Synthsis Of The Derivatives Of Hexachlorocyclotriphosphazene And Impact On Polyester Flame-restartant Properties

Polyester materials, particularly polyethylene terephthalate (PET) material are the most used synthetic resin in the world, which is widely applied in textile, high volume automotive, electrical, and other fields. However, the PET polymer is very easy to burn, often accompanied by the serious droplet phenomenon in the combustion process. In order to expand the scope of application of PET, it is very necessary to research and develop the flame retardant polyester. Over the past decades, the halogen flame retardants have dominated the market, but the halogen-based flame retardant materials release a lot of smoke and toxic gases when they burned. It needs to develop non-halogenated flame retardants to meet the requirements of environmental protection. Phosphazene derivatives exhibit the excellent thermal stability and flame retardancy for the synergistic flame retardant effect of phosphorus and nitrogen. They also produce less toxic gas and smoke as burning. So, they can be able to fulfill the requirements of flame retardant which have low toxicity and pollution. In this paper, three kinds of cyclotriphosphazene derivatives containing different types of functional groups are synthesized, and the chemical structure of them are characterized. Then, the effects of flame retardants on flame retardant properties for PET were studied, and also we explored the flame retardant mechanism and mechanical properties.Hexakis(4-methylphenoxy)cyclotriphosphazene,Hexakis(4-hydroxymethylphenoxy)cyclotrip hosphazene and Hexakis(4-imidazol-methylenephenoxy)cyclotriphosphazene were synthesized and characterized by Melting point test, Fourier transform infrared spectroscopy(FTIR), Nuclear magnetic resonance(NMR). Thermogravimetric analysis(TGA) showed that HMCP, HHMCP and HIMCP had the excellent thermal stability, and the residual mass of the materials, respectively, is39.67%,63.15%and57.62%in the air at600℃.The3%,6%,9%and12%of HMCP, HHMCP and HIMCP used as the flame retardant were added into PET by melt blending. Different proportions of HMCP-PET, HHMCP-PET and HIMCP-PET flame retardant materials were prepared. The effects of HMCP on the thermal stability and residual mass of pure PET wereinvestigated by TGA．The results showed that the HMCP could reduce the initial degradationtemperature and the maximum mass loss rate while the char formation of PET was improved byHMCP, and the maximum char residue is20.66%. The flame retardancy of HMCP-PET wasstudied by Limiting Oxygen Index (LOI) and vertical burning test (UL-94test). It was found thatwhen the addition of HMCP is12%, the LOI value was up to32.6%; all of HMCP-PET could passUL-94V-0, but the HMCP only reduces the droplet phenomenon for PET, does not have the effectof anti-droplet. By9%HMCP-PET gaseous products of pyrolysis analysis showed HMCP can besuppressed certain depth cleavage reaction of PET. And the pyrolysis and FTIR of carbon residueshowed the phosphorus and nitrogen of HMCP still exist in the form of phosphate-basedcompounds in carbon residue. Scanning electron microscopy (SEM) photographs revealed theinternal of residue of HMCP-PET after the combustion residue appeared porous structure, and theouter surface, which gradually appeared ruptured bubbles with HMCP ratio increasing,non-uniformly distributed the carbon layer. Mechanical tensile tests showed the HMCP addedmade the maximum breaking strength of PET decreased. With the added amount increasing, themaximum breaking strength has decreased significantly.For the HHMCP-PET, TGA showed the HHMCP could decrease the initial degradationtemperature and the maximum mass loss rate and the char formation of PET was improved byHHMCP, which the maximum char residue is32.6%. LOI demonstrated that when the addition ofHHMCP is6%, the LOI value was up to32.5%; except9%HHMCP-PET pass UL-94V-1, otherscould pass V-0. Most of all,when the addition of HHMCP reached9%, PET had the effect ofanti-droplet. Gaseous products of pyrolysis analysis showed HHMCP not only can be suppressedcertain depth cleavage reaction of PET, but also can promote decarboxylation of benzoic acidsubstances to improve the CO2concentration. The pyrolysis and FTIR of carbon residue showedthe phosphorus and nitrogen of HMCP still exist in the form of phosphate-based compounds incarbon residue. SEM revealed the internal of residue of HHMCP-PET after the combustionresidue appeared porous structure, and the outer surface uniformly distributed the char. TheHHMCP added into PET makes the mechanical properties of material decreased.For the HIMCP-PET, TGA showed the HIMCP could also reduce the initial degradationtemperature and the maximum mass loss rate and the char formation of PET was improved byHHMCP, which the maximum char residue is26.44%. LOI demonstrated that when the addition ofHHMCP is6%, the LOI value was up to33.3%; all of HIMCP-PET could pass UL-94V-0, but theHIMCP only reduces the droplet phenomenon for PET, does not have the effect of anti-droplet. Gaseous products of pyrolysis analysis showed HIMCP not only can be restrained certain depthcleavage reaction of PET, but also to promote certain related primary pyrolysis productscrosslinking rearrangement to form more stable structure. The pyrolysis and FTIR of carbonresidue showed the phosphorus and nitrogen of HMCP still exist in the form of phosphate-basedcompounds in carbon residue. SEM revealed the internal of residue of HIMCP-PET after thecombustion residue appeared porous structure, and the outer surface, which gradually appearedruptured bubbles with HMCP ratio increasing, non-uniformly distributed the char. The HIMCPadded into PET makes the mechanical properties of material decreased.Compared HHMCP-PET and HIMCP-PET system with HMCP-PET, it revealed HHMCPcontaining reactive groups with PET can not only improve the flame retardancy of PET, but alsoexhibit anti-droplet. Its flame retardant mechanism mainly is the condensed phase flame, and gasflame supplemented. HIMCP containing non-reactive groups that can increase the nitrogen contentof the flame retardant, can only reduce flammability and droplet phenomenon of the PET, but doesnot have the effect of anti-droplet. Its flame retardant mechanism mainly is the gas flame.