Effect of modified layered double hydroxide on the flammability of intumescent flame retardant PP nanocomposites

The dodecyl sulfate intercalated CaMgAl-hydrotalcites (layered double hydroxides [LDHs]) were successfully prepared by co-precipitation method, and characterized by X-ray diffraction analysis, infrared spectroscopy (Fourier transform infrared spectra [FT-IR]), thermogravimetry (TG-DTA), scanning electron microscope, and Brunner−Emmet−Teller (BET). The prepared LDHs were added to the intumescent flame retardant (IFR) polypropylene (PP) nanocomposites, and the limiting oxygen index method (LOI), vertical combustion method (UL-94), cone calorimetry (CCT), and other test methods were used to study its thermal stability and combustion performance. The results showed that when the flame retardant was composed of 23 wt% IFR and 2 wt% O-SDS-LDHs, the LOI value of the material was increased to 31.5%, reaching the V-0 level, and the flame retardant performance was significantly improved. The results also showed that there was a significant synergistic effect between IFR and O-SDS-LDHs, which could improve the thermal stability and graphitization degree of PP nanocomposites. In addition, the peak heat release rate, total heat release, and total smoke production of the PP/IFR/O-SDS-LDHs system were 177 kW/m², 101 MJ/m², and 15.4 m², respectively, which were 82.2%, 51.0%, and 23.0% lower than those of pure PP, respectively. These improvements could be attributed to the presence of dense and continuous char layer formed by the synergistic effect.     

水滑石的制备及其阻燃性能研究进展

由于聚合物受热易燃烧,常存在火灾风险,通常需要引入阻燃剂来提升其阻燃性能。水滑石(LDHs)因其无卤、无毒且抑烟性能优异,在阻燃领域受到了越来越多的关注。基于此,对LDHs的结构、制备方法及其阻燃机理进行了介绍,特别是对提高LDHs阻燃性能的途径即从层板阳离子掺杂、层间阴离子插层和表面改性进行了重点综述,并对不同结构LDHs的阻燃机理及阻燃性能进行了总结,最后展望了LDHs作为阻燃剂今后的发展趋势。     

水滑石的制备及其阻燃性能研究进展

由于聚合物受热易燃烧,常存在火灾风险,因此通常需要引入阻燃剂来提升其阻燃性能。水滑石（LDHs）因其无卤、无毒且抑烟性能优异,在阻燃领域受到了越来越多的关注。基于此,本文对LDHs的结构、制备方法及其阻燃机理进行了总结,特别是对提高水滑石阻燃性能的途径即从层板阳离子掺杂、层间阴离子插层和表面改性等方面进行了重点综述,并对不同结构水滑石的阻燃机理及阻燃性能进行了归纳总结,最后展望了水滑石作为阻燃剂今后的发展趋势,以期为水滑石类阻燃剂的发展及相关研究者提供指导作用。     

The dynamic flammability and toxicity of magnesium hydroxide filled intumescent fire retardant polypropylene

The flammability properties of an intumescent fire retardant polypropylene added with magnesium hydroxide was discussed in this study. To evaluate the flammability of the material, limit oxygen index, smoke emission, tensile strength, and our exploitation dynamic flammability evaluation system, tests were assessed in experiments. The results showed that the intumescent flame retardant ammonium polyphosphate-filled polypropylene has superior flammability properties but higher carbon oxide (CO) concentration and smoke density. By adding some magnesium hydroxide additives in intumescent fire retarded polypropylene, the smoke density and CO concentration decrease; and the compound also has superior fire properties. It is concluded that intumescent system and magnesium hydroxide additives are effective on improving combustion properties for polypropylene. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:989–995, 1998     

Morphology and properties of stearate‐intercalated layered double hydroxide nanoplatelet‐reinforced thermoplastic polyurethane

