Aluminum Hypophosphite Research Articles

Preparation and characterization of microencapsulated aluminum hypophosphite and its performance on the thermal, flame retardancy, and mechanical properties of epoxy resin

AbstractA novel microcapsule flame retardant microencapsulated aluminum hypophosphite (MAHP) was introduced. Fourier transform infrared spectroscopy, scanning electron microscopy, and x‐ray photoelectron spectroscopy were used to characterize the shell material on the surface of MAHP. The water contact angle (WCA) experiments show that the WCA of MAHP (71.4°) is significantly larger than that of aluminum hypophosphite (34.4°). And the interfacial free energy between MAHP and epoxy resin (EP) is only 7.89 mJ/m2, which results in good compatibility with EP. The results from differential scanning calorimeter test indicate that the addition of MAHP can improve the heat resistance of EP matrix. Thermogravimetric (TG) tests show that EP/MAHP has the largest amount of residue (32.03 wt%). The combustion behaviors of flame‐retardant EP (FR‐EP) composites were evaluated by limiting oxygen index, UL‐94, and cone calorimetry. The results show that the microencapsulation to AHP in this study can significantly improve the flame retardancy of EP. Thermogravimetric infrared analysis was used to investigate the gas‐phase products. Surface morphology and structure of char residues of EP and FR‐EP was also studied. The carbon layer became quite dense and continuous when MAHP was added. On the premise of improving the flame retardancy, the mechanical properties of the material are retained. The tensile strength and bending strength of EP/MAHP‐3 were 23.98 and 50.75 MPa, respectively.

Research on two sides horizontal flame spread over rigid polyurethane with different flame retardants

In order to reveal the effect of flame retardant to rigid polyurethane foam (RPUF), a medium-scale experimental platform was built to study horizontal two sides flame spread with non-flame retardant rigid polyurethane and rigid polyurethane with expanded graphite (EG) (5 mass% and 10 mass%), aluminum hypophosphite (AHP) (5 mass%) and aluminum diethylhypophosphite (ADP) (5 mass%), respectively. The results show that the flame retardant will limit the flame combustion intensity, and the combustion intensity of five samples follows the order as RPUF > RPUF/EG5 > RPUF/AHP5 > RPUF/ADP5 > RPUF/EG10. Meanwhile, with the addition of flame retardant, the combustion mechanism is different. The specimen with the addition of EG has the most obvious bending deformation, and the bending deformation of RPUF/EG10 is significantly higher than others, which is mainly caused by the low strength of EG. For RPUF/ADP5, the flame spread gives the maximum value, which can be attributed to the decreased ignition time and no reduction FGI. Due to the intumescent carbon layers formation when adding AHP, hindering mass and heat transportation, extinguishment happens eventually. On the other hand, the flame retardant of ADP shows better retardancy including the decreasing flame height, flame width, heat flux and flame temperature than others.

The Charring Effect and Flame Retardant Properties of Thermoplastic Elastomers Composites Applied for Cable

The halogen-free flame retardant (HFFR) thermoplastic elastomers (TPEs) composites filled with aluminum hypophosphite had been prepared by twin-screw extruder. The flame retardancy, thermal stability, charring-effect, mechanical and rheological properties of TPE composites had been investigated by cone calorimeter, limiting oxygen index (LOI), UL-94 (vertical flame) test, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), ultimate tensile and rheometer. The research results indicated that the flame retardancy and thermal stability of flame retardant (FR) TPEs had been dramatically improved. Obvious char-forming effect can be found for the samples with the addition of polyphenylene oxide (PPO) during high heat flow conditions, which presented more content and more compact of residue compared to the samples without PPO after combustion of cone calorimeter. Mechanical and rheological characteristics showed that the tensile strength and processability can be well maintained for FR TPEs composites, which was very important for industrial applications.

The effect of 3D structure design on fire behavior of polyethylene terephthalate glycol containing aluminum hypophosphite and melamine cyanurate

AbstractEffect of the shape of 3D printed samples on fire behavior of polyethylene terephthalate glycol (PET‐G) and PET‐G additivated with a mix of aluminum hypophosphite (AHP) and melamine cyanurate as flame retardant, was investigated. The additives improved fire performance (e.g., maximum average rate of heat emission, total oxygen consumption, heat release rate indices) irrespective of structural complexity, favoring carbonaceous char formation. However, at increasing structural complexity, they promoted higher release of smoke, compared to neat PET‐G, because of a change in the prevalent retardation mechanism, which became dominated by the flame inhibition action of AHP. Consequently, the synergistic effect obtained combining the two additives, was hindered. Impact of product design on mechanisms of fire retardation helps in devising engineering solutions aimed at meeting required level of fire‐safety performance, which should be tailored to the specific product.

