Synthesis of Organic-Inorganic Hybrid Aluminum Hypophosphite Microspheres Flame Retardant and Its Flame Retardant Research on Thermoplastic Polyurethane

Abstract

Aluminum hypophosphite microspheres (AHP) were synthesized by hydrothermal method using NaH₂PO₂-H₂O and AlCl₃·6H₂O as raw materials, and then the AHP microspheres were polymerized by surface polymerization of micro-nanospheres with cyclic cross-linked poly(cyclotriphosphazene-co-4. 4′-sulfonyldiphenol) (PZS). A new organic-inorganic poly(phosphonitrile)-modified aluminum hypophosphite microspheres (PZS-AHP) were synthesized by encapsulation and applied to flame retardant thermoplastic polyurethane (TPU). The microstructure and chemical composition of the PZS-AHP microsphere were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray spectroscopy. The thermal stability of PZS-AHP microsphere was explored with thermogravimetric analysis. Thermogravimetric data indicate that the PZS-AHP microspheres have excellent thermal stability. The thermal and flame-retarding properties of the TPU composites were evaluated by thermogravimetric (TG), limited oxygen index tests (LOI), and cone calorimeter test (CCT). The TPU composite achieved vertical burning (UL-94) V-0 grade and LOI value reached 29.2% when 10 wt% PZS-AHP was incorporated. Compared with those of pure TPU, the peak heat release rate (pHRR) and total heat release (THR) of TPU/10%PZS-AHP decreased by 82.2% and 42.5%, respectively. The results of CCT indicated that PZS-AHP microsphere could improve the flame retardancy of TPU composites.

Keywords

polyphosphazene / thermoplastic polyurethane / flame retardancy / aluminum hypophosphite / surface polymerization

References

[1] Tabuani D, Bellucci F, Terenzi A, et al. Flame Retarded Thermoplastic Polyurethane (Tpu) for Cable Jacketing Application[J]. Polym. Degrad. Stabil., 2012, 97(12): 2 594-2 601.

[2] Choi J, Jang J U, Yin W B, et al. Synthesis of Highly Functionalized Thermoplastic Polyurethanes and Their Potential Applications[J]. Polymer, 2017, 116: 287-294.

[3] Jiao CM, Wang HZ, Li SX, et al. Fire Hazard Reduction of Hollow Glass Microspheres in Thermoplastic Polyurethane Composites[J]. J. Hazard. Mater., 2017, 332: 176-184.

[4] Wang XC, Geng T, Han J, et al. Effects of Nanoclays on the Thermal Stability and Flame Retardancy of Microcellular Thermoplastic Polyurethane Nanocomposites[J]. Polym. Composite., 2018, 39(S3): E1 429-E1 440.

[5] Kemmlein S, Herzke D, Law R J. Brominated Flame Retardants in the European Chemicals Policy of Reach—Regulation and Determination in Materials[J]. J. Chromatogr. A, 2009, 1216(3): 320-333.

[6] Wei P, Wu D, Zhong HF, et al. Effect of Flame Retardant Containing Phosphorus and Silicone on Thermal Performance of Pc/Abs[J]. J. Wuhan Univ. Technol.-Mat. Sci. Edit., 2009, 24(2): 235-240.

[7] Zeng LJ, Yang L, Ai LH, et al. Synergistic Flame Retardant Effect of Ammonium Polyphosphate and Aluminum Hydroxide on Polyurethane[J]. J. Wuhan Univ. Technol. -Mat. Sci. Edit., 2022, 37(3): 533-539.

[8] Lin YQ, Jiang SH, Hu Y, et al. Hybrids of Aluminum Hypophosphite and Ammonium Polyphosphate: Highly Effective Flame Retardant System for Unsaturated Polyester Resin[J]. Polym. Composite., 2018, 39(5): 1 763-1 770.

[9] Wu NJ, Xiu ZX. Surface Microencapsulation Modification of Aluminum Hypophosphite and Improved Flame Retardancy and Mechanical Properties of Flame-Retardant Acrylonitrile-Butadiene-Styrene Composites[J]. RSC Adv., 2015, 5(61): 49 143-49 152.

[10] Shi YQ, Fu LB, Chen XL, et al. Hypophosphite/Graphitic Carbon Nitride Hybrids: Preparation and Flame-Retardant Application in Thermoplastic Polyurethane[J]. Nanomaterials, 2017, 7(9): 259-271.

[11] Yang W, Song L, Hu Y, et al. Enhancement of Fire Retardancy Performance of Glass-Fibre Reinforced Poly(Ethylene Terephthalate) Composites with the Incorporation of Aluminum Hypophosphite and Melamine Cyanurate[J]. Compos. B. Eng., 2011, 42(5): 1 057-1 065.

