Improvement of thermoplastic polyurethane's flame retardancy and thermal conductivity by leaf‐shaped cobalt‐zeolitic imidazolate framework–modified graphene and intumescent flame retardant

In this work, a new type of leaf‐shaped cobalt‐zeolitic imidazolate framework–modified graphene (Co‐ZIF‐L@RGO) hybrid was successfully prepared and blended with an intumescent flame retardant (IFR). It was added into thermoplastic polyurethane (TPU) to study the effect of its combination with IFR on the thermal conductivity and flame retardant performance of TPU. The morphology and structure of the Co‐ZIF‐L@RGO hybrid were characterized by scanning electron microscope (SEM), Fourier transform infrared and X‐ray diffraction (XRD). The results showed that Co‐ZIF‐L were uniformly loaded on the surface of graphene. Furthermore, compared with pure TPU, the limiting oxygen index values of the composite material with 3 wt% Co‐ZIF‐L and 27 wt% IFR increased to 32.6%. Their UL‐94 rating reached V‐0 rating. Their peak heat release rate, total heat release, peak smoke production rate and total smoke production were also greatly reduced by 84.4%, 70.1%, 60.3% and 62.5%, respectively. The thermogravimetric‐infrared test results showed that the amount of toxic gas emissions was effectively suppressed. The residual carbon was analyzed by SEM, laser Raman spectroscopy and XRD, and flame retardant mechanism was further investigated. Besides, the addition of this hybrid improved the thermal conductivity of TPU.     

Influences of coupling agent on thermal properties, flammability and mechanical properties of polypropylene/thermoplastic polyurethanes composites filled with expanded graphite

In this study, polypropylene (PP)/thermoplastic polyurethanes (TPU) filled with inorganic intumescent flame retardant expanded graphite (EG) was prepared by melt blending in a twin-screw extruder. The thermal stability, fire retardancy, mechanical properties, and fracture morphology of PP/TPU composites with treated and untreated EG were investigated by thermogravimetric analysis, cone calorimeter, and scanning electron microscope. The results showed that both untreated and treated EG can greatly enhance the thermal stability and fire resistance of polymer matrix materials. Compared with untreated EG, treated EG can further improve the flame retardancy of the composites. For example, treated EG can further reduce the heat release rate, total heat release, and CO emissions of the composites in the combustion. Surface treatment of EG could significantly improve elongation at break and impact strength of PP/TPU/EG composites due to its enhanced interfacial adhesion and the good dispersion of EG particles in the polymer matrix.     

Thermal degradation and flame retardancy of fumaric acid in thermoplastic polyurethane elastomer

In this paper, fumaric acid (FA) which was a new type of environmental and low‐cost flame retardant was applied for thermoplastic polyurethane elastomer (TPU). The flame‐retardant properties of TPU were tested using limiting oxygen index, cone calorimeter test, smoke density test, and thermogravimetric/Fourier transform infrared spectroscopy. It has been proved that FA could improve the difficulty of the ignition of the sample; the limiting oxygen index value of the sample (FA‐4) increased by 29.7% when 2.0 wt% FA was added to TPU. The cone calorimeter test showed that FA can greatly reduce heat release and smoke production during the combustion process of TPU composites. For example, compared with the pure TPU, the peak heat release rate and total smoke release of the sample (FA‐4) with 2.0 wt% FA were decreased by 50.8% and 51.5% respectively. The results of smoke density test showed that the luminous flux of the samples contained 0.5 wt% FA was increased by 79.2% compared with the pure TPU. The TG results revealed that the sample of FA‐4 had higher char residue content compared with the sample of TPU. The results of thermogravimetric/Fourier transform infrared spectroscopy proved that FA could decrease the initial decomposition temperature for TPU composites and increase the release of CO₂ and H₂O. All results of test illustrated that FA had good flame‐retardant effect on TPU.     