Organic Aluminum Hypophosphite/Graphitic Carbon Nitride Hybrids as Halogen-Free Flame Retardants for Polyamide 6.

The novel organic aluminum hypophosphite (ALCPA) and its hybrid (CNALCPA) with graphitic carbon nitride (g-C3N4) were successfully synthesized and applied as halogen-free flame retardants in polyamide 6 (PA6). Their structures, morphology, thermal stability, and fire properties were characterized. Results showed that both ALCPA and CNALCPA had good flame retardancy. PA6/CNALCPA composites achieved a high limited-oxygen-index (LOI) value of 38.3% and a V-0 rating for UL94 at 20 wt % loading, while PA6/ALCPA composites could reach a V-1 rating for UL94. The flame-retardant mechanism was also studied. On the one hand, the incorporation of g-C3N4 produced more gas-phase products, which indicated a gas-phase mechanism. On the other hand, g-C3N4 could catalyze the thermal degradation of ALCPA and PA6 to form a compact char layer that was evidence for a solid-phase mechanism. The tensile test of the PA6 composites also displayed good mechanical properties.

Preparation of microencapsulated aluminum hypophosphite and its flame retardancy of the unsaturated polyester resin composites

A novel microencapsulated flame retardant (CP@AHP), aluminum hypophosphite (AHP) as the core material and chlorinated paraffin (CP) as the shell material, was successfully prepared and applied in unsaturated polyester resin (UPR) to prepare the UPR composites in this paper. The aim of microencapsulation AHP was to enhance the fire safety of the UPR composites. The structure, morphology and thermal behavior of CP@AHP were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis (TG), respectively. The thermal and flame-retardant properties of the UPR composites were evaluated by TG and cone calorimetry test (CCT), respectively. At the same time, the tensile and flexural properties of UPR composites were tested. Compared with pure UPR, the residue at 800 °C of UPR/CP@AHP-1:2 (UPR/CP@AHP with the mass ratio of CP:AHP = 1:2) under nitrogen atmosphere is from 6.9 to 31.6. The CCT results showed that the peak heat release rate (pHRR) and total heat release of UPR/CP@AHP-1:2 decreased by 58.4 and 46.1%, respectively, in comparison with pure UPR. The results of TG and CCT indicated that CP@AHP could improve the thermal stability and flame retardancy of the UPR composites. Finally, based on the above results, the flame retardancy mechanism of CP@AHP was proposed.

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part II: Thermal Degradation, Gas Phase, and Elemental Analyses.

Bamboo charcoal (BC) and aluminum hypophosphite (AHP) singly and in combination were investigated as flame-retardant fillers for polylactic acid (PLA). A set of BC/PLA/AHP composites were prepared by melt-blending and tested for thermal and flame-retardancy properties in Part I. Here, in Part II, the results for differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), X-ray diffraction (XRD), and X-ray photoelectron analysis (XPS) are presented. The fillers either singly or together promoted earlier initial thermal degradation of the surface of BC/PLA/AHP composites, with a carbon residue rate up to 40.3%, providing a protective layer of char. Additionally, BC promotes heterogeneous nucleation of PLA, while AHP improves the mechanical properties and machinability. Gaseous combustion products CO, aromatic compounds, and carbonyl groups were significantly suppressed in only the BC-PLA composite, but not pure PLA or the BC/PLA/AHP system. The flame-retardant effects of AHP and BC-AHP co-addition combine effective gas-phase and condensed-phase surface phenomena that provide a heat and oxygen barrier, protecting the inner matrix. While it generated much CO2 and smoke during combustion, it is not yet clear whether BC addition on its own contributes any significant gas phase protection for PLA.

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part I: Thermal and Elemental Analyses.