In the past few years, layered double hydroxides (LDHs) with monolayer structure have been much studied for the development of polymer nanocomposites. LDHs with intercalated stearate anions form a bilayer structure with increased interlayer spacing and are expected to be better nanofillers in polymers. In the work reported, thermoplastic polyurethane (PU)/stearate‐intercalated LDH nanocomposites were prepared by solution intercalation and characterized. X‐ray diffraction and transmission electron microscopy confirmed the exfoliation at lower filler loading followed by intercalation at higher filler loading in PU matrix. As regards mechanical properties, these nanocomposites showed maximum improvements in tensile strength (45%) and elongation at break (53%) at 1 and 3 wt% loadings. Maximum improvements in storage and loss moduli (20%) with a shift of glass transition temperature (15 °C) and an increase in thermal stability (32 °C) at 50% weight loss were observed at 8 wt% loading in PU. Differential scanning calorimetry showed a shift of melting temperature of the soft segment in the nanocomposites compared to neat PU, possibly due to the nucleating effect of stearate‐intercalated LDH on the crystal structure of PU. All these findings are promising for the development of mechanically improved, thermally stable novel PU nanocomposites. Copyright © 2011 Society of Chemical Industry     

Preparation and characterization of polyimide/modified layered double hydroxide nanocomposites

Polyimide (PI)/modified layered double hydroxide (m‐LDH) nanocomposites were prepared in this study. For this work, m‐LDHs were prepared from layered double hydroxides (LDHs) through an anionic exchange reaction with pyromellitic dianhydride (PMDA), succinic acid or terephthalic acid. PMDA and 4,4′‐oxydianiline were used to make the poly(amic acid) precursor for PI. X‐ray diffraction and transmission electron microscopy measurements confirmed that the PMDA‐modified LDH (PMH) and terephthalic acid‐modified LDH (TMH) were well dispersed in the PI matrix. For the succinic acid‐modified LDH, some of the LDH was intercalated with the succinic acid molecules but most maintained its original structure. Thus, the PI/PMH and PI/TMH nanocomposites exhibited improved mechanical, thermal and electrical properties compared to pure PI. The PMH has aromatic groups and is expected to have better π–π interactions with the PI chains than the other m‐LDHs. Thus, the PI/PMH nanocomposites exhibited the best properties among the nanocomposites investigated. Copyright © 2010 Society of Chemical Industry     

Combined effects of layered nanofillers and intumescent flame retardant on thermal and fire behavior of ABS resin

The application of acrylonitrile-butadiene-styrene (ABS) copolymer as construction material is largely restricted by its inherent flammability and the release of a great amount of smoke and toxic gases during combustion. To address this issue, the combination of conventional flame retardants and nanoadditives was proven to be a promising way. Herein, both intumescent flame retardants (IFR) and layered nanofillers, that is, graphene and layered double hydroxide were added into ABS resin. These nanofillers exhibited superior dispersion in the ABS matrix. Thermal and fire behaviors of ABS resin were investigated by thermogravimetry analysis, UL-94 vertical burning test, limiting oxygen index test, and cone calorimetry. The ABS composites containing IFR and layered nanofillers presented remarkable decline in total heat release, peak heat release rate, and volume of toxic effluents released in the burning process compared with those of neat ABS, indicating the significantly improved fire safety of ABS. Moreover, introducing layered nanofillers could further enhance the heat stability and fire safety of the flame-retardant ABS composites, indicating the presence of synergistic effect between IFR and layered nanofillers. The scanning electron microscopy and Raman spectroscopy results confirmed the formation of compact and dense intumescent chars, which could obstruct the spread of heat and mass, and thus improved the heat stability and flame retardancy of ABS resin. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48220.     

Synthesis of 5‐sulfosalicylic acid‐intercalated layered double hydroxide and its effects on wood flour/polypropylene composites during accelerated UV weathering

In this study, 5‐sulfosalicylic acid (SA) anions have been intercalated into Mg₃Al‐NO₃ layered double hydroxide (LDH) to synthesize SA‐intercalated Mg₃Al‐NO₃‐LDH (LDH‐SA) by ion‐exchange reaction. Then, the effects of LDH, SA, and LDH‐SA on the photostability of wood flour/polypropylene (WF/PP) composites during accelerated ultraviolet (UV) weathering were investigated. The surface color, surface gloss, and mechanical properties of the composites during weathering were tested, accompanied by characterizations using SEM, ATR‐FTIR, and TG. The results showed that (1) SA anions completely replaced the anions in LDH and the thermal stability of LDH‐SA was considerably enhanced; (2) composites with LDH or LDH‐SA exhibited less color change, fewer surface cracks, better thermal stability, and less losses of mechanical properties than the control group; (3) LDH‐SA showed a long‐term efficiency and alleviated the photo‐oxidation of WF/PP composites successfully; (4) LDH‐SA blocked UV light by physical shield effect of the layer sheets, as well as the chemical absorbability of the interlayer anions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44597.     