Properties of flame‐retardant TPU based on para‐aramid fiber modified with iron diethyl phosphinate

In this paper, a new type of flame retardant (AF‐Fe) based on para‐aramid fiber (AF) which was modified with iron diethyl phosphinate was applied for thermoplastic polyurethane elastomer (TPU). The flame‐retardant properties of TPU were tested using cone calorimeter test, smoke density test, and thermogravimetric analysis/infrared spectrometry. The cone calorimeter test showed that AF‐Fe can greatly reduce the heat release rate, total heat release, smoke factor, and other parameters of TPU composites compared with the sample of TPU/AF. For example, the pHRR of the composite with 1.0 wt% AF‐Fe was reduced by 15.19% compared with the sample with the same content of pure AF. In addition, the smoke factor of TPU/AFFe3 was reduced by 50.52% and 15.63% compared with TPU0 and TPU/AF respectively. The results of smoke density test showed that the luminous flux of TPU/AFFe3 was increased by 79.26% compared with the sample of TPU/AF. The TG results revealed that the sample with TPU/AFFe3 had lower weight loss rate and higher char residue content at 700°C compared with the sample of TPU/AF.     

Improving Thermal and Flame Retardant Properties of Epoxy Resin with Organic NiFe‐Layered Double Hydroxide‐Carbon Nanotubes Hybrids

To improve the dispersion of carbon nanotubes (CNTs) and flame retardancy of layered double hydroxide (LDH) in epoxy resin (EP), organic nickel‐iron layered double hydroxide (ONiFe‐LDH‐CNTs) hybrids were assembled through co‐precipitation. These hybrids were further used as reinforcing filler in EP. EP/ONiFe‐LDH‐CNTs nanocomposites containing 4 wt% of ONiFe‐LDH‐CNTs with different ratios of ONiFe‐LDH and CNTs were prepared by ultrasonic dispersion and program temperature curing. The structure and morphology of the obtained hybrids were characterized by different techniques. The dispersion of nanofillers in the EP matrix was observed by transmission electron microscopy (TEM). The results revealed a coexistence of exfoliated and intercalated ONiFe‐LDH‐ CNTs in polymer matrix. Strong combination of the above nanofillers with the EP matrix provided an efficient thermal and flame retardant improvement for the nanocomposites. It showed that EP/ONiFe‐LDH‐CNTs nanocomposites exhibited superior flame retardant and thermal properties compared with EP. Such improved thermal properties could be attributed to the better homogeneous dispersion, stronger interfacial interaction, excellent charring performance of ONiFe‐LDH and synergistic effect between ONiFe‐LDH and CNTs.     

Synergistic effects between iron–graphene and melamine salt of pentaerythritol phosphate on flame retardant thermoplastic polyurethane

A comparison of melamine salt of pentaerythritol phosphate (MPP), and a synergistic agents, iron–graphene (IG) was performed in thermoplastic polyurethane (TPU) by masterbatch‐melt blending on thermal and flame retardant properties. The flame retardant properties of TPU composites were characterized by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT). The CCT results revealed that IG can significantly enhance flame retardant properties of MPP in TPU. The peak heat release rate of neat TPU and flame retardant TPU/MPP composites decreased from 2192.6 and 226.7 to 187.2 kW/m² compared with that of TPU containing 0.25 wt% IG. The thermal stability and thermal decomposition of TPU composites were characterized by thermogravimetric analysis (TGA) and thermogravimetric/Fourier infrared spectrum analysis (TG‐IR). The results indicated IG and MPP can improve the thermal stability of TPU. The formation of thermal conductive network by IG can promote the decomposition of MPP into nonflammable melt, which can play the role of heat barrier and restrict the diffusion of fuels into combustion zone and access of oxygen to the unburned fuels. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect on thermal and combustion behaviors of montmorillonite intercalation nickel compounds in polypropylene/IFR system

A new montmorillonite intercalation nickel compound (MINC) was devised and synthesized. MINC was modified by cetyl trimethyl ammonium bromide to obtain organic MINC (OMINC). The results of X‐ray diffraction show that the layer spacing was expanded by nickel compound and cetyl trimethyl ammonium bromide, indicating that OMINC was prepared successfully. OMINC was further incorporated into polypropylene (PP)/intumescent flame retardant (IFR) system for preparing PP/IFR/OMINC nanocomposites via melt blending. In thermogravimetric analysis, PP/IFR/OMINC nanocomposites exhibit an enhanced thermal behavior and residue amount. Vertical burning test (UL‐94) and limited oxygen index results show that PP/IFR/OMINC nanocomposites have excellent flame retardance, i.e. the limited oxygen index value at 29.5 and UL‐94 V0 level for PP/IFR/4 wt% OMINC nanocomposites. According to cone calorimeter testing, the addition of OMINC brings an efficient reduction of flammability parameters, such as peak heat release rate, total heat release, and smoke production rate. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and properties of an efficient smoke suppressant and flame‐retardant agent for thermoplastic polyurethane

