A Vanillin-Derived,DOPO-Contained Bisphenol as a Reactive Flame Retardant for High-Performance Epoxy Thermosets

Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa-10-phosphophene-10-oxide(DOPO)and phenol via a facile way.VDP is characterized with^(1)H NMR,^(31)P NMR,FTIR and Time of Flight Mass Spectrometry,and used as a new reactive flame retardant for bisphenol epoxy thermosets.Thermogravimetry analysis shows that when the VDP loading is only 0.5P%(based on phosphorus content),the residue increases from 14.2%to 21.1%at 750℃ in N_(2)compare with neat DGEBA.Correspondingly,the limit oxygen index increased to 29.6%,and flame retardancy reaches UL-94 V0 grade.Micro combustion calorimetry(MCC)and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset.With only 0.5P%of VDP,the heat release rate,total heat release rate and smoke production are reduced markedly.At the same time,the mechanical properties of the modified epoxy thermosets are also improved.The impact strength increases by 34%and the flexural strength increased by 23%,with 1.5P%of VDP.In short,VDP not only improves the flame retardancy,but also improves the mechanical properties of the epoxy thermosets.

A New DOPO-Eugenol Adduct as an Effective Flame Retardant for Epoxy Thermosets with Improved Mechanical Properties

The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials.In this work,a monoepoxide is synthesized through O-glycidylation of eugenol,and then reacted with DOPO(9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide)to obtain a new bio-based flame retardant,DOPO-GE.DOPO-GE is blended with a bisphenol A epoxy prepolymer exhibiting good compatibility and DDS(4,4′-diaminodiphenylsulfone)is used as the curing agent to afford epoxy thermosets.Although DOPO-GE leads to the reduced glass transition temperature of the thermosets,the storage modulus increases considerably.The DOPO-GE-modified thermosets exhibit the high thermal stability with the onset thermal decomposition temperature in nitrogen and air exceeding 300℃.When the phosphorus content in the thermoset is 1.0%,the residual yield of the thermosets at 750℃ in nitrogen increases from 13.9%to 30.6%,due to the increased charring ability.More interestingly,when the phosphorus content is only 0.5%,the limiting oxygen index is as high as 30.3%with UL94 V0 achieved.Cone calorimeter results reveals the significantly decreased heat release rate,total heat release,mass loss and total smoke production.Furthermore,DOPO-GE can notably improve the flexural strength,flexural modulus and fracture toughness,whereas the shear and impact strength are reduced to varied extents.In short,DOPO-GE can be obtained via a facile way,and shows the good flame-retardant effect on the epoxy thermosets with an application potential.