Effects of layered double hydroxides on the thermal and flame retardant properties of intumescent flame retardant high density polyethylene composites

In this study, two layered double hydroxides (LDHs), ZnAl-LDH, and MgAl-LDH, were combined with intumescent flame retardant (IFR) consisting of ammonium polyphosphate and tris (2-hydroxyethyl) isocyanurate to prepare flame retardant high density polyethylene composites. The thermal and flame retardant properties of these composites were investigated by thermogravimetric analysis, limiting oxygen index measurement, and cone calorimetry, while the morphology and chemical structure of the char residue were analyzed by scanning electron microscopy, Fourier transfer infrared spectroscopy, and laser Raman spectroscopy. The results showed that the peak heat release rate (PHRR) of both HD/IFR/Zn-LDH and HD/IFR/Mg-LDH composites was 52.0% and 12.0% lower than that of HD and HD/IFR, respectively, suggesting that there was no difference in the reduction of PHRR between the two LDHs. The use of LDHs resulted in the formation of compact char residue with a high graphitic degree, but no significant increase in tensile strength.     

Synthesis and properties of polypropylene/layered double hydroxide nanocomposites with different LDHs particle sizes

In order to investigate whether the particle sizes of inorganic additives in polymer have an influence on the flame‐retardant and other properties of the polymer, five types of Mg₃Al–CO₃ layered double hydroxide (LDHs) with particle diameters of 80–100, 200–350, 500–550, 550–600, and 700–900 nm were synthesized using a hydrothermal method. The obtained Mg₃Al–CO₃ LDHs were treated using the aqueous miscible organic solvent treatment method to give highly dispersed platelets in Polypropylene (PP). The thermal stability, flame retardancy, and mechanical properties of the PP/AMO–LDH nanocomposites were investigated systematically. The results showed that the thermal stability and flame retardancy of PP could be improved after incorporating AMO–LDHs. The temperature at 50% weight loss (T_0.5) of PP/LDH (700–900 nm) nanocomposites with a LDH loading of 15 wt % was increased by 57 °C. When the LDHs loading was 40 wt %, the peak heat release rate (PHRR) of the PP/LDH nanocomposites with small LDHs particle sizes (<350 nm) was decreased by ca. 58%. The limiting oxygen index was increased by 5% for PP/LDH (80–100 nm) nanocomposites. The response surface regression results also indicated that both LDH particle size and loading have influence on PHRR, heat release capacity, tensile strength, and elongation at break. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46204.     

Synergistic flame retardant effect of piperazine salt and ammonium polyphosphate as intumescent flame retardant system for polypropylene

Amino trimethylene phosphonic acid piperazine (ATPIP) salt, as a novel charring agent, is prepared via a simple ionic reaction in distilled water using amino trimethylene phosphate (ATMP) and piperazine as raw materials. The synergistic flame retardant effect of ATPIP and ammonium polyphosphate (APP) as an intumescent flame retardant (IFR) is investigated by various characterization and testing methods. The results show that the polypropylene (PP)/modified APP with piperazine (MAPP)/ATPIP ternary blend passes UL-94 V-0 rating and achieve a limiting oxygen index (LOI) of 30% at a loading level of 25 wt% IFR (MAPP:ATPIP = 3:1). Meanwhile, the total smoke production (TSP) value of IFR-PP samples is 3.3 m², which decreases by 93.2% compared with that of pure PP, exhibiting excellent smoke suppression performance. Besides, the analysis of gaseous pyrolysis products and char residue indicates that the IFR-PP samples show a synergistic flame-retardant mechanism including the gas phase and the condensed phase.     