[12] Yang W, Hu Y, Tai QL, et al. Fire and Mechanical Performance of Nanoclay Reinforced Glass-Fiber/Pbt Composites Containing Aluminum Hypophosphite Particles[J]. Compos. Part A: Appl. Sci. Manuf., 2011, 42(7): 794-800.

[13] Braun U, Schartel B, Fichera MA, et al. Flame Retardancy Mechanisms of Aluminium Phosphinate in Combination with Melamine Polyphosphate and Zinc Borate in Glass-Fibre Reinforced Polyamide 6, 6[J]. Polym. Degrad. Stabil., 2007, 92(8): 1 528-1 545.

[14] Li QF, Li B, Zhang SQ, et al. Investigation on Effects of Aluminum and Magnesium Hypophosphites on Flame Retardancy and Thermal Degradation of Polyamide 6[J]. J. Appl. Polym. Sci., 2012, 125(3): 1 782-1 789.

[15] Zhao B, Chen L, Long JW, et al. Aluminum Hypophosphite versus Alkyl-Substituted Phosphinate in Polyamide 6: Flame Retardance, Thermal Degradation, and Pyrolysis Behavior[J]. Ind. Eng. Chem. Res., 2013, 52(8): 2 875-2 886.

[16] Tang G, Wang X, Xing WY, et al. Thermal Degradation and Flame Retardance of Biobased Polylactide Composites Based On Aluminum Hypophosphite[J]. Ind. Eng. Chem. Res., 2012, 51(37): 12 009-12 016.

[17] Li YY, Li XM, Pan YT, et al. Mitigation the Release of Toxic Ph3 and the Fire Hazard of Pa6/Ahp Composite by Mofs[J]. J. Hazard. Mater., 2020, 395: 122 604.

[18] Liu XD, Sun J, Zhang S, et al. Effects of Carboxymethyl Chitosan Microencapsulated Melamine Polyphosphate on the Flame Retardancy and Water Resistance of Thermoplastic Polyurethane[J]. Polym. Degrad. Stabil., 2019, 160: 168-176.

[19] Wen PY, Wang D, Liu JJ, et al. Organically Modified Montmorillonite as a Synergist for Intumescent Flame Retardant Against the Flammable Polypropylene[J]. Polym. Advan. Technol., 2017, 28(6): 679-685.

[20] Yuan BH, Sun YR, Chen XF, et al. Poorly-/Well-Dispersed Graphene: Abnormal Influence on Flammability and Fire Behavior of Intumescent Flame Retardant[J]. Compos. Part A: Appl. Sci. Manuf., 2018, 109: 345-354.

[21] Wu K, Zhang YK, Hu WG, et al. Influence of Ammonium Polyphosphate Microencapsulation on Flame Retardancy, Thermal Degradation and Crystal Structure of Polypropylene Composite[J]. Compos. Sci. Technol., 2013, 81: 17-23.

[22] Chen C, Liu X, Tian ZC, et al. Trichloroethoxy-Substituted Polyphosphazenes: Synthesis, Characterization, and Properties[J]. Macromolecules., 2012, 45(22): 9 085-9 091.

[23] Tian ZC, Hess A, Fellin CR, et al. Phosphazene High Polymers and Models with Cyclic Aliphatic Side Groups: New Structure-Property Relationships[J]. Macromolecules, 2015, 48(13): 4 301-4 311.

[24] Gleria M, de Jaeger R. Aspects of Phosphazene Research[J]. J. Inorg. Organomet. Polym., 2001, 11(1): 1-45.

[25] Henke H, Brüggemann O, Teasdale I. Branched Macromolecular Architectures for Degradable, Multifunctional Phosphorus-Based Polymers[J]. Macromol. Rapid Comm., 2017, 38(4): 1 600 644

[26] Pan QC. Phosphazene Compound Comprising Cyano Group, Preparation Method and Uses Thereof[P]. US201797998, 2017

[27] Xu LF, Lei CH, Xu RJ, et al. Hybridization of α-Zirconium Phosphate with Hexachlorocyclotriphosphazene and Its Application in the Flame Retardant Poly (Vinyl Alcohol) Composites[J]. Polym. Degrad. Stabil., 2016, 133: 378-388.

[28] Qiu SL, Ma C, Wang X, et al. Melamine-Containing Polyphosphazene Wrapped Ammonium Polyphosphate: A Novel Multifunctional Organic-Inorganic Hybrid Flame Retardant[J]. J. Hazard. Mater., 2018, 344(1): 839-848.