APP@ETA, as a new type of flame retardant, was prepared by chemically modifying ammonium polyphosphate (APP) with ethanolamine (ETA) and applied to thermoplastic polyurethane (TPU) in this study. Then, the smoke suppression properties and flame‐retardant effects of APP@ETA in TPU composites were evaluated using smoke density test, cone calorimeter test, etc. And, the thermal degradation properties of flame‐retardant TPU composites were investigated by thermogravimetric analysis/infrared spectrometry. The smoke density test results indicated that APP@ETA could obviously improve the luminous flux of TPU composites in the test with or without flame. The cone calorimeter test results showed that total smoke release, smoke production rate and smoke factor of the composites with APP@ETA were significantly decreased than those of the composites with APP. For example, when the loading of APP@ETA or APP was 12.5 wt%, the total smoke release of the sample with APP@ETA decreased to 3.5 m²/m² from 6.0 m²/m², which was much lower than that of the sample with APP, reduced by 41.7%. The thermogravimetric analysis results demonstrated that APP@ETA could decrease the initial decomposition temperature and improve the thermal stability at high temperature for TPU composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Modified boron nitride as an efficient synergist to flame retardant natural rubber: preparation and properties

A new flame retardant system with organic modified boron nitride (m‐BN) and intumescent flame retardant (IFR) was used in this paper, and the synergistic flame retardancy of m‐BN and IFR on natural rubber (NR) was studied. NR/IFR/m‐BN composites were characterized by X‐ray photoelectron spectroscopy(XPS), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis, UL‐94, limiting oxygen index (LOI), tensile testing, cone calorimeter testing, and thermal conductivity testing. When 4 wt% m‐BN was added, the flame retardancy and mechanical properties of the composites were improved. The LOI value of NR/IFR/4 phr m‐BN reached 26.8%, and suppressed fire spread in a UL‐94 test. Compared with pure NR, the peak heat release rate (pHRR) was reduced by 52.2%, the total heat release (THR) was reduced by 27.6%, and CO yields were reduced by 51.4%. As a key aspect of fire safety, the ignition time is effectively delayed to 23 seconds due to the increased thermal conductivity of NR/IFR/m‐BN. Since the synergistic effect of m‐BN effectively improves the flame retardancy of NR, it provides a feasible method for improving the fire safety of polymers.     

Effect of natural basalt fiber for EVA composites with nickel alginate‐brucite based flame retardant on improving fire safety and mechanical properties

The natural basalt fiber (BF) was incorporated into EVA composites with environmental‐friendly nickel alginate‐brucite based flame retardant (NiFR), to further improve the flame‐retardant effect and mechanical properties. The flame retardancy of EVA composites were characterized by LOI, UL 94, and cone test. With 55 wt% loading, 3BF/52NiFR had the highest LOI value of 31.9 vol.% in all fiber reinforced composites and pass UL 94V‐0 ratting. And comparing to 55B composite with untreated brucite, 3BF/52NiFR decreased peak of heat release rate by 47.8%, total heat release by 21.9%, and total smoke production by 35.5% and kept more residue 54.0% during cone test. Moreover, 3BF/52NiFR also enhanced the mechanical properties of composites by better compatibility with EVA matrix. BF/NiFR exert synergistic flame‐retardant effect major in promoting charring effect in condensed phase during combustion. The fire‐resisted and rigid BF into the char layer reinforced the intensity of protective barrier which prolonged the residence time of pyrolysis carbonaceous groups degraded from EVA matrix, resulting in less heat and smoke release.     

Silane surface modification of boron nitride for high thermal conductivity with polyphenylene sulfide via melt mixing method

Polyphenylene sulfide (PPS) is a promising engineering polymer, which is used for various industrial applications. In this study, we developed a highly thermally conductive PPS composite containing boron nitride (BN) as a thermally conductive ceramic filler. (3‐Aminopropyl) triethoxysilane was doped onto the surface of hydroxyl‐functionalized BN using a simple sol–gel process. The modified BN particles were embedded in a PPS matrix via a melt mixing process using a twin extruder to form BN‐Si composites. The maximum thermal conductivity 3.09 W/m·K was exhibited by the surface‐modified BN‐Si containing 60 wt%. This value was 116% higher than the thermal conductivities of the pristine BN and PPS matrix, respectively. The surface‐treated composites also showed an improved storage modulus because of an improvement in the interfacial adhesion and interaction between the BN filler and the PPS matrix. Copyright © 2017 John Wiley & Sons, Ltd.     