The flame retardant and thermal performances of polypropylene with a novel intumescent flame retardant

A novel mono-component intumescent flame retardant(m-IFR), called poly-(spirocyclic pentaerythritol bisphosphonate-1,3,5-triazine-O-bicyclic pentaerythritol phosphate) (PSTBP) was synthesized and characterized. PSTBP was used in polypropylene (PP) to obtain PP/PSTBP mixture whose flame retardancy, thermostability, and water resistance were studied by limiting oxygen index (LOI), vertical burning test (UL-94 V) and thermogravimetric analysis (TGA). In addition, flame-retardant mechanism of the PSTBP was investigated. The results showed that the residue of PSTBP reached 34.58% at 800°C and the volume of the PSTBP increased by dozens of times. When the content of PSTBP was 30.0 wt%, the PP/PSTBP mixture could achieve an LOI value of 32.5% and an UL-94 V-0 rating. Compared with PP/APP/PER system, PP/PSTBP mixture showed better water resistance. The TGA and Fourier transform infrared spectroscopy (FTIR) results showed that PSTBP could generate free radicals and capture the free radicals of the thermal decomposition of PP, and form a dense, strong, and thick intumescent char on the substrate, thus effectively retard the degradation and combustion of PP.     

The mechanical properties and thermal performances of polypropylene with a novel intumescent flame retardant

A novel intumescent flame retardant: tetra‐spirophosphoryl‐benzoguanamine (TSPB) containing three constituents was used as a new flame retardant for polypropylene to prepare flame‐retardant materials, whose flammability and thermal behavior were studied by the limited oxygen index (LOI), thermogravimetric analysis (TGA), in addition whose mechanical properties were investigated in this work. It was found that when the addition of TSPB was 25 wt %, the LOI value of the PP could achieve to 29.5 and pass the UL‐94 V‐0 rating test. The TGA data showed that TSPB could enhance the thermal stability of PP and effectively increase the char residue formation. The mechanical performance test showed that the addition of TSPB improve the mechanical performances of PP to some extent. Thus, the trinity intumescent flame retardant TSPB is good to modify PP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

层状双金属氢氧化物形成机理的研究现状

近年来,层状双金属氢氧化物（LDH）凭借特殊的层状结构、极强的可调控性能、优异的环境兼容性及显著的应用效果等特点,在环保、催化、储能、传感等领域得到广泛关注。国内外多数研究集中于LDH可控合成工艺的改进完善及LDH的应用探索,但迄今对制备LDH时涉及其组成结构形貌的变化过程,即其形成机理的关注较少,相关机制解释模糊,深入研究其形成过程对于可控制备具有独特形貌和特定组成的LDH及开发更深层次的应用具有至关重要的作用。本文介绍了LDH层板形成机理的3个主要研究方向,即以二价金属氢氧化物的存在为基础、以三价金属氢氧化物的存在为基础和拓扑相变机制,并分别进行了阐述辨析及对比分析,发现LDH层板的形成是一个极其复杂的过程,多种机制往往共同作用,总结认为固液及液液反应在初期成核阶段占据主导地位,各自作用程度及不同层板构筑机制产生的主导作用易受到外界环境因素影响,而更为普遍的LDH形成机制解释需要归纳总结更多LDH层板构筑的区别和规律,宏观和微观上探索形成过程的内在机理及科学本质,以期为LDH开发拓展提供理论基础。     

Polymorphism and spherulite morphology of poly(1,4‐butylene adipate)/organically‐modified layered double hydroxide nanocomposites

A novel biodegradable poly(1,4‐butylene adipate)/organically‐modified layered double hydroxide (PBA/m‐LDH) nanocomposites are synthesized using the solution mixing process. The m‐LDH is originally prepared with magnesium nitrate hexahydrote (Mg(NO₃)₂ 6H₂O), aluminum nitrate‐9‐hydrate (Al(NO₃)₃ 9H₂O), oleic acid, and sorbitol by a novel one‐step co‐precipitation method to intercalate the organo‐modifier of oleic acid and sorbitol into the interlayer of LDH. The structure and morphology of the PBA/m‐LDH nanocomposites are characterized using X‐ray diffraction and transmission electron microscopy (TEM). It has been shown that the m‐LDH is exfoliated and well distributed in PBA matrix. The effect of m‐LDH on the polymorphic crystal and morphology of PBA at various crystallization temperatures (T_cs) would be investigated using WAXD and POM. Both data indicate that the addition of m‐LDH can change the starting formation temperature of α‐form crystals. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42526.     