In this study, bamboo charcoal (BC) was used as a substitute filler for bamboo powder (BP) in a lignocellulose-plastic composite made from polylactic acid (PLA), with aluminum hypophosphite (AHP) added as a fire retardant. A set of BC/PLA/AHP composites were successfully prepared and tested for flame-retardancy properties. Objectives were to (a) assess compatibility and dispersibility of BC and AHP fillers in PLA matrix, and (b) improve flame-retardant properties of PLA composite. BC reduced flexural properties while co-addition of AHP enhanced bonding between PLA and BC, improving strength and ductility properties. Adding AHP drastically reduced the heat release rate and total heat release of the composites by 72.2% compared with pure PLA. The formation of carbonized surface layers in the BC/PLA/AHP composites effectively improved the fire performance index (FPI) and reduced the fire growth index (FGI). Flame-retardant performance was significantly improved with limiting oxygen index (LOI) of BC/PLA/AHP composite increased to 31 vol%, providing a V-0 rating in UL-94 vertical flame test. Adding AHP promoted earlier initial thermal degradation of the surface of BC/PLA/AHP composites with a carbon residue rate up to 40.3%, providing a protective layer of char. Further raw material and char residue analysis are presented in Part II of this series.

Fire‐retardant synergy of tris(1‐methoxy‐2,2,6,6‐tetramethyl‐4‐piperidinyl)phosphite and aluminum hypophosphite/melamine hydrobromide in polypropylene

AbstractFire‐retardant synergy of tris(1‐methoxy‐2,2,6,6‐tetramethyl‐4‐piperidinyl) phosphite (NORPM) and aluminum hypophosphite (ALHP)/melamine hydrobromide (MHB) in polypropylene (PP) was researched by limiting oxygen index (LOI) measurement, vertical burning test, and cone calorimetric test (CCT). The results reveal that NORPM, together with ALHP/MHB, has an exceptional fire‐retardant synergy in PP. For the FR‐PP containing 1.0 wt% of ALHP and 1.5 wt% of MHB, combining NORPM in 0.20 wt% concentration can make its LOI value increases from 19.0% to 26.1%, the fire‐retardant efficiency (EFF) increases from 0.48 to 3.07, synergistic efficiency (SE) is as high as 2.18, the vertical combustion rating can be improved from none to UL 94 V‐2, fire performance index (FPI) increases from 58.7 to 84.9, and various heat release parameter values are reduced markedly. NORPM induces the synergy with ALHP/MHB primarily by the mechanisms as follows: active free radicals formed through the decomposition of NORPM, such as CH3, CH3O, nitro radicals and amino radicals, together with PH3 and HBr, trap active radicals (HO·) for combustion. Consequently, the reaction chain of combustion is terminated, which makes gaseous phase fire retardancy more efficient.

Mitigation the release of toxic PH3 and the fire hazard of PA6/AHP composite by MOFs

Aluminum hypophosphite (AHP) is a high-efficiency phosphorus-based flame retardant with high P content, which is widely used in Polyamide 6 (PA6). However, AHP releases phosphine gas (PH3) at high temperatures, which is highly toxic to human’s health and environment. Metal-organic frameworks (MOFs) have porous structure exhibiting high performance in gas adsorption. Therefore, mesoporous iron (III) carboxylate [MIL-100 (Fe)] was synthesized in this work and employed to study the adsorption capacity of toxic PH3 in PA6/AHP composite during processing. AHP was combined with melamine cyanurate (MCA) and MIL-100 (Fe) followed by blending with PA6 to prepare PA6 composites (PA6/MA and PA6/MAF). PA6/MAF with the weight ratio of 5:5 performed well in inhibiting the release of PH3 during the processing of composite as well as the accelerated thermal experiment devised by our group. Besides, PA6/MAF (5:5) showed relatively low fire hazard reflected by the reduction of the peak of heat release rate of PA6 composite from 962 to 260 kW/m2 compared with that of pure PA6 in the cone calorimeter test, and MIL-100 (Fe) along with MCA also presented synergistic effect in suppressing the emission of carbon monoxide. The subtle selection of MOFs herein has the potential to be used as a promising synergist for hazardous gases released from polymer composites to improve the occupational and fire safety in the society.

Curing Kinetics and Thermal Stability of Epoxy Composites Containing Newly Obtained Nano-Scale Aluminum Hypophosphite (AlPO2).