Flame retardancy and thermal decomposition behavior of TPU/chitosan composites

The application of chitosan (CS) in new materials is a hot research topic. In this paper, CS was used alone as flame retardant to prepare thermoplastic polyurethane elastomer (TPU) composites. Then, the flame retardancy and thermal decomposition behavior of TPU/CS composites were intensively investigated using cone calorimeter test (CCT), scanning electron microscope (SEM), microscale combustion colorimeter (MCC) test, thermogravimetric analysis/infrared spectrometry (TG‐IR), and gas chromatography‐mass spectrometry (GC‐MS). The results showed that CS can reduce the fire risk of TPU; 2.0‐wt% CS could make the peak value of heat release rate (pHRR) decreased to 457.2 kW/m², reduced by 65.9% compared with TPU. And the peak value of smoke production rate (pSPR) and total smoke release (TSR) of the same sample was decreased by 79.4% and 54.2%, respectively. The TG‐IR and GC‐MS results confirmed that CS could promote TPU decomposition in advance, reacting with the decomposition products of TPU. Therefore, the production of combustible gas was reduced. The GC‐MS results showed that the production of isocyanates and ethers was reduced with the addition of CS. The digital photographs of SEM for the samples after CCT were shown that the char residue layer of the sample containing 2.0‐wt% CS was fibrous in shape. It could be speculated that the thermal decomposition products from TPU could react with CS at low temperature, which reduced the production of flammable gases. So CS had a good prospect in reducing the fire hazard for TPU.     

Synergistic fire safety improvement between oyster shell powder and ammonium polyphosphate in TPU composites

In this article, oyster shell powder (OSP) was used as fire safety agent with ammonium polyphosphate (APP) in thermoplastic polyurethane (TPU) composites. The synergistic fire safety improvement between OSP and APP was intensively investigated using limiting oxygen index (LOI), UL‐94, smoke density test (SDT), and cone calorimeter test (CCT). There is a good synergistic effect of reducing the fire hazards when OSP was used with APP in TPU. The peak heat release rate (pHRR) of the sample with 2.0‐wt% OSP and 8.0‐wt% APP decreased to 86.8 kW/m² from 175.7 kW/m² of the sample with only 10.0‐wt% APP. The SDT results showed that the luminous flux of sample OSP2/APP8 was up to 28.9% at the end of experiment with flame, which was much higher than that of pure TPU (1.5%). The thermal stability and thermal decomposition of TPU composites were characterized by thermogravimetric analysis/Fourier infrared spectrum analysis (TG‐IR). The result revealed the inert gasses (including CO₂ and water vapor) produced by the reaction between OSP and APP. A char formed on the surface of composites, hindered the flame spread, reduced the release of combustible gas, and restricted the precursor of smoke into combustion zone.     

Hugely enhanced flame retardancy and smoke suppression properties of UHMWPE composites with silicone‐coated expandable graphite

In this paper, silicone‐coated intumescent flame retardants was prepared by an efficient and simple approach, aiming at enhancing the flame‐retardant efficiency and smoke suppression properties. The surface of expandable graphite (EG) was treated prior to the coverage of nonflammable silicone. The resultant silicone‐modified EG hybrid (SEG) was combined with ammonium polyphosphate (APP) and applied as a flame‐retardant and smoke‐suppressant for ultrahigh molecular weight polyethylene (UHMWPE). Compared with UHMWPE/APP/EG (with 15 wt% APP/EG), UHMWPE/APP/SEG (with 15 wt% APP/SEG) gives decrement by 18.5% in the peaks of the heat release rate, 6.33% in total heat release and 13.6% in total smoke release, whereas increment by 23% in tensile strength and 12.1% in elongation at break, respectively. It is suggested that the introduction of silicone on the surface of EG can improve the interfacial compatibility between EG and UHMWPE. Moreover, it can lead to forming more char residue and reducing the release of smoke particulates during combustion process of the composites.     

纳米阻燃高分子材料:现状、问题及展望

纳米阻燃体系是一种新型的聚合物阻燃体系,被誉为阻燃技术的革命.极少量(≤5wt%)纳米阻燃剂的加入即能显著降低高分子材料燃烧时的热释放速率(HRR)和烟密度(SEA),延缓其燃烧过程,还能不同程度地提高材料的力学性能.本文总结了近年来国内外纳米阻燃领域的进展,介绍了本课题组在纳米阻燃方面所做的工作,探讨了纳米阻燃研究中存在的问题,并对其未来的发展进行了展望.     