Polydimethylsiloxane based polyurethane and its composite with layered double hydroxide: Synthesis and its thermal properties

This investigation reports the synthesis of a new class of polyurethane (PU) based on bis(hydroxyalkyl) polydimethylsiloxane (PDMS) as diol and isophorone diisocyanate as diisocyanate followed by the preparation of PU/layered double hydroxide (PU/LDH) nanocomposite via ex-situ technique. Nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies confirm the formation of PU and incorporation of PDMS into the PU backbone. Thermogravimetry analysis revealed that thermal stability of the composite improves significantly with incorporation of LDH into the PU matrix. This may be accredited to the barrier effect rendered by the LDH layers. Differential scanning calorimetry study reveals that with the incorporation of LDH, glass transition temperature (T_g) of the composite increases for an optimum level of loading beyond which it remains constant.     

Bamboo fiber reinforced polypropylene composites and their mechanical,thermal, and morphological properties

Short bamboo fiber reinforced polypropylene composites were prepared by incorporation of various loadings of chemically modified bamboo fibers. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as compatibilizer to improve fiber–matrix adhesion. The effects of bamboo fiber loading and modification of the resin on the physical, mechanical, thermal, and morphological properties of the bamboo reinforced modified PP composites were studied. Scanning electron microscopy studies of the composites were carried out on the interface and fractured surfaces. Thermogravimetric analysis and IR spectroscopy were also carried out. At 50% volume fraction of the extracted bamboo fiber in the composites, considerable increase in mechanical properties like impact, flexural, tensile, and thermal behavior like heat deflection temperature were observed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of a novel phosphorus‐containing compound on the flame retardancy and thermal degradation of intumescent flame retardant polypropylene

A novel flame retardant, tetra(5,5‐dimethyl‐1,3‐ dioxaphosphorinanyl‐2‐oxy) neopentane (DOPNP), was synthesized successfully, and its structure was characterized by FT‐IR, ¹H NMR, and ³¹P NMR. The thermogravimetric analysis (TGA) results demonstrate that DOPNP showed a good char‐forming ability. Its initial decomposition temperature was 236.4°C based on 1% mass loss, and its char residue was 41.2 wt % at 600°C, and 22.9 wt % at 800°C, respectively. The flame retardancy and thermal degradation behavior of novel intumescent flame‐retardant polypropylene (IFR‐PP) composites containing DOPNP were investigated using limiting oxygen index (LOI), UL‐94 test, TGA, cone calorimeter (CONE) test, and scanning electron microscopy (SEM). The results demonstrate that DOPNP effectively raised LOI value of IFR‐PP. When the loading of IFR was 30 wt %, LOI of IFR‐PP reached 31.3%, and it passed UL‐94 V‐0. TGA results show that DOPNP made the thermal decomposition of IFR‐PP take place in advance; reduced the thermal decomposition rate and raised the residual char amount. CONE results show that DOPNP could effectively decrease the heat release rate peak of IFR‐PP. A continuous and compact char layer observed from the SEM further proved the flame retardance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

氢氧化镁阻燃剂的表面改性及其在聚丙烯中的应用

采用不同改性剂对氢氧化镁进行表面改性处理，通过实验发现采用4％的硬脂酸钠处理后的氢氧化镁阻燃剂在聚丙烯体系中分散均匀，当氢氧化镁在聚丙烯体系中的添加量达65％时，达到了理想的阻燃效果。     

Kaolin modified with new resin–iron chelate as flame retardant system for polypropylene

Polypropylene's fire‐retardant properties can be improved by using modified kaolin. Modification was done by reaction of kaolin with a prepared resin–iron chelate. Polypropylene samples were loaded with different amounts of kaolin, modified kaolin, and their mixture. Ignition properties of the produced samples were evaluated using cone calorimeter, UL 94, and thermogravimetric analysis techniques. It was found that sample S2 loaded with a mixture of kaolin and modified kaolin had significantly reduced the smoke generation and had a heat release rate comparable to that with kaolin. It was also found that samples S4 and S5 loaded with modified kaolin burned out earlier than did the other samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3119–3125, 2004