastomer composites based on ammonium polyphosphate

Phosphorus-containing organic-inorganic hybrid nanoparticles for the smoke suppression and flame retardancy of thermoplastic polyurethane

It is always a big challenge for fabricating flame-retarded and smoke-suppressed polymers with excellent mechanical properties in fire-safety material field. In this work, novel organic-inorganic hybrid nanoparticles named phosphoryl polyethyleneimine amide-layered double hydroxide (PPEIA-LDH) were prepared via a simple reaction process. When the PPEIA-LDH nanoparticles were used to prepare flame-retardant thermoplastic polyurethane (TPU), it was found that a small amount of PPEIA-LDH remarkably reduced the fire hazard of TPU via a typical intumescent flame-retardant mode. Only 6.0 wt% PPEIA-LDH endowed TPU with a limiting oxygen index of 29.0% and a UL-94 V-0 rating, and also reduced total smoke production and total heat release of TPU by 31.6 and 49.9%, respectively, moreover, mechanical properties of TPU did not show any decrease in this case. The analysis for flame-retardant and smoke-suppression mechanisms demonstrated that synergistic charring between the organic component and the inorganic component in PPEIA-LDH played a crucial role in reducing the fire hazard of TPU. Excellent mechanical properties of TPU/PPEIA-LDH is ascribed to the uniform dispersion of PPEIA-LDH and good interfacial interaction with TPU. This work demonstrates that organic-inorganic hybrid nanoparticle may provide a promising solution for fabricating fire-safety polymers with excellent overall performance.

Effect of organically intercalation modified layered double hydroxides-graphene oxide hybrids on flame retardancy of thermoplastic polyurethane nanocomposites

Flame retardant thermoplastic polyurethane (TPU) nanocomposites were prepared by melt blending using organically intercalation modified layered double hydroxides-graphene oxide hybrids (LDHs-GO). Modification process of LDHs-GO was carried out by using sodium dodecyl sulfate (SDS) in water/ethanol medium. X-ray diffraction, Fourier transform infrared spectra and scanning electron microscope micrograph results showed the SDS intercalation modified LDHs-GO (SDS-LDHs-GO) was synthesized successfully. Flame retardancy, suppression smoke and thermal stability properties of the well-dispersed TPU nanocomposites were evaluated and compared with each other. The CCT results showed that the pHRR was significantly decreased after incorporating SDS-LDHs-GO nanoparticles. In particular, the pHRR of the TPU5 containing 20 mass% SDS-LDHs-5%GO hybrid was decreased by 77.2% compared to that of pure TPU. The addition of SDS-LDHs-GO hybrids can enhance the suppression smoke performance of TPU nanocomposites as well, and the efficiency was dependent on the catalytic carbonization of lamellar LDHs and both the adsorption and barrier effect of GO. The TG results confirmed that GO can improve the thermal stability of nanocomposites by promoting char formation. This work provides a novel modification strategy for enhancing the dispersion and flame retardant efficiency of LDHs.