[29] Zhou X, Qiu SL, Xing WY, et al. Hierarchical Polyphosphazene@Molybdenum Disulfide Hybrid Structure for Enhancing the Flame Retardancy and Mechanical Property of Epoxy Resins[J]. ACS Appl. Mater Inter., 2017, 9(34): 29 147-29 156.

[30] Xu LF, Lei CH, Xu RJ, et al. Functionalization of α-Zirconium Phosphate by Polyphosphazene and Its Effect on the Flame Retardance of an Intumescent Flame Retardant Polypropylene System[J]. RSC Adv., 2016, 6(81): 77 545-77 552.

[31] Qiu SL, Zhou YF, Zhou X, et al. Air-Stable Polyphosphazene-Functionalized Few-Layer Black Phosphorene for Flame Retardancy of Epoxy Resins[J]. Small., 2019, 15(10): 1 805 175

[32] Li T, Li S, Ma TJ, et al. Novel Organic-Inorganic Hybrid Polyphosphazene Modified Manganese Hypophosphite Shuttles Towards the Fire Retardance and Anti-Dripping of Pet[J]. Eur. Polym. J., 2019, 120: 109 270.

[33] Zhao SS, He M, Song WY, et al. Synthesis of a Phosphorus/Nitrogen/Sulphur Containing Phosphazene Micro-Nanotube and Its Flame Retardancy on Epoxy Nanocomposite[J]. Chem. J. Chinese U., 2017, 38(12): 2 337-2 343.

[34] Zhu ZM, Lin PL, Wang H, et al. A Facile One-Step Synthesis of Highly Efficient Melamine Salt Reactive Flame Retardant for Epoxy Resin[J]. J. Mater. Sci., 2020, 55(27): 12 836-12 847.

[35] Liu J, Tang JY, Wang XD, et al. Synthesis, Characterization and Curing Properties of a Novel Cyclolinear Phosphazene-Based Epoxy Resin for Halogen-Free Flame Retardancy and High Performance[J]. RSC Adv., 2012, 2(13): 5 789-5 799.

[36] Sun J, Wang XD, Wu DZ. Novel Spirocyclic Phosphazene-Based Epoxy Resin for Halogen-Free Fire Resistance: Synthesis, Curing Behaviors, and Flammability Characteristics[J]. ACS Appl. Mater. Inter., 2012, 4(8): 4 047-4 061.

[37] Xue BX, Niu M, Yang YZ, et al. Influence of Graphitization Degree of Carbon Microspheres on Properties of Pet Flame Retardant[J]. Polym. Eng. Sci., 2018, 58(8): 1 399-1 408.

[38] Bai YW, Wang XD, Wu DZ. Novel Cyclolinear Cyclotriphosphazene-Linked Epoxy Resin for Halogen-Free Fire Resistance: Synthesis, Characterization, and Flammability Characteristics[J]. Ind. Eng. Chem. Res., 2012, 51(46): 15 064-15 074.

[39] Liu H, Wang XD, Wu DZ. Novel Cyclotriphosphazene-Based Epoxy Compound and Its Application in Halogen-Free Epoxy Thermosetting Systems: Synthesis, Curing Behaviors, and Flame Retardancy[J]. Polym. Degrad. Stabil., 2014, 103: 96-112.

[40] Liu H, Wang XD, Wu DZ. Preparation, Isothermal Kinetics, and Performance of a Novel Epoxy Thermosetting System Based on Phosphazene-Cyclomatrix Network for Halogen-Free Flame Retardancy and High Thermal Stability[J]. Thermochim. Acta., 2015, 607: 60-73.

[41] Zhang T, Cai Q, Wu DZ, et al. Phosphazene Cyclomatrix Network Polymers: Some Aspects of the Synthesis, Characterization, and Flame-Retardant Mechanisms of Polymer[J]. J. Appl. Polym. Sci., 2005, 95(4): 880-889.

[42] Li ZQ, Lu CJ, Xia ZP, et al. X-Ray Diffraction Patterns of Graphite and Turbostratic Carbon[J]. Carbon, 2007, 45(8): 1 686-1 695.

[43] Du HF, Ai W, Zhao ZL, et al. Engineering Morphologies of Cobalt Pyrophosphates Nanostructures Toward Greatly Enhanced Electrocatalytic Performance of Oxygen Evolution Reaction[J]. Small., 2018, 14(31): 1 801 068

[44] Zhou X, Li J, Wu YG. Synergistic Effect of Aluminum Hypophosphite and Intumescent Flame Retardants in Polylactide[J]. Polym. Advan. Technol., 2015, 26(3): 255-265.