For the first time, nano-scale aluminum hypophosphite (AlPO2) was simply obtained in a two-step milling process and applied in preparation of epoxy nanocomposites varying concentration (0.1, 0.3, and 0.5 wt.% based on resin weight). Studying the cure kinetics and thermal stability of these nanocomposites would pave the way toward the design of high-performance nanocomposites for special applications. Scanning electron microscopy (SEM) and transmittance electron microscopy (TEM) revealed AlPO2 particles having domains less than 60 nm with high potential for agglomeration. Excellent (at heating rate of 5 °C/min) and Good (at heating rates of 10, 15 and 20 °C/min) cure states were detected for nanocomposites under nonisothermal differential scanning calorimetry (DSC). While the dimensionless curing temperature interval (ΔT*) was almost equal for epoxy/AlPO2 nanocomposites, dimensionless heat release (ΔH*) changed by densification of polymeric network. Quantitative cure analysis based on isoconversional Friedman and Kissinger methods gave rise to the kinetic parameters such as activation energy and the order of reaction as well as frequency factor. Variation of glass transition temperature (Tg) was monitored to explain the molecular interaction in the system, where Tg increased from 73.2 °C for neat epoxy to just 79.5 °C for the system containing 0.1 wt.% AlPO2. Moreover, thermogravimetric analysis (TGA) showed that nanocomposites were thermally stable.

Flame retardancy and smoke suppression of silicone foams with microcapsulated aluminum hypophosphite and zinc borate

The flame‐retardant microcapsules were successfully fabricated with an aluminum hypophosphite (AHP) core. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) were used to verify that AHP was encapsulated in the microcapsules, and thermogravimetry analysis showed that microencapsulated AHP (MAHP) possessed higher thermal stability than that of AHP. Then, a flame‐retardant and smoke suppression system for silicone foams (SiFs) was obtained through a synergistic effect of MAHP and zinc borate (2ZnO·3B2O3·3.5H2O). The mechanical properties, flame retardance, and smoke suppression of SiFs with MAHP and zinc borate were tested using the tensile test, limiting oxygen index (LOI) test, UL‐94 test, and cone calorimeter test. The mechanical properties indicated that the tensile strength and elongation at break of SiFs could evidently improve with the incorporation of MAHP. Compared with pure SiF, SiF8 with 4.5‐wt% MAHP and 1.5‐wt% zinc borate could achieve an LOI value of 30.7 vol% and an UL‐94 V‐0 rating, the time to ignition amplified almost six times, the peak heat release rate and total heat release were 51.10% and 46.00% less than that of pure SiF, respectively, the fire performance index increased nearly 13 times, and the fire growth index value was only 13.18% of pure SiF. Moreover, the partial substitution of zinc borate imparted a substantial improvement in both flame retardancy and smoke suppression. Especially, the peak smoke production rate and total smoke production of SiF8 were merely 38.46% and 38.84% of pure SiF.

A facile and efficient flame-retardant and smoke-suppressant resin coating for expanded polystyrene foams

Flame-retardant and smoke-suppressant expanded polystyrene (EPS) foams were prepared by coating a mixture of thermoplastic phenolic resin (PF) and aluminum hypophosphite (AP) or expandable graphene (EG) onto EPS spheres. The PF reacting with AP by hydrogen-bond interaction formed a facile flame-retardant coating PF/AP, which not only greatly reduced flammability and smoke release, but also remained the thermal conductivities of EPS foams at low level. Compared with those of EPS/PF/EG, EPS/PF/AP could pass the UL-94 test and showed better flame-retardant performances with lower heat release rates and fire growth rates. Especially, the time to ignition (TTI) of EPS/PF/AP achieved 52 s, much higher than those of EPS/PF/EG (9 s) and neat EPS (2 s). Also, the peak of smoke production rate (PSPR) and the total smoke production (TSP) of both composites were significantly reduced, showing an excellent smoke-suppressant performance. The mechanism analysis suggested that the PF/AP coating could form a compact P–O–C cross-linked char layer and effectively protect the matrix from further combusting. Particularly, the EPS/PF/AP had a higher compressive strength and lower thermal conductivity in comparison with EPS/PF/EG. These above results show that the EPS/PF/AP composite has enormous potential in building thermal insulation field.

Investigation of the Flame-Retardant and Mechanical Properties of Bamboo Fiber-Reinforced Polypropylene Composites with Melamine Pyrophosphate and Aluminum Hypophosphite Addition

To improve the flame-retardant performance of bamboo fiber (BF) reinforced polypropylene (PP) composites, melamine pyrophosphate (MPP) and aluminum hypophosphite (AP) at a constant mass ratio of 2:1 were added. The influence of the MPP/AP mass fraction on the mechanical and flame-retardant properties of the BF reinforced PP composites were evaluated by mechanical testing, limiting oxygen index (LOI) and cone calorimetry. Mechanical tests demonstrate that tensile properties of BF/PP decreased with the increase of MPP/AP mass fraction, while flexural properties of composites exhibited very different tendencies. Both flexural strength and modulus increased slightly with the addition of MPP/AP at first, and then decreased significantly after a relatively high content of MPP/AP was loaded. This was due to the poor interfacial compatibility between PP and MPP/AP. The flame retardancy of BF/PP composites has been greatly improved. When 30% MPP/AP was loaded into the composites, the LOI increased to 27.2%, which was 42.4% higher than that of the composite without flame retardant addition. Cone calorimetry results indicated that MPP/AP worked in both gas and condensed phases during the combustion process. Peak heat release rate, total smoke production and mass loss of the composites were significantly reduced because of the addition of MPP/AP.