Microencapsulation of ammonium polyphosphate with hydroxyl silicone oil and its flame retardance in thermoplastic polyurethane

Microencapsulated ammonium polyphosphate (MAPP) is prepared using hydroxyl silicone oil by in situ polymerization and characterized by XPS. Microencapsulation gives MAPP better water resistance and flame retardance compared with APP in thermoplastic polyurethane (TPU). Thermal stability and fire resistance behavior have been analyzed and compared. The LOI value of the TPU/MAPP composite is higher than that of the TPU/APP composite. The UL 94 rating of the TPU/MAPP composite is V-0 at the 20 wt% additive level, whereas TPU/APP gives V-2 rating at the same loading level. The water resistant properties of the TPU composites are studied. Results of the cone calorimeter and microscale combustion calorimeter experiment show that MAPP is an effective flame retardant in TPU compared with APP.     

A facile strategy to fabricate intumescent fire-retardant and smoke suppression protective coatings for natural rubber

As flammable natural rubber (NR) becomes more ubiquitous in industrial fields, there is a growing need for safe and effective flame retardant treatments through efficient techniques. Remarkably, our developed highly efficient natural tannic acid (TA)-based intumescent flame-retardant system (AGT) has the unique function in the rubber flame retardant aspect. Meanwhile, the developed coating method through polyurethane elastomer (PU) both as adhesive medium and a carbonforming agent can not only minimize the influence of flame retardant on the desirable intrinsic properties of base polymer and also maximize the efficiency of flame retardant. The flame-retardant coating (AGT/PU) exhibits highly efficient flame retardant performances reflected by a 31.9% reduction in peak heat release rate and a 27.3% reduction in total heat release and a 26.2% reduction in total smoke production with 50 wt% loading in 1 mm thick coating due to synergistic flame retardant effects. More importantly, the excellent flame retardancy performance are obtained by the PU@AGT10, as reflected in flame retardancy index (FRI) value of 11.88 makes it as excellent flame retardancy performance. While many physically mixed flame retardants are usually seriously detrimental to mechanical properties of NR, the influence of AGT/PU coating on mechanical properties of NR decreases obviously because fire retardant just directly impacts on PU adhesive layer rather than NR matrix, and the reinforcement function of graphene is also much significant. Moreover, the coating method requires just less flame retardant to achieve high flame retardant effect for NR. These findings suggest that significant opportunities for flame retardant polymer materials in industry.     

Synergistic effect between solid wastes and intumescent flame retardant on flammability and smoke suppression of thermoplastic polyurethane composites

Phosphorus tailings and fly ash both are solid wastes and do harm to the environment. Here, they were added into thermoplastic polyurethane (TPU) matrices together with intumescent flame retardants (IFR), and the synergistic effects between IFR and phosphorus tailings or fly ash for improving the flame retardancy of TPU were investigated. The cone calorimeter test (CCT) results indicated that adding phosphorus tailings or fly ash substitute for part of IFR could obtain a better flame retardant effect. The peak heart release rate (PHRR) of TPU/25 wt% IFR composites exhibited a reduction of 77% than that of neat TPU, and the total smoke production presented a reduction of 16%. However, the PHRR value and total smoke production of the sample TPU/20 wt% IFR/5 wt% phosphorus tailings were reduced by 91% and 57%, respectively, compared to that of neat TPU. The dense char promoted by the presence of IFR and phosphorus tailings or fly ash delayed the diffusion of volatile pyrolysis products and transmission of heat and oxygen to the underlying material. Therefore, a certain amount of phosphorus tailings or fly ash can be used as synergistic agents with IFR to enhance the fire safety of TPU materials. From another aspect, it also provides a promising way for recycling use of phosphorus tailings and fly ash.     

Flame retarded polymer nanocomposites: Development,trend and future perspective

Polymer nanocomposites are a new class of flame retarded materials which have attracted much attention and considered as a revolutionary new flame retardant approach.A very small amount of nano flame retardants (normally < 5 wt%) can significantly reduce the heat release rate (HRR) and smoke emission (SEA) during the combustion of polymer materials.Moreover,the addition of nano flame retardants can also improve the mechanical properties of polymer materials compared with the deterioration of traditional fla...     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.