The Flame Retardancy Of Phytates And Its Coated Magnesium Hydroxide In Flexible PVC

Polyvinyl chloride?PVC?is one of the most widely used general-purpose polymer materials.However,with the addition of traditional plasticizers,flexible PVC has flammability and a large amount of smoke generation when burning.Therefore,it is of great significance to study the flame retardancy and smoke suppression of flexible PVC.The flame retardant of metal hydroxide is widely used in the flame retardancy research of PVC because of its green pollution-free characteristics.Among them,magnesium hydroxide?Mg?OH?₂?is the most widely used.However,the flame-retardant efficiency of Mg?OH?₂ is low,and when it is added in large quantities,it will have an adverse effect on the mechanical properties of the matrix.In recent years,due to the increasing awareness of environmental protection,bio-based flame retardants have received more and more attention.Phytic acid?PA?is gradually used as a bio-based phosphorus-containing flame retardant in polymer materials such as polylactide?PLA?and ethylene-vinyl acetate copolymer?EVA?.In this paper,aluminum phytate?Al-Phyt?,copper phytate?Cu-Phyt?,zinc phytate?Zn-Phyt?and tin phytate?Sn-Phyt?four phytates?M-Phyt?were prepared.With Mg?OH?₂ as the core and M-Phyt as the shell to prepare three phytate coated Mg?OH?₂?Mg?OH?₂@M-Phyt?:Mg?OH?₂@Cu-Phyt,Mg?OH?₂@Zn-Phyt,Mg?OH?₂@Sn-Phyt.After that,their effects on the flame retardant and smoke suppression properties of PVC were tested by limiting oxygen index?LOI?and cone calorimetry?CONE?tests.The details were as follows:Firstly,the four kinds of M-phyt were synthesized by direct precipitation method:Al-Phyt,Cu-Phyt,Zn-Phyt,and Sn-Phyt.Using X-ray diffraction?XRD?and scanning electron microscopy?SEM?tests,it was observed that all four M-Phyt were amorphous and agglomerated.Using Mg?OH?₂ as core and M-Phyt as shell,three brucite-type flame retardants were prepared:Mg?OH?₂@Cu-Phyt,Mg?OH?₂@Zn-Phyt,Mg?OH?₂@Sn-Phyt.SEM and transmission electron microscopy?TEM?were used to observe the same morphology as the original Mg?OH?₂,both of which are core-shell structures.Secondly,the limiting oxygen index?LOI?,the cone calorimetry test?CONE?data,tensile strength and impact toughness were measured for flexible poly?vinyl chloride??PVC?containing 15 wt%of M-Phyt salts.The tests showed that M-Phyt salts have good flame retardancy and smoke suppression effects.The LOI value of PVC/Sn-Phyt was the highest,reaching 30.3%.The the value of the total of smoke release?TSP?and the peak of heat release rate?pHRR?of PVC/Cu-Phyt were 62.63%and 44.48%lower than those of neat PVC,respectively.Thermogravimetric analyzer?TG?test results show that Zn-Phyt can catalyze the dehydrochlorination of PVC significantly and promote its cross-linking to charcoal.Rmax1 of PVC/Zn-Phyt material reached-86.67%/min,which is 7.3 times that of pure PVC.Effective combustion heat?EHC?data show that the Sn-Phyt's gas phase flame retardant effect is the most significant.The elongation at break of the PVC/Sn-Phyt sample only decreased by12.89%and the impact strength reached 6.40 KJ/m².Thirdly,Mg?OH?₂@M-Phyt and Mg?OH?₂ are applied to flexible PVC respectively.The LOI and CONE test results show that Mg?OH?₂@M-Phyt has good flame retardant and smoke suppression effect in flexible PVC when the addition amount is 10 wt%.Among them,the LOI value of PVC/Mg?OH?₂@Sn-Phyt is the highest,reached 30.5%;and the TSP of PVC/Mg?OH?₂@Sn-Phyt decreased most,it reduced by 24.07%compared with the PVC/Mg?OH?₂ sample.The peak of smoke release rate?pSPR?of PVC/Mg?OH?₂@Cu-Phyt was the lowest,which was 35%lower than that of PVC/Mg?OH?₂.TG,SEM,XRD,X-ray energy dispersive spectroscopy?EDX?and other test results show that Mg?OH?₂@M-Phyt can achieve effective flame retardant effect in flexible PVC.The main reason is that it can absorb more heat during the thermal degradation of PVC,and can promote PVC to form more carbon residue during combustion.The tensile properties and low temperature impact test results show that PVC/Mg?OH?₂@M-Phyt has various degrees of improvement in the mechanical properties of the material.The mechanical properties of PVC/Mg?OH?₂@Cu-Phyt samples are the best.Compared with PVC/Mg?OH?₂ samples,the tensile strength and impact toughness are increased by 11.98%and 44.28%,respectively.