Comparative Study on the Flame-Retardant Properties and Mechanical Properties of PA66 with Different Dicyclohexyl Hypophosphite Acid Metal Salts.

Three metal salts of dicyclohexyl hypophosphite, namely dicyclohexyl aluminum hypophosphite (ADCP), dicyclohexyl magnesium hypophosphite (MDCP), and dicyclohexyl zinc hypophosphite (ZDCP), were synthesized. These flame retardants were subjected to thermogravimetric analysis, and the results showed that ADCP and ZDCP had higher thermal stabilities than MDCP. They were then separately mixed with polyamide 66 (PA66)to prepare composite materials, of which the combustion properties were determined by the limiting oxygen index method and horizontal/vertical burning experiments. The mechanical properties of the materials were further evaluated using an electronic universal testing machine. The results showed that all the three flame retardants exerted a flame-retardant effect on PA66, but the flame-retardant effect of MDCP was inferior to those of ADCP and ZDCP. All the composites also showed similar mechanical properties. Among the three flame retardants, ADCP had the best overall performance for raw materials, showing good flame-retardant properties while maintaining the mechanical properties of the raw materials. The optimal dosage of ADCP was 15 wt %, at which a V-0 rating in the vertical burning test (UL 94 test) can be obtained.

Flame retardancy and thermal degradation of rigid polyurethane foams composites based on aluminum hypophosphite

Rigid polyurethane foam/aluminum hypophosphite (RUPF/AHP) composites were fabricated by one-step water-blown method. Furthermore, thermal conductivity test and scanning electron microscope (SEM) confirmed RPUF/AHP composites presented well cell structure with thermal conductivity of 0.0434–0.0466 k W/m · k and density of 59.0–60.3 kg m−3. Thermogravimetric analysis test showed significantly enhanced Tmax value of RPUF/AHP in second stage, indicating enhanced thermal stability of the composites, which was as also confirmed by thermal degradation kinetics analysis. Flame retardant test revealed that AHP presented high flame retardancy efficiency to RPUF, only 5 php AHP incorporation can make RPUF/AHP5 reach V-1 rating in UL-94 test. Microscale combustion calorimetry (MCC) test showed that AHP could effectively decrease peak of heat release rate (PHRR) of RPUF/AHP composites. RPUF with 30 php AHP loading presented PHRR value of 164 W g−1, which was 20.3% decreased compared with that of virgin RPUF. Thermogravimetric analysis-Fourier transform infrared spectroscopy (TG-FTIR) was introduced to investigate gaseous products in degradation process of RPUF/AHP composites. It can be found that AHP enhanced the release of CO2, isocyanate compound while inhibit the release of hydrocarbons, aromatic compounds and esters. Furthermore, scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS) were applied to research char residue of the RPUF/AHP composites. It was confirmed that AHP could promote C and N elements in RPUF matrix to form aromatic and aromatic heterocyclic structure, which combined with aluminum phosphate to form compact char residue, thus significantly inhibit mass and heat transmission in combustion. Consequently, a possible gas-solid flame-retardant mechanism of RPUF/AHP composites was proposed.

An insight into gas phase flame retardant mechanisms of AHP versus AlPi in PBT: Online pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry

