Applications and Synergistic Effects of Phenoxycycloposphazene as an Eco-Friendly Flame Retardant

Introduction

Phenoxycycloposphazene is the environmental protection phosphazene flame retardant. It does not produce pollutants after burning. It is mainly used in PC and ABS resins. It has good flame retardancy resin, it can be used to make EMC for IC Packaging, its flame retardancy is much better than Brominated flame retardant, and the flame retardancy can reach UL-94V0 grade. Oxygen index could reach 33.1%. When it is used in benzoxazine resin glass cloth laminate, if the Phenoxycycloposphazene is 10%, the grade of burning could reach V-0 grade, the parallel breakdown voltage is 47KV. When it is used in Polyethylene, the LOI of final flame retardancy polyethylene could reach 30-33. After used in viscose spinning solution, the flame retardant viscose fiber with oxygen index 25.3-26.7. If the added amount is 12% in PC/ ABS, it could pass the UL-94 V0 test. It also can be used in LED, powder coating, potting material and polymers. [1]

The properties of Flame-retardant Epoxy Resin HPCTP-DOPS/EP with Double Groups Synergistic Flame Retardant Effect

The flame retardant effect of single phosphaphenanthrene and phosphazenes was limited. In order to improve the flame retardant effect of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (DOPS) on epoxy resin (EP), DOPS and phenoxycycloposphazene (HPCTP) were compounded and applied in EP. When the total P content was 1.2wt%, DOPS and phenoxycycloposphazene (HPCTP) were added to EP by adjusting the ratio of P content in the phosphaphenanthrene and phosphazene groups to prepare EP composites. The limiting oxygen index test (LOI), vertical flame test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CONE), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and thermogravimetric-infrared spectroscopy analysis (TG-IR) were used to study the effects of different proportions of phosphaphenanthrene and phosphazene groups on the thermal stability, and combustion performance of EP, and explored the law and mechanism of double groups synergistic flame retardancy. The results show that there is synergistic flame retardancy between P and S elements. When the total P content is 1.2wt%, the LOI value and UL-94 grade of HPCTP-DOPS/EP increase with the increase of S content in the composite system. and the ratio of P content between HPCTP and DOPS is 0.2∶1, the LOI of HPCTP-DOPS/EP composite system is 30.4%, reaching UL-94 V-0 grade, the total heat release (THR) and peak heat release rate (PHRR) decreased significantly, The EP/HPCTP/DOPS composite has a more dense and stable expanding carbon layer after combustion, which is superior to the flame retardant effect of the two flame retardants on EP solely, there is a synergistic flame retardant effect between the phosphazene and phosphaphenanthrene flame retardants. From the perspective of flame retardant mechanism, DOPS and HPCTP plays a flame retardant role in gas phase and condensed phase respectively. [2]

Fabrication of New Flame Retarding Bismaleimide Resin System

Phenoxycycloposphazene usually has poor compatibility with most polymers due to their different polarities and shortage of active groups, so phenoxycycloposphazene is hard to be well dispersed in the parent polymers and easy to leach out, tending to weaken the flame retarding effect and degrade other properties of polymers. On the other hand, note that PFRs have been found to be easily enriched in water and soil; this will cause cancer, cardiovascular and other diseases, so it is necessary to reduce the usage amount of phosphorus flame retardancy while making full use of the advantages of PFRs. Hence, microencapsule-type flame retardant (MH) was designed and developed through coating phenoxycycloposphazene with PA. MH/BD resins exhibit outstanding flame retardancy and smoke suppression even the content of P is as low as 0.33 wt%, overcoming the drawbacks of traditional P-containing flame retardants. Microencapsulation brings additional flame retarding effect in gaseous phase as well as stronger effect in condensed phases. These effects mainly include avoiding the loss of phenoxycycloposphazene during fabrication of modified resin, endowing MH with good dispersion in BD resin, releasing more non-flammable gases, forming more stable crosslinked charring, and increasing the charring ability and strength of char; in addition, modified resins, especially MH/BD resins have lower dielectric constant and loss than BD resin, demonstrating that MH is a multifunctional flame retardant for BD resin. [3]

References:

[1] Data, P. (2014). Technical data sheet. Dimensions (H x W x D), 2000(1,315), x510x815.

[2] XU Zhiyan, HOU Zeming, YE Xiaolin, et al. Study on the properties of flame-retardant epoxy resin HPCTP-DOPS/EP  with double groups synergistic flame retardant effect[J]. Acta Materiae Compositae Sinica, 2023, 40(4): 2187-2198. DOI: 10.13801/j.cnki.fhclxb.20220607.006

[3] Cao, T., Yuan, L., Gu, A., & Liang, G. (2015). Fabrication and origin of new flame retarding bismaleimide resin system with low dielectric constant and loss based on microencapsulated hexaphenoxycyclotriphosphazene in low phosphorus content. Polymer Degradation and Stability, 121, 157-170.