As is well known, gas phase flame retardant mechanisms are very hard to be understood for the extremely intricate burning process but they are crucial for developing highly efficient flame retardants. Pyrolysis provides a valid way for this purpose because combustion proceeds after it. In this work, the pyrolysis behaviors of aluminum hypophosphite (AHP), aluminum diethylphosphinate (AlPi), poly(1,4-butylene terephthalate) (PBT) and PBT composites (with 10 wt% AHP or AlPi) were investigated by the fragment-free pyrolysis vacuum ultraviolet photoionization time of flight mass spectrometry (PY-PI-TOFMS) at different temperatures in real time. The gas phase flame retardant mechanism of AHP in PBT is proposed to be the flame inhibition effect of PH3, H3PO2 and P4 pyrolyzed from AHP. That of AlPi in PBT is speculated to be phosphorus-containing compounds and a kind of phosphorus radical pyrolyzed from AlPi as flame inhibitors and the promoted pyrolysis of AlPi by PBT matrix to be synchronous with it. The eight-membered cyclic non-covalent adduct of C2H5–(O=)P•–OH radical and a molecule of diethylphosphinic acid via intermolecular double hydrogen-bond interaction can produce PO type radicals more effectively in flame. Thermogravimetric analysis results are in accordance with those of pyrolysis. And the much better gas phase flame retardant effect of AlPi than AHP in PBT concluded from combustion tests are interpreted by pyrolysis results, which provides powerful guidance for developing highly efficient flame retardants.

Synergistic Flame-Retardant Mechanism of Dicyclohexenyl Aluminum Hypophosphite and Nano-Silica.

The flame retardant dicyclohexenyl aluminum hypophosphite (ADCP) and nano-silica are added to PA66 to improve flame retardant property of the composite. The flame-retardant property of the composite is tested via oxygen index test, vertical burning test, and cone calorimetry test. Combustion residues are tested using scanning electron microscopy, EDS spectroscopy, and Fourier infrared analysis. Results show that flame-retardant ADCP can effectively promote the formation of a porous carbon layer on the combustion surface of PA66. Nano-silica easily migrates to the material surface to improve the oxidation resistance of the carbon layer and the density of the carbon layer’s structure. It can also effectively prevent heat, flammable gases, and oxygen from entering the flame zone and enhance the flame retardant properties of ADCP.

Synergistic effect between phosphorus tailings and aluminum hypophosphite in flame‐retardant thermoplastic polyurethane composites

The massive accumulation of phosphorus tailings (PT) not only occupies land resources and also causes great threat to ecological environment and human security. It is of great significance to explore the resource utilization of PT in some fields. Herein, aluminum hypophosphite (AHP) and PT are blended together to enhance the flame retardancy of thermoplastic polyurethane (TPU) composites, and the synergistic effects between AHP and PT are investigated systematically. Cone calorimeter test (CCT) results indicate that the peak heat release rate (PHRR) and total heat release (THR) of the samples containing 25 wt% AHP are decreased by 89% and 68%, respectively, and the total smoke release (TSR) show a reduction of 58.8%, in comparison with those of neat TPU. For the sample TPU/22.5AHP/2.5PT, the PHRR, THR, and TSR are decreased by 91.2%, 70%, and 63%, respectively. Scanning electron microscopy (SEM) analysis results demonstrate that the addition of PT can facilitate the generation of dense and compact char layers, preventing the release of heat and smoke effectively. All the abovementioned results indicate that the synergistic effects are existed between AHP and PT for enhancing the fire safety of TPU composites, which can provide a new way for the utilization of PT.

Flame Retardancy and Toughness of Poly(Lactic Acid)/GNR/SiAHP Composites.

A novel flame-retardant and toughened bio-based poly(lactic acid) (PLA)/glycidyl methacrylate-grafted natural rubber (GNR) composite was fabricated by sequentially dynamical vulcanizing and reactive melt-blending. The surface modification of aluminum hypophosphite (AHP) enhanced the interfacial compatibility between the modified aluminum hypophosphite by silane (SiAHP) and PLA/GNR matrix and the charring ability of the PLA/GNR/SiAHP composites to a certain extent, and the toughness and flame retardancy of the PLA/GNR/SiAHP composites were slightly higher than those of PLA/GNR/AHP composites, respectively. The notched impact strength and elongation of the PLA composite with 20 wt. %GNR and 18 wt.% SiAHP were 13.1 kJ/m2 and 72%, approximately 385% and 17 fold higher than those of PLA, respectively, and its limiting oxygen index increased to 26.5% and a UL-94 V-0 rating was achieved. Notedly, the very serious melt-dripping characteristics of PLA during combustion was completely suppressed. The peak heat release rate and total heat release values of the PLA/GNR/SiAHP composites dramatically reduced, and the char yield obviously increased with an increasing SiAHP content in the cone calorimeter test. The good flame retardancy of the PLA/GNR/SiAHP composites was suggested to be the result of a synergistic effect involving gaseous and condensed phase flame-retardant mechanisms. The high-performance flame-retardant PLA/GNR/SiAHP composites have great potential application as replacements for petroleum-based polymers in the automotive interior and building fields.